diff --git a/absl/strings/BUILD.bazel b/absl/strings/BUILD.bazel
new file mode 100644
index 0000000..eae75d8
--- /dev/null
+++ b/absl/strings/BUILD.bazel
@@ -0,0 +1,679 @@
+#
+# Copyright 2017 The Abseil Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+load("@rules_cc//cc:defs.bzl", "cc_library", "cc_test")
+load(
+    "//absl:copts/configure_copts.bzl",
+    "ABSL_DEFAULT_COPTS",
+    "ABSL_TEST_COPTS",
+)
+
+package(
+    default_visibility = ["//visibility:public"],
+    features = ["parse_headers"],
+)
+
+licenses(["notice"])  # Apache 2.0
+
+cc_library(
+    name = "strings",
+    srcs = [
+        "ascii.cc",
+        "charconv.cc",
+        "escaping.cc",
+        "internal/charconv_bigint.cc",
+        "internal/charconv_bigint.h",
+        "internal/charconv_parse.cc",
+        "internal/charconv_parse.h",
+        "internal/memutil.cc",
+        "internal/memutil.h",
+        "internal/stl_type_traits.h",
+        "internal/str_join_internal.h",
+        "internal/str_split_internal.h",
+        "match.cc",
+        "numbers.cc",
+        "str_cat.cc",
+        "str_replace.cc",
+        "str_split.cc",
+        "string_view.cc",
+        "substitute.cc",
+    ],
+    hdrs = [
+        "ascii.h",
+        "charconv.h",
+        "escaping.h",
+        "match.h",
+        "numbers.h",
+        "str_cat.h",
+        "str_join.h",
+        "str_replace.h",
+        "str_split.h",
+        "string_view.h",
+        "strip.h",
+        "substitute.h",
+    ],
+    copts = ABSL_DEFAULT_COPTS,
+    deps = [
+        ":internal",
+        "//absl/base",
+        "//absl/base:bits",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/base:endian",
+        "//absl/base:raw_logging_internal",
+        "//absl/base:throw_delegate",
+        "//absl/memory",
+        "//absl/meta:type_traits",
+        "//absl/numeric:int128",
+    ],
+)
+
+cc_library(
+    name = "internal",
+    srcs = [
+        "internal/ostringstream.cc",
+        "internal/utf8.cc",
+    ],
+    hdrs = [
+        "internal/char_map.h",
+        "internal/ostringstream.h",
+        "internal/resize_uninitialized.h",
+        "internal/utf8.h",
+    ],
+    copts = ABSL_DEFAULT_COPTS,
+    deps = [
+        "//absl/base:core_headers",
+        "//absl/base:endian",
+        "//absl/meta:type_traits",
+    ],
+)
+
+cc_test(
+    name = "match_test",
+    size = "small",
+    srcs = ["match_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "escaping_test",
+    size = "small",
+    srcs = [
+        "escaping_test.cc",
+        "internal/escaping_test_common.h",
+    ],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:core_headers",
+        "//absl/container:fixed_array",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "escaping_benchmark",
+    srcs = [
+        "escaping_benchmark.cc",
+        "internal/escaping_test_common.h",
+    ],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:raw_logging_internal",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "ascii_test",
+    size = "small",
+    srcs = ["ascii_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:core_headers",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "ascii_benchmark",
+    srcs = ["ascii_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "memutil_benchmark",
+    srcs = [
+        "internal/memutil.h",
+        "internal/memutil_benchmark.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:core_headers",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "memutil_test",
+    size = "small",
+    srcs = [
+        "internal/memutil.h",
+        "internal/memutil_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:core_headers",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "utf8_test",
+    size = "small",
+    srcs = [
+        "internal/utf8_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":internal",
+        "//absl/base:core_headers",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "string_view_benchmark",
+    srcs = ["string_view_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:core_headers",
+        "//absl/base:raw_logging_internal",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "string_view_test",
+    size = "small",
+    srcs = ["string_view_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/base:dynamic_annotations",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "substitute_test",
+    size = "small",
+    srcs = ["substitute_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:core_headers",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_replace_benchmark",
+    srcs = ["str_replace_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:raw_logging_internal",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "str_replace_test",
+    size = "small",
+    srcs = ["str_replace_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_split_test",
+    srcs = ["str_split_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:core_headers",
+        "//absl/base:dynamic_annotations",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_split_benchmark",
+    srcs = ["str_split_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:raw_logging_internal",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "ostringstream_test",
+    size = "small",
+    srcs = ["internal/ostringstream_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":internal",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "ostringstream_benchmark",
+    srcs = ["internal/ostringstream_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":internal",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "resize_uninitialized_test",
+    size = "small",
+    srcs = [
+        "internal/resize_uninitialized.h",
+        "internal/resize_uninitialized_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        "//absl/base:core_headers",
+        "//absl/meta:type_traits",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_join_test",
+    size = "small",
+    srcs = ["str_join_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:core_headers",
+        "//absl/memory",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_join_benchmark",
+    srcs = ["str_join_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "str_cat_test",
+    size = "small",
+    srcs = ["str_cat_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:core_headers",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_cat_benchmark",
+    srcs = ["str_cat_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "numbers_test",
+    size = "medium",
+    srcs = [
+        "internal/numbers_test_common.h",
+        "numbers_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":pow10_helper",
+        ":strings",
+        "//absl/base:core_headers",
+        "//absl/base:raw_logging_internal",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "numbers_benchmark",
+    srcs = ["numbers_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:raw_logging_internal",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "strip_test",
+    size = "small",
+    srcs = ["strip_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "char_map_test",
+    srcs = ["internal/char_map_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    deps = [
+        ":internal",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "char_map_benchmark",
+    srcs = ["internal/char_map_benchmark.cc"],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    deps = [
+        ":internal",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_test(
+    name = "charconv_test",
+    srcs = ["charconv_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    deps = [
+        ":pow10_helper",
+        ":str_format",
+        ":strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "charconv_parse_test",
+    srcs = [
+        "internal/charconv_parse.h",
+        "internal/charconv_parse_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    deps = [
+        ":strings",
+        "//absl/base:raw_logging_internal",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "charconv_bigint_test",
+    srcs = [
+        "internal/charconv_bigint.h",
+        "internal/charconv_bigint_test.cc",
+        "internal/charconv_parse.h",
+    ],
+    copts = ABSL_TEST_COPTS,
+    deps = [
+        ":strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "charconv_benchmark",
+    srcs = [
+        "charconv_benchmark.cc",
+    ],
+    tags = [
+        "benchmark",
+    ],
+    deps = [
+        ":strings",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
+cc_library(
+    name = "str_format",
+    hdrs = [
+        "str_format.h",
+    ],
+    copts = ABSL_DEFAULT_COPTS,
+    deps = [
+        ":str_format_internal",
+    ],
+)
+
+cc_library(
+    name = "str_format_internal",
+    srcs = [
+        "internal/str_format/arg.cc",
+        "internal/str_format/bind.cc",
+        "internal/str_format/extension.cc",
+        "internal/str_format/float_conversion.cc",
+        "internal/str_format/output.cc",
+        "internal/str_format/parser.cc",
+    ],
+    hdrs = [
+        "internal/str_format/arg.h",
+        "internal/str_format/bind.h",
+        "internal/str_format/checker.h",
+        "internal/str_format/extension.h",
+        "internal/str_format/float_conversion.h",
+        "internal/str_format/output.h",
+        "internal/str_format/parser.h",
+    ],
+    copts = ABSL_DEFAULT_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":strings",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/meta:type_traits",
+        "//absl/numeric:int128",
+        "//absl/types:span",
+    ],
+)
+
+cc_test(
+    name = "str_format_test",
+    srcs = ["str_format_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":str_format",
+        ":strings",
+        "//absl/base:core_headers",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_format_extension_test",
+    srcs = [
+        "internal/str_format/extension_test.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":str_format",
+        ":str_format_internal",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_format_arg_test",
+    srcs = ["internal/str_format/arg_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":str_format",
+        ":str_format_internal",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_format_bind_test",
+    srcs = ["internal/str_format/bind_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":str_format_internal",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_format_checker_test",
+    srcs = ["internal/str_format/checker_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":str_format",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_format_convert_test",
+    size = "medium",
+    srcs = ["internal/str_format/convert_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":str_format_internal",
+        "//absl/numeric:int128",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_format_output_test",
+    srcs = ["internal/str_format/output_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":str_format_internal",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "str_format_parser_test",
+    srcs = ["internal/str_format/parser_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":str_format_internal",
+        "//absl/base:core_headers",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_library(
+    name = "pow10_helper",
+    testonly = True,
+    srcs = ["internal/pow10_helper.cc"],
+    hdrs = ["internal/pow10_helper.h"],
+    visibility = ["//visibility:private"],
+)
+
+cc_test(
+    name = "pow10_helper_test",
+    srcs = ["internal/pow10_helper_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":pow10_helper",
+        ":str_format",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
diff --git a/absl/strings/CMakeLists.txt b/absl/strings/CMakeLists.txt
new file mode 100644
index 0000000..ccff444
--- /dev/null
+++ b/absl/strings/CMakeLists.txt
@@ -0,0 +1,516 @@
+#
+# Copyright 2017 The Abseil Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+absl_cc_library(
+  NAME
+    strings
+  HDRS
+    "ascii.h"
+    "charconv.h"
+    "escaping.h"
+    "match.h"
+    "numbers.h"
+    "str_cat.h"
+    "str_join.h"
+    "str_replace.h"
+    "str_split.h"
+    "string_view.h"
+    "strip.h"
+    "substitute.h"
+  SRCS
+    "ascii.cc"
+    "charconv.cc"
+    "escaping.cc"
+    "internal/charconv_bigint.cc"
+    "internal/charconv_bigint.h"
+    "internal/charconv_parse.cc"
+    "internal/charconv_parse.h"
+    "internal/memutil.cc"
+    "internal/memutil.h"
+    "internal/stl_type_traits.h"
+    "internal/str_join_internal.h"
+    "internal/str_split_internal.h"
+    "match.cc"
+    "numbers.cc"
+    "str_cat.cc"
+    "str_replace.cc"
+    "str_split.cc"
+    "string_view.cc"
+    "substitute.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::strings_internal
+    absl::base
+    absl::bits
+    absl::config
+    absl::core_headers
+    absl::endian
+    absl::int128
+    absl::memory
+    absl::raw_logging_internal
+    absl::throw_delegate
+    absl::type_traits
+  PUBLIC
+)
+
+absl_cc_library(
+  NAME
+    strings_internal
+  HDRS
+    "internal/char_map.h"
+    "internal/ostringstream.h"
+    "internal/resize_uninitialized.h"
+    "internal/utf8.h"
+  SRCS
+    "internal/ostringstream.cc"
+    "internal/utf8.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::core_headers
+    absl::endian
+    absl::type_traits
+)
+
+absl_cc_test(
+  NAME
+    match_test
+  SRCS
+    "match_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::base
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    escaping_test
+  SRCS
+    "escaping_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::core_headers
+    absl::fixed_array
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    ascii_test
+  SRCS
+    "ascii_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::core_headers
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    memutil_test
+  SRCS
+    "internal/memutil.h"
+    "internal/memutil_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::core_headers
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    utf8_test
+  SRCS
+    "internal/utf8_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings_internal
+    absl::base
+    absl::core_headers
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    string_view_test
+  SRCS
+    "string_view_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::config
+    absl::core_headers
+    absl::dynamic_annotations
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    substitute_test
+  SRCS
+    "substitute_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::core_headers
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_replace_test
+  SRCS
+    "str_replace_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_split_test
+  SRCS
+    "str_split_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::base
+    absl::core_headers
+    absl::dynamic_annotations
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    ostringstream_test
+  SRCS
+    "internal/ostringstream_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings_internal
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    resize_uninitialized_test
+  SRCS
+    "internal/resize_uninitialized.h"
+    "internal/resize_uninitialized_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::base
+    absl::core_headers
+    absl::type_traits
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_join_test
+  SRCS
+    "str_join_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::base
+    absl::core_headers
+    absl::memory
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_cat_test
+  SRCS
+    "str_cat_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::core_headers
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    numbers_test
+  SRCS
+    "internal/numbers_test_common.h"
+    "numbers_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::core_headers
+    absl::pow10_helper
+    absl::raw_logging_internal
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    strip_test
+  SRCS
+    "strip_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::base
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    char_map_test
+  SRCS
+    "internal/char_map_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings_internal
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    charconv_test
+  SRCS
+    "charconv_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::str_format
+    absl::pow10_helper
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    charconv_parse_test
+  SRCS
+    "internal/charconv_parse.h"
+    "internal/charconv_parse_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    absl::raw_logging_internal
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    charconv_bigint_test
+  SRCS
+    "internal/charconv_bigint.h"
+    "internal/charconv_bigint_test.cc"
+    "internal/charconv_parse.h"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::strings
+    gmock_main
+)
+
+absl_cc_library(
+  NAME
+    str_format
+  HDRS
+    "str_format.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::str_format_internal
+  PUBLIC
+)
+
+absl_cc_library(
+  NAME
+    str_format_internal
+  HDRS
+    "internal/str_format/arg.h"
+    "internal/str_format/bind.h"
+    "internal/str_format/checker.h"
+    "internal/str_format/extension.h"
+    "internal/str_format/float_conversion.h"
+    "internal/str_format/output.h"
+    "internal/str_format/parser.h"
+  SRCS
+    "internal/str_format/arg.cc"
+    "internal/str_format/bind.cc"
+    "internal/str_format/extension.cc"
+    "internal/str_format/float_conversion.cc"
+    "internal/str_format/output.cc"
+    "internal/str_format/parser.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::strings
+    absl::config
+    absl::core_headers
+    absl::type_traits
+    absl::int128
+    absl::span
+)
+
+absl_cc_test(
+  NAME
+    str_format_test
+  SRCS
+    "str_format_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::str_format
+    absl::strings
+    absl::core_headers
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_format_extension_test
+  SRCS
+    "internal/str_format/extension_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::str_format
+    absl::str_format_internal
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_format_arg_test
+  SRCS
+    "internal/str_format/arg_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::str_format
+    absl::str_format_internal
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_format_bind_test
+  SRCS
+    "internal/str_format/bind_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::str_format_internal
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_format_checker_test
+  SRCS
+    "internal/str_format/checker_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::str_format
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_format_convert_test
+  SRCS
+    "internal/str_format/convert_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::str_format_internal
+    absl::int128
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_format_output_test
+  SRCS
+    "internal/str_format/output_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::str_format_internal
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    str_format_parser_test
+  SRCS
+    "internal/str_format/parser_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::str_format_internal
+    absl::core_headers
+    gmock_main
+)
+
+absl_cc_library(
+  NAME
+    pow10_helper
+  HDRS
+    "internal/pow10_helper.h"
+  SRCS
+    "internal/pow10_helper.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  TESTONLY
+)
+
+absl_cc_test(
+  NAME
+    pow10_helper_test
+  SRCS
+    "internal/pow10_helper_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::pow10_helper
+    absl::str_format
+    gmock_main
+)
diff --git a/absl/strings/ascii.cc b/absl/strings/ascii.cc
new file mode 100644
index 0000000..3f7c581
--- /dev/null
+++ b/absl/strings/ascii.cc
@@ -0,0 +1,198 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/ascii.h"
+
+namespace absl {
+namespace ascii_internal {
+
+// # Table generated by this Python code (bit 0x02 is currently unused):
+// TODO(mbar) Move Python code for generation of table to BUILD and link here.
+
+// NOTE: The kAsciiPropertyBits table used within this code was generated by
+// Python code of the following form. (Bit 0x02 is currently unused and
+// available.)
+//
+// def Hex2(n):
+//   return '0x' + hex(n/16)[2:] + hex(n%16)[2:]
+// def IsPunct(ch):
+//   return (ord(ch) >= 32 and ord(ch) < 127 and
+//           not ch.isspace() and not ch.isalnum())
+// def IsBlank(ch):
+//   return ch in ' \t'
+// def IsCntrl(ch):
+//   return ord(ch) < 32 or ord(ch) == 127
+// def IsXDigit(ch):
+//   return ch.isdigit() or ch.lower() in 'abcdef'
+// for i in range(128):
+//   ch = chr(i)
+//   mask = ((ch.isalpha() and 0x01 or 0) |
+//           (ch.isalnum() and 0x04 or 0) |
+//           (ch.isspace() and 0x08 or 0) |
+//           (IsPunct(ch) and 0x10 or 0) |
+//           (IsBlank(ch) and 0x20 or 0) |
+//           (IsCntrl(ch) and 0x40 or 0) |
+//           (IsXDigit(ch) and 0x80 or 0))
+//   print Hex2(mask) + ',',
+//   if i % 16 == 7:
+//     print ' //', Hex2(i & 0x78)
+//   elif i % 16 == 15:
+//     print
+
+// clang-format off
+// Array of bitfields holding character information. Each bit value corresponds
+// to a particular character feature. For readability, and because the value
+// of these bits is tightly coupled to this implementation, the individual bits
+// are not named. Note that bitfields for all characters above ASCII 127 are
+// zero-initialized.
+const unsigned char kPropertyBits[256] = {
+    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0x00
+    0x40, 0x68, 0x48, 0x48, 0x48, 0x48, 0x40, 0x40,
+    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0x10
+    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
+    0x28, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10,  // 0x20
+    0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10,
+    0x84, 0x84, 0x84, 0x84, 0x84, 0x84, 0x84, 0x84,  // 0x30
+    0x84, 0x84, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10,
+    0x10, 0x85, 0x85, 0x85, 0x85, 0x85, 0x85, 0x05,  // 0x40
+    0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05,
+    0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05,  // 0x50
+    0x05, 0x05, 0x05, 0x10, 0x10, 0x10, 0x10, 0x10,
+    0x10, 0x85, 0x85, 0x85, 0x85, 0x85, 0x85, 0x05,  // 0x60
+    0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05,
+    0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05,  // 0x70
+    0x05, 0x05, 0x05, 0x10, 0x10, 0x10, 0x10, 0x40,
+};
+
+// Array of characters for the ascii_tolower() function. For values 'A'
+// through 'Z', return the lower-case character; otherwise, return the
+// identity of the passed character.
+const char kToLower[256] = {
+  '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', '\x07',
+  '\x08', '\x09', '\x0a', '\x0b', '\x0c', '\x0d', '\x0e', '\x0f',
+  '\x10', '\x11', '\x12', '\x13', '\x14', '\x15', '\x16', '\x17',
+  '\x18', '\x19', '\x1a', '\x1b', '\x1c', '\x1d', '\x1e', '\x1f',
+  '\x20', '\x21', '\x22', '\x23', '\x24', '\x25', '\x26', '\x27',
+  '\x28', '\x29', '\x2a', '\x2b', '\x2c', '\x2d', '\x2e', '\x2f',
+  '\x30', '\x31', '\x32', '\x33', '\x34', '\x35', '\x36', '\x37',
+  '\x38', '\x39', '\x3a', '\x3b', '\x3c', '\x3d', '\x3e', '\x3f',
+  '\x40',    'a',    'b',    'c',    'd',    'e',    'f',    'g',
+     'h',    'i',    'j',    'k',    'l',    'm',    'n',    'o',
+     'p',    'q',    'r',    's',    't',    'u',    'v',    'w',
+     'x',    'y',    'z', '\x5b', '\x5c', '\x5d', '\x5e', '\x5f',
+  '\x60', '\x61', '\x62', '\x63', '\x64', '\x65', '\x66', '\x67',
+  '\x68', '\x69', '\x6a', '\x6b', '\x6c', '\x6d', '\x6e', '\x6f',
+  '\x70', '\x71', '\x72', '\x73', '\x74', '\x75', '\x76', '\x77',
+  '\x78', '\x79', '\x7a', '\x7b', '\x7c', '\x7d', '\x7e', '\x7f',
+  '\x80', '\x81', '\x82', '\x83', '\x84', '\x85', '\x86', '\x87',
+  '\x88', '\x89', '\x8a', '\x8b', '\x8c', '\x8d', '\x8e', '\x8f',
+  '\x90', '\x91', '\x92', '\x93', '\x94', '\x95', '\x96', '\x97',
+  '\x98', '\x99', '\x9a', '\x9b', '\x9c', '\x9d', '\x9e', '\x9f',
+  '\xa0', '\xa1', '\xa2', '\xa3', '\xa4', '\xa5', '\xa6', '\xa7',
+  '\xa8', '\xa9', '\xaa', '\xab', '\xac', '\xad', '\xae', '\xaf',
+  '\xb0', '\xb1', '\xb2', '\xb3', '\xb4', '\xb5', '\xb6', '\xb7',
+  '\xb8', '\xb9', '\xba', '\xbb', '\xbc', '\xbd', '\xbe', '\xbf',
+  '\xc0', '\xc1', '\xc2', '\xc3', '\xc4', '\xc5', '\xc6', '\xc7',
+  '\xc8', '\xc9', '\xca', '\xcb', '\xcc', '\xcd', '\xce', '\xcf',
+  '\xd0', '\xd1', '\xd2', '\xd3', '\xd4', '\xd5', '\xd6', '\xd7',
+  '\xd8', '\xd9', '\xda', '\xdb', '\xdc', '\xdd', '\xde', '\xdf',
+  '\xe0', '\xe1', '\xe2', '\xe3', '\xe4', '\xe5', '\xe6', '\xe7',
+  '\xe8', '\xe9', '\xea', '\xeb', '\xec', '\xed', '\xee', '\xef',
+  '\xf0', '\xf1', '\xf2', '\xf3', '\xf4', '\xf5', '\xf6', '\xf7',
+  '\xf8', '\xf9', '\xfa', '\xfb', '\xfc', '\xfd', '\xfe', '\xff',
+};
+
+// Array of characters for the ascii_toupper() function. For values 'a'
+// through 'z', return the upper-case character; otherwise, return the
+// identity of the passed character.
+const char kToUpper[256] = {
+  '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', '\x07',
+  '\x08', '\x09', '\x0a', '\x0b', '\x0c', '\x0d', '\x0e', '\x0f',
+  '\x10', '\x11', '\x12', '\x13', '\x14', '\x15', '\x16', '\x17',
+  '\x18', '\x19', '\x1a', '\x1b', '\x1c', '\x1d', '\x1e', '\x1f',
+  '\x20', '\x21', '\x22', '\x23', '\x24', '\x25', '\x26', '\x27',
+  '\x28', '\x29', '\x2a', '\x2b', '\x2c', '\x2d', '\x2e', '\x2f',
+  '\x30', '\x31', '\x32', '\x33', '\x34', '\x35', '\x36', '\x37',
+  '\x38', '\x39', '\x3a', '\x3b', '\x3c', '\x3d', '\x3e', '\x3f',
+  '\x40', '\x41', '\x42', '\x43', '\x44', '\x45', '\x46', '\x47',
+  '\x48', '\x49', '\x4a', '\x4b', '\x4c', '\x4d', '\x4e', '\x4f',
+  '\x50', '\x51', '\x52', '\x53', '\x54', '\x55', '\x56', '\x57',
+  '\x58', '\x59', '\x5a', '\x5b', '\x5c', '\x5d', '\x5e', '\x5f',
+  '\x60',    'A',    'B',    'C',    'D',    'E',    'F',    'G',
+     'H',    'I',    'J',    'K',    'L',    'M',    'N',    'O',
+     'P',    'Q',    'R',    'S',    'T',    'U',    'V',    'W',
+     'X',    'Y',    'Z', '\x7b', '\x7c', '\x7d', '\x7e', '\x7f',
+  '\x80', '\x81', '\x82', '\x83', '\x84', '\x85', '\x86', '\x87',
+  '\x88', '\x89', '\x8a', '\x8b', '\x8c', '\x8d', '\x8e', '\x8f',
+  '\x90', '\x91', '\x92', '\x93', '\x94', '\x95', '\x96', '\x97',
+  '\x98', '\x99', '\x9a', '\x9b', '\x9c', '\x9d', '\x9e', '\x9f',
+  '\xa0', '\xa1', '\xa2', '\xa3', '\xa4', '\xa5', '\xa6', '\xa7',
+  '\xa8', '\xa9', '\xaa', '\xab', '\xac', '\xad', '\xae', '\xaf',
+  '\xb0', '\xb1', '\xb2', '\xb3', '\xb4', '\xb5', '\xb6', '\xb7',
+  '\xb8', '\xb9', '\xba', '\xbb', '\xbc', '\xbd', '\xbe', '\xbf',
+  '\xc0', '\xc1', '\xc2', '\xc3', '\xc4', '\xc5', '\xc6', '\xc7',
+  '\xc8', '\xc9', '\xca', '\xcb', '\xcc', '\xcd', '\xce', '\xcf',
+  '\xd0', '\xd1', '\xd2', '\xd3', '\xd4', '\xd5', '\xd6', '\xd7',
+  '\xd8', '\xd9', '\xda', '\xdb', '\xdc', '\xdd', '\xde', '\xdf',
+  '\xe0', '\xe1', '\xe2', '\xe3', '\xe4', '\xe5', '\xe6', '\xe7',
+  '\xe8', '\xe9', '\xea', '\xeb', '\xec', '\xed', '\xee', '\xef',
+  '\xf0', '\xf1', '\xf2', '\xf3', '\xf4', '\xf5', '\xf6', '\xf7',
+  '\xf8', '\xf9', '\xfa', '\xfb', '\xfc', '\xfd', '\xfe', '\xff',
+};
+// clang-format on
+
+}  // namespace ascii_internal
+
+void AsciiStrToLower(std::string* s) {
+  for (auto& ch : *s) {
+    ch = absl::ascii_tolower(ch);
+  }
+}
+
+void AsciiStrToUpper(std::string* s) {
+  for (auto& ch : *s) {
+    ch = absl::ascii_toupper(ch);
+  }
+}
+
+void RemoveExtraAsciiWhitespace(std::string* str) {
+  auto stripped = StripAsciiWhitespace(*str);
+
+  if (stripped.empty()) {
+    str->clear();
+    return;
+  }
+
+  auto input_it = stripped.begin();
+  auto input_end = stripped.end();
+  auto output_it = &(*str)[0];
+  bool is_ws = false;
+
+  for (; input_it < input_end; ++input_it) {
+    if (is_ws) {
+      // Consecutive whitespace?  Keep only the last.
+      is_ws = absl::ascii_isspace(*input_it);
+      if (is_ws) --output_it;
+    } else {
+      is_ws = absl::ascii_isspace(*input_it);
+    }
+
+    *output_it = *input_it;
+    ++output_it;
+  }
+
+  str->erase(output_it - &(*str)[0]);
+}
+
+}  // namespace absl
diff --git a/absl/strings/ascii.h b/absl/strings/ascii.h
new file mode 100644
index 0000000..f9e4fd1
--- /dev/null
+++ b/absl/strings/ascii.h
@@ -0,0 +1,239 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: ascii.h
+// -----------------------------------------------------------------------------
+//
+// This package contains functions operating on characters and strings
+// restricted to standard ASCII. These include character classification
+// functions analogous to those found in the ANSI C Standard Library <ctype.h>
+// header file.
+//
+// C++ implementations provide <ctype.h> functionality based on their
+// C environment locale. In general, reliance on such a locale is not ideal, as
+// the locale standard is problematic (and may not return invariant information
+// for the same character set, for example). These `ascii_*()` functions are
+// hard-wired for standard ASCII, much faster, and guaranteed to behave
+// consistently.  They will never be overloaded, nor will their function
+// signature change.
+//
+// `ascii_isalnum()`, `ascii_isalpha()`, `ascii_isascii()`, `ascii_isblank()`,
+// `ascii_iscntrl()`, `ascii_isdigit()`, `ascii_isgraph()`, `ascii_islower()`,
+// `ascii_isprint()`, `ascii_ispunct()`, `ascii_isspace()`, `ascii_isupper()`,
+// `ascii_isxdigit()`
+//   Analogous to the <ctype.h> functions with similar names, these
+//   functions take an unsigned char and return a bool, based on whether the
+//   character matches the condition specified.
+//
+//   If the input character has a numerical value greater than 127, these
+//   functions return `false`.
+//
+// `ascii_tolower()`, `ascii_toupper()`
+//   Analogous to the <ctype.h> functions with similar names, these functions
+//   take an unsigned char and return a char.
+//
+//   If the input character is not an ASCII {lower,upper}-case letter (including
+//   numerical values greater than 127) then the functions return the same value
+//   as the input character.
+
+#ifndef ABSL_STRINGS_ASCII_H_
+#define ABSL_STRINGS_ASCII_H_
+
+#include <algorithm>
+#include <string>
+
+#include "absl/base/attributes.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+namespace ascii_internal {
+
+// Declaration for an array of bitfields holding character information.
+extern const unsigned char kPropertyBits[256];
+
+// Declaration for the array of characters to upper-case characters.
+extern const char kToUpper[256];
+
+// Declaration for the array of characters to lower-case characters.
+extern const char kToLower[256];
+
+}  // namespace ascii_internal
+
+// ascii_isalpha()
+//
+// Determines whether the given character is an alphabetic character.
+inline bool ascii_isalpha(unsigned char c) {
+  return (ascii_internal::kPropertyBits[c] & 0x01) != 0;
+}
+
+// ascii_isalnum()
+//
+// Determines whether the given character is an alphanumeric character.
+inline bool ascii_isalnum(unsigned char c) {
+  return (ascii_internal::kPropertyBits[c] & 0x04) != 0;
+}
+
+// ascii_isspace()
+//
+// Determines whether the given character is a whitespace character (space,
+// tab, vertical tab, formfeed, linefeed, or carriage return).
+inline bool ascii_isspace(unsigned char c) {
+  return (ascii_internal::kPropertyBits[c] & 0x08) != 0;
+}
+
+// ascii_ispunct()
+//
+// Determines whether the given character is a punctuation character.
+inline bool ascii_ispunct(unsigned char c) {
+  return (ascii_internal::kPropertyBits[c] & 0x10) != 0;
+}
+
+// ascii_isblank()
+//
+// Determines whether the given character is a blank character (tab or space).
+inline bool ascii_isblank(unsigned char c) {
+  return (ascii_internal::kPropertyBits[c] & 0x20) != 0;
+}
+
+// ascii_iscntrl()
+//
+// Determines whether the given character is a control character.
+inline bool ascii_iscntrl(unsigned char c) {
+  return (ascii_internal::kPropertyBits[c] & 0x40) != 0;
+}
+
+// ascii_isxdigit()
+//
+// Determines whether the given character can be represented as a hexadecimal
+// digit character (i.e. {0-9} or {A-F}).
+inline bool ascii_isxdigit(unsigned char c) {
+  return (ascii_internal::kPropertyBits[c] & 0x80) != 0;
+}
+
+// ascii_isdigit()
+//
+// Determines whether the given character can be represented as a decimal
+// digit character (i.e. {0-9}).
+inline bool ascii_isdigit(unsigned char c) { return c >= '0' && c <= '9'; }
+
+// ascii_isprint()
+//
+// Determines whether the given character is printable, including whitespace.
+inline bool ascii_isprint(unsigned char c) { return c >= 32 && c < 127; }
+
+// ascii_isgraph()
+//
+// Determines whether the given character has a graphical representation.
+inline bool ascii_isgraph(unsigned char c) { return c > 32 && c < 127; }
+
+// ascii_isupper()
+//
+// Determines whether the given character is uppercase.
+inline bool ascii_isupper(unsigned char c) { return c >= 'A' && c <= 'Z'; }
+
+// ascii_islower()
+//
+// Determines whether the given character is lowercase.
+inline bool ascii_islower(unsigned char c) { return c >= 'a' && c <= 'z'; }
+
+// ascii_isascii()
+//
+// Determines whether the given character is ASCII.
+inline bool ascii_isascii(unsigned char c) { return c < 128; }
+
+// ascii_tolower()
+//
+// Returns an ASCII character, converting to lowercase if uppercase is
+// passed. Note that character values > 127 are simply returned.
+inline char ascii_tolower(unsigned char c) {
+  return ascii_internal::kToLower[c];
+}
+
+// Converts the characters in `s` to lowercase, changing the contents of `s`.
+void AsciiStrToLower(std::string* s);
+
+// Creates a lowercase string from a given absl::string_view.
+ABSL_MUST_USE_RESULT inline std::string AsciiStrToLower(absl::string_view s) {
+  std::string result(s);
+  absl::AsciiStrToLower(&result);
+  return result;
+}
+
+// ascii_toupper()
+//
+// Returns the ASCII character, converting to upper-case if lower-case is
+// passed. Note that characters values > 127 are simply returned.
+inline char ascii_toupper(unsigned char c) {
+  return ascii_internal::kToUpper[c];
+}
+
+// Converts the characters in `s` to uppercase, changing the contents of `s`.
+void AsciiStrToUpper(std::string* s);
+
+// Creates an uppercase string from a given absl::string_view.
+ABSL_MUST_USE_RESULT inline std::string AsciiStrToUpper(absl::string_view s) {
+  std::string result(s);
+  absl::AsciiStrToUpper(&result);
+  return result;
+}
+
+// Returns absl::string_view with whitespace stripped from the beginning of the
+// given string_view.
+ABSL_MUST_USE_RESULT inline absl::string_view StripLeadingAsciiWhitespace(
+    absl::string_view str) {
+  auto it = std::find_if_not(str.begin(), str.end(), absl::ascii_isspace);
+  return str.substr(it - str.begin());
+}
+
+// Strips in place whitespace from the beginning of the given string.
+inline void StripLeadingAsciiWhitespace(std::string* str) {
+  auto it = std::find_if_not(str->begin(), str->end(), absl::ascii_isspace);
+  str->erase(str->begin(), it);
+}
+
+// Returns absl::string_view with whitespace stripped from the end of the given
+// string_view.
+ABSL_MUST_USE_RESULT inline absl::string_view StripTrailingAsciiWhitespace(
+    absl::string_view str) {
+  auto it = std::find_if_not(str.rbegin(), str.rend(), absl::ascii_isspace);
+  return str.substr(0, str.rend() - it);
+}
+
+// Strips in place whitespace from the end of the given string
+inline void StripTrailingAsciiWhitespace(std::string* str) {
+  auto it = std::find_if_not(str->rbegin(), str->rend(), absl::ascii_isspace);
+  str->erase(str->rend() - it);
+}
+
+// Returns absl::string_view with whitespace stripped from both ends of the
+// given string_view.
+ABSL_MUST_USE_RESULT inline absl::string_view StripAsciiWhitespace(
+    absl::string_view str) {
+  return StripTrailingAsciiWhitespace(StripLeadingAsciiWhitespace(str));
+}
+
+// Strips in place whitespace from both ends of the given string
+inline void StripAsciiWhitespace(std::string* str) {
+  StripTrailingAsciiWhitespace(str);
+  StripLeadingAsciiWhitespace(str);
+}
+
+// Removes leading, trailing, and consecutive internal whitespace.
+void RemoveExtraAsciiWhitespace(std::string*);
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_ASCII_H_
diff --git a/absl/strings/ascii_benchmark.cc b/absl/strings/ascii_benchmark.cc
new file mode 100644
index 0000000..aca458c
--- /dev/null
+++ b/absl/strings/ascii_benchmark.cc
@@ -0,0 +1,120 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/ascii.h"
+
+#include <cctype>
+#include <string>
+#include <array>
+#include <random>
+
+#include "benchmark/benchmark.h"
+
+namespace {
+
+std::array<unsigned char, 256> MakeShuffledBytes() {
+  std::array<unsigned char, 256> bytes;
+  for (size_t i = 0; i < 256; ++i) bytes[i] = static_cast<unsigned char>(i);
+  std::random_device rd;
+  std::seed_seq seed({rd(), rd(), rd(), rd(), rd(), rd(), rd(), rd()});
+  std::mt19937 g(seed);
+  std::shuffle(bytes.begin(), bytes.end(), g);
+  return bytes;
+}
+
+template <typename Function>
+void AsciiBenchmark(benchmark::State& state, Function f) {
+  std::array<unsigned char, 256> bytes = MakeShuffledBytes();
+  size_t sum = 0;
+  for (auto _ : state) {
+    for (unsigned char b : bytes) sum += f(b) ? 1 : 0;
+  }
+  // Make a copy of `sum` before calling `DoNotOptimize` to make sure that `sum`
+  // can be put in a CPU register and not degrade performance in the loop above.
+  size_t sum2 = sum;
+  benchmark::DoNotOptimize(sum2);
+  state.SetBytesProcessed(state.iterations() * bytes.size());
+}
+
+using StdAsciiFunction = int (*)(int);
+template <StdAsciiFunction f>
+void BM_Ascii(benchmark::State& state) {
+  AsciiBenchmark(state, f);
+}
+
+using AbslAsciiIsFunction = bool (*)(unsigned char);
+template <AbslAsciiIsFunction f>
+void BM_Ascii(benchmark::State& state) {
+  AsciiBenchmark(state, f);
+}
+
+using AbslAsciiToFunction = char (*)(unsigned char);
+template <AbslAsciiToFunction f>
+void BM_Ascii(benchmark::State& state) {
+  AsciiBenchmark(state, f);
+}
+
+inline char Noop(unsigned char b) { return static_cast<char>(b); }
+
+BENCHMARK_TEMPLATE(BM_Ascii, Noop);
+BENCHMARK_TEMPLATE(BM_Ascii, std::isalpha);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_isalpha);
+BENCHMARK_TEMPLATE(BM_Ascii, std::isdigit);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_isdigit);
+BENCHMARK_TEMPLATE(BM_Ascii, std::isalnum);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_isalnum);
+BENCHMARK_TEMPLATE(BM_Ascii, std::isspace);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_isspace);
+BENCHMARK_TEMPLATE(BM_Ascii, std::ispunct);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_ispunct);
+BENCHMARK_TEMPLATE(BM_Ascii, std::isblank);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_isblank);
+BENCHMARK_TEMPLATE(BM_Ascii, std::iscntrl);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_iscntrl);
+BENCHMARK_TEMPLATE(BM_Ascii, std::isxdigit);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_isxdigit);
+BENCHMARK_TEMPLATE(BM_Ascii, std::isprint);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_isprint);
+BENCHMARK_TEMPLATE(BM_Ascii, std::isgraph);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_isgraph);
+BENCHMARK_TEMPLATE(BM_Ascii, std::isupper);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_isupper);
+BENCHMARK_TEMPLATE(BM_Ascii, std::islower);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_islower);
+BENCHMARK_TEMPLATE(BM_Ascii, isascii);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_isascii);
+BENCHMARK_TEMPLATE(BM_Ascii, std::tolower);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_tolower);
+BENCHMARK_TEMPLATE(BM_Ascii, std::toupper);
+BENCHMARK_TEMPLATE(BM_Ascii, absl::ascii_toupper);
+
+static void BM_StrToLower(benchmark::State& state) {
+  const int size = state.range(0);
+  std::string s(size, 'X');
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(absl::AsciiStrToLower(s));
+  }
+}
+BENCHMARK(BM_StrToLower)->Range(1, 1 << 20);
+
+static void BM_StrToUpper(benchmark::State& state) {
+  const int size = state.range(0);
+  std::string s(size, 'x');
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(absl::AsciiStrToUpper(s));
+  }
+}
+BENCHMARK(BM_StrToUpper)->Range(1, 1 << 20);
+
+}  // namespace
diff --git a/absl/strings/ascii_test.cc b/absl/strings/ascii_test.cc
new file mode 100644
index 0000000..5ecd23f
--- /dev/null
+++ b/absl/strings/ascii_test.cc
@@ -0,0 +1,361 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/ascii.h"
+
+#include <cctype>
+#include <clocale>
+#include <cstring>
+#include <string>
+
+#include "gtest/gtest.h"
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+
+namespace {
+
+TEST(AsciiIsFoo, All) {
+  for (int i = 0; i < 256; i++) {
+    if ((i >= 'a' && i <= 'z') || (i >= 'A' && i <= 'Z'))
+      EXPECT_TRUE(absl::ascii_isalpha(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_isalpha(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if ((i >= '0' && i <= '9'))
+      EXPECT_TRUE(absl::ascii_isdigit(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_isdigit(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if (absl::ascii_isalpha(i) || absl::ascii_isdigit(i))
+      EXPECT_TRUE(absl::ascii_isalnum(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_isalnum(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if (i != '\0' && strchr(" \r\n\t\v\f", i))
+      EXPECT_TRUE(absl::ascii_isspace(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_isspace(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if (i >= 32 && i < 127)
+      EXPECT_TRUE(absl::ascii_isprint(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_isprint(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if (absl::ascii_isprint(i) && !absl::ascii_isspace(i) &&
+        !absl::ascii_isalnum(i))
+      EXPECT_TRUE(absl::ascii_ispunct(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_ispunct(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if (i == ' ' || i == '\t')
+      EXPECT_TRUE(absl::ascii_isblank(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_isblank(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if (i < 32 || i == 127)
+      EXPECT_TRUE(absl::ascii_iscntrl(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_iscntrl(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if (absl::ascii_isdigit(i) || (i >= 'A' && i <= 'F') ||
+        (i >= 'a' && i <= 'f'))
+      EXPECT_TRUE(absl::ascii_isxdigit(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_isxdigit(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if (i > 32 && i < 127)
+      EXPECT_TRUE(absl::ascii_isgraph(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_isgraph(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if (i >= 'A' && i <= 'Z')
+      EXPECT_TRUE(absl::ascii_isupper(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_isupper(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 256; i++) {
+    if (i >= 'a' && i <= 'z')
+      EXPECT_TRUE(absl::ascii_islower(i)) << ": failed on " << i;
+    else
+      EXPECT_TRUE(!absl::ascii_islower(i)) << ": failed on " << i;
+  }
+  for (int i = 0; i < 128; i++) {
+    EXPECT_TRUE(absl::ascii_isascii(i)) << ": failed on " << i;
+  }
+  for (int i = 128; i < 256; i++) {
+    EXPECT_TRUE(!absl::ascii_isascii(i)) << ": failed on " << i;
+  }
+
+  // The official is* functions don't accept negative signed chars, but
+  // our absl::ascii_is* functions do.
+  for (int i = 0; i < 256; i++) {
+    signed char sc = static_cast<signed char>(static_cast<unsigned char>(i));
+    EXPECT_EQ(absl::ascii_isalpha(i), absl::ascii_isalpha(sc)) << i;
+    EXPECT_EQ(absl::ascii_isdigit(i), absl::ascii_isdigit(sc)) << i;
+    EXPECT_EQ(absl::ascii_isalnum(i), absl::ascii_isalnum(sc)) << i;
+    EXPECT_EQ(absl::ascii_isspace(i), absl::ascii_isspace(sc)) << i;
+    EXPECT_EQ(absl::ascii_ispunct(i), absl::ascii_ispunct(sc)) << i;
+    EXPECT_EQ(absl::ascii_isblank(i), absl::ascii_isblank(sc)) << i;
+    EXPECT_EQ(absl::ascii_iscntrl(i), absl::ascii_iscntrl(sc)) << i;
+    EXPECT_EQ(absl::ascii_isxdigit(i), absl::ascii_isxdigit(sc)) << i;
+    EXPECT_EQ(absl::ascii_isprint(i), absl::ascii_isprint(sc)) << i;
+    EXPECT_EQ(absl::ascii_isgraph(i), absl::ascii_isgraph(sc)) << i;
+    EXPECT_EQ(absl::ascii_isupper(i), absl::ascii_isupper(sc)) << i;
+    EXPECT_EQ(absl::ascii_islower(i), absl::ascii_islower(sc)) << i;
+    EXPECT_EQ(absl::ascii_isascii(i), absl::ascii_isascii(sc)) << i;
+  }
+}
+
+// Checks that absl::ascii_isfoo returns the same value as isfoo in the C
+// locale.
+TEST(AsciiIsFoo, SameAsIsFoo) {
+#ifndef __ANDROID__
+  // temporarily change locale to C. It should already be C, but just for safety
+  const char* old_locale = setlocale(LC_CTYPE, "C");
+  ASSERT_TRUE(old_locale != nullptr);
+#endif
+
+  for (int i = 0; i < 256; i++) {
+    EXPECT_EQ(isalpha(i) != 0, absl::ascii_isalpha(i)) << i;
+    EXPECT_EQ(isdigit(i) != 0, absl::ascii_isdigit(i)) << i;
+    EXPECT_EQ(isalnum(i) != 0, absl::ascii_isalnum(i)) << i;
+    EXPECT_EQ(isspace(i) != 0, absl::ascii_isspace(i)) << i;
+    EXPECT_EQ(ispunct(i) != 0, absl::ascii_ispunct(i)) << i;
+    EXPECT_EQ(isblank(i) != 0, absl::ascii_isblank(i)) << i;
+    EXPECT_EQ(iscntrl(i) != 0, absl::ascii_iscntrl(i)) << i;
+    EXPECT_EQ(isxdigit(i) != 0, absl::ascii_isxdigit(i)) << i;
+    EXPECT_EQ(isprint(i) != 0, absl::ascii_isprint(i)) << i;
+    EXPECT_EQ(isgraph(i) != 0, absl::ascii_isgraph(i)) << i;
+    EXPECT_EQ(isupper(i) != 0, absl::ascii_isupper(i)) << i;
+    EXPECT_EQ(islower(i) != 0, absl::ascii_islower(i)) << i;
+    EXPECT_EQ(isascii(i) != 0, absl::ascii_isascii(i)) << i;
+  }
+
+#ifndef __ANDROID__
+  // restore the old locale.
+  ASSERT_TRUE(setlocale(LC_CTYPE, old_locale));
+#endif
+}
+
+TEST(AsciiToFoo, All) {
+#ifndef __ANDROID__
+  // temporarily change locale to C. It should already be C, but just for safety
+  const char* old_locale = setlocale(LC_CTYPE, "C");
+  ASSERT_TRUE(old_locale != nullptr);
+#endif
+
+  for (int i = 0; i < 256; i++) {
+    if (absl::ascii_islower(i))
+      EXPECT_EQ(absl::ascii_toupper(i), 'A' + (i - 'a')) << i;
+    else
+      EXPECT_EQ(absl::ascii_toupper(i), static_cast<char>(i)) << i;
+
+    if (absl::ascii_isupper(i))
+      EXPECT_EQ(absl::ascii_tolower(i), 'a' + (i - 'A')) << i;
+    else
+      EXPECT_EQ(absl::ascii_tolower(i), static_cast<char>(i)) << i;
+
+    // These CHECKs only hold in a C locale.
+    EXPECT_EQ(static_cast<char>(tolower(i)), absl::ascii_tolower(i)) << i;
+    EXPECT_EQ(static_cast<char>(toupper(i)), absl::ascii_toupper(i)) << i;
+
+    // The official to* functions don't accept negative signed chars, but
+    // our absl::ascii_to* functions do.
+    signed char sc = static_cast<signed char>(static_cast<unsigned char>(i));
+    EXPECT_EQ(absl::ascii_tolower(i), absl::ascii_tolower(sc)) << i;
+    EXPECT_EQ(absl::ascii_toupper(i), absl::ascii_toupper(sc)) << i;
+  }
+#ifndef __ANDROID__
+  // restore the old locale.
+  ASSERT_TRUE(setlocale(LC_CTYPE, old_locale));
+#endif
+}
+
+TEST(AsciiStrTo, Lower) {
+  const char buf[] = "ABCDEF";
+  const std::string str("GHIJKL");
+  const std::string str2("MNOPQR");
+  const absl::string_view sp(str2);
+
+  EXPECT_EQ("abcdef", absl::AsciiStrToLower(buf));
+  EXPECT_EQ("ghijkl", absl::AsciiStrToLower(str));
+  EXPECT_EQ("mnopqr", absl::AsciiStrToLower(sp));
+
+  char mutable_buf[] = "Mutable";
+  std::transform(mutable_buf, mutable_buf + strlen(mutable_buf),
+                 mutable_buf, absl::ascii_tolower);
+  EXPECT_STREQ("mutable", mutable_buf);
+}
+
+TEST(AsciiStrTo, Upper) {
+  const char buf[] = "abcdef";
+  const std::string str("ghijkl");
+  const std::string str2("mnopqr");
+  const absl::string_view sp(str2);
+
+  EXPECT_EQ("ABCDEF", absl::AsciiStrToUpper(buf));
+  EXPECT_EQ("GHIJKL", absl::AsciiStrToUpper(str));
+  EXPECT_EQ("MNOPQR", absl::AsciiStrToUpper(sp));
+
+  char mutable_buf[] = "Mutable";
+  std::transform(mutable_buf, mutable_buf + strlen(mutable_buf),
+                 mutable_buf, absl::ascii_toupper);
+  EXPECT_STREQ("MUTABLE", mutable_buf);
+}
+
+TEST(StripLeadingAsciiWhitespace, FromStringView) {
+  EXPECT_EQ(absl::string_view{},
+            absl::StripLeadingAsciiWhitespace(absl::string_view{}));
+  EXPECT_EQ("foo", absl::StripLeadingAsciiWhitespace({"foo"}));
+  EXPECT_EQ("foo", absl::StripLeadingAsciiWhitespace({"\t  \n\f\r\n\vfoo"}));
+  EXPECT_EQ("foo foo\n ",
+            absl::StripLeadingAsciiWhitespace({"\t  \n\f\r\n\vfoo foo\n "}));
+  EXPECT_EQ(absl::string_view{}, absl::StripLeadingAsciiWhitespace(
+                                     {"\t  \n\f\r\v\n\t  \n\f\r\v\n"}));
+}
+
+TEST(StripLeadingAsciiWhitespace, InPlace) {
+  std::string str;
+
+  absl::StripLeadingAsciiWhitespace(&str);
+  EXPECT_EQ("", str);
+
+  str = "foo";
+  absl::StripLeadingAsciiWhitespace(&str);
+  EXPECT_EQ("foo", str);
+
+  str = "\t  \n\f\r\n\vfoo";
+  absl::StripLeadingAsciiWhitespace(&str);
+  EXPECT_EQ("foo", str);
+
+  str = "\t  \n\f\r\n\vfoo foo\n ";
+  absl::StripLeadingAsciiWhitespace(&str);
+  EXPECT_EQ("foo foo\n ", str);
+
+  str = "\t  \n\f\r\v\n\t  \n\f\r\v\n";
+  absl::StripLeadingAsciiWhitespace(&str);
+  EXPECT_EQ(absl::string_view{}, str);
+}
+
+TEST(StripTrailingAsciiWhitespace, FromStringView) {
+  EXPECT_EQ(absl::string_view{},
+            absl::StripTrailingAsciiWhitespace(absl::string_view{}));
+  EXPECT_EQ("foo", absl::StripTrailingAsciiWhitespace({"foo"}));
+  EXPECT_EQ("foo", absl::StripTrailingAsciiWhitespace({"foo\t  \n\f\r\n\v"}));
+  EXPECT_EQ(" \nfoo foo",
+            absl::StripTrailingAsciiWhitespace({" \nfoo foo\t  \n\f\r\n\v"}));
+  EXPECT_EQ(absl::string_view{}, absl::StripTrailingAsciiWhitespace(
+                                     {"\t  \n\f\r\v\n\t  \n\f\r\v\n"}));
+}
+
+TEST(StripTrailingAsciiWhitespace, InPlace) {
+  std::string str;
+
+  absl::StripTrailingAsciiWhitespace(&str);
+  EXPECT_EQ("", str);
+
+  str = "foo";
+  absl::StripTrailingAsciiWhitespace(&str);
+  EXPECT_EQ("foo", str);
+
+  str = "foo\t  \n\f\r\n\v";
+  absl::StripTrailingAsciiWhitespace(&str);
+  EXPECT_EQ("foo", str);
+
+  str = " \nfoo foo\t  \n\f\r\n\v";
+  absl::StripTrailingAsciiWhitespace(&str);
+  EXPECT_EQ(" \nfoo foo", str);
+
+  str = "\t  \n\f\r\v\n\t  \n\f\r\v\n";
+  absl::StripTrailingAsciiWhitespace(&str);
+  EXPECT_EQ(absl::string_view{}, str);
+}
+
+TEST(StripAsciiWhitespace, FromStringView) {
+  EXPECT_EQ(absl::string_view{},
+            absl::StripAsciiWhitespace(absl::string_view{}));
+  EXPECT_EQ("foo", absl::StripAsciiWhitespace({"foo"}));
+  EXPECT_EQ("foo",
+            absl::StripAsciiWhitespace({"\t  \n\f\r\n\vfoo\t  \n\f\r\n\v"}));
+  EXPECT_EQ("foo foo", absl::StripAsciiWhitespace(
+                           {"\t  \n\f\r\n\vfoo foo\t  \n\f\r\n\v"}));
+  EXPECT_EQ(absl::string_view{},
+            absl::StripAsciiWhitespace({"\t  \n\f\r\v\n\t  \n\f\r\v\n"}));
+}
+
+TEST(StripAsciiWhitespace, InPlace) {
+  std::string str;
+
+  absl::StripAsciiWhitespace(&str);
+  EXPECT_EQ("", str);
+
+  str = "foo";
+  absl::StripAsciiWhitespace(&str);
+  EXPECT_EQ("foo", str);
+
+  str = "\t  \n\f\r\n\vfoo\t  \n\f\r\n\v";
+  absl::StripAsciiWhitespace(&str);
+  EXPECT_EQ("foo", str);
+
+  str = "\t  \n\f\r\n\vfoo foo\t  \n\f\r\n\v";
+  absl::StripAsciiWhitespace(&str);
+  EXPECT_EQ("foo foo", str);
+
+  str = "\t  \n\f\r\v\n\t  \n\f\r\v\n";
+  absl::StripAsciiWhitespace(&str);
+  EXPECT_EQ(absl::string_view{}, str);
+}
+
+TEST(RemoveExtraAsciiWhitespace, InPlace) {
+  const char* inputs[] = {"No extra space",
+                          "  Leading whitespace",
+                          "Trailing whitespace  ",
+                          "  Leading and trailing  ",
+                          " Whitespace \t  in\v   middle  ",
+                          "'Eeeeep!  \n Newlines!\n",
+                          "nospaces",
+                          "",
+                          "\n\t a\t\n\nb \t\n"};
+
+  const char* outputs[] = {
+      "No extra space",
+      "Leading whitespace",
+      "Trailing whitespace",
+      "Leading and trailing",
+      "Whitespace in middle",
+      "'Eeeeep! Newlines!",
+      "nospaces",
+      "",
+      "a\nb",
+  };
+  const int NUM_TESTS = ABSL_ARRAYSIZE(inputs);
+
+  for (int i = 0; i < NUM_TESTS; i++) {
+    std::string s(inputs[i]);
+    absl::RemoveExtraAsciiWhitespace(&s);
+    EXPECT_EQ(outputs[i], s);
+  }
+}
+
+}  // namespace
diff --git a/absl/strings/charconv.cc b/absl/strings/charconv.cc
new file mode 100644
index 0000000..bc07e7a
--- /dev/null
+++ b/absl/strings/charconv.cc
@@ -0,0 +1,983 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/charconv.h"
+
+#include <algorithm>
+#include <cassert>
+#include <cmath>
+#include <cstring>
+
+#include "absl/base/casts.h"
+#include "absl/base/internal/bits.h"
+#include "absl/numeric/int128.h"
+#include "absl/strings/internal/charconv_bigint.h"
+#include "absl/strings/internal/charconv_parse.h"
+
+// The macro ABSL_BIT_PACK_FLOATS is defined on x86-64, where IEEE floating
+// point numbers have the same endianness in memory as a bitfield struct
+// containing the corresponding parts.
+//
+// When set, we replace calls to ldexp() with manual bit packing, which is
+// faster and is unaffected by floating point environment.
+#ifdef ABSL_BIT_PACK_FLOATS
+#error ABSL_BIT_PACK_FLOATS cannot be directly set
+#elif defined(__x86_64__) || defined(_M_X64)
+#define ABSL_BIT_PACK_FLOATS 1
+#endif
+
+// A note about subnormals:
+//
+// The code below talks about "normals" and "subnormals".  A normal IEEE float
+// has a fixed-width mantissa and power of two exponent.  For example, a normal
+// `double` has a 53-bit mantissa.  Because the high bit is always 1, it is not
+// stored in the representation.  The implicit bit buys an extra bit of
+// resolution in the datatype.
+//
+// The downside of this scheme is that there is a large gap between DBL_MIN and
+// zero.  (Large, at least, relative to the different between DBL_MIN and the
+// next representable number).  This gap is softened by the "subnormal" numbers,
+// which have the same power-of-two exponent as DBL_MIN, but no implicit 53rd
+// bit.  An all-bits-zero exponent in the encoding represents subnormals.  (Zero
+// is represented as a subnormal with an all-bits-zero mantissa.)
+//
+// The code below, in calculations, represents the mantissa as a uint64_t.  The
+// end result normally has the 53rd bit set.  It represents subnormals by using
+// narrower mantissas.
+
+namespace absl {
+namespace {
+
+template <typename FloatType>
+struct FloatTraits;
+
+template <>
+struct FloatTraits<double> {
+  // The number of mantissa bits in the given float type.  This includes the
+  // implied high bit.
+  static constexpr int kTargetMantissaBits = 53;
+
+  // The largest supported IEEE exponent, in our integral mantissa
+  // representation.
+  //
+  // If `m` is the largest possible int kTargetMantissaBits bits wide, then
+  // m * 2**kMaxExponent is exactly equal to DBL_MAX.
+  static constexpr int kMaxExponent = 971;
+
+  // The smallest supported IEEE normal exponent, in our integral mantissa
+  // representation.
+  //
+  // If `m` is the smallest possible int kTargetMantissaBits bits wide, then
+  // m * 2**kMinNormalExponent is exactly equal to DBL_MIN.
+  static constexpr int kMinNormalExponent = -1074;
+
+  static double MakeNan(const char* tagp) {
+    // Support nan no matter which namespace it's in.  Some platforms
+    // incorrectly don't put it in namespace std.
+    using namespace std;  // NOLINT
+    return nan(tagp);
+  }
+
+  // Builds a nonzero floating point number out of the provided parts.
+  //
+  // This is intended to do the same operation as ldexp(mantissa, exponent),
+  // but using purely integer math, to avoid -ffastmath and floating
+  // point environment issues.  Using type punning is also faster. We fall back
+  // to ldexp on a per-platform basis for portability.
+  //
+  // `exponent` must be between kMinNormalExponent and kMaxExponent.
+  //
+  // `mantissa` must either be exactly kTargetMantissaBits wide, in which case
+  // a normal value is made, or it must be less narrow than that, in which case
+  // `exponent` must be exactly kMinNormalExponent, and a subnormal value is
+  // made.
+  static double Make(uint64_t mantissa, int exponent, bool sign) {
+#ifndef ABSL_BIT_PACK_FLOATS
+    // Support ldexp no matter which namespace it's in.  Some platforms
+    // incorrectly don't put it in namespace std.
+    using namespace std;  // NOLINT
+    return sign ? -ldexp(mantissa, exponent) : ldexp(mantissa, exponent);
+#else
+    constexpr uint64_t kMantissaMask =
+        (uint64_t(1) << (kTargetMantissaBits - 1)) - 1;
+    uint64_t dbl = static_cast<uint64_t>(sign) << 63;
+    if (mantissa > kMantissaMask) {
+      // Normal value.
+      // Adjust by 1023 for the exponent representation bias, and an additional
+      // 52 due to the implied decimal point in the IEEE mantissa represenation.
+      dbl += uint64_t{exponent + 1023u + kTargetMantissaBits - 1} << 52;
+      mantissa &= kMantissaMask;
+    } else {
+      // subnormal value
+      assert(exponent == kMinNormalExponent);
+    }
+    dbl += mantissa;
+    return absl::bit_cast<double>(dbl);
+#endif  // ABSL_BIT_PACK_FLOATS
+  }
+};
+
+// Specialization of floating point traits for the `float` type.  See the
+// FloatTraits<double> specialization above for meaning of each of the following
+// members and methods.
+template <>
+struct FloatTraits<float> {
+  static constexpr int kTargetMantissaBits = 24;
+  static constexpr int kMaxExponent = 104;
+  static constexpr int kMinNormalExponent = -149;
+  static float MakeNan(const char* tagp) {
+    // Support nanf no matter which namespace it's in.  Some platforms
+    // incorrectly don't put it in namespace std.
+    using namespace std;  // NOLINT
+    return nanf(tagp);
+  }
+  static float Make(uint32_t mantissa, int exponent, bool sign) {
+#ifndef ABSL_BIT_PACK_FLOATS
+    // Support ldexpf no matter which namespace it's in.  Some platforms
+    // incorrectly don't put it in namespace std.
+    using namespace std;  // NOLINT
+    return sign ? -ldexpf(mantissa, exponent) : ldexpf(mantissa, exponent);
+#else
+    constexpr uint32_t kMantissaMask =
+        (uint32_t(1) << (kTargetMantissaBits - 1)) - 1;
+    uint32_t flt = static_cast<uint32_t>(sign) << 31;
+    if (mantissa > kMantissaMask) {
+      // Normal value.
+      // Adjust by 127 for the exponent representation bias, and an additional
+      // 23 due to the implied decimal point in the IEEE mantissa represenation.
+      flt += uint32_t{exponent + 127u + kTargetMantissaBits - 1} << 23;
+      mantissa &= kMantissaMask;
+    } else {
+      // subnormal value
+      assert(exponent == kMinNormalExponent);
+    }
+    flt += mantissa;
+    return absl::bit_cast<float>(flt);
+#endif  // ABSL_BIT_PACK_FLOATS
+  }
+};
+
+// Decimal-to-binary conversions require coercing powers of 10 into a mantissa
+// and a power of 2.  The two helper functions Power10Mantissa(n) and
+// Power10Exponent(n) perform this task.  Together, these represent a hand-
+// rolled floating point value which is equal to or just less than 10**n.
+//
+// The return values satisfy two range guarantees:
+//
+//   Power10Mantissa(n) * 2**Power10Exponent(n) <= 10**n
+//     < (Power10Mantissa(n) + 1) * 2**Power10Exponent(n)
+//
+//   2**63 <= Power10Mantissa(n) < 2**64.
+//
+// Lookups into the power-of-10 table must first check the Power10Overflow() and
+// Power10Underflow() functions, to avoid out-of-bounds table access.
+//
+// Indexes into these tables are biased by -kPower10TableMin, and the table has
+// values in the range [kPower10TableMin, kPower10TableMax].
+extern const uint64_t kPower10MantissaTable[];
+extern const int16_t kPower10ExponentTable[];
+
+// The smallest allowed value for use with the Power10Mantissa() and
+// Power10Exponent() functions below.  (If a smaller exponent is needed in
+// calculations, the end result is guaranteed to underflow.)
+constexpr int kPower10TableMin = -342;
+
+// The largest allowed value for use with the Power10Mantissa() and
+// Power10Exponent() functions below.  (If a smaller exponent is needed in
+// calculations, the end result is guaranteed to overflow.)
+constexpr int kPower10TableMax = 308;
+
+uint64_t Power10Mantissa(int n) {
+  return kPower10MantissaTable[n - kPower10TableMin];
+}
+
+int Power10Exponent(int n) {
+  return kPower10ExponentTable[n - kPower10TableMin];
+}
+
+// Returns true if n is large enough that 10**n always results in an IEEE
+// overflow.
+bool Power10Overflow(int n) { return n > kPower10TableMax; }
+
+// Returns true if n is small enough that 10**n times a ParsedFloat mantissa
+// always results in an IEEE underflow.
+bool Power10Underflow(int n) { return n < kPower10TableMin; }
+
+// Returns true if Power10Mantissa(n) * 2**Power10Exponent(n) is exactly equal
+// to 10**n numerically.  Put another way, this returns true if there is no
+// truncation error in Power10Mantissa(n).
+bool Power10Exact(int n) { return n >= 0 && n <= 27; }
+
+// Sentinel exponent values for representing numbers too large or too close to
+// zero to represent in a double.
+constexpr int kOverflow = 99999;
+constexpr int kUnderflow = -99999;
+
+// Struct representing the calculated conversion result of a positive (nonzero)
+// floating point number.
+//
+// The calculated number is mantissa * 2**exponent (mantissa is treated as an
+// integer.)  `mantissa` is chosen to be the correct width for the IEEE float
+// representation being calculated.  (`mantissa` will always have the same bit
+// width for normal values, and narrower bit widths for subnormals.)
+//
+// If the result of conversion was an underflow or overflow, exponent is set
+// to kUnderflow or kOverflow.
+struct CalculatedFloat {
+  uint64_t mantissa = 0;
+  int exponent = 0;
+};
+
+// Returns the bit width of the given uint128.  (Equivalently, returns 128
+// minus the number of leading zero bits.)
+int BitWidth(uint128 value) {
+  if (Uint128High64(value) == 0) {
+    return 64 - base_internal::CountLeadingZeros64(Uint128Low64(value));
+  }
+  return 128 - base_internal::CountLeadingZeros64(Uint128High64(value));
+}
+
+// Calculates how far to the right a mantissa needs to be shifted to create a
+// properly adjusted mantissa for an IEEE floating point number.
+//
+// `mantissa_width` is the bit width of the mantissa to be shifted, and
+// `binary_exponent` is the exponent of the number before the shift.
+//
+// This accounts for subnormal values, and will return a larger-than-normal
+// shift if binary_exponent would otherwise be too low.
+template <typename FloatType>
+int NormalizedShiftSize(int mantissa_width, int binary_exponent) {
+  const int normal_shift =
+      mantissa_width - FloatTraits<FloatType>::kTargetMantissaBits;
+  const int minimum_shift =
+      FloatTraits<FloatType>::kMinNormalExponent - binary_exponent;
+  return std::max(normal_shift, minimum_shift);
+}
+
+// Right shifts a uint128 so that it has the requested bit width.  (The
+// resulting value will have 128 - bit_width leading zeroes.)  The initial
+// `value` must be wider than the requested bit width.
+//
+// Returns the number of bits shifted.
+int TruncateToBitWidth(int bit_width, uint128* value) {
+  const int current_bit_width = BitWidth(*value);
+  const int shift = current_bit_width - bit_width;
+  *value >>= shift;
+  return shift;
+}
+
+// Checks if the given ParsedFloat represents one of the edge cases that are
+// not dependent on number base: zero, infinity, or NaN.  If so, sets *value
+// the appropriate double, and returns true.
+template <typename FloatType>
+bool HandleEdgeCase(const strings_internal::ParsedFloat& input, bool negative,
+                    FloatType* value) {
+  if (input.type == strings_internal::FloatType::kNan) {
+    // A bug in both clang and gcc would cause the compiler to optimize away the
+    // buffer we are building below.  Declaring the buffer volatile avoids the
+    // issue, and has no measurable performance impact in microbenchmarks.
+    //
+    // https://bugs.llvm.org/show_bug.cgi?id=37778
+    // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86113
+    constexpr ptrdiff_t kNanBufferSize = 128;
+    volatile char n_char_sequence[kNanBufferSize];
+    if (input.subrange_begin == nullptr) {
+      n_char_sequence[0] = '\0';
+    } else {
+      ptrdiff_t nan_size = input.subrange_end - input.subrange_begin;
+      nan_size = std::min(nan_size, kNanBufferSize - 1);
+      std::copy_n(input.subrange_begin, nan_size, n_char_sequence);
+      n_char_sequence[nan_size] = '\0';
+    }
+    char* nan_argument = const_cast<char*>(n_char_sequence);
+    *value = negative ? -FloatTraits<FloatType>::MakeNan(nan_argument)
+                      : FloatTraits<FloatType>::MakeNan(nan_argument);
+    return true;
+  }
+  if (input.type == strings_internal::FloatType::kInfinity) {
+    *value = negative ? -std::numeric_limits<FloatType>::infinity()
+                      : std::numeric_limits<FloatType>::infinity();
+    return true;
+  }
+  if (input.mantissa == 0) {
+    *value = negative ? -0.0 : 0.0;
+    return true;
+  }
+  return false;
+}
+
+// Given a CalculatedFloat result of a from_chars conversion, generate the
+// correct output values.
+//
+// CalculatedFloat can represent an underflow or overflow, in which case the
+// error code in *result is set.  Otherwise, the calculated floating point
+// number is stored in *value.
+template <typename FloatType>
+void EncodeResult(const CalculatedFloat& calculated, bool negative,
+                  absl::from_chars_result* result, FloatType* value) {
+  if (calculated.exponent == kOverflow) {
+    result->ec = std::errc::result_out_of_range;
+    *value = negative ? -std::numeric_limits<FloatType>::max()
+                      : std::numeric_limits<FloatType>::max();
+    return;
+  } else if (calculated.mantissa == 0 || calculated.exponent == kUnderflow) {
+    result->ec = std::errc::result_out_of_range;
+    *value = negative ? -0.0 : 0.0;
+    return;
+  }
+  *value = FloatTraits<FloatType>::Make(calculated.mantissa,
+                                        calculated.exponent, negative);
+}
+
+// Returns the given uint128 shifted to the right by `shift` bits, and rounds
+// the remaining bits using round_to_nearest logic.  The value is returned as a
+// uint64_t, since this is the type used by this library for storing calculated
+// floating point mantissas.
+//
+// It is expected that the width of the input value shifted by `shift` will
+// be the correct bit-width for the target mantissa, which is strictly narrower
+// than a uint64_t.
+//
+// If `input_exact` is false, then a nonzero error epsilon is assumed.  For
+// rounding purposes, the true value being rounded is strictly greater than the
+// input value.  The error may represent a single lost carry bit.
+//
+// When input_exact, shifted bits of the form 1000000... represent a tie, which
+// is broken by rounding to even -- the rounding direction is chosen so the low
+// bit of the returned value is 0.
+//
+// When !input_exact, shifted bits of the form 10000000... represent a value
+// strictly greater than one half (due to the error epsilon), and so ties are
+// always broken by rounding up.
+//
+// When !input_exact, shifted bits of the form 01111111... are uncertain;
+// the true value may or may not be greater than 10000000..., due to the
+// possible lost carry bit.  The correct rounding direction is unknown.  In this
+// case, the result is rounded down, and `output_exact` is set to false.
+//
+// Zero and negative values of `shift` are accepted, in which case the word is
+// shifted left, as necessary.
+uint64_t ShiftRightAndRound(uint128 value, int shift, bool input_exact,
+                            bool* output_exact) {
+  if (shift <= 0) {
+    *output_exact = input_exact;
+    return static_cast<uint64_t>(value << -shift);
+  }
+  if (shift >= 128) {
+    // Exponent is so small that we are shifting away all significant bits.
+    // Answer will not be representable, even as a subnormal, so return a zero
+    // mantissa (which represents underflow).
+    *output_exact = true;
+    return 0;
+  }
+
+  *output_exact = true;
+  const uint128 shift_mask = (uint128(1) << shift) - 1;
+  const uint128 halfway_point = uint128(1) << (shift - 1);
+
+  const uint128 shifted_bits = value & shift_mask;
+  value >>= shift;
+  if (shifted_bits > halfway_point) {
+    // Shifted bits greater than 10000... require rounding up.
+    return static_cast<uint64_t>(value + 1);
+  }
+  if (shifted_bits == halfway_point) {
+    // In exact mode, shifted bits of 10000... mean we're exactly halfway
+    // between two numbers, and we must round to even.  So only round up if
+    // the low bit of `value` is set.
+    //
+    // In inexact mode, the nonzero error means the actual value is greater
+    // than the halfway point and we must alway round up.
+    if ((value & 1) == 1 || !input_exact) {
+      ++value;
+    }
+    return static_cast<uint64_t>(value);
+  }
+  if (!input_exact && shifted_bits == halfway_point - 1) {
+    // Rounding direction is unclear, due to error.
+    *output_exact = false;
+  }
+  // Otherwise, round down.
+  return static_cast<uint64_t>(value);
+}
+
+// Checks if a floating point guess needs to be rounded up, using high precision
+// math.
+//
+// `guess_mantissa` and `guess_exponent` represent a candidate guess for the
+// number represented by `parsed_decimal`.
+//
+// The exact number represented by `parsed_decimal` must lie between the two
+// numbers:
+//   A = `guess_mantissa * 2**guess_exponent`
+//   B = `(guess_mantissa + 1) * 2**guess_exponent`
+//
+// This function returns false if `A` is the better guess, and true if `B` is
+// the better guess, with rounding ties broken by rounding to even.
+bool MustRoundUp(uint64_t guess_mantissa, int guess_exponent,
+                 const strings_internal::ParsedFloat& parsed_decimal) {
+  // 768 is the number of digits needed in the worst case.  We could determine a
+  // better limit dynamically based on the value of parsed_decimal.exponent.
+  // This would optimize pathological input cases only.  (Sane inputs won't have
+  // hundreds of digits of mantissa.)
+  absl::strings_internal::BigUnsigned<84> exact_mantissa;
+  int exact_exponent = exact_mantissa.ReadFloatMantissa(parsed_decimal, 768);
+
+  // Adjust the `guess` arguments to be halfway between A and B.
+  guess_mantissa = guess_mantissa * 2 + 1;
+  guess_exponent -= 1;
+
+  // In our comparison:
+  // lhs = exact = exact_mantissa * 10**exact_exponent
+  //             = exact_mantissa * 5**exact_exponent * 2**exact_exponent
+  // rhs = guess = guess_mantissa * 2**guess_exponent
+  //
+  // Because we are doing integer math, we can't directly deal with negative
+  // exponents.  We instead move these to the other side of the inequality.
+  absl::strings_internal::BigUnsigned<84>& lhs = exact_mantissa;
+  int comparison;
+  if (exact_exponent >= 0) {
+    lhs.MultiplyByFiveToTheNth(exact_exponent);
+    absl::strings_internal::BigUnsigned<84> rhs(guess_mantissa);
+    // There are powers of 2 on both sides of the inequality; reduce this to
+    // a single bit-shift.
+    if (exact_exponent > guess_exponent) {
+      lhs.ShiftLeft(exact_exponent - guess_exponent);
+    } else {
+      rhs.ShiftLeft(guess_exponent - exact_exponent);
+    }
+    comparison = Compare(lhs, rhs);
+  } else {
+    // Move the power of 5 to the other side of the equation, giving us:
+    // lhs = exact_mantissa * 2**exact_exponent
+    // rhs = guess_mantissa * 5**(-exact_exponent) * 2**guess_exponent
+    absl::strings_internal::BigUnsigned<84> rhs =
+        absl::strings_internal::BigUnsigned<84>::FiveToTheNth(-exact_exponent);
+    rhs.MultiplyBy(guess_mantissa);
+    if (exact_exponent > guess_exponent) {
+      lhs.ShiftLeft(exact_exponent - guess_exponent);
+    } else {
+      rhs.ShiftLeft(guess_exponent - exact_exponent);
+    }
+    comparison = Compare(lhs, rhs);
+  }
+  if (comparison < 0) {
+    return false;
+  } else if (comparison > 0) {
+    return true;
+  } else {
+    // When lhs == rhs, the decimal input is exactly between A and B.
+    // Round towards even -- round up only if the low bit of the initial
+    // `guess_mantissa` was a 1.  We shifted guess_mantissa left 1 bit at
+    // the beginning of this function, so test the 2nd bit here.
+    return (guess_mantissa & 2) == 2;
+  }
+}
+
+// Constructs a CalculatedFloat from a given mantissa and exponent, but
+// with the following normalizations applied:
+//
+// If rounding has caused mantissa to increase just past the allowed bit
+// width, shift and adjust exponent.
+//
+// If exponent is too high, sets kOverflow.
+//
+// If mantissa is zero (representing a non-zero value not representable, even
+// as a subnormal), sets kUnderflow.
+template <typename FloatType>
+CalculatedFloat CalculatedFloatFromRawValues(uint64_t mantissa, int exponent) {
+  CalculatedFloat result;
+  if (mantissa == uint64_t(1) << FloatTraits<FloatType>::kTargetMantissaBits) {
+    mantissa >>= 1;
+    exponent += 1;
+  }
+  if (exponent > FloatTraits<FloatType>::kMaxExponent) {
+    result.exponent = kOverflow;
+  } else if (mantissa == 0) {
+    result.exponent = kUnderflow;
+  } else {
+    result.exponent = exponent;
+    result.mantissa = mantissa;
+  }
+  return result;
+}
+
+template <typename FloatType>
+CalculatedFloat CalculateFromParsedHexadecimal(
+    const strings_internal::ParsedFloat& parsed_hex) {
+  uint64_t mantissa = parsed_hex.mantissa;
+  int exponent = parsed_hex.exponent;
+  int mantissa_width = 64 - base_internal::CountLeadingZeros64(mantissa);
+  const int shift = NormalizedShiftSize<FloatType>(mantissa_width, exponent);
+  bool result_exact;
+  exponent += shift;
+  mantissa = ShiftRightAndRound(mantissa, shift,
+                                /* input exact= */ true, &result_exact);
+  // ParseFloat handles rounding in the hexadecimal case, so we don't have to
+  // check `result_exact` here.
+  return CalculatedFloatFromRawValues<FloatType>(mantissa, exponent);
+}
+
+template <typename FloatType>
+CalculatedFloat CalculateFromParsedDecimal(
+    const strings_internal::ParsedFloat& parsed_decimal) {
+  CalculatedFloat result;
+
+  // Large or small enough decimal exponents will always result in overflow
+  // or underflow.
+  if (Power10Underflow(parsed_decimal.exponent)) {
+    result.exponent = kUnderflow;
+    return result;
+  } else if (Power10Overflow(parsed_decimal.exponent)) {
+    result.exponent = kOverflow;
+    return result;
+  }
+
+  // Otherwise convert our power of 10 into a power of 2 times an integer
+  // mantissa, and multiply this by our parsed decimal mantissa.
+  uint128 wide_binary_mantissa = parsed_decimal.mantissa;
+  wide_binary_mantissa *= Power10Mantissa(parsed_decimal.exponent);
+  int binary_exponent = Power10Exponent(parsed_decimal.exponent);
+
+  // Discard bits that are inaccurate due to truncation error.  The magic
+  // `mantissa_width` constants below are justified in
+  // https://abseil.io/about/design/charconv. They represent the number of bits
+  // in `wide_binary_mantissa` that are guaranteed to be unaffected by error
+  // propagation.
+  bool mantissa_exact;
+  int mantissa_width;
+  if (parsed_decimal.subrange_begin) {
+    // Truncated mantissa
+    mantissa_width = 58;
+    mantissa_exact = false;
+    binary_exponent +=
+        TruncateToBitWidth(mantissa_width, &wide_binary_mantissa);
+  } else if (!Power10Exact(parsed_decimal.exponent)) {
+    // Exact mantissa, truncated power of ten
+    mantissa_width = 63;
+    mantissa_exact = false;
+    binary_exponent +=
+        TruncateToBitWidth(mantissa_width, &wide_binary_mantissa);
+  } else {
+    // Product is exact
+    mantissa_width = BitWidth(wide_binary_mantissa);
+    mantissa_exact = true;
+  }
+
+  // Shift into an FloatType-sized mantissa, and round to nearest.
+  const int shift =
+      NormalizedShiftSize<FloatType>(mantissa_width, binary_exponent);
+  bool result_exact;
+  binary_exponent += shift;
+  uint64_t binary_mantissa = ShiftRightAndRound(wide_binary_mantissa, shift,
+                                                mantissa_exact, &result_exact);
+  if (!result_exact) {
+    // We could not determine the rounding direction using int128 math.  Use
+    // full resolution math instead.
+    if (MustRoundUp(binary_mantissa, binary_exponent, parsed_decimal)) {
+      binary_mantissa += 1;
+    }
+  }
+
+  return CalculatedFloatFromRawValues<FloatType>(binary_mantissa,
+                                                 binary_exponent);
+}
+
+template <typename FloatType>
+from_chars_result FromCharsImpl(const char* first, const char* last,
+                                FloatType& value, chars_format fmt_flags) {
+  from_chars_result result;
+  result.ptr = first;  // overwritten on successful parse
+  result.ec = std::errc();
+
+  bool negative = false;
+  if (first != last && *first == '-') {
+    ++first;
+    negative = true;
+  }
+  // If the `hex` flag is *not* set, then we will accept a 0x prefix and try
+  // to parse a hexadecimal float.
+  if ((fmt_flags & chars_format::hex) == chars_format{} && last - first >= 2 &&
+      *first == '0' && (first[1] == 'x' || first[1] == 'X')) {
+    const char* hex_first = first + 2;
+    strings_internal::ParsedFloat hex_parse =
+        strings_internal::ParseFloat<16>(hex_first, last, fmt_flags);
+    if (hex_parse.end == nullptr ||
+        hex_parse.type != strings_internal::FloatType::kNumber) {
+      // Either we failed to parse a hex float after the "0x", or we read
+      // "0xinf" or "0xnan" which we don't want to match.
+      //
+      // However, a std::string that begins with "0x" also begins with "0", which
+      // is normally a valid match for the number zero.  So we want these
+      // strings to match zero unless fmt_flags is `scientific`.  (This flag
+      // means an exponent is required, which the std::string "0" does not have.)
+      if (fmt_flags == chars_format::scientific) {
+        result.ec = std::errc::invalid_argument;
+      } else {
+        result.ptr = first + 1;
+        value = negative ? -0.0 : 0.0;
+      }
+      return result;
+    }
+    // We matched a value.
+    result.ptr = hex_parse.end;
+    if (HandleEdgeCase(hex_parse, negative, &value)) {
+      return result;
+    }
+    CalculatedFloat calculated =
+        CalculateFromParsedHexadecimal<FloatType>(hex_parse);
+    EncodeResult(calculated, negative, &result, &value);
+    return result;
+  }
+  // Otherwise, we choose the number base based on the flags.
+  if ((fmt_flags & chars_format::hex) == chars_format::hex) {
+    strings_internal::ParsedFloat hex_parse =
+        strings_internal::ParseFloat<16>(first, last, fmt_flags);
+    if (hex_parse.end == nullptr) {
+      result.ec = std::errc::invalid_argument;
+      return result;
+    }
+    result.ptr = hex_parse.end;
+    if (HandleEdgeCase(hex_parse, negative, &value)) {
+      return result;
+    }
+    CalculatedFloat calculated =
+        CalculateFromParsedHexadecimal<FloatType>(hex_parse);
+    EncodeResult(calculated, negative, &result, &value);
+    return result;
+  } else {
+    strings_internal::ParsedFloat decimal_parse =
+        strings_internal::ParseFloat<10>(first, last, fmt_flags);
+    if (decimal_parse.end == nullptr) {
+      result.ec = std::errc::invalid_argument;
+      return result;
+    }
+    result.ptr = decimal_parse.end;
+    if (HandleEdgeCase(decimal_parse, negative, &value)) {
+      return result;
+    }
+    CalculatedFloat calculated =
+        CalculateFromParsedDecimal<FloatType>(decimal_parse);
+    EncodeResult(calculated, negative, &result, &value);
+    return result;
+  }
+  return result;
+}
+}  // namespace
+
+from_chars_result from_chars(const char* first, const char* last, double& value,
+                             chars_format fmt) {
+  return FromCharsImpl(first, last, value, fmt);
+}
+
+from_chars_result from_chars(const char* first, const char* last, float& value,
+                             chars_format fmt) {
+  return FromCharsImpl(first, last, value, fmt);
+}
+
+namespace {
+
+// Table of powers of 10, from kPower10TableMin to kPower10TableMax.
+//
+// kPower10MantissaTable[i - kPower10TableMin] stores the 64-bit mantissa (high
+// bit always on), and kPower10ExponentTable[i - kPower10TableMin] stores the
+// power-of-two exponent.  For a given number i, this gives the unique mantissa
+// and exponent such that mantissa * 2**exponent <= 10**i < (mantissa + 1) *
+// 2**exponent.
+
+const uint64_t kPower10MantissaTable[] = {
+    0xeef453d6923bd65aU, 0x9558b4661b6565f8U, 0xbaaee17fa23ebf76U,
+    0xe95a99df8ace6f53U, 0x91d8a02bb6c10594U, 0xb64ec836a47146f9U,
+    0xe3e27a444d8d98b7U, 0x8e6d8c6ab0787f72U, 0xb208ef855c969f4fU,
+    0xde8b2b66b3bc4723U, 0x8b16fb203055ac76U, 0xaddcb9e83c6b1793U,
+    0xd953e8624b85dd78U, 0x87d4713d6f33aa6bU, 0xa9c98d8ccb009506U,
+    0xd43bf0effdc0ba48U, 0x84a57695fe98746dU, 0xa5ced43b7e3e9188U,
+    0xcf42894a5dce35eaU, 0x818995ce7aa0e1b2U, 0xa1ebfb4219491a1fU,
+    0xca66fa129f9b60a6U, 0xfd00b897478238d0U, 0x9e20735e8cb16382U,
+    0xc5a890362fddbc62U, 0xf712b443bbd52b7bU, 0x9a6bb0aa55653b2dU,
+    0xc1069cd4eabe89f8U, 0xf148440a256e2c76U, 0x96cd2a865764dbcaU,
+    0xbc807527ed3e12bcU, 0xeba09271e88d976bU, 0x93445b8731587ea3U,
+    0xb8157268fdae9e4cU, 0xe61acf033d1a45dfU, 0x8fd0c16206306babU,
+    0xb3c4f1ba87bc8696U, 0xe0b62e2929aba83cU, 0x8c71dcd9ba0b4925U,
+    0xaf8e5410288e1b6fU, 0xdb71e91432b1a24aU, 0x892731ac9faf056eU,
+    0xab70fe17c79ac6caU, 0xd64d3d9db981787dU, 0x85f0468293f0eb4eU,
+    0xa76c582338ed2621U, 0xd1476e2c07286faaU, 0x82cca4db847945caU,
+    0xa37fce126597973cU, 0xcc5fc196fefd7d0cU, 0xff77b1fcbebcdc4fU,
+    0x9faacf3df73609b1U, 0xc795830d75038c1dU, 0xf97ae3d0d2446f25U,
+    0x9becce62836ac577U, 0xc2e801fb244576d5U, 0xf3a20279ed56d48aU,
+    0x9845418c345644d6U, 0xbe5691ef416bd60cU, 0xedec366b11c6cb8fU,
+    0x94b3a202eb1c3f39U, 0xb9e08a83a5e34f07U, 0xe858ad248f5c22c9U,
+    0x91376c36d99995beU, 0xb58547448ffffb2dU, 0xe2e69915b3fff9f9U,
+    0x8dd01fad907ffc3bU, 0xb1442798f49ffb4aU, 0xdd95317f31c7fa1dU,
+    0x8a7d3eef7f1cfc52U, 0xad1c8eab5ee43b66U, 0xd863b256369d4a40U,
+    0x873e4f75e2224e68U, 0xa90de3535aaae202U, 0xd3515c2831559a83U,
+    0x8412d9991ed58091U, 0xa5178fff668ae0b6U, 0xce5d73ff402d98e3U,
+    0x80fa687f881c7f8eU, 0xa139029f6a239f72U, 0xc987434744ac874eU,
+    0xfbe9141915d7a922U, 0x9d71ac8fada6c9b5U, 0xc4ce17b399107c22U,
+    0xf6019da07f549b2bU, 0x99c102844f94e0fbU, 0xc0314325637a1939U,
+    0xf03d93eebc589f88U, 0x96267c7535b763b5U, 0xbbb01b9283253ca2U,
+    0xea9c227723ee8bcbU, 0x92a1958a7675175fU, 0xb749faed14125d36U,
+    0xe51c79a85916f484U, 0x8f31cc0937ae58d2U, 0xb2fe3f0b8599ef07U,
+    0xdfbdcece67006ac9U, 0x8bd6a141006042bdU, 0xaecc49914078536dU,
+    0xda7f5bf590966848U, 0x888f99797a5e012dU, 0xaab37fd7d8f58178U,
+    0xd5605fcdcf32e1d6U, 0x855c3be0a17fcd26U, 0xa6b34ad8c9dfc06fU,
+    0xd0601d8efc57b08bU, 0x823c12795db6ce57U, 0xa2cb1717b52481edU,
+    0xcb7ddcdda26da268U, 0xfe5d54150b090b02U, 0x9efa548d26e5a6e1U,
+    0xc6b8e9b0709f109aU, 0xf867241c8cc6d4c0U, 0x9b407691d7fc44f8U,
+    0xc21094364dfb5636U, 0xf294b943e17a2bc4U, 0x979cf3ca6cec5b5aU,
+    0xbd8430bd08277231U, 0xece53cec4a314ebdU, 0x940f4613ae5ed136U,
+    0xb913179899f68584U, 0xe757dd7ec07426e5U, 0x9096ea6f3848984fU,
+    0xb4bca50b065abe63U, 0xe1ebce4dc7f16dfbU, 0x8d3360f09cf6e4bdU,
+    0xb080392cc4349decU, 0xdca04777f541c567U, 0x89e42caaf9491b60U,
+    0xac5d37d5b79b6239U, 0xd77485cb25823ac7U, 0x86a8d39ef77164bcU,
+    0xa8530886b54dbdebU, 0xd267caa862a12d66U, 0x8380dea93da4bc60U,
+    0xa46116538d0deb78U, 0xcd795be870516656U, 0x806bd9714632dff6U,
+    0xa086cfcd97bf97f3U, 0xc8a883c0fdaf7df0U, 0xfad2a4b13d1b5d6cU,
+    0x9cc3a6eec6311a63U, 0xc3f490aa77bd60fcU, 0xf4f1b4d515acb93bU,
+    0x991711052d8bf3c5U, 0xbf5cd54678eef0b6U, 0xef340a98172aace4U,
+    0x9580869f0e7aac0eU, 0xbae0a846d2195712U, 0xe998d258869facd7U,
+    0x91ff83775423cc06U, 0xb67f6455292cbf08U, 0xe41f3d6a7377eecaU,
+    0x8e938662882af53eU, 0xb23867fb2a35b28dU, 0xdec681f9f4c31f31U,
+    0x8b3c113c38f9f37eU, 0xae0b158b4738705eU, 0xd98ddaee19068c76U,
+    0x87f8a8d4cfa417c9U, 0xa9f6d30a038d1dbcU, 0xd47487cc8470652bU,
+    0x84c8d4dfd2c63f3bU, 0xa5fb0a17c777cf09U, 0xcf79cc9db955c2ccU,
+    0x81ac1fe293d599bfU, 0xa21727db38cb002fU, 0xca9cf1d206fdc03bU,
+    0xfd442e4688bd304aU, 0x9e4a9cec15763e2eU, 0xc5dd44271ad3cdbaU,
+    0xf7549530e188c128U, 0x9a94dd3e8cf578b9U, 0xc13a148e3032d6e7U,
+    0xf18899b1bc3f8ca1U, 0x96f5600f15a7b7e5U, 0xbcb2b812db11a5deU,
+    0xebdf661791d60f56U, 0x936b9fcebb25c995U, 0xb84687c269ef3bfbU,
+    0xe65829b3046b0afaU, 0x8ff71a0fe2c2e6dcU, 0xb3f4e093db73a093U,
+    0xe0f218b8d25088b8U, 0x8c974f7383725573U, 0xafbd2350644eeacfU,
+    0xdbac6c247d62a583U, 0x894bc396ce5da772U, 0xab9eb47c81f5114fU,
+    0xd686619ba27255a2U, 0x8613fd0145877585U, 0xa798fc4196e952e7U,
+    0xd17f3b51fca3a7a0U, 0x82ef85133de648c4U, 0xa3ab66580d5fdaf5U,
+    0xcc963fee10b7d1b3U, 0xffbbcfe994e5c61fU, 0x9fd561f1fd0f9bd3U,
+    0xc7caba6e7c5382c8U, 0xf9bd690a1b68637bU, 0x9c1661a651213e2dU,
+    0xc31bfa0fe5698db8U, 0xf3e2f893dec3f126U, 0x986ddb5c6b3a76b7U,
+    0xbe89523386091465U, 0xee2ba6c0678b597fU, 0x94db483840b717efU,
+    0xba121a4650e4ddebU, 0xe896a0d7e51e1566U, 0x915e2486ef32cd60U,
+    0xb5b5ada8aaff80b8U, 0xe3231912d5bf60e6U, 0x8df5efabc5979c8fU,
+    0xb1736b96b6fd83b3U, 0xddd0467c64bce4a0U, 0x8aa22c0dbef60ee4U,
+    0xad4ab7112eb3929dU, 0xd89d64d57a607744U, 0x87625f056c7c4a8bU,
+    0xa93af6c6c79b5d2dU, 0xd389b47879823479U, 0x843610cb4bf160cbU,
+    0xa54394fe1eedb8feU, 0xce947a3da6a9273eU, 0x811ccc668829b887U,
+    0xa163ff802a3426a8U, 0xc9bcff6034c13052U, 0xfc2c3f3841f17c67U,
+    0x9d9ba7832936edc0U, 0xc5029163f384a931U, 0xf64335bcf065d37dU,
+    0x99ea0196163fa42eU, 0xc06481fb9bcf8d39U, 0xf07da27a82c37088U,
+    0x964e858c91ba2655U, 0xbbe226efb628afeaU, 0xeadab0aba3b2dbe5U,
+    0x92c8ae6b464fc96fU, 0xb77ada0617e3bbcbU, 0xe55990879ddcaabdU,
+    0x8f57fa54c2a9eab6U, 0xb32df8e9f3546564U, 0xdff9772470297ebdU,
+    0x8bfbea76c619ef36U, 0xaefae51477a06b03U, 0xdab99e59958885c4U,
+    0x88b402f7fd75539bU, 0xaae103b5fcd2a881U, 0xd59944a37c0752a2U,
+    0x857fcae62d8493a5U, 0xa6dfbd9fb8e5b88eU, 0xd097ad07a71f26b2U,
+    0x825ecc24c873782fU, 0xa2f67f2dfa90563bU, 0xcbb41ef979346bcaU,
+    0xfea126b7d78186bcU, 0x9f24b832e6b0f436U, 0xc6ede63fa05d3143U,
+    0xf8a95fcf88747d94U, 0x9b69dbe1b548ce7cU, 0xc24452da229b021bU,
+    0xf2d56790ab41c2a2U, 0x97c560ba6b0919a5U, 0xbdb6b8e905cb600fU,
+    0xed246723473e3813U, 0x9436c0760c86e30bU, 0xb94470938fa89bceU,
+    0xe7958cb87392c2c2U, 0x90bd77f3483bb9b9U, 0xb4ecd5f01a4aa828U,
+    0xe2280b6c20dd5232U, 0x8d590723948a535fU, 0xb0af48ec79ace837U,
+    0xdcdb1b2798182244U, 0x8a08f0f8bf0f156bU, 0xac8b2d36eed2dac5U,
+    0xd7adf884aa879177U, 0x86ccbb52ea94baeaU, 0xa87fea27a539e9a5U,
+    0xd29fe4b18e88640eU, 0x83a3eeeef9153e89U, 0xa48ceaaab75a8e2bU,
+    0xcdb02555653131b6U, 0x808e17555f3ebf11U, 0xa0b19d2ab70e6ed6U,
+    0xc8de047564d20a8bU, 0xfb158592be068d2eU, 0x9ced737bb6c4183dU,
+    0xc428d05aa4751e4cU, 0xf53304714d9265dfU, 0x993fe2c6d07b7fabU,
+    0xbf8fdb78849a5f96U, 0xef73d256a5c0f77cU, 0x95a8637627989aadU,
+    0xbb127c53b17ec159U, 0xe9d71b689dde71afU, 0x9226712162ab070dU,
+    0xb6b00d69bb55c8d1U, 0xe45c10c42a2b3b05U, 0x8eb98a7a9a5b04e3U,
+    0xb267ed1940f1c61cU, 0xdf01e85f912e37a3U, 0x8b61313bbabce2c6U,
+    0xae397d8aa96c1b77U, 0xd9c7dced53c72255U, 0x881cea14545c7575U,
+    0xaa242499697392d2U, 0xd4ad2dbfc3d07787U, 0x84ec3c97da624ab4U,
+    0xa6274bbdd0fadd61U, 0xcfb11ead453994baU, 0x81ceb32c4b43fcf4U,
+    0xa2425ff75e14fc31U, 0xcad2f7f5359a3b3eU, 0xfd87b5f28300ca0dU,
+    0x9e74d1b791e07e48U, 0xc612062576589ddaU, 0xf79687aed3eec551U,
+    0x9abe14cd44753b52U, 0xc16d9a0095928a27U, 0xf1c90080baf72cb1U,
+    0x971da05074da7beeU, 0xbce5086492111aeaU, 0xec1e4a7db69561a5U,
+    0x9392ee8e921d5d07U, 0xb877aa3236a4b449U, 0xe69594bec44de15bU,
+    0x901d7cf73ab0acd9U, 0xb424dc35095cd80fU, 0xe12e13424bb40e13U,
+    0x8cbccc096f5088cbU, 0xafebff0bcb24aafeU, 0xdbe6fecebdedd5beU,
+    0x89705f4136b4a597U, 0xabcc77118461cefcU, 0xd6bf94d5e57a42bcU,
+    0x8637bd05af6c69b5U, 0xa7c5ac471b478423U, 0xd1b71758e219652bU,
+    0x83126e978d4fdf3bU, 0xa3d70a3d70a3d70aU, 0xccccccccccccccccU,
+    0x8000000000000000U, 0xa000000000000000U, 0xc800000000000000U,
+    0xfa00000000000000U, 0x9c40000000000000U, 0xc350000000000000U,
+    0xf424000000000000U, 0x9896800000000000U, 0xbebc200000000000U,
+    0xee6b280000000000U, 0x9502f90000000000U, 0xba43b74000000000U,
+    0xe8d4a51000000000U, 0x9184e72a00000000U, 0xb5e620f480000000U,
+    0xe35fa931a0000000U, 0x8e1bc9bf04000000U, 0xb1a2bc2ec5000000U,
+    0xde0b6b3a76400000U, 0x8ac7230489e80000U, 0xad78ebc5ac620000U,
+    0xd8d726b7177a8000U, 0x878678326eac9000U, 0xa968163f0a57b400U,
+    0xd3c21bcecceda100U, 0x84595161401484a0U, 0xa56fa5b99019a5c8U,
+    0xcecb8f27f4200f3aU, 0x813f3978f8940984U, 0xa18f07d736b90be5U,
+    0xc9f2c9cd04674edeU, 0xfc6f7c4045812296U, 0x9dc5ada82b70b59dU,
+    0xc5371912364ce305U, 0xf684df56c3e01bc6U, 0x9a130b963a6c115cU,
+    0xc097ce7bc90715b3U, 0xf0bdc21abb48db20U, 0x96769950b50d88f4U,
+    0xbc143fa4e250eb31U, 0xeb194f8e1ae525fdU, 0x92efd1b8d0cf37beU,
+    0xb7abc627050305adU, 0xe596b7b0c643c719U, 0x8f7e32ce7bea5c6fU,
+    0xb35dbf821ae4f38bU, 0xe0352f62a19e306eU, 0x8c213d9da502de45U,
+    0xaf298d050e4395d6U, 0xdaf3f04651d47b4cU, 0x88d8762bf324cd0fU,
+    0xab0e93b6efee0053U, 0xd5d238a4abe98068U, 0x85a36366eb71f041U,
+    0xa70c3c40a64e6c51U, 0xd0cf4b50cfe20765U, 0x82818f1281ed449fU,
+    0xa321f2d7226895c7U, 0xcbea6f8ceb02bb39U, 0xfee50b7025c36a08U,
+    0x9f4f2726179a2245U, 0xc722f0ef9d80aad6U, 0xf8ebad2b84e0d58bU,
+    0x9b934c3b330c8577U, 0xc2781f49ffcfa6d5U, 0xf316271c7fc3908aU,
+    0x97edd871cfda3a56U, 0xbde94e8e43d0c8ecU, 0xed63a231d4c4fb27U,
+    0x945e455f24fb1cf8U, 0xb975d6b6ee39e436U, 0xe7d34c64a9c85d44U,
+    0x90e40fbeea1d3a4aU, 0xb51d13aea4a488ddU, 0xe264589a4dcdab14U,
+    0x8d7eb76070a08aecU, 0xb0de65388cc8ada8U, 0xdd15fe86affad912U,
+    0x8a2dbf142dfcc7abU, 0xacb92ed9397bf996U, 0xd7e77a8f87daf7fbU,
+    0x86f0ac99b4e8dafdU, 0xa8acd7c0222311bcU, 0xd2d80db02aabd62bU,
+    0x83c7088e1aab65dbU, 0xa4b8cab1a1563f52U, 0xcde6fd5e09abcf26U,
+    0x80b05e5ac60b6178U, 0xa0dc75f1778e39d6U, 0xc913936dd571c84cU,
+    0xfb5878494ace3a5fU, 0x9d174b2dcec0e47bU, 0xc45d1df942711d9aU,
+    0xf5746577930d6500U, 0x9968bf6abbe85f20U, 0xbfc2ef456ae276e8U,
+    0xefb3ab16c59b14a2U, 0x95d04aee3b80ece5U, 0xbb445da9ca61281fU,
+    0xea1575143cf97226U, 0x924d692ca61be758U, 0xb6e0c377cfa2e12eU,
+    0xe498f455c38b997aU, 0x8edf98b59a373fecU, 0xb2977ee300c50fe7U,
+    0xdf3d5e9bc0f653e1U, 0x8b865b215899f46cU, 0xae67f1e9aec07187U,
+    0xda01ee641a708de9U, 0x884134fe908658b2U, 0xaa51823e34a7eedeU,
+    0xd4e5e2cdc1d1ea96U, 0x850fadc09923329eU, 0xa6539930bf6bff45U,
+    0xcfe87f7cef46ff16U, 0x81f14fae158c5f6eU, 0xa26da3999aef7749U,
+    0xcb090c8001ab551cU, 0xfdcb4fa002162a63U, 0x9e9f11c4014dda7eU,
+    0xc646d63501a1511dU, 0xf7d88bc24209a565U, 0x9ae757596946075fU,
+    0xc1a12d2fc3978937U, 0xf209787bb47d6b84U, 0x9745eb4d50ce6332U,
+    0xbd176620a501fbffU, 0xec5d3fa8ce427affU, 0x93ba47c980e98cdfU,
+    0xb8a8d9bbe123f017U, 0xe6d3102ad96cec1dU, 0x9043ea1ac7e41392U,
+    0xb454e4a179dd1877U, 0xe16a1dc9d8545e94U, 0x8ce2529e2734bb1dU,
+    0xb01ae745b101e9e4U, 0xdc21a1171d42645dU, 0x899504ae72497ebaU,
+    0xabfa45da0edbde69U, 0xd6f8d7509292d603U, 0x865b86925b9bc5c2U,
+    0xa7f26836f282b732U, 0xd1ef0244af2364ffU, 0x8335616aed761f1fU,
+    0xa402b9c5a8d3a6e7U, 0xcd036837130890a1U, 0x802221226be55a64U,
+    0xa02aa96b06deb0fdU, 0xc83553c5c8965d3dU, 0xfa42a8b73abbf48cU,
+    0x9c69a97284b578d7U, 0xc38413cf25e2d70dU, 0xf46518c2ef5b8cd1U,
+    0x98bf2f79d5993802U, 0xbeeefb584aff8603U, 0xeeaaba2e5dbf6784U,
+    0x952ab45cfa97a0b2U, 0xba756174393d88dfU, 0xe912b9d1478ceb17U,
+    0x91abb422ccb812eeU, 0xb616a12b7fe617aaU, 0xe39c49765fdf9d94U,
+    0x8e41ade9fbebc27dU, 0xb1d219647ae6b31cU, 0xde469fbd99a05fe3U,
+    0x8aec23d680043beeU, 0xada72ccc20054ae9U, 0xd910f7ff28069da4U,
+    0x87aa9aff79042286U, 0xa99541bf57452b28U, 0xd3fa922f2d1675f2U,
+    0x847c9b5d7c2e09b7U, 0xa59bc234db398c25U, 0xcf02b2c21207ef2eU,
+    0x8161afb94b44f57dU, 0xa1ba1ba79e1632dcU, 0xca28a291859bbf93U,
+    0xfcb2cb35e702af78U, 0x9defbf01b061adabU, 0xc56baec21c7a1916U,
+    0xf6c69a72a3989f5bU, 0x9a3c2087a63f6399U, 0xc0cb28a98fcf3c7fU,
+    0xf0fdf2d3f3c30b9fU, 0x969eb7c47859e743U, 0xbc4665b596706114U,
+    0xeb57ff22fc0c7959U, 0x9316ff75dd87cbd8U, 0xb7dcbf5354e9beceU,
+    0xe5d3ef282a242e81U, 0x8fa475791a569d10U, 0xb38d92d760ec4455U,
+    0xe070f78d3927556aU, 0x8c469ab843b89562U, 0xaf58416654a6babbU,
+    0xdb2e51bfe9d0696aU, 0x88fcf317f22241e2U, 0xab3c2fddeeaad25aU,
+    0xd60b3bd56a5586f1U, 0x85c7056562757456U, 0xa738c6bebb12d16cU,
+    0xd106f86e69d785c7U, 0x82a45b450226b39cU, 0xa34d721642b06084U,
+    0xcc20ce9bd35c78a5U, 0xff290242c83396ceU, 0x9f79a169bd203e41U,
+    0xc75809c42c684dd1U, 0xf92e0c3537826145U, 0x9bbcc7a142b17ccbU,
+    0xc2abf989935ddbfeU, 0xf356f7ebf83552feU, 0x98165af37b2153deU,
+    0xbe1bf1b059e9a8d6U, 0xeda2ee1c7064130cU, 0x9485d4d1c63e8be7U,
+    0xb9a74a0637ce2ee1U, 0xe8111c87c5c1ba99U, 0x910ab1d4db9914a0U,
+    0xb54d5e4a127f59c8U, 0xe2a0b5dc971f303aU, 0x8da471a9de737e24U,
+    0xb10d8e1456105dadU, 0xdd50f1996b947518U, 0x8a5296ffe33cc92fU,
+    0xace73cbfdc0bfb7bU, 0xd8210befd30efa5aU, 0x8714a775e3e95c78U,
+    0xa8d9d1535ce3b396U, 0xd31045a8341ca07cU, 0x83ea2b892091e44dU,
+    0xa4e4b66b68b65d60U, 0xce1de40642e3f4b9U, 0x80d2ae83e9ce78f3U,
+    0xa1075a24e4421730U, 0xc94930ae1d529cfcU, 0xfb9b7cd9a4a7443cU,
+    0x9d412e0806e88aa5U, 0xc491798a08a2ad4eU, 0xf5b5d7ec8acb58a2U,
+    0x9991a6f3d6bf1765U, 0xbff610b0cc6edd3fU, 0xeff394dcff8a948eU,
+    0x95f83d0a1fb69cd9U, 0xbb764c4ca7a4440fU, 0xea53df5fd18d5513U,
+    0x92746b9be2f8552cU, 0xb7118682dbb66a77U, 0xe4d5e82392a40515U,
+    0x8f05b1163ba6832dU, 0xb2c71d5bca9023f8U, 0xdf78e4b2bd342cf6U,
+    0x8bab8eefb6409c1aU, 0xae9672aba3d0c320U, 0xda3c0f568cc4f3e8U,
+    0x8865899617fb1871U, 0xaa7eebfb9df9de8dU, 0xd51ea6fa85785631U,
+    0x8533285c936b35deU, 0xa67ff273b8460356U, 0xd01fef10a657842cU,
+    0x8213f56a67f6b29bU, 0xa298f2c501f45f42U, 0xcb3f2f7642717713U,
+    0xfe0efb53d30dd4d7U, 0x9ec95d1463e8a506U, 0xc67bb4597ce2ce48U,
+    0xf81aa16fdc1b81daU, 0x9b10a4e5e9913128U, 0xc1d4ce1f63f57d72U,
+    0xf24a01a73cf2dccfU, 0x976e41088617ca01U, 0xbd49d14aa79dbc82U,
+    0xec9c459d51852ba2U, 0x93e1ab8252f33b45U, 0xb8da1662e7b00a17U,
+    0xe7109bfba19c0c9dU, 0x906a617d450187e2U, 0xb484f9dc9641e9daU,
+    0xe1a63853bbd26451U, 0x8d07e33455637eb2U, 0xb049dc016abc5e5fU,
+    0xdc5c5301c56b75f7U, 0x89b9b3e11b6329baU, 0xac2820d9623bf429U,
+    0xd732290fbacaf133U, 0x867f59a9d4bed6c0U, 0xa81f301449ee8c70U,
+    0xd226fc195c6a2f8cU, 0x83585d8fd9c25db7U, 0xa42e74f3d032f525U,
+    0xcd3a1230c43fb26fU, 0x80444b5e7aa7cf85U, 0xa0555e361951c366U,
+    0xc86ab5c39fa63440U, 0xfa856334878fc150U, 0x9c935e00d4b9d8d2U,
+    0xc3b8358109e84f07U, 0xf4a642e14c6262c8U, 0x98e7e9cccfbd7dbdU,
+    0xbf21e44003acdd2cU, 0xeeea5d5004981478U, 0x95527a5202df0ccbU,
+    0xbaa718e68396cffdU, 0xe950df20247c83fdU, 0x91d28b7416cdd27eU,
+    0xb6472e511c81471dU, 0xe3d8f9e563a198e5U, 0x8e679c2f5e44ff8fU,
+};
+
+const int16_t kPower10ExponentTable[] = {
+    -1200, -1196, -1193, -1190, -1186, -1183, -1180, -1176, -1173, -1170, -1166,
+    -1163, -1160, -1156, -1153, -1150, -1146, -1143, -1140, -1136, -1133, -1130,
+    -1127, -1123, -1120, -1117, -1113, -1110, -1107, -1103, -1100, -1097, -1093,
+    -1090, -1087, -1083, -1080, -1077, -1073, -1070, -1067, -1063, -1060, -1057,
+    -1053, -1050, -1047, -1043, -1040, -1037, -1034, -1030, -1027, -1024, -1020,
+    -1017, -1014, -1010, -1007, -1004, -1000, -997,  -994,  -990,  -987,  -984,
+    -980,  -977,  -974,  -970,  -967,  -964,  -960,  -957,  -954,  -950,  -947,
+    -944,  -940,  -937,  -934,  -931,  -927,  -924,  -921,  -917,  -914,  -911,
+    -907,  -904,  -901,  -897,  -894,  -891,  -887,  -884,  -881,  -877,  -874,
+    -871,  -867,  -864,  -861,  -857,  -854,  -851,  -847,  -844,  -841,  -838,
+    -834,  -831,  -828,  -824,  -821,  -818,  -814,  -811,  -808,  -804,  -801,
+    -798,  -794,  -791,  -788,  -784,  -781,  -778,  -774,  -771,  -768,  -764,
+    -761,  -758,  -754,  -751,  -748,  -744,  -741,  -738,  -735,  -731,  -728,
+    -725,  -721,  -718,  -715,  -711,  -708,  -705,  -701,  -698,  -695,  -691,
+    -688,  -685,  -681,  -678,  -675,  -671,  -668,  -665,  -661,  -658,  -655,
+    -651,  -648,  -645,  -642,  -638,  -635,  -632,  -628,  -625,  -622,  -618,
+    -615,  -612,  -608,  -605,  -602,  -598,  -595,  -592,  -588,  -585,  -582,
+    -578,  -575,  -572,  -568,  -565,  -562,  -558,  -555,  -552,  -549,  -545,
+    -542,  -539,  -535,  -532,  -529,  -525,  -522,  -519,  -515,  -512,  -509,
+    -505,  -502,  -499,  -495,  -492,  -489,  -485,  -482,  -479,  -475,  -472,
+    -469,  -465,  -462,  -459,  -455,  -452,  -449,  -446,  -442,  -439,  -436,
+    -432,  -429,  -426,  -422,  -419,  -416,  -412,  -409,  -406,  -402,  -399,
+    -396,  -392,  -389,  -386,  -382,  -379,  -376,  -372,  -369,  -366,  -362,
+    -359,  -356,  -353,  -349,  -346,  -343,  -339,  -336,  -333,  -329,  -326,
+    -323,  -319,  -316,  -313,  -309,  -306,  -303,  -299,  -296,  -293,  -289,
+    -286,  -283,  -279,  -276,  -273,  -269,  -266,  -263,  -259,  -256,  -253,
+    -250,  -246,  -243,  -240,  -236,  -233,  -230,  -226,  -223,  -220,  -216,
+    -213,  -210,  -206,  -203,  -200,  -196,  -193,  -190,  -186,  -183,  -180,
+    -176,  -173,  -170,  -166,  -163,  -160,  -157,  -153,  -150,  -147,  -143,
+    -140,  -137,  -133,  -130,  -127,  -123,  -120,  -117,  -113,  -110,  -107,
+    -103,  -100,  -97,   -93,   -90,   -87,   -83,   -80,   -77,   -73,   -70,
+    -67,   -63,   -60,   -57,   -54,   -50,   -47,   -44,   -40,   -37,   -34,
+    -30,   -27,   -24,   -20,   -17,   -14,   -10,   -7,    -4,    0,     3,
+    6,     10,    13,    16,    20,    23,    26,    30,    33,    36,    39,
+    43,    46,    49,    53,    56,    59,    63,    66,    69,    73,    76,
+    79,    83,    86,    89,    93,    96,    99,    103,   106,   109,   113,
+    116,   119,   123,   126,   129,   132,   136,   139,   142,   146,   149,
+    152,   156,   159,   162,   166,   169,   172,   176,   179,   182,   186,
+    189,   192,   196,   199,   202,   206,   209,   212,   216,   219,   222,
+    226,   229,   232,   235,   239,   242,   245,   249,   252,   255,   259,
+    262,   265,   269,   272,   275,   279,   282,   285,   289,   292,   295,
+    299,   302,   305,   309,   312,   315,   319,   322,   325,   328,   332,
+    335,   338,   342,   345,   348,   352,   355,   358,   362,   365,   368,
+    372,   375,   378,   382,   385,   388,   392,   395,   398,   402,   405,
+    408,   412,   415,   418,   422,   425,   428,   431,   435,   438,   441,
+    445,   448,   451,   455,   458,   461,   465,   468,   471,   475,   478,
+    481,   485,   488,   491,   495,   498,   501,   505,   508,   511,   515,
+    518,   521,   524,   528,   531,   534,   538,   541,   544,   548,   551,
+    554,   558,   561,   564,   568,   571,   574,   578,   581,   584,   588,
+    591,   594,   598,   601,   604,   608,   611,   614,   617,   621,   624,
+    627,   631,   634,   637,   641,   644,   647,   651,   654,   657,   661,
+    664,   667,   671,   674,   677,   681,   684,   687,   691,   694,   697,
+    701,   704,   707,   711,   714,   717,   720,   724,   727,   730,   734,
+    737,   740,   744,   747,   750,   754,   757,   760,   764,   767,   770,
+    774,   777,   780,   784,   787,   790,   794,   797,   800,   804,   807,
+    810,   813,   817,   820,   823,   827,   830,   833,   837,   840,   843,
+    847,   850,   853,   857,   860,   863,   867,   870,   873,   877,   880,
+    883,   887,   890,   893,   897,   900,   903,   907,   910,   913,   916,
+    920,   923,   926,   930,   933,   936,   940,   943,   946,   950,   953,
+    956,   960,
+};
+
+}  // namespace
+}  // namespace absl
diff --git a/absl/strings/charconv.h b/absl/strings/charconv.h
new file mode 100644
index 0000000..3f5891b
--- /dev/null
+++ b/absl/strings/charconv.h
@@ -0,0 +1,115 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_CHARCONV_H_
+#define ABSL_STRINGS_CHARCONV_H_
+
+#include <system_error>  // NOLINT(build/c++11)
+
+namespace absl {
+
+// Workalike compatibilty version of std::chars_format from C++17.
+//
+// This is an bitfield enumerator which can be passed to absl::from_chars to
+// configure the string-to-float conversion.
+enum class chars_format {
+  scientific = 1,
+  fixed = 2,
+  hex = 4,
+  general = fixed | scientific,
+};
+
+// The return result of a string-to-number conversion.
+//
+// `ec` will be set to `invalid_argument` if a well-formed number was not found
+// at the start of the input range, `result_out_of_range` if a well-formed
+// number was found, but it was out of the representable range of the requested
+// type, or to std::errc() otherwise.
+//
+// If a well-formed number was found, `ptr` is set to one past the sequence of
+// characters that were successfully parsed.  If none was found, `ptr` is set
+// to the `first` argument to from_chars.
+struct from_chars_result {
+  const char* ptr;
+  std::errc ec;
+};
+
+// Workalike compatibilty version of std::from_chars from C++17.  Currently
+// this only supports the `double` and `float` types.
+//
+// This interface incorporates the proposed resolutions for library issues
+// DR 3080 and DR 3081.  If these are adopted with different wording,
+// Abseil's behavior will change to match the standard.  (The behavior most
+// likely to change is for DR 3081, which says what `value` will be set to in
+// the case of overflow and underflow.  Code that wants to avoid possible
+// breaking changes in this area should not depend on `value` when the returned
+// from_chars_result indicates a range error.)
+//
+// Searches the range [first, last) for the longest matching pattern beginning
+// at `first` that represents a floating point number.  If one is found, store
+// the result in `value`.
+//
+// The matching pattern format is almost the same as that of strtod(), except
+// that C locale is not respected, and an initial '+' character in the input
+// range will never be matched.
+//
+// If `fmt` is set, it must be one of the enumerator values of the chars_format.
+// (This is despite the fact that chars_format is a bitmask type.)  If set to
+// `scientific`, a matching number must contain an exponent.  If set to `fixed`,
+// then an exponent will never match.  (For example, the string "1e5" will be
+// parsed as "1".)  If set to `hex`, then a hexadecimal float is parsed in the
+// format that strtod() accepts, except that a "0x" prefix is NOT matched.
+// (In particular, in `hex` mode, the input "0xff" results in the largest
+// matching pattern "0".)
+absl::from_chars_result from_chars(const char* first, const char* last,
+                                   double& value,  // NOLINT
+                                   chars_format fmt = chars_format::general);
+
+absl::from_chars_result from_chars(const char* first, const char* last,
+                                   float& value,  // NOLINT
+                                   chars_format fmt = chars_format::general);
+
+// std::chars_format is specified as a bitmask type, which means the following
+// operations must be provided:
+inline constexpr chars_format operator&(chars_format lhs, chars_format rhs) {
+  return static_cast<chars_format>(static_cast<int>(lhs) &
+                                   static_cast<int>(rhs));
+}
+inline constexpr chars_format operator|(chars_format lhs, chars_format rhs) {
+  return static_cast<chars_format>(static_cast<int>(lhs) |
+                                   static_cast<int>(rhs));
+}
+inline constexpr chars_format operator^(chars_format lhs, chars_format rhs) {
+  return static_cast<chars_format>(static_cast<int>(lhs) ^
+                                   static_cast<int>(rhs));
+}
+inline constexpr chars_format operator~(chars_format arg) {
+  return static_cast<chars_format>(~static_cast<int>(arg));
+}
+inline chars_format& operator&=(chars_format& lhs, chars_format rhs) {
+  lhs = lhs & rhs;
+  return lhs;
+}
+inline chars_format& operator|=(chars_format& lhs, chars_format rhs) {
+  lhs = lhs | rhs;
+  return lhs;
+}
+inline chars_format& operator^=(chars_format& lhs, chars_format rhs) {
+  lhs = lhs ^ rhs;
+  return lhs;
+}
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_CHARCONV_H_
diff --git a/absl/strings/charconv_benchmark.cc b/absl/strings/charconv_benchmark.cc
new file mode 100644
index 0000000..644b2ab
--- /dev/null
+++ b/absl/strings/charconv_benchmark.cc
@@ -0,0 +1,204 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/charconv.h"
+
+#include <cstdlib>
+#include <cstring>
+#include <string>
+
+#include "benchmark/benchmark.h"
+
+namespace {
+
+void BM_Strtod_Pi(benchmark::State& state) {
+  const char* pi = "3.14159";
+  for (auto s : state) {
+    benchmark::DoNotOptimize(pi);
+    benchmark::DoNotOptimize(strtod(pi, nullptr));
+  }
+}
+BENCHMARK(BM_Strtod_Pi);
+
+void BM_Absl_Pi(benchmark::State& state) {
+  const char* pi = "3.14159";
+  const char* pi_end = pi + strlen(pi);
+  for (auto s : state) {
+    benchmark::DoNotOptimize(pi);
+    double v;
+    absl::from_chars(pi, pi_end, v);
+    benchmark::DoNotOptimize(v);
+  }
+}
+BENCHMARK(BM_Absl_Pi);
+
+void BM_Strtod_Pi_float(benchmark::State& state) {
+  const char* pi = "3.14159";
+  for (auto s : state) {
+    benchmark::DoNotOptimize(pi);
+    benchmark::DoNotOptimize(strtof(pi, nullptr));
+  }
+}
+BENCHMARK(BM_Strtod_Pi_float);
+
+void BM_Absl_Pi_float(benchmark::State& state) {
+  const char* pi = "3.14159";
+  const char* pi_end = pi + strlen(pi);
+  for (auto s : state) {
+    benchmark::DoNotOptimize(pi);
+    float v;
+    absl::from_chars(pi, pi_end, v);
+    benchmark::DoNotOptimize(v);
+  }
+}
+BENCHMARK(BM_Absl_Pi_float);
+
+void BM_Strtod_HardLarge(benchmark::State& state) {
+  const char* num = "272104041512242479.e200";
+  for (auto s : state) {
+    benchmark::DoNotOptimize(num);
+    benchmark::DoNotOptimize(strtod(num, nullptr));
+  }
+}
+BENCHMARK(BM_Strtod_HardLarge);
+
+void BM_Absl_HardLarge(benchmark::State& state) {
+  const char* numstr = "272104041512242479.e200";
+  const char* numstr_end = numstr + strlen(numstr);
+  for (auto s : state) {
+    benchmark::DoNotOptimize(numstr);
+    double v;
+    absl::from_chars(numstr, numstr_end, v);
+    benchmark::DoNotOptimize(v);
+  }
+}
+BENCHMARK(BM_Absl_HardLarge);
+
+void BM_Strtod_HardSmall(benchmark::State& state) {
+  const char* num = "94080055902682397.e-242";
+  for (auto s : state) {
+    benchmark::DoNotOptimize(num);
+    benchmark::DoNotOptimize(strtod(num, nullptr));
+  }
+}
+BENCHMARK(BM_Strtod_HardSmall);
+
+void BM_Absl_HardSmall(benchmark::State& state) {
+  const char* numstr = "94080055902682397.e-242";
+  const char* numstr_end = numstr + strlen(numstr);
+  for (auto s : state) {
+    benchmark::DoNotOptimize(numstr);
+    double v;
+    absl::from_chars(numstr, numstr_end, v);
+    benchmark::DoNotOptimize(v);
+  }
+}
+BENCHMARK(BM_Absl_HardSmall);
+
+void BM_Strtod_HugeMantissa(benchmark::State& state) {
+  std::string huge(200, '3');
+  const char* num = huge.c_str();
+  for (auto s : state) {
+    benchmark::DoNotOptimize(num);
+    benchmark::DoNotOptimize(strtod(num, nullptr));
+  }
+}
+BENCHMARK(BM_Strtod_HugeMantissa);
+
+void BM_Absl_HugeMantissa(benchmark::State& state) {
+  std::string huge(200, '3');
+  const char* num = huge.c_str();
+  const char* num_end = num + 200;
+  for (auto s : state) {
+    benchmark::DoNotOptimize(num);
+    double v;
+    absl::from_chars(num, num_end, v);
+    benchmark::DoNotOptimize(v);
+  }
+}
+BENCHMARK(BM_Absl_HugeMantissa);
+
+std::string MakeHardCase(int length) {
+  // The number 1.1521...e-297 is exactly halfway between 12345 * 2**-1000 and
+  // the next larger representable number.  The digits of this number are in
+  // the std::string below.
+  const std::string digits =
+      "1."
+      "152113937042223790993097181572444900347587985074226836242307364987727724"
+      "831384300183638649152607195040591791364113930628852279348613864894524591"
+      "272746490313676832900762939595690019745859128071117417798540258114233761"
+      "012939937017879509401007964861774960297319002612457273148497158989073482"
+      "171377406078223015359818300988676687994537274548940612510414856761641652"
+      "513434981938564294004070500716200446656421722229202383105446378511678258"
+      "370570631774499359748259931676320916632111681001853983492795053244971606"
+      "922718923011680846577744433974087653954904214152517799883551075537146316"
+      "168973685866425605046988661997658648354773076621610279716804960009043764"
+      "038392994055171112475093876476783502487512538082706095923790634572014823"
+      "78877699375152587890625" +
+      std::string(5000, '0');
+  // generate the hard cases on either side for the given length.
+  // Lengths between 3 and 1000 are reasonable.
+  return digits.substr(0, length) + "1e-297";
+}
+
+void BM_Strtod_Big_And_Difficult(benchmark::State& state) {
+  std::string testcase = MakeHardCase(state.range(0));
+  const char* begin = testcase.c_str();
+  for (auto s : state) {
+    benchmark::DoNotOptimize(begin);
+    benchmark::DoNotOptimize(strtod(begin, nullptr));
+  }
+}
+BENCHMARK(BM_Strtod_Big_And_Difficult)->Range(3, 5000);
+
+void BM_Absl_Big_And_Difficult(benchmark::State& state) {
+  std::string testcase = MakeHardCase(state.range(0));
+  const char* begin = testcase.c_str();
+  const char* end = begin + testcase.size();
+  for (auto s : state) {
+    benchmark::DoNotOptimize(begin);
+    double v;
+    absl::from_chars(begin, end, v);
+    benchmark::DoNotOptimize(v);
+  }
+}
+BENCHMARK(BM_Absl_Big_And_Difficult)->Range(3, 5000);
+
+}  // namespace
+
+// ------------------------------------------------------------------------
+// Benchmark                                 Time           CPU Iterations
+// ------------------------------------------------------------------------
+// BM_Strtod_Pi                             96 ns         96 ns    6337454
+// BM_Absl_Pi                               35 ns         35 ns   20031996
+// BM_Strtod_Pi_float                       91 ns         91 ns    7745851
+// BM_Absl_Pi_float                         35 ns         35 ns   20430298
+// BM_Strtod_HardLarge                     133 ns        133 ns    5288341
+// BM_Absl_HardLarge                       181 ns        181 ns    3855615
+// BM_Strtod_HardSmall                     279 ns        279 ns    2517243
+// BM_Absl_HardSmall                       287 ns        287 ns    2458744
+// BM_Strtod_HugeMantissa                  433 ns        433 ns    1604293
+// BM_Absl_HugeMantissa                    160 ns        160 ns    4403671
+// BM_Strtod_Big_And_Difficult/3           236 ns        236 ns    2942496
+// BM_Strtod_Big_And_Difficult/8           232 ns        232 ns    2983796
+// BM_Strtod_Big_And_Difficult/64          437 ns        437 ns    1591951
+// BM_Strtod_Big_And_Difficult/512        1738 ns       1738 ns     402519
+// BM_Strtod_Big_And_Difficult/4096       3943 ns       3943 ns     176128
+// BM_Strtod_Big_And_Difficult/5000       4397 ns       4397 ns     157878
+// BM_Absl_Big_And_Difficult/3              39 ns         39 ns   17799583
+// BM_Absl_Big_And_Difficult/8              43 ns         43 ns   16096859
+// BM_Absl_Big_And_Difficult/64            550 ns        550 ns    1259717
+// BM_Absl_Big_And_Difficult/512          4167 ns       4167 ns     171414
+// BM_Absl_Big_And_Difficult/4096         9160 ns       9159 ns      76297
+// BM_Absl_Big_And_Difficult/5000         9738 ns       9738 ns      70140
diff --git a/absl/strings/charconv_test.cc b/absl/strings/charconv_test.cc
new file mode 100644
index 0000000..b58fad2
--- /dev/null
+++ b/absl/strings/charconv_test.cc
@@ -0,0 +1,773 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/charconv.h"
+
+#include <cstdlib>
+#include <string>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/strings/internal/pow10_helper.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_format.h"
+
+#ifdef _MSC_FULL_VER
+#define ABSL_COMPILER_DOES_EXACT_ROUNDING 0
+#define ABSL_STRTOD_HANDLES_NAN_CORRECTLY 0
+#else
+#define ABSL_COMPILER_DOES_EXACT_ROUNDING 1
+#define ABSL_STRTOD_HANDLES_NAN_CORRECTLY 1
+#endif
+
+namespace {
+
+using absl::strings_internal::Pow10;
+
+#if ABSL_COMPILER_DOES_EXACT_ROUNDING
+
+// Tests that the given string is accepted by absl::from_chars, and that it
+// converts exactly equal to the given number.
+void TestDoubleParse(absl::string_view str, double expected_number) {
+  SCOPED_TRACE(str);
+  double actual_number = 0.0;
+  absl::from_chars_result result =
+      absl::from_chars(str.data(), str.data() + str.length(), actual_number);
+  EXPECT_EQ(result.ec, std::errc());
+  EXPECT_EQ(result.ptr, str.data() + str.length());
+  EXPECT_EQ(actual_number, expected_number);
+}
+
+void TestFloatParse(absl::string_view str, float expected_number) {
+  SCOPED_TRACE(str);
+  float actual_number = 0.0;
+  absl::from_chars_result result =
+      absl::from_chars(str.data(), str.data() + str.length(), actual_number);
+  EXPECT_EQ(result.ec, std::errc());
+  EXPECT_EQ(result.ptr, str.data() + str.length());
+  EXPECT_EQ(actual_number, expected_number);
+}
+
+// Tests that the given double or single precision floating point literal is
+// parsed correctly by absl::from_chars.
+//
+// These convenience macros assume that the C++ compiler being used also does
+// fully correct decimal-to-binary conversions.
+#define FROM_CHARS_TEST_DOUBLE(number)     \
+  {                                        \
+    TestDoubleParse(#number, number);      \
+    TestDoubleParse("-" #number, -number); \
+  }
+
+#define FROM_CHARS_TEST_FLOAT(number)        \
+  {                                          \
+    TestFloatParse(#number, number##f);      \
+    TestFloatParse("-" #number, -number##f); \
+  }
+
+TEST(FromChars, NearRoundingCases) {
+  // Cases from "A Program for Testing IEEE Decimal-Binary Conversion"
+  // by Vern Paxson.
+
+  // Forms that should round towards zero.  (These are the hardest cases for
+  // each decimal mantissa size.)
+  FROM_CHARS_TEST_DOUBLE(5.e125);
+  FROM_CHARS_TEST_DOUBLE(69.e267);
+  FROM_CHARS_TEST_DOUBLE(999.e-026);
+  FROM_CHARS_TEST_DOUBLE(7861.e-034);
+  FROM_CHARS_TEST_DOUBLE(75569.e-254);
+  FROM_CHARS_TEST_DOUBLE(928609.e-261);
+  FROM_CHARS_TEST_DOUBLE(9210917.e080);
+  FROM_CHARS_TEST_DOUBLE(84863171.e114);
+  FROM_CHARS_TEST_DOUBLE(653777767.e273);
+  FROM_CHARS_TEST_DOUBLE(5232604057.e-298);
+  FROM_CHARS_TEST_DOUBLE(27235667517.e-109);
+  FROM_CHARS_TEST_DOUBLE(653532977297.e-123);
+  FROM_CHARS_TEST_DOUBLE(3142213164987.e-294);
+  FROM_CHARS_TEST_DOUBLE(46202199371337.e-072);
+  FROM_CHARS_TEST_DOUBLE(231010996856685.e-073);
+  FROM_CHARS_TEST_DOUBLE(9324754620109615.e212);
+  FROM_CHARS_TEST_DOUBLE(78459735791271921.e049);
+  FROM_CHARS_TEST_DOUBLE(272104041512242479.e200);
+  FROM_CHARS_TEST_DOUBLE(6802601037806061975.e198);
+  FROM_CHARS_TEST_DOUBLE(20505426358836677347.e-221);
+  FROM_CHARS_TEST_DOUBLE(836168422905420598437.e-234);
+  FROM_CHARS_TEST_DOUBLE(4891559871276714924261.e222);
+  FROM_CHARS_TEST_FLOAT(5.e-20);
+  FROM_CHARS_TEST_FLOAT(67.e14);
+  FROM_CHARS_TEST_FLOAT(985.e15);
+  FROM_CHARS_TEST_FLOAT(7693.e-42);
+  FROM_CHARS_TEST_FLOAT(55895.e-16);
+  FROM_CHARS_TEST_FLOAT(996622.e-44);
+  FROM_CHARS_TEST_FLOAT(7038531.e-32);
+  FROM_CHARS_TEST_FLOAT(60419369.e-46);
+  FROM_CHARS_TEST_FLOAT(702990899.e-20);
+  FROM_CHARS_TEST_FLOAT(6930161142.e-48);
+  FROM_CHARS_TEST_FLOAT(25933168707.e-13);
+  FROM_CHARS_TEST_FLOAT(596428896559.e20);
+
+  // Similarly, forms that should round away from zero.
+  FROM_CHARS_TEST_DOUBLE(9.e-265);
+  FROM_CHARS_TEST_DOUBLE(85.e-037);
+  FROM_CHARS_TEST_DOUBLE(623.e100);
+  FROM_CHARS_TEST_DOUBLE(3571.e263);
+  FROM_CHARS_TEST_DOUBLE(81661.e153);
+  FROM_CHARS_TEST_DOUBLE(920657.e-023);
+  FROM_CHARS_TEST_DOUBLE(4603285.e-024);
+  FROM_CHARS_TEST_DOUBLE(87575437.e-309);
+  FROM_CHARS_TEST_DOUBLE(245540327.e122);
+  FROM_CHARS_TEST_DOUBLE(6138508175.e120);
+  FROM_CHARS_TEST_DOUBLE(83356057653.e193);
+  FROM_CHARS_TEST_DOUBLE(619534293513.e124);
+  FROM_CHARS_TEST_DOUBLE(2335141086879.e218);
+  FROM_CHARS_TEST_DOUBLE(36167929443327.e-159);
+  FROM_CHARS_TEST_DOUBLE(609610927149051.e-255);
+  FROM_CHARS_TEST_DOUBLE(3743626360493413.e-165);
+  FROM_CHARS_TEST_DOUBLE(94080055902682397.e-242);
+  FROM_CHARS_TEST_DOUBLE(899810892172646163.e283);
+  FROM_CHARS_TEST_DOUBLE(7120190517612959703.e120);
+  FROM_CHARS_TEST_DOUBLE(25188282901709339043.e-252);
+  FROM_CHARS_TEST_DOUBLE(308984926168550152811.e-052);
+  FROM_CHARS_TEST_DOUBLE(6372891218502368041059.e064);
+  FROM_CHARS_TEST_FLOAT(3.e-23);
+  FROM_CHARS_TEST_FLOAT(57.e18);
+  FROM_CHARS_TEST_FLOAT(789.e-35);
+  FROM_CHARS_TEST_FLOAT(2539.e-18);
+  FROM_CHARS_TEST_FLOAT(76173.e28);
+  FROM_CHARS_TEST_FLOAT(887745.e-11);
+  FROM_CHARS_TEST_FLOAT(5382571.e-37);
+  FROM_CHARS_TEST_FLOAT(82381273.e-35);
+  FROM_CHARS_TEST_FLOAT(750486563.e-38);
+  FROM_CHARS_TEST_FLOAT(3752432815.e-39);
+  FROM_CHARS_TEST_FLOAT(75224575729.e-45);
+  FROM_CHARS_TEST_FLOAT(459926601011.e15);
+}
+
+#undef FROM_CHARS_TEST_DOUBLE
+#undef FROM_CHARS_TEST_FLOAT
+#endif
+
+float ToFloat(absl::string_view s) {
+  float f;
+  absl::from_chars(s.data(), s.data() + s.size(), f);
+  return f;
+}
+
+double ToDouble(absl::string_view s) {
+  double d;
+  absl::from_chars(s.data(), s.data() + s.size(), d);
+  return d;
+}
+
+// A duplication of the test cases in "NearRoundingCases" above, but with
+// expected values expressed with integers, using ldexp/ldexpf.  These test
+// cases will work even on compilers that do not accurately round floating point
+// literals.
+TEST(FromChars, NearRoundingCasesExplicit) {
+  EXPECT_EQ(ToDouble("5.e125"), ldexp(6653062250012735, 365));
+  EXPECT_EQ(ToDouble("69.e267"), ldexp(4705683757438170, 841));
+  EXPECT_EQ(ToDouble("999.e-026"), ldexp(6798841691080350, -129));
+  EXPECT_EQ(ToDouble("7861.e-034"), ldexp(8975675289889240, -153));
+  EXPECT_EQ(ToDouble("75569.e-254"), ldexp(6091718967192243, -880));
+  EXPECT_EQ(ToDouble("928609.e-261"), ldexp(7849264900213743, -900));
+  EXPECT_EQ(ToDouble("9210917.e080"), ldexp(8341110837370930, 236));
+  EXPECT_EQ(ToDouble("84863171.e114"), ldexp(4625202867375927, 353));
+  EXPECT_EQ(ToDouble("653777767.e273"), ldexp(5068902999763073, 884));
+  EXPECT_EQ(ToDouble("5232604057.e-298"), ldexp(5741343011915040, -1010));
+  EXPECT_EQ(ToDouble("27235667517.e-109"), ldexp(6707124626673586, -380));
+  EXPECT_EQ(ToDouble("653532977297.e-123"), ldexp(7078246407265384, -422));
+  EXPECT_EQ(ToDouble("3142213164987.e-294"), ldexp(8219991337640559, -988));
+  EXPECT_EQ(ToDouble("46202199371337.e-072"), ldexp(5224462102115359, -246));
+  EXPECT_EQ(ToDouble("231010996856685.e-073"), ldexp(5224462102115359, -247));
+  EXPECT_EQ(ToDouble("9324754620109615.e212"), ldexp(5539753864394442, 705));
+  EXPECT_EQ(ToDouble("78459735791271921.e049"), ldexp(8388176519442766, 166));
+  EXPECT_EQ(ToDouble("272104041512242479.e200"), ldexp(5554409530847367, 670));
+  EXPECT_EQ(ToDouble("6802601037806061975.e198"), ldexp(5554409530847367, 668));
+  EXPECT_EQ(ToDouble("20505426358836677347.e-221"),
+            ldexp(4524032052079546, -722));
+  EXPECT_EQ(ToDouble("836168422905420598437.e-234"),
+            ldexp(5070963299887562, -760));
+  EXPECT_EQ(ToDouble("4891559871276714924261.e222"),
+            ldexp(6452687840519111, 757));
+  EXPECT_EQ(ToFloat("5.e-20"), ldexpf(15474250, -88));
+  EXPECT_EQ(ToFloat("67.e14"), ldexpf(12479722, 29));
+  EXPECT_EQ(ToFloat("985.e15"), ldexpf(14333636, 36));
+  EXPECT_EQ(ToFloat("7693.e-42"), ldexpf(10979816, -150));
+  EXPECT_EQ(ToFloat("55895.e-16"), ldexpf(12888509, -61));
+  EXPECT_EQ(ToFloat("996622.e-44"), ldexpf(14224264, -150));
+  EXPECT_EQ(ToFloat("7038531.e-32"), ldexpf(11420669, -107));
+  EXPECT_EQ(ToFloat("60419369.e-46"), ldexpf(8623340, -150));
+  EXPECT_EQ(ToFloat("702990899.e-20"), ldexpf(16209866, -61));
+  EXPECT_EQ(ToFloat("6930161142.e-48"), ldexpf(9891056, -150));
+  EXPECT_EQ(ToFloat("25933168707.e-13"), ldexpf(11138211, -32));
+  EXPECT_EQ(ToFloat("596428896559.e20"), ldexpf(12333860, 82));
+
+
+  EXPECT_EQ(ToDouble("9.e-265"), ldexp(8168427841980010, -930));
+  EXPECT_EQ(ToDouble("85.e-037"), ldexp(6360455125664090, -169));
+  EXPECT_EQ(ToDouble("623.e100"), ldexp(6263531988747231, 289));
+  EXPECT_EQ(ToDouble("3571.e263"), ldexp(6234526311072170, 833));
+  EXPECT_EQ(ToDouble("81661.e153"), ldexp(6696636728760206, 472));
+  EXPECT_EQ(ToDouble("920657.e-023"), ldexp(5975405561110124, -109));
+  EXPECT_EQ(ToDouble("4603285.e-024"), ldexp(5975405561110124, -110));
+  EXPECT_EQ(ToDouble("87575437.e-309"), ldexp(8452160731874668, -1053));
+  EXPECT_EQ(ToDouble("245540327.e122"), ldexp(4985336549131723, 381));
+  EXPECT_EQ(ToDouble("6138508175.e120"), ldexp(4985336549131723, 379));
+  EXPECT_EQ(ToDouble("83356057653.e193"), ldexp(5986732817132056, 625));
+  EXPECT_EQ(ToDouble("619534293513.e124"), ldexp(4798406992060657, 399));
+  EXPECT_EQ(ToDouble("2335141086879.e218"), ldexp(5419088166961646, 713));
+  EXPECT_EQ(ToDouble("36167929443327.e-159"), ldexp(8135819834632444, -536));
+  EXPECT_EQ(ToDouble("609610927149051.e-255"), ldexp(4576664294594737, -850));
+  EXPECT_EQ(ToDouble("3743626360493413.e-165"), ldexp(6898586531774201, -549));
+  EXPECT_EQ(ToDouble("94080055902682397.e-242"), ldexp(6273271706052298, -800));
+  EXPECT_EQ(ToDouble("899810892172646163.e283"), ldexp(7563892574477827, 947));
+  EXPECT_EQ(ToDouble("7120190517612959703.e120"), ldexp(5385467232557565, 409));
+  EXPECT_EQ(ToDouble("25188282901709339043.e-252"),
+            ldexp(5635662608542340, -825));
+  EXPECT_EQ(ToDouble("308984926168550152811.e-052"),
+            ldexp(5644774693823803, -157));
+  EXPECT_EQ(ToDouble("6372891218502368041059.e064"),
+            ldexp(4616868614322430, 233));
+
+  EXPECT_EQ(ToFloat("3.e-23"), ldexpf(9507380, -98));
+  EXPECT_EQ(ToFloat("57.e18"), ldexpf(12960300, 42));
+  EXPECT_EQ(ToFloat("789.e-35"), ldexpf(10739312, -130));
+  EXPECT_EQ(ToFloat("2539.e-18"), ldexpf(11990089, -72));
+  EXPECT_EQ(ToFloat("76173.e28"), ldexpf(9845130, 86));
+  EXPECT_EQ(ToFloat("887745.e-11"), ldexpf(9760860, -40));
+  EXPECT_EQ(ToFloat("5382571.e-37"), ldexpf(11447463, -124));
+  EXPECT_EQ(ToFloat("82381273.e-35"), ldexpf(8554961, -113));
+  EXPECT_EQ(ToFloat("750486563.e-38"), ldexpf(9975678, -120));
+  EXPECT_EQ(ToFloat("3752432815.e-39"), ldexpf(9975678, -121));
+  EXPECT_EQ(ToFloat("75224575729.e-45"), ldexpf(13105970, -137));
+  EXPECT_EQ(ToFloat("459926601011.e15"), ldexpf(12466336, 65));
+}
+
+// Common test logic for converting a string which lies exactly halfway between
+// two target floats.
+//
+// mantissa and exponent represent the precise value between two floating point
+// numbers, `expected_low` and `expected_high`.  The floating point
+// representation to parse in `StrCat(mantissa, "e", exponent)`.
+//
+// This function checks that an input just slightly less than the exact value
+// is rounded down to `expected_low`, and an input just slightly greater than
+// the exact value is rounded up to `expected_high`.
+//
+// The exact value should round to `expected_half`, which must be either
+// `expected_low` or `expected_high`.
+template <typename FloatType>
+void TestHalfwayValue(const std::string& mantissa, int exponent,
+                      FloatType expected_low, FloatType expected_high,
+                      FloatType expected_half) {
+  std::string low_rep = mantissa;
+  low_rep[low_rep.size() - 1] -= 1;
+  absl::StrAppend(&low_rep, std::string(1000, '9'), "e", exponent);
+
+  FloatType actual_low = 0;
+  absl::from_chars(low_rep.data(), low_rep.data() + low_rep.size(), actual_low);
+  EXPECT_EQ(expected_low, actual_low);
+
+  std::string high_rep =
+      absl::StrCat(mantissa, std::string(1000, '0'), "1e", exponent);
+  FloatType actual_high = 0;
+  absl::from_chars(high_rep.data(), high_rep.data() + high_rep.size(),
+                   actual_high);
+  EXPECT_EQ(expected_high, actual_high);
+
+  std::string halfway_rep = absl::StrCat(mantissa, "e", exponent);
+  FloatType actual_half = 0;
+  absl::from_chars(halfway_rep.data(), halfway_rep.data() + halfway_rep.size(),
+                   actual_half);
+  EXPECT_EQ(expected_half, actual_half);
+}
+
+TEST(FromChars, DoubleRounding) {
+  const double zero = 0.0;
+  const double first_subnormal = nextafter(zero, 1.0);
+  const double second_subnormal = nextafter(first_subnormal, 1.0);
+
+  const double first_normal = DBL_MIN;
+  const double last_subnormal = nextafter(first_normal, 0.0);
+  const double second_normal = nextafter(first_normal, 1.0);
+
+  const double last_normal = DBL_MAX;
+  const double penultimate_normal = nextafter(last_normal, 0.0);
+
+  // Various test cases for numbers between two representable floats.  Each
+  // call to TestHalfwayValue tests a number just below and just above the
+  // halfway point, as well as the number exactly between them.
+
+  // Test between zero and first_subnormal.  Round-to-even tie rounds down.
+  TestHalfwayValue(
+      "2."
+      "470328229206232720882843964341106861825299013071623822127928412503377536"
+      "351043759326499181808179961898982823477228588654633283551779698981993873"
+      "980053909390631503565951557022639229085839244910518443593180284993653615"
+      "250031937045767824921936562366986365848075700158576926990370631192827955"
+      "855133292783433840935197801553124659726357957462276646527282722005637400"
+      "648549997709659947045402082816622623785739345073633900796776193057750674"
+      "017632467360096895134053553745851666113422376667860416215968046191446729"
+      "184030053005753084904876539171138659164623952491262365388187963623937328"
+      "042389101867234849766823508986338858792562830275599565752445550725518931"
+      "369083625477918694866799496832404970582102851318545139621383772282614543"
+      "7693412532098591327667236328125",
+      -324, zero, first_subnormal, zero);
+
+  // first_subnormal and second_subnormal.  Round-to-even tie rounds up.
+  TestHalfwayValue(
+      "7."
+      "410984687618698162648531893023320585475897039214871466383785237510132609"
+      "053131277979497545424539885696948470431685765963899850655339096945981621"
+      "940161728171894510697854671067917687257517734731555330779540854980960845"
+      "750095811137303474765809687100959097544227100475730780971111893578483867"
+      "565399878350301522805593404659373979179073872386829939581848166016912201"
+      "945649993128979841136206248449867871357218035220901702390328579173252022"
+      "052897402080290685402160661237554998340267130003581248647904138574340187"
+      "552090159017259254714629617513415977493871857473787096164563890871811984"
+      "127167305601704549300470526959016576377688490826798697257336652176556794"
+      "107250876433756084600398490497214911746308553955635418864151316847843631"
+      "3080237596295773983001708984375",
+      -324, first_subnormal, second_subnormal, second_subnormal);
+
+  // last_subnormal and first_normal.  Round-to-even tie rounds up.
+  TestHalfwayValue(
+      "2."
+      "225073858507201136057409796709131975934819546351645648023426109724822222"
+      "021076945516529523908135087914149158913039621106870086438694594645527657"
+      "207407820621743379988141063267329253552286881372149012981122451451889849"
+      "057222307285255133155755015914397476397983411801999323962548289017107081"
+      "850690630666655994938275772572015763062690663332647565300009245888316433"
+      "037779791869612049497390377829704905051080609940730262937128958950003583"
+      "799967207254304360284078895771796150945516748243471030702609144621572289"
+      "880258182545180325707018860872113128079512233426288368622321503775666622"
+      "503982534335974568884423900265498198385487948292206894721689831099698365"
+      "846814022854243330660339850886445804001034933970427567186443383770486037"
+      "86162277173854562306587467901408672332763671875",
+      -308, last_subnormal, first_normal, first_normal);
+
+  // first_normal and second_normal.  Round-to-even tie rounds down.
+  TestHalfwayValue(
+      "2."
+      "225073858507201630123055637955676152503612414573018013083228724049586647"
+      "606759446192036794116886953213985520549032000903434781884412325572184367"
+      "563347617020518175998922941393629966742598285899994830148971433555578567"
+      "693279306015978183162142425067962460785295885199272493577688320732492479"
+      "924816869232247165964934329258783950102250973957579510571600738343645738"
+      "494324192997092179207389919761694314131497173265255020084997973676783743"
+      "155205818804439163810572367791175177756227497413804253387084478193655533"
+      "073867420834526162513029462022730109054820067654020201547112002028139700"
+      "141575259123440177362244273712468151750189745559978653234255886219611516"
+      "335924167958029604477064946470184777360934300451421683607013647479513962"
+      "13837722826145437693412532098591327667236328125",
+      -308, first_normal, second_normal, first_normal);
+
+  // penultimate_normal and last_normal.  Round-to-even rounds down.
+  TestHalfwayValue(
+      "1."
+      "797693134862315608353258760581052985162070023416521662616611746258695532"
+      "672923265745300992879465492467506314903358770175220871059269879629062776"
+      "047355692132901909191523941804762171253349609463563872612866401980290377"
+      "995141836029815117562837277714038305214839639239356331336428021390916694"
+      "57927874464075218944",
+      308, penultimate_normal, last_normal, penultimate_normal);
+}
+
+// Same test cases as DoubleRounding, now with new and improved Much Smaller
+// Precision!
+TEST(FromChars, FloatRounding) {
+  const float zero = 0.0;
+  const float first_subnormal = nextafterf(zero, 1.0);
+  const float second_subnormal = nextafterf(first_subnormal, 1.0);
+
+  const float first_normal = FLT_MIN;
+  const float last_subnormal = nextafterf(first_normal, 0.0);
+  const float second_normal = nextafterf(first_normal, 1.0);
+
+  const float last_normal = FLT_MAX;
+  const float penultimate_normal = nextafterf(last_normal, 0.0);
+
+  // Test between zero and first_subnormal.  Round-to-even tie rounds down.
+  TestHalfwayValue(
+      "7."
+      "006492321624085354618647916449580656401309709382578858785341419448955413"
+      "42930300743319094181060791015625",
+      -46, zero, first_subnormal, zero);
+
+  // first_subnormal and second_subnormal.  Round-to-even tie rounds up.
+  TestHalfwayValue(
+      "2."
+      "101947696487225606385594374934874196920392912814773657635602425834686624"
+      "028790902229957282543182373046875",
+      -45, first_subnormal, second_subnormal, second_subnormal);
+
+  // last_subnormal and first_normal.  Round-to-even tie rounds up.
+  TestHalfwayValue(
+      "1."
+      "175494280757364291727882991035766513322858992758990427682963118425003064"
+      "9651730385585324256680905818939208984375",
+      -38, last_subnormal, first_normal, first_normal);
+
+  // first_normal and second_normal.  Round-to-even tie rounds down.
+  TestHalfwayValue(
+      "1."
+      "175494420887210724209590083408724842314472120785184615334540294131831453"
+      "9442813071445925743319094181060791015625",
+      -38, first_normal, second_normal, first_normal);
+
+  // penultimate_normal and last_normal.  Round-to-even rounds down.
+  TestHalfwayValue("3.40282336497324057985868971510891282432", 38,
+                   penultimate_normal, last_normal, penultimate_normal);
+}
+
+TEST(FromChars, Underflow) {
+  // Check that underflow is handled correctly, according to the specification
+  // in DR 3081.
+  double d;
+  float f;
+  absl::from_chars_result result;
+
+  std::string negative_underflow = "-1e-1000";
+  const char* begin = negative_underflow.data();
+  const char* end = begin + negative_underflow.size();
+  d = 100.0;
+  result = absl::from_chars(begin, end, d);
+  EXPECT_EQ(result.ptr, end);
+  EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+  EXPECT_TRUE(std::signbit(d));  // negative
+  EXPECT_GE(d, -std::numeric_limits<double>::min());
+  f = 100.0;
+  result = absl::from_chars(begin, end, f);
+  EXPECT_EQ(result.ptr, end);
+  EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+  EXPECT_TRUE(std::signbit(f));  // negative
+  EXPECT_GE(f, -std::numeric_limits<float>::min());
+
+  std::string positive_underflow = "1e-1000";
+  begin = positive_underflow.data();
+  end = begin + positive_underflow.size();
+  d = -100.0;
+  result = absl::from_chars(begin, end, d);
+  EXPECT_EQ(result.ptr, end);
+  EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+  EXPECT_FALSE(std::signbit(d));  // positive
+  EXPECT_LE(d, std::numeric_limits<double>::min());
+  f = -100.0;
+  result = absl::from_chars(begin, end, f);
+  EXPECT_EQ(result.ptr, end);
+  EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+  EXPECT_FALSE(std::signbit(f));  // positive
+  EXPECT_LE(f, std::numeric_limits<float>::min());
+}
+
+TEST(FromChars, Overflow) {
+  // Check that overflow is handled correctly, according to the specification
+  // in DR 3081.
+  double d;
+  float f;
+  absl::from_chars_result result;
+
+  std::string negative_overflow = "-1e1000";
+  const char* begin = negative_overflow.data();
+  const char* end = begin + negative_overflow.size();
+  d = 100.0;
+  result = absl::from_chars(begin, end, d);
+  EXPECT_EQ(result.ptr, end);
+  EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+  EXPECT_TRUE(std::signbit(d));  // negative
+  EXPECT_EQ(d, -std::numeric_limits<double>::max());
+  f = 100.0;
+  result = absl::from_chars(begin, end, f);
+  EXPECT_EQ(result.ptr, end);
+  EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+  EXPECT_TRUE(std::signbit(f));  // negative
+  EXPECT_EQ(f, -std::numeric_limits<float>::max());
+
+  std::string positive_overflow = "1e1000";
+  begin = positive_overflow.data();
+  end = begin + positive_overflow.size();
+  d = -100.0;
+  result = absl::from_chars(begin, end, d);
+  EXPECT_EQ(result.ptr, end);
+  EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+  EXPECT_FALSE(std::signbit(d));  // positive
+  EXPECT_EQ(d, std::numeric_limits<double>::max());
+  f = -100.0;
+  result = absl::from_chars(begin, end, f);
+  EXPECT_EQ(result.ptr, end);
+  EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+  EXPECT_FALSE(std::signbit(f));  // positive
+  EXPECT_EQ(f, std::numeric_limits<float>::max());
+}
+
+TEST(FromChars, ReturnValuePtr) {
+  // Check that `ptr` points one past the number scanned, even if that number
+  // is not representable.
+  double d;
+  absl::from_chars_result result;
+
+  std::string normal = "3.14@#$%@#$%";
+  result = absl::from_chars(normal.data(), normal.data() + normal.size(), d);
+  EXPECT_EQ(result.ec, std::errc());
+  EXPECT_EQ(result.ptr - normal.data(), 4);
+
+  std::string overflow = "1e1000@#$%@#$%";
+  result = absl::from_chars(overflow.data(),
+                            overflow.data() + overflow.size(), d);
+  EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+  EXPECT_EQ(result.ptr - overflow.data(), 6);
+
+  std::string garbage = "#$%@#$%";
+  result = absl::from_chars(garbage.data(),
+                            garbage.data() + garbage.size(), d);
+  EXPECT_EQ(result.ec, std::errc::invalid_argument);
+  EXPECT_EQ(result.ptr - garbage.data(), 0);
+}
+
+// Check for a wide range of inputs that strtod() and absl::from_chars() exactly
+// agree on the conversion amount.
+//
+// This test assumes the platform's strtod() uses perfect round_to_nearest
+// rounding.
+TEST(FromChars, TestVersusStrtod) {
+  for (int mantissa = 1000000; mantissa <= 9999999; mantissa += 501) {
+    for (int exponent = -300; exponent < 300; ++exponent) {
+      std::string candidate = absl::StrCat(mantissa, "e", exponent);
+      double strtod_value = strtod(candidate.c_str(), nullptr);
+      double absl_value = 0;
+      absl::from_chars(candidate.data(), candidate.data() + candidate.size(),
+                       absl_value);
+      ASSERT_EQ(strtod_value, absl_value) << candidate;
+    }
+  }
+}
+
+// Check for a wide range of inputs that strtof() and absl::from_chars() exactly
+// agree on the conversion amount.
+//
+// This test assumes the platform's strtof() uses perfect round_to_nearest
+// rounding.
+TEST(FromChars, TestVersusStrtof) {
+  for (int mantissa = 1000000; mantissa <= 9999999; mantissa += 501) {
+    for (int exponent = -43; exponent < 32; ++exponent) {
+      std::string candidate = absl::StrCat(mantissa, "e", exponent);
+      float strtod_value = strtof(candidate.c_str(), nullptr);
+      float absl_value = 0;
+      absl::from_chars(candidate.data(), candidate.data() + candidate.size(),
+                       absl_value);
+      ASSERT_EQ(strtod_value, absl_value) << candidate;
+    }
+  }
+}
+
+// Tests if two floating point values have identical bit layouts.  (EXPECT_EQ
+// is not suitable for NaN testing, since NaNs are never equal.)
+template <typename Float>
+bool Identical(Float a, Float b) {
+  return 0 == memcmp(&a, &b, sizeof(Float));
+}
+
+// Check that NaNs are parsed correctly.  The spec requires that
+// std::from_chars on "NaN(123abc)" return the same value as std::nan("123abc").
+// How such an n-char-sequence affects the generated NaN is unspecified, so we
+// just test for symmetry with std::nan and strtod here.
+//
+// (In Linux, this parses the value as a number and stuffs that number into the
+// free bits of a quiet NaN.)
+TEST(FromChars, NaNDoubles) {
+  for (std::string n_char_sequence :
+       {"", "1", "2", "3", "fff", "FFF", "200000", "400000", "4000000000000",
+        "8000000000000", "abc123", "legal_but_unexpected",
+        "99999999999999999999999", "_"}) {
+    std::string input = absl::StrCat("nan(", n_char_sequence, ")");
+    SCOPED_TRACE(input);
+    double from_chars_double;
+    absl::from_chars(input.data(), input.data() + input.size(),
+                     from_chars_double);
+    double std_nan_double = std::nan(n_char_sequence.c_str());
+    EXPECT_TRUE(Identical(from_chars_double, std_nan_double));
+
+    // Also check that we match strtod()'s behavior.  This test assumes that the
+    // platform has a compliant strtod().
+#if ABSL_STRTOD_HANDLES_NAN_CORRECTLY
+    double strtod_double = strtod(input.c_str(), nullptr);
+    EXPECT_TRUE(Identical(from_chars_double, strtod_double));
+#endif  // ABSL_STRTOD_HANDLES_NAN_CORRECTLY
+
+    // Check that we can parse a negative NaN
+    std::string negative_input = "-" + input;
+    double negative_from_chars_double;
+    absl::from_chars(negative_input.data(),
+                     negative_input.data() + negative_input.size(),
+                     negative_from_chars_double);
+    EXPECT_TRUE(std::signbit(negative_from_chars_double));
+    EXPECT_FALSE(Identical(negative_from_chars_double, from_chars_double));
+    from_chars_double = std::copysign(from_chars_double, -1.0);
+    EXPECT_TRUE(Identical(negative_from_chars_double, from_chars_double));
+  }
+}
+
+TEST(FromChars, NaNFloats) {
+  for (std::string n_char_sequence :
+       {"", "1", "2", "3", "fff", "FFF", "200000", "400000", "4000000000000",
+        "8000000000000", "abc123", "legal_but_unexpected",
+        "99999999999999999999999", "_"}) {
+    std::string input = absl::StrCat("nan(", n_char_sequence, ")");
+    SCOPED_TRACE(input);
+    float from_chars_float;
+    absl::from_chars(input.data(), input.data() + input.size(),
+                     from_chars_float);
+    float std_nan_float = std::nanf(n_char_sequence.c_str());
+    EXPECT_TRUE(Identical(from_chars_float, std_nan_float));
+
+    // Also check that we match strtof()'s behavior.  This test assumes that the
+    // platform has a compliant strtof().
+#if ABSL_STRTOD_HANDLES_NAN_CORRECTLY
+    float strtof_float = strtof(input.c_str(), nullptr);
+    EXPECT_TRUE(Identical(from_chars_float, strtof_float));
+#endif  // ABSL_STRTOD_HANDLES_NAN_CORRECTLY
+
+    // Check that we can parse a negative NaN
+    std::string negative_input = "-" + input;
+    float negative_from_chars_float;
+    absl::from_chars(negative_input.data(),
+                     negative_input.data() + negative_input.size(),
+                     negative_from_chars_float);
+    EXPECT_TRUE(std::signbit(negative_from_chars_float));
+    EXPECT_FALSE(Identical(negative_from_chars_float, from_chars_float));
+    from_chars_float = std::copysign(from_chars_float, -1.0);
+    EXPECT_TRUE(Identical(negative_from_chars_float, from_chars_float));
+  }
+}
+
+// Returns an integer larger than step.  The values grow exponentially.
+int NextStep(int step) {
+  return step + (step >> 2) + 1;
+}
+
+// Test a conversion on a family of input strings, checking that the calculation
+// is correct for in-bounds values, and that overflow and underflow are done
+// correctly for out-of-bounds values.
+//
+// input_generator maps from an integer index to a string to test.
+// expected_generator maps from an integer index to an expected Float value.
+// from_chars conversion of input_generator(i) should result in
+// expected_generator(i).
+//
+// lower_bound and upper_bound denote the smallest and largest values for which
+// the conversion is expected to succeed.
+template <typename Float>
+void TestOverflowAndUnderflow(
+    const std::function<std::string(int)>& input_generator,
+    const std::function<Float(int)>& expected_generator, int lower_bound,
+    int upper_bound) {
+  // test legal values near lower_bound
+  int index, step;
+  for (index = lower_bound, step = 1; index < upper_bound;
+       index += step, step = NextStep(step)) {
+    std::string input = input_generator(index);
+    SCOPED_TRACE(input);
+    Float expected = expected_generator(index);
+    Float actual;
+    auto result =
+        absl::from_chars(input.data(), input.data() + input.size(), actual);
+    EXPECT_EQ(result.ec, std::errc());
+    EXPECT_EQ(expected, actual)
+        << absl::StrFormat("%a vs %a", expected, actual);
+  }
+  // test legal values near upper_bound
+  for (index = upper_bound, step = 1; index > lower_bound;
+       index -= step, step = NextStep(step)) {
+    std::string input = input_generator(index);
+    SCOPED_TRACE(input);
+    Float expected = expected_generator(index);
+    Float actual;
+    auto result =
+        absl::from_chars(input.data(), input.data() + input.size(), actual);
+    EXPECT_EQ(result.ec, std::errc());
+    EXPECT_EQ(expected, actual)
+        << absl::StrFormat("%a vs %a", expected, actual);
+  }
+  // Test underflow values below lower_bound
+  for (index = lower_bound - 1, step = 1; index > -1000000;
+       index -= step, step = NextStep(step)) {
+    std::string input = input_generator(index);
+    SCOPED_TRACE(input);
+    Float actual;
+    auto result =
+        absl::from_chars(input.data(), input.data() + input.size(), actual);
+    EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+    EXPECT_LT(actual, 1.0);  // check for underflow
+  }
+  // Test overflow values above upper_bound
+  for (index = upper_bound + 1, step = 1; index < 1000000;
+       index += step, step = NextStep(step)) {
+    std::string input = input_generator(index);
+    SCOPED_TRACE(input);
+    Float actual;
+    auto result =
+        absl::from_chars(input.data(), input.data() + input.size(), actual);
+    EXPECT_EQ(result.ec, std::errc::result_out_of_range);
+    EXPECT_GT(actual, 1.0);  // check for overflow
+  }
+}
+
+// Check that overflow and underflow are caught correctly for hex doubles.
+//
+// The largest representable double is 0x1.fffffffffffffp+1023, and the
+// smallest representable subnormal is 0x0.0000000000001p-1022, which equals
+// 0x1p-1074.  Therefore 1023 and -1074 are the limits of acceptable exponents
+// in this test.
+TEST(FromChars, HexdecimalDoubleLimits) {
+  auto input_gen = [](int index) { return absl::StrCat("0x1.0p", index); };
+  auto expected_gen = [](int index) { return std::ldexp(1.0, index); };
+  TestOverflowAndUnderflow<double>(input_gen, expected_gen, -1074, 1023);
+}
+
+// Check that overflow and underflow are caught correctly for hex floats.
+//
+// The largest representable float is 0x1.fffffep+127, and the smallest
+// representable subnormal is 0x0.000002p-126, which equals 0x1p-149.
+// Therefore 127 and -149 are the limits of acceptable exponents in this test.
+TEST(FromChars, HexdecimalFloatLimits) {
+  auto input_gen = [](int index) { return absl::StrCat("0x1.0p", index); };
+  auto expected_gen = [](int index) { return std::ldexp(1.0f, index); };
+  TestOverflowAndUnderflow<float>(input_gen, expected_gen, -149, 127);
+}
+
+// Check that overflow and underflow are caught correctly for decimal doubles.
+//
+// The largest representable double is about 1.8e308, and the smallest
+// representable subnormal is about 5e-324.  '1e-324' therefore rounds away from
+// the smallest representable positive value.  -323 and 308 are the limits of
+// acceptable exponents in this test.
+TEST(FromChars, DecimalDoubleLimits) {
+  auto input_gen = [](int index) { return absl::StrCat("1.0e", index); };
+  auto expected_gen = [](int index) { return Pow10(index); };
+  TestOverflowAndUnderflow<double>(input_gen, expected_gen, -323, 308);
+}
+
+// Check that overflow and underflow are caught correctly for decimal floats.
+//
+// The largest representable float is about 3.4e38, and the smallest
+// representable subnormal is about 1.45e-45.  '1e-45' therefore rounds towards
+// the smallest representable positive value.  -45 and 38 are the limits of
+// acceptable exponents in this test.
+TEST(FromChars, DecimalFloatLimits) {
+  auto input_gen = [](int index) { return absl::StrCat("1.0e", index); };
+  auto expected_gen = [](int index) { return Pow10(index); };
+  TestOverflowAndUnderflow<float>(input_gen, expected_gen, -45, 38);
+}
+
+}  // namespace
diff --git a/absl/strings/escaping.cc b/absl/strings/escaping.cc
new file mode 100644
index 0000000..0d336e3
--- /dev/null
+++ b/absl/strings/escaping.cc
@@ -0,0 +1,1129 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/escaping.h"
+
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <cstring>
+#include <iterator>
+#include <limits>
+#include <string>
+
+#include "absl/base/internal/endian.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/unaligned_access.h"
+#include "absl/strings/internal/char_map.h"
+#include "absl/strings/internal/resize_uninitialized.h"
+#include "absl/strings/internal/utf8.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_join.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+namespace {
+
+// Digit conversion.
+constexpr char kHexChar[] = "0123456789abcdef";
+
+constexpr char kHexTable[513] =
+    "000102030405060708090a0b0c0d0e0f"
+    "101112131415161718191a1b1c1d1e1f"
+    "202122232425262728292a2b2c2d2e2f"
+    "303132333435363738393a3b3c3d3e3f"
+    "404142434445464748494a4b4c4d4e4f"
+    "505152535455565758595a5b5c5d5e5f"
+    "606162636465666768696a6b6c6d6e6f"
+    "707172737475767778797a7b7c7d7e7f"
+    "808182838485868788898a8b8c8d8e8f"
+    "909192939495969798999a9b9c9d9e9f"
+    "a0a1a2a3a4a5a6a7a8a9aaabacadaeaf"
+    "b0b1b2b3b4b5b6b7b8b9babbbcbdbebf"
+    "c0c1c2c3c4c5c6c7c8c9cacbcccdcecf"
+    "d0d1d2d3d4d5d6d7d8d9dadbdcdddedf"
+    "e0e1e2e3e4e5e6e7e8e9eaebecedeeef"
+    "f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff";
+
+// These are used for the leave_nulls_escaped argument to CUnescapeInternal().
+constexpr bool kUnescapeNulls = false;
+
+inline bool is_octal_digit(char c) { return ('0' <= c) && (c <= '7'); }
+
+inline int hex_digit_to_int(char c) {
+  static_assert('0' == 0x30 && 'A' == 0x41 && 'a' == 0x61,
+                "Character set must be ASCII.");
+  assert(absl::ascii_isxdigit(c));
+  int x = static_cast<unsigned char>(c);
+  if (x > '9') {
+    x += 9;
+  }
+  return x & 0xf;
+}
+
+inline bool IsSurrogate(char32_t c, absl::string_view src, std::string* error) {
+  if (c >= 0xD800 && c <= 0xDFFF) {
+    if (error) {
+      *error = absl::StrCat("invalid surrogate character (0xD800-DFFF): \\",
+                            src);
+    }
+    return true;
+  }
+  return false;
+}
+
+// ----------------------------------------------------------------------
+// CUnescapeInternal()
+//    Implements both CUnescape() and CUnescapeForNullTerminatedString().
+//
+//    Unescapes C escape sequences and is the reverse of CEscape().
+//
+//    If 'source' is valid, stores the unescaped string and its size in
+//    'dest' and 'dest_len' respectively, and returns true. Otherwise
+//    returns false and optionally stores the error description in
+//    'error'. Set 'error' to nullptr to disable error reporting.
+//
+//    'dest' should point to a buffer that is at least as big as 'source'.
+//    'source' and 'dest' may be the same.
+//
+//     NOTE: any changes to this function must also be reflected in the older
+//     UnescapeCEscapeSequences().
+// ----------------------------------------------------------------------
+bool CUnescapeInternal(absl::string_view source, bool leave_nulls_escaped,
+                       char* dest, ptrdiff_t* dest_len, std::string* error) {
+  char* d = dest;
+  const char* p = source.data();
+  const char* end = p + source.size();
+  const char* last_byte = end - 1;
+
+  // Small optimization for case where source = dest and there's no escaping
+  while (p == d && p < end && *p != '\\') p++, d++;
+
+  while (p < end) {
+    if (*p != '\\') {
+      *d++ = *p++;
+    } else {
+      if (++p > last_byte) {  // skip past the '\\'
+        if (error) *error = "String cannot end with \\";
+        return false;
+      }
+      switch (*p) {
+        case 'a':  *d++ = '\a';  break;
+        case 'b':  *d++ = '\b';  break;
+        case 'f':  *d++ = '\f';  break;
+        case 'n':  *d++ = '\n';  break;
+        case 'r':  *d++ = '\r';  break;
+        case 't':  *d++ = '\t';  break;
+        case 'v':  *d++ = '\v';  break;
+        case '\\': *d++ = '\\';  break;
+        case '?':  *d++ = '\?';  break;    // \?  Who knew?
+        case '\'': *d++ = '\'';  break;
+        case '"':  *d++ = '\"';  break;
+        case '0':
+        case '1':
+        case '2':
+        case '3':
+        case '4':
+        case '5':
+        case '6':
+        case '7': {
+          // octal digit: 1 to 3 digits
+          const char* octal_start = p;
+          unsigned int ch = *p - '0';
+          if (p < last_byte && is_octal_digit(p[1])) ch = ch * 8 + *++p - '0';
+          if (p < last_byte && is_octal_digit(p[1]))
+            ch = ch * 8 + *++p - '0';      // now points at last digit
+          if (ch > 0xff) {
+            if (error) {
+              *error = "Value of \\" +
+                       std::string(octal_start, p + 1 - octal_start) +
+                       " exceeds 0xff";
+            }
+            return false;
+          }
+          if ((ch == 0) && leave_nulls_escaped) {
+            // Copy the escape sequence for the null character
+            const ptrdiff_t octal_size = p + 1 - octal_start;
+            *d++ = '\\';
+            memcpy(d, octal_start, octal_size);
+            d += octal_size;
+            break;
+          }
+          *d++ = ch;
+          break;
+        }
+        case 'x':
+        case 'X': {
+          if (p >= last_byte) {
+            if (error) *error = "String cannot end with \\x";
+            return false;
+          } else if (!absl::ascii_isxdigit(p[1])) {
+            if (error) *error = "\\x cannot be followed by a non-hex digit";
+            return false;
+          }
+          unsigned int ch = 0;
+          const char* hex_start = p;
+          while (p < last_byte && absl::ascii_isxdigit(p[1]))
+            // Arbitrarily many hex digits
+            ch = (ch << 4) + hex_digit_to_int(*++p);
+          if (ch > 0xFF) {
+            if (error) {
+              *error = "Value of \\" +
+                       std::string(hex_start, p + 1 - hex_start) +
+                       " exceeds 0xff";
+            }
+            return false;
+          }
+          if ((ch == 0) && leave_nulls_escaped) {
+            // Copy the escape sequence for the null character
+            const ptrdiff_t hex_size = p + 1 - hex_start;
+            *d++ = '\\';
+            memcpy(d, hex_start, hex_size);
+            d += hex_size;
+            break;
+          }
+          *d++ = ch;
+          break;
+        }
+        case 'u': {
+          // \uhhhh => convert 4 hex digits to UTF-8
+          char32_t rune = 0;
+          const char* hex_start = p;
+          if (p + 4 >= end) {
+            if (error) {
+              *error = "\\u must be followed by 4 hex digits: \\" +
+                       std::string(hex_start, p + 1 - hex_start);
+            }
+            return false;
+          }
+          for (int i = 0; i < 4; ++i) {
+            // Look one char ahead.
+            if (absl::ascii_isxdigit(p[1])) {
+              rune = (rune << 4) + hex_digit_to_int(*++p);  // Advance p.
+            } else {
+              if (error) {
+                *error = "\\u must be followed by 4 hex digits: \\" +
+                         std::string(hex_start, p + 1 - hex_start);
+              }
+              return false;
+            }
+          }
+          if ((rune == 0) && leave_nulls_escaped) {
+            // Copy the escape sequence for the null character
+            *d++ = '\\';
+            memcpy(d, hex_start, 5);  // u0000
+            d += 5;
+            break;
+          }
+          if (IsSurrogate(rune, absl::string_view(hex_start, 5), error)) {
+            return false;
+          }
+          d += strings_internal::EncodeUTF8Char(d, rune);
+          break;
+        }
+        case 'U': {
+          // \Uhhhhhhhh => convert 8 hex digits to UTF-8
+          char32_t rune = 0;
+          const char* hex_start = p;
+          if (p + 8 >= end) {
+            if (error) {
+              *error = "\\U must be followed by 8 hex digits: \\" +
+                       std::string(hex_start, p + 1 - hex_start);
+            }
+            return false;
+          }
+          for (int i = 0; i < 8; ++i) {
+            // Look one char ahead.
+            if (absl::ascii_isxdigit(p[1])) {
+              // Don't change rune until we're sure this
+              // is within the Unicode limit, but do advance p.
+              uint32_t newrune = (rune << 4) + hex_digit_to_int(*++p);
+              if (newrune > 0x10FFFF) {
+                if (error) {
+                  *error = "Value of \\" +
+                           std::string(hex_start, p + 1 - hex_start) +
+                           " exceeds Unicode limit (0x10FFFF)";
+                }
+                return false;
+              } else {
+                rune = newrune;
+              }
+            } else {
+              if (error) {
+                *error = "\\U must be followed by 8 hex digits: \\" +
+                         std::string(hex_start, p + 1 - hex_start);
+              }
+              return false;
+            }
+          }
+          if ((rune == 0) && leave_nulls_escaped) {
+            // Copy the escape sequence for the null character
+            *d++ = '\\';
+            memcpy(d, hex_start, 9);  // U00000000
+            d += 9;
+            break;
+          }
+          if (IsSurrogate(rune, absl::string_view(hex_start, 9), error)) {
+            return false;
+          }
+          d += strings_internal::EncodeUTF8Char(d, rune);
+          break;
+        }
+        default: {
+          if (error) *error = std::string("Unknown escape sequence: \\") + *p;
+          return false;
+        }
+      }
+      p++;                                 // read past letter we escaped
+    }
+  }
+  *dest_len = d - dest;
+  return true;
+}
+
+// ----------------------------------------------------------------------
+// CUnescapeInternal()
+//
+//    Same as above but uses a std::string for output. 'source' and 'dest'
+//    may be the same.
+// ----------------------------------------------------------------------
+bool CUnescapeInternal(absl::string_view source, bool leave_nulls_escaped,
+                       std::string* dest, std::string* error) {
+  strings_internal::STLStringResizeUninitialized(dest, source.size());
+
+  ptrdiff_t dest_size;
+  if (!CUnescapeInternal(source,
+                         leave_nulls_escaped,
+                         &(*dest)[0],
+                         &dest_size,
+                         error)) {
+    return false;
+  }
+  dest->erase(dest_size);
+  return true;
+}
+
+// ----------------------------------------------------------------------
+// CEscape()
+// CHexEscape()
+// Utf8SafeCEscape()
+// Utf8SafeCHexEscape()
+//    Escapes 'src' using C-style escape sequences.  This is useful for
+//    preparing query flags.  The 'Hex' version uses hexadecimal rather than
+//    octal sequences.  The 'Utf8Safe' version does not touch UTF-8 bytes.
+//
+//    Escaped chars: \n, \r, \t, ", ', \, and !absl::ascii_isprint().
+// ----------------------------------------------------------------------
+std::string CEscapeInternal(absl::string_view src, bool use_hex,
+                            bool utf8_safe) {
+  std::string dest;
+  bool last_hex_escape = false;  // true if last output char was \xNN.
+
+  for (unsigned char c : src) {
+    bool is_hex_escape = false;
+    switch (c) {
+      case '\n': dest.append("\\" "n"); break;
+      case '\r': dest.append("\\" "r"); break;
+      case '\t': dest.append("\\" "t"); break;
+      case '\"': dest.append("\\" "\""); break;
+      case '\'': dest.append("\\" "'"); break;
+      case '\\': dest.append("\\" "\\"); break;
+      default:
+        // Note that if we emit \xNN and the src character after that is a hex
+        // digit then that digit must be escaped too to prevent it being
+        // interpreted as part of the character code by C.
+        if ((!utf8_safe || c < 0x80) &&
+            (!absl::ascii_isprint(c) ||
+             (last_hex_escape && absl::ascii_isxdigit(c)))) {
+          if (use_hex) {
+            dest.append("\\" "x");
+            dest.push_back(kHexChar[c / 16]);
+            dest.push_back(kHexChar[c % 16]);
+            is_hex_escape = true;
+          } else {
+            dest.append("\\");
+            dest.push_back(kHexChar[c / 64]);
+            dest.push_back(kHexChar[(c % 64) / 8]);
+            dest.push_back(kHexChar[c % 8]);
+          }
+        } else {
+          dest.push_back(c);
+          break;
+        }
+    }
+    last_hex_escape = is_hex_escape;
+  }
+
+  return dest;
+}
+
+/* clang-format off */
+constexpr char c_escaped_len[256] = {
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 2, 2, 4, 4, 2, 4, 4,  // \t, \n, \r
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1,  // ", '
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  // '0'..'9'
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  // 'A'..'O'
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1,  // 'P'..'Z', '\'
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  // 'a'..'o'
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 4,  // 'p'..'z', DEL
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+};
+/* clang-format on */
+
+// Calculates the length of the C-style escaped version of 'src'.
+// Assumes that non-printable characters are escaped using octal sequences, and
+// that UTF-8 bytes are not handled specially.
+inline size_t CEscapedLength(absl::string_view src) {
+  size_t escaped_len = 0;
+  for (unsigned char c : src) escaped_len += c_escaped_len[c];
+  return escaped_len;
+}
+
+void CEscapeAndAppendInternal(absl::string_view src, std::string* dest) {
+  size_t escaped_len = CEscapedLength(src);
+  if (escaped_len == src.size()) {
+    dest->append(src.data(), src.size());
+    return;
+  }
+
+  size_t cur_dest_len = dest->size();
+  strings_internal::STLStringResizeUninitialized(dest,
+                                                 cur_dest_len + escaped_len);
+  char* append_ptr = &(*dest)[cur_dest_len];
+
+  for (unsigned char c : src) {
+    int char_len = c_escaped_len[c];
+    if (char_len == 1) {
+      *append_ptr++ = c;
+    } else if (char_len == 2) {
+      switch (c) {
+        case '\n':
+          *append_ptr++ = '\\';
+          *append_ptr++ = 'n';
+          break;
+        case '\r':
+          *append_ptr++ = '\\';
+          *append_ptr++ = 'r';
+          break;
+        case '\t':
+          *append_ptr++ = '\\';
+          *append_ptr++ = 't';
+          break;
+        case '\"':
+          *append_ptr++ = '\\';
+          *append_ptr++ = '\"';
+          break;
+        case '\'':
+          *append_ptr++ = '\\';
+          *append_ptr++ = '\'';
+          break;
+        case '\\':
+          *append_ptr++ = '\\';
+          *append_ptr++ = '\\';
+          break;
+      }
+    } else {
+      *append_ptr++ = '\\';
+      *append_ptr++ = '0' + c / 64;
+      *append_ptr++ = '0' + (c % 64) / 8;
+      *append_ptr++ = '0' + c % 8;
+    }
+  }
+}
+
+bool Base64UnescapeInternal(const char* src_param, size_t szsrc, char* dest,
+                            size_t szdest, const signed char* unbase64,
+                            size_t* len) {
+  static const char kPad64Equals = '=';
+  static const char kPad64Dot = '.';
+
+  size_t destidx = 0;
+  int decode = 0;
+  int state = 0;
+  unsigned int ch = 0;
+  unsigned int temp = 0;
+
+  // If "char" is signed by default, using *src as an array index results in
+  // accessing negative array elements. Treat the input as a pointer to
+  // unsigned char to avoid this.
+  const unsigned char* src = reinterpret_cast<const unsigned char*>(src_param);
+
+  // The GET_INPUT macro gets the next input character, skipping
+  // over any whitespace, and stopping when we reach the end of the
+  // std::string or when we read any non-data character.  The arguments are
+  // an arbitrary identifier (used as a label for goto) and the number
+  // of data bytes that must remain in the input to avoid aborting the
+  // loop.
+#define GET_INPUT(label, remain)                                \
+  label:                                                        \
+  --szsrc;                                                      \
+  ch = *src++;                                                  \
+  decode = unbase64[ch];                                        \
+  if (decode < 0) {                                             \
+    if (absl::ascii_isspace(ch) && szsrc >= remain) goto label; \
+    state = 4 - remain;                                         \
+    break;                                                      \
+  }
+
+  // if dest is null, we're just checking to see if it's legal input
+  // rather than producing output.  (I suspect this could just be done
+  // with a regexp...).  We duplicate the loop so this test can be
+  // outside it instead of in every iteration.
+
+  if (dest) {
+    // This loop consumes 4 input bytes and produces 3 output bytes
+    // per iteration.  We can't know at the start that there is enough
+    // data left in the std::string for a full iteration, so the loop may
+    // break out in the middle; if so 'state' will be set to the
+    // number of input bytes read.
+
+    while (szsrc >= 4) {
+      // We'll start by optimistically assuming that the next four
+      // bytes of the std::string (src[0..3]) are four good data bytes
+      // (that is, no nulls, whitespace, padding chars, or illegal
+      // chars).  We need to test src[0..2] for nulls individually
+      // before constructing temp to preserve the property that we
+      // never read past a null in the std::string (no matter how long
+      // szsrc claims the std::string is).
+
+      if (!src[0] || !src[1] || !src[2] ||
+          ((temp = ((unsigned(unbase64[src[0]]) << 18) |
+                    (unsigned(unbase64[src[1]]) << 12) |
+                    (unsigned(unbase64[src[2]]) << 6) |
+                    (unsigned(unbase64[src[3]])))) &
+           0x80000000)) {
+        // Iff any of those four characters was bad (null, illegal,
+        // whitespace, padding), then temp's high bit will be set
+        // (because unbase64[] is -1 for all bad characters).
+        //
+        // We'll back up and resort to the slower decoder, which knows
+        // how to handle those cases.
+
+        GET_INPUT(first, 4);
+        temp = decode;
+        GET_INPUT(second, 3);
+        temp = (temp << 6) | decode;
+        GET_INPUT(third, 2);
+        temp = (temp << 6) | decode;
+        GET_INPUT(fourth, 1);
+        temp = (temp << 6) | decode;
+      } else {
+        // We really did have four good data bytes, so advance four
+        // characters in the std::string.
+
+        szsrc -= 4;
+        src += 4;
+      }
+
+      // temp has 24 bits of input, so write that out as three bytes.
+
+      if (destidx + 3 > szdest) return false;
+      dest[destidx + 2] = temp;
+      temp >>= 8;
+      dest[destidx + 1] = temp;
+      temp >>= 8;
+      dest[destidx] = temp;
+      destidx += 3;
+    }
+  } else {
+    while (szsrc >= 4) {
+      if (!src[0] || !src[1] || !src[2] ||
+          ((temp = ((unsigned(unbase64[src[0]]) << 18) |
+                    (unsigned(unbase64[src[1]]) << 12) |
+                    (unsigned(unbase64[src[2]]) << 6) |
+                    (unsigned(unbase64[src[3]])))) &
+           0x80000000)) {
+        GET_INPUT(first_no_dest, 4);
+        GET_INPUT(second_no_dest, 3);
+        GET_INPUT(third_no_dest, 2);
+        GET_INPUT(fourth_no_dest, 1);
+      } else {
+        szsrc -= 4;
+        src += 4;
+      }
+      destidx += 3;
+    }
+  }
+
+#undef GET_INPUT
+
+  // if the loop terminated because we read a bad character, return
+  // now.
+  if (decode < 0 && ch != kPad64Equals && ch != kPad64Dot &&
+      !absl::ascii_isspace(ch))
+    return false;
+
+  if (ch == kPad64Equals || ch == kPad64Dot) {
+    // if we stopped by hitting an '=' or '.', un-read that character -- we'll
+    // look at it again when we count to check for the proper number of
+    // equals signs at the end.
+    ++szsrc;
+    --src;
+  } else {
+    // This loop consumes 1 input byte per iteration.  It's used to
+    // clean up the 0-3 input bytes remaining when the first, faster
+    // loop finishes.  'temp' contains the data from 'state' input
+    // characters read by the first loop.
+    while (szsrc > 0) {
+      --szsrc;
+      ch = *src++;
+      decode = unbase64[ch];
+      if (decode < 0) {
+        if (absl::ascii_isspace(ch)) {
+          continue;
+        } else if (ch == kPad64Equals || ch == kPad64Dot) {
+          // back up one character; we'll read it again when we check
+          // for the correct number of pad characters at the end.
+          ++szsrc;
+          --src;
+          break;
+        } else {
+          return false;
+        }
+      }
+
+      // Each input character gives us six bits of output.
+      temp = (temp << 6) | decode;
+      ++state;
+      if (state == 4) {
+        // If we've accumulated 24 bits of output, write that out as
+        // three bytes.
+        if (dest) {
+          if (destidx + 3 > szdest) return false;
+          dest[destidx + 2] = temp;
+          temp >>= 8;
+          dest[destidx + 1] = temp;
+          temp >>= 8;
+          dest[destidx] = temp;
+        }
+        destidx += 3;
+        state = 0;
+        temp = 0;
+      }
+    }
+  }
+
+  // Process the leftover data contained in 'temp' at the end of the input.
+  int expected_equals = 0;
+  switch (state) {
+    case 0:
+      // Nothing left over; output is a multiple of 3 bytes.
+      break;
+
+    case 1:
+      // Bad input; we have 6 bits left over.
+      return false;
+
+    case 2:
+      // Produce one more output byte from the 12 input bits we have left.
+      if (dest) {
+        if (destidx + 1 > szdest) return false;
+        temp >>= 4;
+        dest[destidx] = temp;
+      }
+      ++destidx;
+      expected_equals = 2;
+      break;
+
+    case 3:
+      // Produce two more output bytes from the 18 input bits we have left.
+      if (dest) {
+        if (destidx + 2 > szdest) return false;
+        temp >>= 2;
+        dest[destidx + 1] = temp;
+        temp >>= 8;
+        dest[destidx] = temp;
+      }
+      destidx += 2;
+      expected_equals = 1;
+      break;
+
+    default:
+      // state should have no other values at this point.
+      ABSL_RAW_LOG(FATAL, "This can't happen; base64 decoder state = %d",
+                   state);
+  }
+
+  // The remainder of the std::string should be all whitespace, mixed with
+  // exactly 0 equals signs, or exactly 'expected_equals' equals
+  // signs.  (Always accepting 0 equals signs is an Abseil extension
+  // not covered in the RFC, as is accepting dot as the pad character.)
+
+  int equals = 0;
+  while (szsrc > 0) {
+    if (*src == kPad64Equals || *src == kPad64Dot)
+      ++equals;
+    else if (!absl::ascii_isspace(*src))
+      return false;
+    --szsrc;
+    ++src;
+  }
+
+  const bool ok = (equals == 0 || equals == expected_equals);
+  if (ok) *len = destidx;
+  return ok;
+}
+
+// The arrays below were generated by the following code
+// #include <sys/time.h>
+// #include <stdlib.h>
+// #include <string.h>
+// main()
+// {
+//   static const char Base64[] =
+//     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+//   char* pos;
+//   int idx, i, j;
+//   printf("    ");
+//   for (i = 0; i < 255; i += 8) {
+//     for (j = i; j < i + 8; j++) {
+//       pos = strchr(Base64, j);
+//       if ((pos == nullptr) || (j == 0))
+//         idx = -1;
+//       else
+//         idx = pos - Base64;
+//       if (idx == -1)
+//         printf(" %2d,     ", idx);
+//       else
+//         printf(" %2d/*%c*/,", idx, j);
+//     }
+//     printf("\n    ");
+//   }
+// }
+//
+// where the value of "Base64[]" was replaced by one of the base-64 conversion
+// tables from the functions below.
+/* clang-format off */
+constexpr signed char kUnBase64[] = {
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      62/*+*/, -1,      -1,      -1,      63/*/ */,
+    52/*0*/, 53/*1*/, 54/*2*/, 55/*3*/, 56/*4*/, 57/*5*/, 58/*6*/, 59/*7*/,
+    60/*8*/, 61/*9*/, -1,      -1,      -1,      -1,      -1,      -1,
+    -1,       0/*A*/,  1/*B*/,  2/*C*/,  3/*D*/,  4/*E*/,  5/*F*/,  6/*G*/,
+    07/*H*/,  8/*I*/,  9/*J*/, 10/*K*/, 11/*L*/, 12/*M*/, 13/*N*/, 14/*O*/,
+    15/*P*/, 16/*Q*/, 17/*R*/, 18/*S*/, 19/*T*/, 20/*U*/, 21/*V*/, 22/*W*/,
+    23/*X*/, 24/*Y*/, 25/*Z*/, -1,      -1,      -1,      -1,      -1,
+    -1,      26/*a*/, 27/*b*/, 28/*c*/, 29/*d*/, 30/*e*/, 31/*f*/, 32/*g*/,
+    33/*h*/, 34/*i*/, 35/*j*/, 36/*k*/, 37/*l*/, 38/*m*/, 39/*n*/, 40/*o*/,
+    41/*p*/, 42/*q*/, 43/*r*/, 44/*s*/, 45/*t*/, 46/*u*/, 47/*v*/, 48/*w*/,
+    49/*x*/, 50/*y*/, 51/*z*/, -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1
+};
+
+constexpr signed char kUnWebSafeBase64[] = {
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      62/*-*/, -1,      -1,
+    52/*0*/, 53/*1*/, 54/*2*/, 55/*3*/, 56/*4*/, 57/*5*/, 58/*6*/, 59/*7*/,
+    60/*8*/, 61/*9*/, -1,      -1,      -1,      -1,      -1,      -1,
+    -1,       0/*A*/,  1/*B*/,  2/*C*/,  3/*D*/,  4/*E*/,  5/*F*/,  6/*G*/,
+    07/*H*/,  8/*I*/,  9/*J*/, 10/*K*/, 11/*L*/, 12/*M*/, 13/*N*/, 14/*O*/,
+    15/*P*/, 16/*Q*/, 17/*R*/, 18/*S*/, 19/*T*/, 20/*U*/, 21/*V*/, 22/*W*/,
+    23/*X*/, 24/*Y*/, 25/*Z*/, -1,      -1,      -1,      -1,      63/*_*/,
+    -1,      26/*a*/, 27/*b*/, 28/*c*/, 29/*d*/, 30/*e*/, 31/*f*/, 32/*g*/,
+    33/*h*/, 34/*i*/, 35/*j*/, 36/*k*/, 37/*l*/, 38/*m*/, 39/*n*/, 40/*o*/,
+    41/*p*/, 42/*q*/, 43/*r*/, 44/*s*/, 45/*t*/, 46/*u*/, 47/*v*/, 48/*w*/,
+    49/*x*/, 50/*y*/, 51/*z*/, -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1
+};
+/* clang-format on */
+
+size_t CalculateBase64EscapedLenInternal(size_t input_len, bool do_padding) {
+  // Base64 encodes three bytes of input at a time. If the input is not
+  // divisible by three, we pad as appropriate.
+  //
+  // (from https://tools.ietf.org/html/rfc3548)
+  // Special processing is performed if fewer than 24 bits are available
+  // at the end of the data being encoded.  A full encoding quantum is
+  // always completed at the end of a quantity.  When fewer than 24 input
+  // bits are available in an input group, zero bits are added (on the
+  // right) to form an integral number of 6-bit groups.  Padding at the
+  // end of the data is performed using the '=' character.  Since all base
+  // 64 input is an integral number of octets, only the following cases
+  // can arise:
+
+  // Base64 encodes each three bytes of input into four bytes of output.
+  size_t len = (input_len / 3) * 4;
+
+  if (input_len % 3 == 0) {
+    // (from https://tools.ietf.org/html/rfc3548)
+    // (1) the final quantum of encoding input is an integral multiple of 24
+    // bits; here, the final unit of encoded output will be an integral
+    // multiple of 4 characters with no "=" padding,
+  } else if (input_len % 3 == 1) {
+    // (from https://tools.ietf.org/html/rfc3548)
+    // (2) the final quantum of encoding input is exactly 8 bits; here, the
+    // final unit of encoded output will be two characters followed by two
+    // "=" padding characters, or
+    len += 2;
+    if (do_padding) {
+      len += 2;
+    }
+  } else {  // (input_len % 3 == 2)
+    // (from https://tools.ietf.org/html/rfc3548)
+    // (3) the final quantum of encoding input is exactly 16 bits; here, the
+    // final unit of encoded output will be three characters followed by one
+    // "=" padding character.
+    len += 3;
+    if (do_padding) {
+      len += 1;
+    }
+  }
+
+  assert(len >= input_len);  // make sure we didn't overflow
+  return len;
+}
+
+size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
+                            size_t szdest, const char* base64,
+                            bool do_padding) {
+  static const char kPad64 = '=';
+
+  if (szsrc * 4 > szdest * 3) return 0;
+
+  char* cur_dest = dest;
+  const unsigned char* cur_src = src;
+
+  char* const limit_dest = dest + szdest;
+  const unsigned char* const limit_src = src + szsrc;
+
+  // Three bytes of data encodes to four characters of cyphertext.
+  // So we can pump through three-byte chunks atomically.
+  if (szsrc >= 3) {  // "limit_src - 3" is UB if szsrc < 3.
+    while (cur_src < limit_src - 3) {  // While we have >= 32 bits.
+      uint32_t in = absl::big_endian::Load32(cur_src) >> 8;
+
+      cur_dest[0] = base64[in >> 18];
+      in &= 0x3FFFF;
+      cur_dest[1] = base64[in >> 12];
+      in &= 0xFFF;
+      cur_dest[2] = base64[in >> 6];
+      in &= 0x3F;
+      cur_dest[3] = base64[in];
+
+      cur_dest += 4;
+      cur_src += 3;
+    }
+  }
+  // To save time, we didn't update szdest or szsrc in the loop.  So do it now.
+  szdest = limit_dest - cur_dest;
+  szsrc = limit_src - cur_src;
+
+  /* now deal with the tail (<=3 bytes) */
+  switch (szsrc) {
+    case 0:
+      // Nothing left; nothing more to do.
+      break;
+    case 1: {
+      // One byte left: this encodes to two characters, and (optionally)
+      // two pad characters to round out the four-character cypherblock.
+      if (szdest < 2) return 0;
+      uint32_t in = cur_src[0];
+      cur_dest[0] = base64[in >> 2];
+      in &= 0x3;
+      cur_dest[1] = base64[in << 4];
+      cur_dest += 2;
+      szdest -= 2;
+      if (do_padding) {
+        if (szdest < 2) return 0;
+        cur_dest[0] = kPad64;
+        cur_dest[1] = kPad64;
+        cur_dest += 2;
+        szdest -= 2;
+      }
+      break;
+    }
+    case 2: {
+      // Two bytes left: this encodes to three characters, and (optionally)
+      // one pad character to round out the four-character cypherblock.
+      if (szdest < 3) return 0;
+      uint32_t in = absl::big_endian::Load16(cur_src);
+      cur_dest[0] = base64[in >> 10];
+      in &= 0x3FF;
+      cur_dest[1] = base64[in >> 4];
+      in &= 0x00F;
+      cur_dest[2] = base64[in << 2];
+      cur_dest += 3;
+      szdest -= 3;
+      if (do_padding) {
+        if (szdest < 1) return 0;
+        cur_dest[0] = kPad64;
+        cur_dest += 1;
+        szdest -= 1;
+      }
+      break;
+    }
+    case 3: {
+      // Three bytes left: same as in the big loop above.  We can't do this in
+      // the loop because the loop above always reads 4 bytes, and the fourth
+      // byte is past the end of the input.
+      if (szdest < 4) return 0;
+      uint32_t in = (cur_src[0] << 16) + absl::big_endian::Load16(cur_src + 1);
+      cur_dest[0] = base64[in >> 18];
+      in &= 0x3FFFF;
+      cur_dest[1] = base64[in >> 12];
+      in &= 0xFFF;
+      cur_dest[2] = base64[in >> 6];
+      in &= 0x3F;
+      cur_dest[3] = base64[in];
+      cur_dest += 4;
+      szdest -= 4;
+      break;
+    }
+    default:
+      // Should not be reached: blocks of 4 bytes are handled
+      // in the while loop before this switch statement.
+      ABSL_RAW_LOG(FATAL, "Logic problem? szsrc = %zu", szsrc);
+      break;
+  }
+  return (cur_dest - dest);
+}
+
+constexpr char kBase64Chars[] =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+constexpr char kWebSafeBase64Chars[] =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+template <typename String>
+void Base64EscapeInternal(const unsigned char* src, size_t szsrc, String* dest,
+                          bool do_padding, const char* base64_chars) {
+  const size_t calc_escaped_size =
+      CalculateBase64EscapedLenInternal(szsrc, do_padding);
+  strings_internal::STLStringResizeUninitialized(dest, calc_escaped_size);
+
+  const size_t escaped_len = Base64EscapeInternal(
+      src, szsrc, &(*dest)[0], dest->size(), base64_chars, do_padding);
+  assert(calc_escaped_size == escaped_len);
+  dest->erase(escaped_len);
+}
+
+template <typename String>
+bool Base64UnescapeInternal(const char* src, size_t slen, String* dest,
+                            const signed char* unbase64) {
+  // Determine the size of the output std::string.  Base64 encodes every 3 bytes into
+  // 4 characters.  any leftover chars are added directly for good measure.
+  // This is documented in the base64 RFC: http://tools.ietf.org/html/rfc3548
+  const size_t dest_len = 3 * (slen / 4) + (slen % 4);
+
+  strings_internal::STLStringResizeUninitialized(dest, dest_len);
+
+  // We are getting the destination buffer by getting the beginning of the
+  // std::string and converting it into a char *.
+  size_t len;
+  const bool ok =
+      Base64UnescapeInternal(src, slen, &(*dest)[0], dest_len, unbase64, &len);
+  if (!ok) {
+    dest->clear();
+    return false;
+  }
+
+  // could be shorter if there was padding
+  assert(len <= dest_len);
+  dest->erase(len);
+
+  return true;
+}
+
+/* clang-format off */
+constexpr char kHexValue[256] = {
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  1,  2,  3,  4,  5,  6, 7, 8, 9, 0, 0, 0, 0, 0, 0,  // '0'..'9'
+    0, 10, 11, 12, 13, 14, 15, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 'A'..'F'
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0, 10, 11, 12, 13, 14, 15, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 'a'..'f'
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+};
+/* clang-format on */
+
+// This is a templated function so that T can be either a char*
+// or a string.  This works because we use the [] operator to access
+// individual characters at a time.
+template <typename T>
+void HexStringToBytesInternal(const char* from, T to, ptrdiff_t num) {
+  for (int i = 0; i < num; i++) {
+    to[i] = (kHexValue[from[i * 2] & 0xFF] << 4) +
+            (kHexValue[from[i * 2 + 1] & 0xFF]);
+  }
+}
+
+// This is a templated function so that T can be either a char* or a
+// std::string.
+template <typename T>
+void BytesToHexStringInternal(const unsigned char* src, T dest, ptrdiff_t num) {
+  auto dest_ptr = &dest[0];
+  for (auto src_ptr = src; src_ptr != (src + num); ++src_ptr, dest_ptr += 2) {
+    const char* hex_p = &kHexTable[*src_ptr * 2];
+    std::copy(hex_p, hex_p + 2, dest_ptr);
+  }
+}
+
+}  // namespace
+
+// ----------------------------------------------------------------------
+// CUnescape()
+//
+// See CUnescapeInternal() for implementation details.
+// ----------------------------------------------------------------------
+bool CUnescape(absl::string_view source, std::string* dest,
+               std::string* error) {
+  return CUnescapeInternal(source, kUnescapeNulls, dest, error);
+}
+
+std::string CEscape(absl::string_view src) {
+  std::string dest;
+  CEscapeAndAppendInternal(src, &dest);
+  return dest;
+}
+
+std::string CHexEscape(absl::string_view src) {
+  return CEscapeInternal(src, true, false);
+}
+
+std::string Utf8SafeCEscape(absl::string_view src) {
+  return CEscapeInternal(src, false, true);
+}
+
+std::string Utf8SafeCHexEscape(absl::string_view src) {
+  return CEscapeInternal(src, true, true);
+}
+
+// ----------------------------------------------------------------------
+// Base64Unescape() - base64 decoder
+// Base64Escape() - base64 encoder
+// WebSafeBase64Unescape() - Google's variation of base64 decoder
+// WebSafeBase64Escape() - Google's variation of base64 encoder
+//
+// Check out
+// http://tools.ietf.org/html/rfc2045 for formal description, but what we
+// care about is that...
+//   Take the encoded stuff in groups of 4 characters and turn each
+//   character into a code 0 to 63 thus:
+//           A-Z map to 0 to 25
+//           a-z map to 26 to 51
+//           0-9 map to 52 to 61
+//           +(- for WebSafe) maps to 62
+//           /(_ for WebSafe) maps to 63
+//   There will be four numbers, all less than 64 which can be represented
+//   by a 6 digit binary number (aaaaaa, bbbbbb, cccccc, dddddd respectively).
+//   Arrange the 6 digit binary numbers into three bytes as such:
+//   aaaaaabb bbbbcccc ccdddddd
+//   Equals signs (one or two) are used at the end of the encoded block to
+//   indicate that the text was not an integer multiple of three bytes long.
+// ----------------------------------------------------------------------
+
+bool Base64Unescape(absl::string_view src, std::string* dest) {
+  return Base64UnescapeInternal(src.data(), src.size(), dest, kUnBase64);
+}
+
+bool WebSafeBase64Unescape(absl::string_view src, std::string* dest) {
+  return Base64UnescapeInternal(src.data(), src.size(), dest, kUnWebSafeBase64);
+}
+
+void Base64Escape(absl::string_view src, std::string* dest) {
+  Base64EscapeInternal(reinterpret_cast<const unsigned char*>(src.data()),
+                       src.size(), dest, true, kBase64Chars);
+}
+
+void WebSafeBase64Escape(absl::string_view src, std::string* dest) {
+  Base64EscapeInternal(reinterpret_cast<const unsigned char*>(src.data()),
+                       src.size(), dest, false, kWebSafeBase64Chars);
+}
+
+std::string Base64Escape(absl::string_view src) {
+  std::string dest;
+  Base64EscapeInternal(reinterpret_cast<const unsigned char*>(src.data()),
+                       src.size(), &dest, true, kBase64Chars);
+  return dest;
+}
+
+std::string WebSafeBase64Escape(absl::string_view src) {
+  std::string dest;
+  Base64EscapeInternal(reinterpret_cast<const unsigned char*>(src.data()),
+                       src.size(), &dest, false, kWebSafeBase64Chars);
+  return dest;
+}
+
+std::string HexStringToBytes(absl::string_view from) {
+  std::string result;
+  const auto num = from.size() / 2;
+  strings_internal::STLStringResizeUninitialized(&result, num);
+  absl::HexStringToBytesInternal<std::string&>(from.data(), result, num);
+  return result;
+}
+
+std::string BytesToHexString(absl::string_view from) {
+  std::string result;
+  strings_internal::STLStringResizeUninitialized(&result, 2 * from.size());
+  absl::BytesToHexStringInternal<std::string&>(
+      reinterpret_cast<const unsigned char*>(from.data()), result, from.size());
+  return result;
+}
+
+}  // namespace absl
diff --git a/absl/strings/escaping.h b/absl/strings/escaping.h
new file mode 100644
index 0000000..198b934
--- /dev/null
+++ b/absl/strings/escaping.h
@@ -0,0 +1,162 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: escaping.h
+// -----------------------------------------------------------------------------
+//
+// This header file contains string utilities involved in escaping and
+// unescaping strings in various ways.
+
+#ifndef ABSL_STRINGS_ESCAPING_H_
+#define ABSL_STRINGS_ESCAPING_H_
+
+#include <cstddef>
+#include <string>
+#include <vector>
+
+#include "absl/base/macros.h"
+#include "absl/strings/ascii.h"
+#include "absl/strings/str_join.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+
+// CUnescape()
+//
+// Unescapes a `source` string and copies it into `dest`, rewriting C-style
+// escape sequences (https://en.cppreference.com/w/cpp/language/escape) into
+// their proper code point equivalents, returning `true` if successful.
+//
+// The following unescape sequences can be handled:
+//
+//   * ASCII escape sequences ('\n','\r','\\', etc.) to their ASCII equivalents
+//   * Octal escape sequences ('\nnn') to byte nnn. The unescaped value must
+//     resolve to a single byte or an error will occur. E.g. values greater than
+//     0xff will produce an error.
+//   * Hexadecimal escape sequences ('\xnn') to byte nn. While an arbitrary
+//     number of following digits are allowed, the unescaped value must resolve
+//     to a single byte or an error will occur. E.g. '\x0045' is equivalent to
+//     '\x45', but '\x1234' will produce an error.
+//   * Unicode escape sequences ('\unnnn' for exactly four hex digits or
+//     '\Unnnnnnnn' for exactly eight hex digits, which will be encoded in
+//     UTF-8. (E.g., `\u2019` unescapes to the three bytes 0xE2, 0x80, and
+//     0x99).
+//
+// If any errors are encountered, this function returns `false`, leaving the
+// `dest` output parameter in an unspecified state, and stores the first
+// encountered error in `error`. To disable error reporting, set `error` to
+// `nullptr` or use the overload with no error reporting below.
+//
+// Example:
+//
+//   std::string s = "foo\\rbar\\nbaz\\t";
+//   std::string unescaped_s;
+//   if (!absl::CUnescape(s, &unescaped_s) {
+//     ...
+//   }
+//   EXPECT_EQ(unescaped_s, "foo\rbar\nbaz\t");
+bool CUnescape(absl::string_view source, std::string* dest, std::string* error);
+
+// Overload of `CUnescape()` with no error reporting.
+inline bool CUnescape(absl::string_view source, std::string* dest) {
+  return CUnescape(source, dest, nullptr);
+}
+
+// CEscape()
+//
+// Escapes a 'src' string using C-style escapes sequences
+// (https://en.cppreference.com/w/cpp/language/escape), escaping other
+// non-printable/non-whitespace bytes as octal sequences (e.g. "\377").
+//
+// Example:
+//
+//   std::string s = "foo\rbar\tbaz\010\011\012\013\014\x0d\n";
+//   std::string escaped_s = absl::CEscape(s);
+//   EXPECT_EQ(escaped_s, "foo\\rbar\\tbaz\\010\\t\\n\\013\\014\\r\\n");
+std::string CEscape(absl::string_view src);
+
+// CHexEscape()
+//
+// Escapes a 'src' string using C-style escape sequences, escaping
+// other non-printable/non-whitespace bytes as hexadecimal sequences (e.g.
+// "\xFF").
+//
+// Example:
+//
+//   std::string s = "foo\rbar\tbaz\010\011\012\013\014\x0d\n";
+//   std::string escaped_s = absl::CHexEscape(s);
+//   EXPECT_EQ(escaped_s, "foo\\rbar\\tbaz\\x08\\t\\n\\x0b\\x0c\\r\\n");
+std::string CHexEscape(absl::string_view src);
+
+// Utf8SafeCEscape()
+//
+// Escapes a 'src' string using C-style escape sequences, escaping bytes as
+// octal sequences, and passing through UTF-8 characters without conversion.
+// I.e., when encountering any bytes with their high bit set, this function
+// will not escape those values, whether or not they are valid UTF-8.
+std::string Utf8SafeCEscape(absl::string_view src);
+
+// Utf8SafeCHexEscape()
+//
+// Escapes a 'src' string using C-style escape sequences, escaping bytes as
+// hexadecimal sequences, and passing through UTF-8 characters without
+// conversion.
+std::string Utf8SafeCHexEscape(absl::string_view src);
+
+// Base64Unescape()
+//
+// Converts a `src` string encoded in Base64 to its binary equivalent, writing
+// it to a `dest` buffer, returning `true` on success. If `src` contains invalid
+// characters, `dest` is cleared and returns `false`.
+bool Base64Unescape(absl::string_view src, std::string* dest);
+
+// WebSafeBase64Unescape()
+//
+// Converts a `src` string encoded in Base64 to its binary equivalent, writing
+// it to a `dest` buffer, but using '-' instead of '+', and '_' instead of '/'.
+// If `src` contains invalid characters, `dest` is cleared and returns `false`.
+bool WebSafeBase64Unescape(absl::string_view src, std::string* dest);
+
+// Base64Escape()
+//
+// Encodes a `src` string into a base64-encoded string, with padding characters.
+// This function conforms with RFC 4648 section 4 (base64).
+void Base64Escape(absl::string_view src, std::string* dest);
+std::string Base64Escape(absl::string_view src);
+
+// WebSafeBase64Escape()
+//
+// Encodes a `src` string into a base64-like string, using '-' instead of '+'
+// and '_' instead of '/', and without padding. This function conforms with RFC
+// 4648 section 5 (base64url).
+void WebSafeBase64Escape(absl::string_view src, std::string* dest);
+std::string WebSafeBase64Escape(absl::string_view src);
+
+// HexStringToBytes()
+//
+// Converts an ASCII hex string into bytes, returning binary data of length
+// `from.size()/2`.
+std::string HexStringToBytes(absl::string_view from);
+
+// BytesToHexString()
+//
+// Converts binary data into an ASCII text string, returning a string of size
+// `2*from.size()`.
+std::string BytesToHexString(absl::string_view from);
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_ESCAPING_H_
diff --git a/absl/strings/escaping_benchmark.cc b/absl/strings/escaping_benchmark.cc
new file mode 100644
index 0000000..10d5b03
--- /dev/null
+++ b/absl/strings/escaping_benchmark.cc
@@ -0,0 +1,94 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/escaping.h"
+
+#include <cstdio>
+#include <cstring>
+#include <random>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/strings/internal/escaping_test_common.h"
+
+namespace {
+
+void BM_CUnescapeHexString(benchmark::State& state) {
+  std::string src;
+  for (int i = 0; i < 50; i++) {
+    src += "\\x55";
+  }
+  std::string dest;
+  for (auto _ : state) {
+    absl::CUnescape(src, &dest);
+  }
+}
+BENCHMARK(BM_CUnescapeHexString);
+
+void BM_WebSafeBase64Escape_string(benchmark::State& state) {
+  std::string raw;
+  for (int i = 0; i < 10; ++i) {
+    for (const auto& test_set : absl::strings_internal::base64_strings()) {
+      raw += std::string(test_set.plaintext);
+    }
+  }
+
+  // The actual benchmark loop is tiny...
+  std::string escaped;
+  for (auto _ : state) {
+    absl::WebSafeBase64Escape(raw, &escaped);
+  }
+
+  // We want to be sure the compiler doesn't throw away the loop above,
+  // and the easiest way to ensure that is to round-trip the results and verify
+  // them.
+  std::string round_trip;
+  absl::WebSafeBase64Unescape(escaped, &round_trip);
+  ABSL_RAW_CHECK(round_trip == raw, "");
+}
+BENCHMARK(BM_WebSafeBase64Escape_string);
+
+// Used for the CEscape benchmarks
+const char kStringValueNoEscape[] = "1234567890";
+const char kStringValueSomeEscaped[] = "123\n56789\xA1";
+const char kStringValueMostEscaped[] = "\xA1\xA2\ny\xA4\xA5\xA6z\b\r";
+
+void CEscapeBenchmarkHelper(benchmark::State& state, const char* string_value,
+                            int max_len) {
+  std::string src;
+  while (src.size() < max_len) {
+    absl::StrAppend(&src, string_value);
+  }
+
+  for (auto _ : state) {
+    absl::CEscape(src);
+  }
+}
+
+void BM_CEscape_NoEscape(benchmark::State& state) {
+  CEscapeBenchmarkHelper(state, kStringValueNoEscape, state.range(0));
+}
+BENCHMARK(BM_CEscape_NoEscape)->Range(1, 1 << 14);
+
+void BM_CEscape_SomeEscaped(benchmark::State& state) {
+  CEscapeBenchmarkHelper(state, kStringValueSomeEscaped, state.range(0));
+}
+BENCHMARK(BM_CEscape_SomeEscaped)->Range(1, 1 << 14);
+
+void BM_CEscape_MostEscaped(benchmark::State& state) {
+  CEscapeBenchmarkHelper(state, kStringValueMostEscaped, state.range(0));
+}
+BENCHMARK(BM_CEscape_MostEscaped)->Range(1, 1 << 14);
+
+}  // namespace
diff --git a/absl/strings/escaping_test.cc b/absl/strings/escaping_test.cc
new file mode 100644
index 0000000..1967975
--- /dev/null
+++ b/absl/strings/escaping_test.cc
@@ -0,0 +1,664 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/escaping.h"
+
+#include <array>
+#include <cstdio>
+#include <cstring>
+#include <memory>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/container/fixed_array.h"
+#include "absl/strings/str_cat.h"
+
+#include "absl/strings/internal/escaping_test_common.h"
+
+namespace {
+
+struct epair {
+  std::string escaped;
+  std::string unescaped;
+};
+
+TEST(CEscape, EscapeAndUnescape) {
+  const std::string inputs[] = {
+      std::string("foo\nxx\r\b\0023"),
+      std::string(""),
+      std::string("abc"),
+      std::string("\1chad_rules"),
+      std::string("\1arnar_drools"),
+      std::string("xxxx\r\t'\"\\"),
+      std::string("\0xx\0", 4),
+      std::string("\x01\x31"),
+      std::string("abc\xb\x42\141bc"),
+      std::string("123\1\x31\x32\x33"),
+      std::string("\xc1\xca\x1b\x62\x19o\xcc\x04"),
+      std::string(
+          "\\\"\xe8\xb0\xb7\xe6\xad\x8c\\\" is Google\\\'s Chinese name"),
+  };
+  // Do this twice, once for octal escapes and once for hex escapes.
+  for (int kind = 0; kind < 4; kind++) {
+    for (const std::string& original : inputs) {
+      std::string escaped;
+      switch (kind) {
+        case 0:
+          escaped = absl::CEscape(original);
+          break;
+        case 1:
+          escaped = absl::CHexEscape(original);
+          break;
+        case 2:
+          escaped = absl::Utf8SafeCEscape(original);
+          break;
+        case 3:
+          escaped = absl::Utf8SafeCHexEscape(original);
+          break;
+      }
+      std::string unescaped_str;
+      EXPECT_TRUE(absl::CUnescape(escaped, &unescaped_str));
+      EXPECT_EQ(unescaped_str, original);
+
+      unescaped_str.erase();
+      std::string error;
+      EXPECT_TRUE(absl::CUnescape(escaped, &unescaped_str, &error));
+      EXPECT_EQ(error, "");
+
+      // Check in-place unescaping
+      std::string s = escaped;
+      EXPECT_TRUE(absl::CUnescape(s, &s));
+      ASSERT_EQ(s, original);
+    }
+  }
+  // Check that all possible two character strings can be escaped then
+  // unescaped successfully.
+  for (int char0 = 0; char0 < 256; char0++) {
+    for (int char1 = 0; char1 < 256; char1++) {
+      char chars[2];
+      chars[0] = char0;
+      chars[1] = char1;
+      std::string s(chars, 2);
+      std::string escaped = absl::CHexEscape(s);
+      std::string unescaped;
+      EXPECT_TRUE(absl::CUnescape(escaped, &unescaped));
+      EXPECT_EQ(s, unescaped);
+    }
+  }
+}
+
+TEST(CEscape, BasicEscaping) {
+  epair oct_values[] = {
+      {"foo\\rbar\\nbaz\\t", "foo\rbar\nbaz\t"},
+      {"\\'full of \\\"sound\\\" and \\\"fury\\\"\\'",
+       "'full of \"sound\" and \"fury\"'"},
+      {"signi\\\\fying\\\\ nothing\\\\", "signi\\fying\\ nothing\\"},
+      {"\\010\\t\\n\\013\\014\\r", "\010\011\012\013\014\015"}
+  };
+  epair hex_values[] = {
+      {"ubik\\rubik\\nubik\\t", "ubik\rubik\nubik\t"},
+      {"I\\\'ve just seen a \\\"face\\\"",
+       "I've just seen a \"face\""},
+      {"hel\\\\ter\\\\skel\\\\ter\\\\", "hel\\ter\\skel\\ter\\"},
+      {"\\x08\\t\\n\\x0b\\x0c\\r", "\010\011\012\013\014\015"}
+  };
+  epair utf8_oct_values[] = {
+      {"\xe8\xb0\xb7\xe6\xad\x8c\\r\xe8\xb0\xb7\xe6\xad\x8c\\nbaz\\t",
+       "\xe8\xb0\xb7\xe6\xad\x8c\r\xe8\xb0\xb7\xe6\xad\x8c\nbaz\t"},
+      {"\\\"\xe8\xb0\xb7\xe6\xad\x8c\\\" is Google\\\'s Chinese name",
+       "\"\xe8\xb0\xb7\xe6\xad\x8c\" is Google\'s Chinese name"},
+      {"\xe3\x83\xa1\xe3\x83\xbc\xe3\x83\xab\\\\are\\\\Japanese\\\\chars\\\\",
+       "\xe3\x83\xa1\xe3\x83\xbc\xe3\x83\xab\\are\\Japanese\\chars\\"},
+      {"\xed\x81\xac\xeb\xa1\xac\\010\\t\\n\\013\\014\\r",
+       "\xed\x81\xac\xeb\xa1\xac\010\011\012\013\014\015"}
+  };
+  epair utf8_hex_values[] = {
+      {"\x20\xe4\xbd\xa0\\t\xe5\xa5\xbd,\\r!\\n",
+       "\x20\xe4\xbd\xa0\t\xe5\xa5\xbd,\r!\n"},
+      {"\xe8\xa9\xa6\xe9\xa8\x93\\\' means \\\"test\\\"",
+       "\xe8\xa9\xa6\xe9\xa8\x93\' means \"test\""},
+      {"\\\\\xe6\x88\x91\\\\:\\\\\xe6\x9d\xa8\xe6\xac\xa2\\\\",
+       "\\\xe6\x88\x91\\:\\\xe6\x9d\xa8\xe6\xac\xa2\\"},
+      {"\xed\x81\xac\xeb\xa1\xac\\x08\\t\\n\\x0b\\x0c\\r",
+       "\xed\x81\xac\xeb\xa1\xac\010\011\012\013\014\015"}
+  };
+
+  for (const epair& val : oct_values) {
+    std::string escaped = absl::CEscape(val.unescaped);
+    EXPECT_EQ(escaped, val.escaped);
+  }
+  for (const epair& val : hex_values) {
+    std::string escaped = absl::CHexEscape(val.unescaped);
+    EXPECT_EQ(escaped, val.escaped);
+  }
+  for (const epair& val : utf8_oct_values) {
+    std::string escaped = absl::Utf8SafeCEscape(val.unescaped);
+    EXPECT_EQ(escaped, val.escaped);
+  }
+  for (const epair& val : utf8_hex_values) {
+    std::string escaped = absl::Utf8SafeCHexEscape(val.unescaped);
+    EXPECT_EQ(escaped, val.escaped);
+  }
+}
+
+TEST(Unescape, BasicFunction) {
+  epair tests[] =
+    {{"", ""},
+     {"\\u0030", "0"},
+     {"\\u00A3", "\xC2\xA3"},
+     {"\\u22FD", "\xE2\x8B\xBD"},
+     {"\\U00010000", "\xF0\x90\x80\x80"},
+     {"\\U0010FFFD", "\xF4\x8F\xBF\xBD"}};
+  for (const epair& val : tests) {
+    std::string out;
+    EXPECT_TRUE(absl::CUnescape(val.escaped, &out));
+    EXPECT_EQ(out, val.unescaped);
+  }
+  std::string bad[] = {"\\u1",         // too short
+                       "\\U1",         // too short
+                       "\\Uffffff",    // exceeds 0x10ffff (largest Unicode)
+                       "\\U00110000",  // exceeds 0x10ffff (largest Unicode)
+                       "\\uD835",      // surrogate character (D800-DFFF)
+                       "\\U0000DD04",  // surrogate character (D800-DFFF)
+                       "\\777",        // exceeds 0xff
+                       "\\xABCD"};     // exceeds 0xff
+  for (const std::string& e : bad) {
+    std::string error;
+    std::string out;
+    EXPECT_FALSE(absl::CUnescape(e, &out, &error));
+    EXPECT_FALSE(error.empty());
+
+    out.erase();
+    EXPECT_FALSE(absl::CUnescape(e, &out));
+  }
+}
+
+class CUnescapeTest : public testing::Test {
+ protected:
+  static const char kStringWithMultipleOctalNulls[];
+  static const char kStringWithMultipleHexNulls[];
+  static const char kStringWithMultipleUnicodeNulls[];
+
+  std::string result_string_;
+};
+
+const char CUnescapeTest::kStringWithMultipleOctalNulls[] =
+    "\\0\\n"    // null escape \0 plus newline
+    "0\\n"      // just a number 0 (not a null escape) plus newline
+    "\\00\\12"  // null escape \00 plus octal newline code
+    "\\000";    // null escape \000
+
+// This has the same ingredients as kStringWithMultipleOctalNulls
+// but with \x hex escapes instead of octal escapes.
+const char CUnescapeTest::kStringWithMultipleHexNulls[] =
+    "\\x0\\n"
+    "0\\n"
+    "\\x00\\xa"
+    "\\x000";
+
+const char CUnescapeTest::kStringWithMultipleUnicodeNulls[] =
+    "\\u0000\\n"    // short-form (4-digit) null escape plus newline
+    "0\\n"          // just a number 0 (not a null escape) plus newline
+    "\\U00000000";  // long-form (8-digit) null escape
+
+TEST_F(CUnescapeTest, Unescapes1CharOctalNull) {
+  std::string original_string = "\\0";
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  EXPECT_EQ(std::string("\0", 1), result_string_);
+}
+
+TEST_F(CUnescapeTest, Unescapes2CharOctalNull) {
+  std::string original_string = "\\00";
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  EXPECT_EQ(std::string("\0", 1), result_string_);
+}
+
+TEST_F(CUnescapeTest, Unescapes3CharOctalNull) {
+  std::string original_string = "\\000";
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  EXPECT_EQ(std::string("\0", 1), result_string_);
+}
+
+TEST_F(CUnescapeTest, Unescapes1CharHexNull) {
+  std::string original_string = "\\x0";
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  EXPECT_EQ(std::string("\0", 1), result_string_);
+}
+
+TEST_F(CUnescapeTest, Unescapes2CharHexNull) {
+  std::string original_string = "\\x00";
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  EXPECT_EQ(std::string("\0", 1), result_string_);
+}
+
+TEST_F(CUnescapeTest, Unescapes3CharHexNull) {
+  std::string original_string = "\\x000";
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  EXPECT_EQ(std::string("\0", 1), result_string_);
+}
+
+TEST_F(CUnescapeTest, Unescapes4CharUnicodeNull) {
+  std::string original_string = "\\u0000";
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  EXPECT_EQ(std::string("\0", 1), result_string_);
+}
+
+TEST_F(CUnescapeTest, Unescapes8CharUnicodeNull) {
+  std::string original_string = "\\U00000000";
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  EXPECT_EQ(std::string("\0", 1), result_string_);
+}
+
+TEST_F(CUnescapeTest, UnescapesMultipleOctalNulls) {
+  std::string original_string(kStringWithMultipleOctalNulls);
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  // All escapes, including newlines and null escapes, should have been
+  // converted to the equivalent characters.
+  EXPECT_EQ(std::string("\0\n"
+                        "0\n"
+                        "\0\n"
+                        "\0",
+                        7),
+            result_string_);
+}
+
+
+TEST_F(CUnescapeTest, UnescapesMultipleHexNulls) {
+  std::string original_string(kStringWithMultipleHexNulls);
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  EXPECT_EQ(std::string("\0\n"
+                        "0\n"
+                        "\0\n"
+                        "\0",
+                        7),
+            result_string_);
+}
+
+TEST_F(CUnescapeTest, UnescapesMultipleUnicodeNulls) {
+  std::string original_string(kStringWithMultipleUnicodeNulls);
+  EXPECT_TRUE(absl::CUnescape(original_string, &result_string_));
+  EXPECT_EQ(std::string("\0\n"
+                        "0\n"
+                        "\0",
+                        5),
+            result_string_);
+}
+
+static struct {
+  absl::string_view plaintext;
+  absl::string_view cyphertext;
+} const base64_tests[] = {
+    // Empty std::string.
+    {{"", 0}, {"", 0}},
+    {{nullptr, 0},
+     {"", 0}},  // if length is zero, plaintext ptr must be ignored!
+
+    // Basic bit patterns;
+    // values obtained with "echo -n '...' | uuencode -m test"
+
+    {{"\000", 1}, "AA=="},
+    {{"\001", 1}, "AQ=="},
+    {{"\002", 1}, "Ag=="},
+    {{"\004", 1}, "BA=="},
+    {{"\010", 1}, "CA=="},
+    {{"\020", 1}, "EA=="},
+    {{"\040", 1}, "IA=="},
+    {{"\100", 1}, "QA=="},
+    {{"\200", 1}, "gA=="},
+
+    {{"\377", 1}, "/w=="},
+    {{"\376", 1}, "/g=="},
+    {{"\375", 1}, "/Q=="},
+    {{"\373", 1}, "+w=="},
+    {{"\367", 1}, "9w=="},
+    {{"\357", 1}, "7w=="},
+    {{"\337", 1}, "3w=="},
+    {{"\277", 1}, "vw=="},
+    {{"\177", 1}, "fw=="},
+    {{"\000\000", 2}, "AAA="},
+    {{"\000\001", 2}, "AAE="},
+    {{"\000\002", 2}, "AAI="},
+    {{"\000\004", 2}, "AAQ="},
+    {{"\000\010", 2}, "AAg="},
+    {{"\000\020", 2}, "ABA="},
+    {{"\000\040", 2}, "ACA="},
+    {{"\000\100", 2}, "AEA="},
+    {{"\000\200", 2}, "AIA="},
+    {{"\001\000", 2}, "AQA="},
+    {{"\002\000", 2}, "AgA="},
+    {{"\004\000", 2}, "BAA="},
+    {{"\010\000", 2}, "CAA="},
+    {{"\020\000", 2}, "EAA="},
+    {{"\040\000", 2}, "IAA="},
+    {{"\100\000", 2}, "QAA="},
+    {{"\200\000", 2}, "gAA="},
+
+    {{"\377\377", 2}, "//8="},
+    {{"\377\376", 2}, "//4="},
+    {{"\377\375", 2}, "//0="},
+    {{"\377\373", 2}, "//s="},
+    {{"\377\367", 2}, "//c="},
+    {{"\377\357", 2}, "/+8="},
+    {{"\377\337", 2}, "/98="},
+    {{"\377\277", 2}, "/78="},
+    {{"\377\177", 2}, "/38="},
+    {{"\376\377", 2}, "/v8="},
+    {{"\375\377", 2}, "/f8="},
+    {{"\373\377", 2}, "+/8="},
+    {{"\367\377", 2}, "9/8="},
+    {{"\357\377", 2}, "7/8="},
+    {{"\337\377", 2}, "3/8="},
+    {{"\277\377", 2}, "v/8="},
+    {{"\177\377", 2}, "f/8="},
+
+    {{"\000\000\000", 3}, "AAAA"},
+    {{"\000\000\001", 3}, "AAAB"},
+    {{"\000\000\002", 3}, "AAAC"},
+    {{"\000\000\004", 3}, "AAAE"},
+    {{"\000\000\010", 3}, "AAAI"},
+    {{"\000\000\020", 3}, "AAAQ"},
+    {{"\000\000\040", 3}, "AAAg"},
+    {{"\000\000\100", 3}, "AABA"},
+    {{"\000\000\200", 3}, "AACA"},
+    {{"\000\001\000", 3}, "AAEA"},
+    {{"\000\002\000", 3}, "AAIA"},
+    {{"\000\004\000", 3}, "AAQA"},
+    {{"\000\010\000", 3}, "AAgA"},
+    {{"\000\020\000", 3}, "ABAA"},
+    {{"\000\040\000", 3}, "ACAA"},
+    {{"\000\100\000", 3}, "AEAA"},
+    {{"\000\200\000", 3}, "AIAA"},
+    {{"\001\000\000", 3}, "AQAA"},
+    {{"\002\000\000", 3}, "AgAA"},
+    {{"\004\000\000", 3}, "BAAA"},
+    {{"\010\000\000", 3}, "CAAA"},
+    {{"\020\000\000", 3}, "EAAA"},
+    {{"\040\000\000", 3}, "IAAA"},
+    {{"\100\000\000", 3}, "QAAA"},
+    {{"\200\000\000", 3}, "gAAA"},
+
+    {{"\377\377\377", 3}, "////"},
+    {{"\377\377\376", 3}, "///+"},
+    {{"\377\377\375", 3}, "///9"},
+    {{"\377\377\373", 3}, "///7"},
+    {{"\377\377\367", 3}, "///3"},
+    {{"\377\377\357", 3}, "///v"},
+    {{"\377\377\337", 3}, "///f"},
+    {{"\377\377\277", 3}, "//+/"},
+    {{"\377\377\177", 3}, "//9/"},
+    {{"\377\376\377", 3}, "//7/"},
+    {{"\377\375\377", 3}, "//3/"},
+    {{"\377\373\377", 3}, "//v/"},
+    {{"\377\367\377", 3}, "//f/"},
+    {{"\377\357\377", 3}, "/+//"},
+    {{"\377\337\377", 3}, "/9//"},
+    {{"\377\277\377", 3}, "/7//"},
+    {{"\377\177\377", 3}, "/3//"},
+    {{"\376\377\377", 3}, "/v//"},
+    {{"\375\377\377", 3}, "/f//"},
+    {{"\373\377\377", 3}, "+///"},
+    {{"\367\377\377", 3}, "9///"},
+    {{"\357\377\377", 3}, "7///"},
+    {{"\337\377\377", 3}, "3///"},
+    {{"\277\377\377", 3}, "v///"},
+    {{"\177\377\377", 3}, "f///"},
+
+    // Random numbers: values obtained with
+    //
+    //  #! /bin/bash
+    //  dd bs=$1 count=1 if=/dev/random of=/tmp/bar.random
+    //  od -N $1 -t o1 /tmp/bar.random
+    //  uuencode -m test < /tmp/bar.random
+    //
+    // where $1 is the number of bytes (2, 3)
+
+    {{"\243\361", 2}, "o/E="},
+    {{"\024\167", 2}, "FHc="},
+    {{"\313\252", 2}, "y6o="},
+    {{"\046\041", 2}, "JiE="},
+    {{"\145\236", 2}, "ZZ4="},
+    {{"\254\325", 2}, "rNU="},
+    {{"\061\330", 2}, "Mdg="},
+    {{"\245\032", 2}, "pRo="},
+    {{"\006\000", 2}, "BgA="},
+    {{"\375\131", 2}, "/Vk="},
+    {{"\303\210", 2}, "w4g="},
+    {{"\040\037", 2}, "IB8="},
+    {{"\261\372", 2}, "sfo="},
+    {{"\335\014", 2}, "3Qw="},
+    {{"\233\217", 2}, "m48="},
+    {{"\373\056", 2}, "+y4="},
+    {{"\247\232", 2}, "p5o="},
+    {{"\107\053", 2}, "Rys="},
+    {{"\204\077", 2}, "hD8="},
+    {{"\276\211", 2}, "vok="},
+    {{"\313\110", 2}, "y0g="},
+    {{"\363\376", 2}, "8/4="},
+    {{"\251\234", 2}, "qZw="},
+    {{"\103\262", 2}, "Q7I="},
+    {{"\142\312", 2}, "Yso="},
+    {{"\067\211", 2}, "N4k="},
+    {{"\220\001", 2}, "kAE="},
+    {{"\152\240", 2}, "aqA="},
+    {{"\367\061", 2}, "9zE="},
+    {{"\133\255", 2}, "W60="},
+    {{"\176\035", 2}, "fh0="},
+    {{"\032\231", 2}, "Gpk="},
+
+    {{"\013\007\144", 3}, "Cwdk"},
+    {{"\030\112\106", 3}, "GEpG"},
+    {{"\047\325\046", 3}, "J9Um"},
+    {{"\310\160\022", 3}, "yHAS"},
+    {{"\131\100\237", 3}, "WUCf"},
+    {{"\064\342\134", 3}, "NOJc"},
+    {{"\010\177\004", 3}, "CH8E"},
+    {{"\345\147\205", 3}, "5WeF"},
+    {{"\300\343\360", 3}, "wOPw"},
+    {{"\061\240\201", 3}, "MaCB"},
+    {{"\225\333\044", 3}, "ldsk"},
+    {{"\215\137\352", 3}, "jV/q"},
+    {{"\371\147\160", 3}, "+Wdw"},
+    {{"\030\320\051", 3}, "GNAp"},
+    {{"\044\174\241", 3}, "JHyh"},
+    {{"\260\127\037", 3}, "sFcf"},
+    {{"\111\045\033", 3}, "SSUb"},
+    {{"\202\114\107", 3}, "gkxH"},
+    {{"\057\371\042", 3}, "L/ki"},
+    {{"\223\247\244", 3}, "k6ek"},
+    {{"\047\216\144", 3}, "J45k"},
+    {{"\203\070\327", 3}, "gzjX"},
+    {{"\247\140\072", 3}, "p2A6"},
+    {{"\124\115\116", 3}, "VE1O"},
+    {{"\157\162\050", 3}, "b3Io"},
+    {{"\357\223\004", 3}, "75ME"},
+    {{"\052\117\156", 3}, "Kk9u"},
+    {{"\347\154\000", 3}, "52wA"},
+    {{"\303\012\142", 3}, "wwpi"},
+    {{"\060\035\362", 3}, "MB3y"},
+    {{"\130\226\361", 3}, "WJbx"},
+    {{"\173\013\071", 3}, "ews5"},
+    {{"\336\004\027", 3}, "3gQX"},
+    {{"\357\366\234", 3}, "7/ac"},
+    {{"\353\304\111", 3}, "68RJ"},
+    {{"\024\264\131", 3}, "FLRZ"},
+    {{"\075\114\251", 3}, "PUyp"},
+    {{"\315\031\225", 3}, "zRmV"},
+    {{"\154\201\276", 3}, "bIG+"},
+    {{"\200\066\072", 3}, "gDY6"},
+    {{"\142\350\267", 3}, "Yui3"},
+    {{"\033\000\166", 3}, "GwB2"},
+    {{"\210\055\077", 3}, "iC0/"},
+    {{"\341\037\124", 3}, "4R9U"},
+    {{"\161\103\152", 3}, "cUNq"},
+    {{"\270\142\131", 3}, "uGJZ"},
+    {{"\337\076\074", 3}, "3z48"},
+    {{"\375\106\362", 3}, "/Uby"},
+    {{"\227\301\127", 3}, "l8FX"},
+    {{"\340\002\234", 3}, "4AKc"},
+    {{"\121\064\033", 3}, "UTQb"},
+    {{"\157\134\143", 3}, "b1xj"},
+    {{"\247\055\327", 3}, "py3X"},
+    {{"\340\142\005", 3}, "4GIF"},
+    {{"\060\260\143", 3}, "MLBj"},
+    {{"\075\203\170", 3}, "PYN4"},
+    {{"\143\160\016", 3}, "Y3AO"},
+    {{"\313\013\063", 3}, "ywsz"},
+    {{"\174\236\135", 3}, "fJ5d"},
+    {{"\103\047\026", 3}, "QycW"},
+    {{"\365\005\343", 3}, "9QXj"},
+    {{"\271\160\223", 3}, "uXCT"},
+    {{"\362\255\172", 3}, "8q16"},
+    {{"\113\012\015", 3}, "SwoN"},
+
+    // various lengths, generated by this python script:
+    //
+    // from std::string import lowercase as lc
+    // for i in range(27):
+    //   print '{ %2d, "%s",%s "%s" },' % (i, lc[:i], ' ' * (26-i),
+    //                                     lc[:i].encode('base64').strip())
+
+    {{"", 0}, {"", 0}},
+    {"a", "YQ=="},
+    {"ab", "YWI="},
+    {"abc", "YWJj"},
+    {"abcd", "YWJjZA=="},
+    {"abcde", "YWJjZGU="},
+    {"abcdef", "YWJjZGVm"},
+    {"abcdefg", "YWJjZGVmZw=="},
+    {"abcdefgh", "YWJjZGVmZ2g="},
+    {"abcdefghi", "YWJjZGVmZ2hp"},
+    {"abcdefghij", "YWJjZGVmZ2hpag=="},
+    {"abcdefghijk", "YWJjZGVmZ2hpams="},
+    {"abcdefghijkl", "YWJjZGVmZ2hpamts"},
+    {"abcdefghijklm", "YWJjZGVmZ2hpamtsbQ=="},
+    {"abcdefghijklmn", "YWJjZGVmZ2hpamtsbW4="},
+    {"abcdefghijklmno", "YWJjZGVmZ2hpamtsbW5v"},
+    {"abcdefghijklmnop", "YWJjZGVmZ2hpamtsbW5vcA=="},
+    {"abcdefghijklmnopq", "YWJjZGVmZ2hpamtsbW5vcHE="},
+    {"abcdefghijklmnopqr", "YWJjZGVmZ2hpamtsbW5vcHFy"},
+    {"abcdefghijklmnopqrs", "YWJjZGVmZ2hpamtsbW5vcHFycw=="},
+    {"abcdefghijklmnopqrst", "YWJjZGVmZ2hpamtsbW5vcHFyc3Q="},
+    {"abcdefghijklmnopqrstu", "YWJjZGVmZ2hpamtsbW5vcHFyc3R1"},
+    {"abcdefghijklmnopqrstuv", "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dg=="},
+    {"abcdefghijklmnopqrstuvw", "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnc="},
+    {"abcdefghijklmnopqrstuvwx", "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4"},
+    {"abcdefghijklmnopqrstuvwxy", "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eQ=="},
+    {"abcdefghijklmnopqrstuvwxyz", "YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXo="},
+};
+
+template <typename StringType>
+void TestEscapeAndUnescape() {
+  // Check the short strings; this tests the math (and boundaries)
+  for (const auto& tc : base64_tests) {
+    StringType encoded("this junk should be ignored");
+    absl::Base64Escape(tc.plaintext, &encoded);
+    EXPECT_EQ(encoded, tc.cyphertext);
+    EXPECT_EQ(absl::Base64Escape(tc.plaintext), tc.cyphertext);
+
+    StringType decoded("this junk should be ignored");
+    EXPECT_TRUE(absl::Base64Unescape(encoded, &decoded));
+    EXPECT_EQ(decoded, tc.plaintext);
+
+    StringType websafe(tc.cyphertext);
+    for (int c = 0; c < websafe.size(); ++c) {
+      if ('+' == websafe[c]) websafe[c] = '-';
+      if ('/' == websafe[c]) websafe[c] = '_';
+      if ('=' == websafe[c]) {
+        websafe.resize(c);
+        break;
+      }
+    }
+
+    encoded = "this junk should be ignored";
+    absl::WebSafeBase64Escape(tc.plaintext, &encoded);
+    EXPECT_EQ(encoded, websafe);
+    EXPECT_EQ(absl::WebSafeBase64Escape(tc.plaintext), websafe);
+
+    // Let's try the std::string version of the decoder
+    decoded = "this junk should be ignored";
+    EXPECT_TRUE(absl::WebSafeBase64Unescape(websafe, &decoded));
+    EXPECT_EQ(decoded, tc.plaintext);
+  }
+
+  // Now try the long strings, this tests the streaming
+  for (const auto& tc : absl::strings_internal::base64_strings()) {
+    StringType buffer;
+    absl::WebSafeBase64Escape(tc.plaintext, &buffer);
+    EXPECT_EQ(tc.cyphertext, buffer);
+    EXPECT_EQ(absl::WebSafeBase64Escape(tc.plaintext), tc.cyphertext);
+  }
+
+  // Verify the behavior when decoding bad data
+  {
+    absl::string_view data_set[] = {"ab-/", absl::string_view("\0bcd", 4),
+                                    absl::string_view("abc.\0", 5)};
+    for (absl::string_view bad_data : data_set) {
+      StringType buf;
+      EXPECT_FALSE(absl::Base64Unescape(bad_data, &buf));
+      EXPECT_FALSE(absl::WebSafeBase64Unescape(bad_data, &buf));
+      EXPECT_TRUE(buf.empty());
+    }
+  }
+}
+
+TEST(Base64, EscapeAndUnescape) {
+  TestEscapeAndUnescape<std::string>();
+}
+
+TEST(Base64, DISABLED_HugeData) {
+  const size_t kSize = size_t(3) * 1000 * 1000 * 1000;
+  static_assert(kSize % 3 == 0, "kSize must be divisible by 3");
+  const std::string huge(kSize, 'x');
+
+  std::string escaped;
+  absl::Base64Escape(huge, &escaped);
+
+  // Generates the std::string that should match a base64 encoded "xxx..." std::string.
+  // "xxx" in base64 is "eHh4".
+  std::string expected_encoding;
+  expected_encoding.reserve(kSize / 3 * 4);
+  for (size_t i = 0; i < kSize / 3; ++i) {
+    expected_encoding.append("eHh4");
+  }
+  EXPECT_EQ(expected_encoding, escaped);
+
+  std::string unescaped;
+  EXPECT_TRUE(absl::Base64Unescape(escaped, &unescaped));
+  EXPECT_EQ(huge, unescaped);
+}
+
+TEST(HexAndBack, HexStringToBytes_and_BytesToHexString) {
+  std::string hex_mixed = "0123456789abcdefABCDEF";
+  std::string bytes_expected = "\x01\x23\x45\x67\x89\xab\xcd\xef\xAB\xCD\xEF";
+  std::string hex_only_lower = "0123456789abcdefabcdef";
+
+  std::string bytes_result = absl::HexStringToBytes(hex_mixed);
+  EXPECT_EQ(bytes_expected, bytes_result);
+
+  std::string prefix_valid = hex_mixed + "?";
+  std::string prefix_valid_result = absl::HexStringToBytes(
+      absl::string_view(prefix_valid.data(), prefix_valid.size() - 1));
+  EXPECT_EQ(bytes_expected, prefix_valid_result);
+
+  std::string infix_valid = "?" + hex_mixed + "???";
+  std::string infix_valid_result = absl::HexStringToBytes(
+      absl::string_view(infix_valid.data() + 1, hex_mixed.size()));
+  EXPECT_EQ(bytes_expected, infix_valid_result);
+
+  std::string hex_result = absl::BytesToHexString(bytes_expected);
+  EXPECT_EQ(hex_only_lower, hex_result);
+}
+
+}  // namespace
diff --git a/absl/strings/internal/char_map.h b/absl/strings/internal/char_map.h
new file mode 100644
index 0000000..b9108b8
--- /dev/null
+++ b/absl/strings/internal/char_map.h
@@ -0,0 +1,154 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Character Map Class
+//
+// A fast, bit-vector map for 8-bit unsigned characters.
+// This class is useful for non-character purposes as well.
+
+#ifndef ABSL_STRINGS_INTERNAL_CHAR_MAP_H_
+#define ABSL_STRINGS_INTERNAL_CHAR_MAP_H_
+
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+
+namespace absl {
+namespace strings_internal {
+
+class Charmap {
+ public:
+  constexpr Charmap() : m_() {}
+
+  // Initializes with a given char*.  Note that NUL is not treated as
+  // a terminator, but rather a char to be flicked.
+  Charmap(const char* str, int len) : m_() {
+    while (len--) SetChar(*str++);
+  }
+
+  // Initializes with a given char*.  NUL is treated as a terminator
+  // and will not be in the charmap.
+  explicit Charmap(const char* str) : m_() {
+    while (*str) SetChar(*str++);
+  }
+
+  constexpr bool contains(unsigned char c) const {
+    return (m_[c / 64] >> (c % 64)) & 0x1;
+  }
+
+  // Returns true if and only if a character exists in both maps.
+  bool IntersectsWith(const Charmap& c) const {
+    for (size_t i = 0; i < ABSL_ARRAYSIZE(m_); ++i) {
+      if ((m_[i] & c.m_[i]) != 0) return true;
+    }
+    return false;
+  }
+
+  bool IsZero() const {
+    for (uint64_t c : m_) {
+      if (c != 0) return false;
+    }
+    return true;
+  }
+
+  // Containing only a single specified char.
+  static constexpr Charmap Char(char x) {
+    return Charmap(CharMaskForWord(x, 0), CharMaskForWord(x, 1),
+                   CharMaskForWord(x, 2), CharMaskForWord(x, 3));
+  }
+
+  // Containing all the chars in the C-std::string 's'.
+  // Note that this is expensively recursive because of the C++11 constexpr
+  // formulation. Use only in constexpr initializers.
+  static constexpr Charmap FromString(const char* s) {
+    return *s == 0 ? Charmap() : (Char(*s) | FromString(s + 1));
+  }
+
+  // Containing all the chars in the closed interval [lo,hi].
+  static constexpr Charmap Range(char lo, char hi) {
+    return Charmap(RangeForWord(lo, hi, 0), RangeForWord(lo, hi, 1),
+                   RangeForWord(lo, hi, 2), RangeForWord(lo, hi, 3));
+  }
+
+  friend constexpr Charmap operator&(const Charmap& a, const Charmap& b) {
+    return Charmap(a.m_[0] & b.m_[0], a.m_[1] & b.m_[1], a.m_[2] & b.m_[2],
+                   a.m_[3] & b.m_[3]);
+  }
+
+  friend constexpr Charmap operator|(const Charmap& a, const Charmap& b) {
+    return Charmap(a.m_[0] | b.m_[0], a.m_[1] | b.m_[1], a.m_[2] | b.m_[2],
+                   a.m_[3] | b.m_[3]);
+  }
+
+  friend constexpr Charmap operator~(const Charmap& a) {
+    return Charmap(~a.m_[0], ~a.m_[1], ~a.m_[2], ~a.m_[3]);
+  }
+
+ private:
+  constexpr Charmap(uint64_t b0, uint64_t b1, uint64_t b2, uint64_t b3)
+      : m_{b0, b1, b2, b3} {}
+
+  static constexpr uint64_t RangeForWord(unsigned char lo, unsigned char hi,
+                                         uint64_t word) {
+    return OpenRangeFromZeroForWord(hi + 1, word) &
+           ~OpenRangeFromZeroForWord(lo, word);
+  }
+
+  // All the chars in the specified word of the range [0, upper).
+  static constexpr uint64_t OpenRangeFromZeroForWord(uint64_t upper,
+                                                     uint64_t word) {
+    return (upper <= 64 * word)
+               ? 0
+               : (upper >= 64 * (word + 1))
+                     ? ~static_cast<uint64_t>(0)
+                     : (~static_cast<uint64_t>(0) >> (64 - upper % 64));
+  }
+
+  static constexpr uint64_t CharMaskForWord(unsigned char x, uint64_t word) {
+    return (x / 64 == word) ? (static_cast<uint64_t>(1) << (x % 64)) : 0;
+  }
+
+ private:
+  void SetChar(unsigned char c) {
+    m_[c / 64] |= static_cast<uint64_t>(1) << (c % 64);
+  }
+
+  uint64_t m_[4];
+};
+
+// Mirror the char-classifying predicates in <cctype>
+constexpr Charmap UpperCharmap() { return Charmap::Range('A', 'Z'); }
+constexpr Charmap LowerCharmap() { return Charmap::Range('a', 'z'); }
+constexpr Charmap DigitCharmap() { return Charmap::Range('0', '9'); }
+constexpr Charmap AlphaCharmap() { return LowerCharmap() | UpperCharmap(); }
+constexpr Charmap AlnumCharmap() { return DigitCharmap() | AlphaCharmap(); }
+constexpr Charmap XDigitCharmap() {
+  return DigitCharmap() | Charmap::Range('A', 'F') | Charmap::Range('a', 'f');
+}
+constexpr Charmap PrintCharmap() { return Charmap::Range(0x20, 0x7e); }
+constexpr Charmap SpaceCharmap() { return Charmap::FromString("\t\n\v\f\r "); }
+constexpr Charmap CntrlCharmap() {
+  return Charmap::Range(0, 0x7f) & ~PrintCharmap();
+}
+constexpr Charmap BlankCharmap() { return Charmap::FromString("\t "); }
+constexpr Charmap GraphCharmap() { return PrintCharmap() & ~SpaceCharmap(); }
+constexpr Charmap PunctCharmap() { return GraphCharmap() & ~AlnumCharmap(); }
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_CHAR_MAP_H_
diff --git a/absl/strings/internal/char_map_benchmark.cc b/absl/strings/internal/char_map_benchmark.cc
new file mode 100644
index 0000000..5cef967
--- /dev/null
+++ b/absl/strings/internal/char_map_benchmark.cc
@@ -0,0 +1,61 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/char_map.h"
+
+#include <cstdint>
+
+#include "benchmark/benchmark.h"
+
+namespace {
+
+absl::strings_internal::Charmap MakeBenchmarkMap() {
+  absl::strings_internal::Charmap m;
+  uint32_t x[] = {0x0, 0x1, 0x2, 0x3, 0xf, 0xe, 0xd, 0xc};
+  for (uint32_t& t : x) t *= static_cast<uint32_t>(0x11111111UL);
+  for (uint32_t i = 0; i < 256; ++i) {
+    if ((x[i / 32] >> (i % 32)) & 1)
+      m = m | absl::strings_internal::Charmap::Char(i);
+  }
+  return m;
+}
+
+// Micro-benchmark for Charmap::contains.
+void BM_Contains(benchmark::State& state) {
+  // Loop-body replicated 10 times to increase time per iteration.
+  // Argument continuously changed to avoid generating common subexpressions.
+  const absl::strings_internal::Charmap benchmark_map = MakeBenchmarkMap();
+  unsigned char c = 0;
+  int ops = 0;
+  for (auto _ : state) {
+    ops += benchmark_map.contains(c++);
+    ops += benchmark_map.contains(c++);
+    ops += benchmark_map.contains(c++);
+    ops += benchmark_map.contains(c++);
+    ops += benchmark_map.contains(c++);
+    ops += benchmark_map.contains(c++);
+    ops += benchmark_map.contains(c++);
+    ops += benchmark_map.contains(c++);
+    ops += benchmark_map.contains(c++);
+    ops += benchmark_map.contains(c++);
+  }
+  benchmark::DoNotOptimize(ops);
+}
+BENCHMARK(BM_Contains);
+
+// We don't bother benchmarking Charmap::IsZero or Charmap::IntersectsWith;
+// their running time is data-dependent and it is not worth characterizing
+// "typical" data.
+
+}  // namespace
diff --git a/absl/strings/internal/char_map_test.cc b/absl/strings/internal/char_map_test.cc
new file mode 100644
index 0000000..d330624
--- /dev/null
+++ b/absl/strings/internal/char_map_test.cc
@@ -0,0 +1,172 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/char_map.h"
+
+#include <cctype>
+#include <string>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+namespace {
+
+constexpr absl::strings_internal::Charmap everything_map =
+    ~absl::strings_internal::Charmap();
+constexpr absl::strings_internal::Charmap nothing_map{};
+
+TEST(Charmap, AllTests) {
+  const absl::strings_internal::Charmap also_nothing_map("", 0);
+  ASSERT_TRUE(everything_map.contains('\0'));
+  ASSERT_TRUE(!nothing_map.contains('\0'));
+  ASSERT_TRUE(!also_nothing_map.contains('\0'));
+  for (unsigned char ch = 1; ch != 0; ++ch) {
+    ASSERT_TRUE(everything_map.contains(ch));
+    ASSERT_TRUE(!nothing_map.contains(ch));
+    ASSERT_TRUE(!also_nothing_map.contains(ch));
+  }
+
+  const absl::strings_internal::Charmap symbols("&@#@^!@?", 5);
+  ASSERT_TRUE(symbols.contains('&'));
+  ASSERT_TRUE(symbols.contains('@'));
+  ASSERT_TRUE(symbols.contains('#'));
+  ASSERT_TRUE(symbols.contains('^'));
+  ASSERT_TRUE(!symbols.contains('!'));
+  ASSERT_TRUE(!symbols.contains('?'));
+  int cnt = 0;
+  for (unsigned char ch = 1; ch != 0; ++ch)
+    cnt += symbols.contains(ch);
+  ASSERT_EQ(cnt, 4);
+
+  const absl::strings_internal::Charmap lets("^abcde", 3);
+  const absl::strings_internal::Charmap lets2("fghij\0klmnop", 10);
+  const absl::strings_internal::Charmap lets3("fghij\0klmnop");
+  ASSERT_TRUE(lets2.contains('k'));
+  ASSERT_TRUE(!lets3.contains('k'));
+
+  ASSERT_TRUE(symbols.IntersectsWith(lets));
+  ASSERT_TRUE(!lets2.IntersectsWith(lets));
+  ASSERT_TRUE(lets.IntersectsWith(symbols));
+  ASSERT_TRUE(!lets.IntersectsWith(lets2));
+
+  ASSERT_TRUE(nothing_map.IsZero());
+  ASSERT_TRUE(!lets.IsZero());
+}
+
+namespace {
+std::string Members(const absl::strings_internal::Charmap& m) {
+  std::string r;
+  for (size_t i = 0; i < 256; ++i)
+    if (m.contains(i)) r.push_back(i);
+  return r;
+}
+
+std::string ClosedRangeString(unsigned char lo, unsigned char hi) {
+  // Don't depend on lo<hi. Just increment until lo==hi.
+  std::string s;
+  while (true) {
+    s.push_back(lo);
+    if (lo == hi) break;
+    ++lo;
+  }
+  return s;
+}
+
+}  // namespace
+
+TEST(Charmap, Constexpr) {
+  constexpr absl::strings_internal::Charmap kEmpty = nothing_map;
+  EXPECT_THAT(Members(kEmpty), "");
+  constexpr absl::strings_internal::Charmap kA =
+      absl::strings_internal::Charmap::Char('A');
+  EXPECT_THAT(Members(kA), "A");
+  constexpr absl::strings_internal::Charmap kAZ =
+      absl::strings_internal::Charmap::Range('A', 'Z');
+  EXPECT_THAT(Members(kAZ), "ABCDEFGHIJKLMNOPQRSTUVWXYZ");
+  constexpr absl::strings_internal::Charmap kIdentifier =
+      absl::strings_internal::Charmap::Range('0', '9') |
+      absl::strings_internal::Charmap::Range('A', 'Z') |
+      absl::strings_internal::Charmap::Range('a', 'z') |
+      absl::strings_internal::Charmap::Char('_');
+  EXPECT_THAT(Members(kIdentifier),
+              "0123456789"
+              "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+              "_"
+              "abcdefghijklmnopqrstuvwxyz");
+  constexpr absl::strings_internal::Charmap kAll = everything_map;
+  for (size_t i = 0; i < 256; ++i) {
+    EXPECT_TRUE(kAll.contains(i)) << i;
+  }
+  constexpr absl::strings_internal::Charmap kHello =
+      absl::strings_internal::Charmap::FromString("Hello, world!");
+  EXPECT_THAT(Members(kHello), " !,Hdelorw");
+
+  // test negation and intersection
+  constexpr absl::strings_internal::Charmap kABC =
+      absl::strings_internal::Charmap::Range('A', 'Z') &
+      ~absl::strings_internal::Charmap::Range('D', 'Z');
+  EXPECT_THAT(Members(kABC), "ABC");
+}
+
+TEST(Charmap, Range) {
+  // Exhaustive testing takes too long, so test some of the boundaries that
+  // are perhaps going to cause trouble.
+  std::vector<size_t> poi = {0,   1,   2,   3,   4,   7,   8,   9,  15,
+                             16,  17,  30,  31,  32,  33,  63,  64, 65,
+                             127, 128, 129, 223, 224, 225, 254, 255};
+  for (auto lo = poi.begin(); lo != poi.end(); ++lo) {
+    SCOPED_TRACE(*lo);
+    for (auto hi = lo; hi != poi.end(); ++hi) {
+      SCOPED_TRACE(*hi);
+      EXPECT_THAT(Members(absl::strings_internal::Charmap::Range(*lo, *hi)),
+                  ClosedRangeString(*lo, *hi));
+    }
+  }
+}
+
+bool AsBool(int x) { return static_cast<bool>(x); }
+
+TEST(CharmapCtype, Match) {
+  for (int c = 0; c < 256; ++c) {
+    SCOPED_TRACE(c);
+    SCOPED_TRACE(static_cast<char>(c));
+    EXPECT_EQ(AsBool(std::isupper(c)),
+              absl::strings_internal::UpperCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::islower(c)),
+              absl::strings_internal::LowerCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::isdigit(c)),
+              absl::strings_internal::DigitCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::isalpha(c)),
+              absl::strings_internal::AlphaCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::isalnum(c)),
+              absl::strings_internal::AlnumCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::isxdigit(c)),
+              absl::strings_internal::XDigitCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::isprint(c)),
+              absl::strings_internal::PrintCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::isspace(c)),
+              absl::strings_internal::SpaceCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::iscntrl(c)),
+              absl::strings_internal::CntrlCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::isblank(c)),
+              absl::strings_internal::BlankCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::isgraph(c)),
+              absl::strings_internal::GraphCharmap().contains(c));
+    EXPECT_EQ(AsBool(std::ispunct(c)),
+              absl::strings_internal::PunctCharmap().contains(c));
+  }
+}
+
+}  // namespace
diff --git a/absl/strings/internal/charconv_bigint.cc b/absl/strings/internal/charconv_bigint.cc
new file mode 100644
index 0000000..95d471d
--- /dev/null
+++ b/absl/strings/internal/charconv_bigint.cc
@@ -0,0 +1,357 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/charconv_bigint.h"
+
+#include <algorithm>
+#include <cassert>
+#include <string>
+
+namespace absl {
+namespace strings_internal {
+
+namespace {
+
+// Table containing some large powers of 5, for fast computation.
+
+// Constant step size for entries in the kLargePowersOfFive table.  Each entry
+// is larger than the previous entry by a factor of 5**kLargePowerOfFiveStep
+// (or 5**27).
+//
+// In other words, the Nth entry in the table is 5**(27*N).
+//
+// 5**27 is the largest power of 5 that fits in 64 bits.
+constexpr int kLargePowerOfFiveStep = 27;
+
+// The largest legal index into the kLargePowersOfFive table.
+//
+// In other words, the largest precomputed power of 5 is 5**(27*20).
+constexpr int kLargestPowerOfFiveIndex = 20;
+
+// Table of powers of (5**27), up to (5**27)**20 == 5**540.
+//
+// Used to generate large powers of 5 while limiting the number of repeated
+// multiplications required.
+//
+// clang-format off
+const uint32_t kLargePowersOfFive[] = {
+// 5**27 (i=1), start=0, end=2
+  0xfa10079dU, 0x6765c793U,
+// 5**54 (i=2), start=2, end=6
+  0x97d9f649U, 0x6664242dU, 0x29939b14U, 0x29c30f10U,
+// 5**81 (i=3), start=6, end=12
+  0xc4f809c5U, 0x7bf3f22aU, 0x67bdae34U, 0xad340517U, 0x369d1b5fU, 0x10de1593U,
+// 5**108 (i=4), start=12, end=20
+  0x92b260d1U, 0x9efff7c7U, 0x81de0ec6U, 0xaeba5d56U, 0x410664a4U, 0x4f40737aU,
+  0x20d3846fU, 0x06d00f73U,
+// 5**135 (i=5), start=20, end=30
+  0xff1b172dU, 0x13a1d71cU, 0xefa07617U, 0x7f682d3dU, 0xff8c90c0U, 0x3f0131e7U,
+  0x3fdcb9feU, 0x917b0177U, 0x16c407a7U, 0x02c06b9dU,
+// 5**162 (i=6), start=30, end=42
+  0x960f7199U, 0x056667ecU, 0xe07aefd8U, 0x80f2b9ccU, 0x8273f5e3U, 0xeb9a214aU,
+  0x40b38005U, 0x0e477ad4U, 0x277d08e6U, 0xfa28b11eU, 0xd3f7d784U, 0x011c835bU,
+// 5**189 (i=7), start=42, end=56
+  0xf723d9d5U, 0x3282d3f3U, 0xe00857d1U, 0x69659d25U, 0x2cf117cfU, 0x24da6d07U,
+  0x954d1417U, 0x3e5d8cedU, 0x7a8bb766U, 0xfd785ae6U, 0x645436d2U, 0x40c78b34U,
+  0x94151217U, 0x0072e9f7U,
+// 5**216 (i=8), start=56, end=72
+  0x2b416aa1U, 0x7893c5a7U, 0xe37dc6d4U, 0x2bad2beaU, 0xf0fc846cU, 0x7575ae4bU,
+  0x62587b14U, 0x83b67a34U, 0x02110cdbU, 0xf7992f55U, 0x00deb022U, 0xa4a23becU,
+  0x8af5c5cdU, 0xb85b654fU, 0x818df38bU, 0x002e69d2U,
+// 5**243 (i=9), start=72, end=90
+  0x3518cbbdU, 0x20b0c15fU, 0x38756c2fU, 0xfb5dc3ddU, 0x22ad2d94U, 0xbf35a952U,
+  0xa699192aU, 0x9a613326U, 0xad2a9cedU, 0xd7f48968U, 0xe87dfb54U, 0xc8f05db6U,
+  0x5ef67531U, 0x31c1ab49U, 0xe202ac9fU, 0x9b2957b5U, 0xa143f6d3U, 0x0012bf07U,
+// 5**270 (i=10), start=90, end=110
+  0x8b971de9U, 0x21aba2e1U, 0x63944362U, 0x57172336U, 0xd9544225U, 0xfb534166U,
+  0x08c563eeU, 0x14640ee2U, 0x24e40d31U, 0x02b06537U, 0x03887f14U, 0x0285e533U,
+  0xb744ef26U, 0x8be3a6c4U, 0x266979b4U, 0x6761ece2U, 0xd9cb39e4U, 0xe67de319U,
+  0x0d39e796U, 0x00079250U,
+// 5**297 (i=11), start=110, end=132
+  0x260eb6e5U, 0xf414a796U, 0xee1a7491U, 0xdb9368ebU, 0xf50c105bU, 0x59157750U,
+  0x9ed2fb5cU, 0xf6e56d8bU, 0xeaee8d23U, 0x0f319f75U, 0x2aa134d6U, 0xac2908e9U,
+  0xd4413298U, 0x02f02a55U, 0x989d5a7aU, 0x70dde184U, 0xba8040a7U, 0x03200981U,
+  0xbe03b11cU, 0x3c1c2a18U, 0xd60427a1U, 0x00030ee0U,
+// 5**324 (i=12), start=132, end=156
+  0xce566d71U, 0xf1c4aa25U, 0x4e93ca53U, 0xa72283d0U, 0x551a73eaU, 0x3d0538e2U,
+  0x8da4303fU, 0x6a58de60U, 0x0e660221U, 0x49cf61a6U, 0x8d058fc1U, 0xb9d1a14cU,
+  0x4bab157dU, 0xc85c6932U, 0x518c8b9eU, 0x9b92b8d0U, 0x0d8a0e21U, 0xbd855df9U,
+  0xb3ea59a1U, 0x8da29289U, 0x4584d506U, 0x3752d80fU, 0xb72569c6U, 0x00013c33U,
+// 5**351 (i=13), start=156, end=182
+  0x190f354dU, 0x83695cfeU, 0xe5a4d0c7U, 0xb60fb7e8U, 0xee5bbcc4U, 0xb922054cU,
+  0xbb4f0d85U, 0x48394028U, 0x1d8957dbU, 0x0d7edb14U, 0x4ecc7587U, 0x505e9e02U,
+  0x4c87f36bU, 0x99e66bd6U, 0x44b9ed35U, 0x753037d4U, 0xe5fe5f27U, 0x2742c203U,
+  0x13b2ed2bU, 0xdc525d2cU, 0xe6fde59aU, 0x77ffb18fU, 0x13c5752cU, 0x08a84bccU,
+  0x859a4940U, 0x00007fb6U,
+// 5**378 (i=14), start=182, end=210
+  0x4f98cb39U, 0xa60edbbcU, 0x83b5872eU, 0xa501acffU, 0x9cc76f78U, 0xbadd4c73U,
+  0x43e989faU, 0xca7acf80U, 0x2e0c824fU, 0xb19f4ffcU, 0x092fd81cU, 0xe4eb645bU,
+  0xa1ff84c2U, 0x8a5a83baU, 0xa8a1fae9U, 0x1db43609U, 0xb0fed50bU, 0x0dd7d2bdU,
+  0x7d7accd8U, 0x91fa640fU, 0x37dcc6c5U, 0x1c417fd5U, 0xe4d462adU, 0xe8a43399U,
+  0x131bf9a5U, 0x8df54d29U, 0x36547dc1U, 0x00003395U,
+// 5**405 (i=15), start=210, end=240
+  0x5bd330f5U, 0x77d21967U, 0x1ac481b7U, 0x6be2f7ceU, 0x7f4792a9U, 0xe84c2c52U,
+  0x84592228U, 0x9dcaf829U, 0xdab44ce1U, 0x3d0c311bU, 0x532e297dU, 0x4704e8b4U,
+  0x9cdc32beU, 0x41e64d9dU, 0x7717bea1U, 0xa824c00dU, 0x08f50b27U, 0x0f198d77U,
+  0x49bbfdf0U, 0x025c6c69U, 0xd4e55cd3U, 0xf083602bU, 0xb9f0fecdU, 0xc0864aeaU,
+  0x9cb98681U, 0xaaf620e9U, 0xacb6df30U, 0x4faafe66U, 0x8af13c3bU, 0x000014d5U,
+// 5**432 (i=16), start=240, end=272
+  0x682bb941U, 0x89a9f297U, 0xcba75d7bU, 0x404217b1U, 0xb4e519e9U, 0xa1bc162bU,
+  0xf7f5910aU, 0x98715af5U, 0x2ff53e57U, 0xe3ef118cU, 0x490c4543U, 0xbc9b1734U,
+  0x2affbe4dU, 0x4cedcb4cU, 0xfb14e99eU, 0x35e34212U, 0xece39c24U, 0x07673ab3U,
+  0xe73115ddU, 0xd15d38e7U, 0x093eed3bU, 0xf8e7eac5U, 0x78a8cc80U, 0x25227aacU,
+  0x3f590551U, 0x413da1cbU, 0xdf643a55U, 0xab65ad44U, 0xd70b23d7U, 0xc672cd76U,
+  0x3364ea62U, 0x0000086aU,
+// 5**459 (i=17), start=272, end=306
+  0x22f163ddU, 0x23cf07acU, 0xbe2af6c2U, 0xf412f6f6U, 0xc3ff541eU, 0x6eeaf7deU,
+  0xa47047e0U, 0x408cda92U, 0x0f0eeb08U, 0x56deba9dU, 0xcfc6b090U, 0x8bbbdf04U,
+  0x3933cdb3U, 0x9e7bb67dU, 0x9f297035U, 0x38946244U, 0xee1d37bbU, 0xde898174U,
+  0x63f3559dU, 0x705b72fbU, 0x138d27d9U, 0xf8603a78U, 0x735eec44U, 0xe30987d5U,
+  0xc6d38070U, 0x9cfe548eU, 0x9ff01422U, 0x7c564aa8U, 0x91cc60baU, 0xcbc3565dU,
+  0x7550a50bU, 0x6909aeadU, 0x13234c45U, 0x00000366U,
+// 5**486 (i=18), start=306, end=342
+  0x17954989U, 0x3a7d7709U, 0x98042de5U, 0xa9011443U, 0x45e723c2U, 0x269ffd6fU,
+  0x58852a46U, 0xaaa1042aU, 0x2eee8153U, 0xb2b6c39eU, 0xaf845b65U, 0xf6c365d7U,
+  0xe4cffb2bU, 0xc840e90cU, 0xabea8abbU, 0x5c58f8d2U, 0x5c19fa3aU, 0x4670910aU,
+  0x4449f21cU, 0xefa645b3U, 0xcc427decU, 0x083c3d73U, 0x467cb413U, 0x6fe10ae4U,
+  0x3caffc72U, 0x9f8da55eU, 0x5e5c8ea7U, 0x490594bbU, 0xf0871b0bU, 0xdd89816cU,
+  0x8e931df8U, 0xe85ce1c9U, 0xcca090a5U, 0x575fa16bU, 0x6b9f106cU, 0x0000015fU,
+// 5**513 (i=19), start=342, end=380
+  0xee20d805U, 0x57bc3c07U, 0xcdea624eU, 0xd3f0f52dU, 0x9924b4f4U, 0xcf968640U,
+  0x61d41962U, 0xe87fb464U, 0xeaaf51c7U, 0x564c8b60U, 0xccda4028U, 0x529428bbU,
+  0x313a1fa8U, 0x96bd0f94U, 0x7a82ebaaU, 0xad99e7e9U, 0xf2668cd4U, 0xbe33a45eU,
+  0xfd0db669U, 0x87ee369fU, 0xd3ec20edU, 0x9c4d7db7U, 0xdedcf0d8U, 0x7cd2ca64U,
+  0xe25a6577U, 0x61003fd4U, 0xe56f54ccU, 0x10b7c748U, 0x40526e5eU, 0x7300ae87U,
+  0x5c439261U, 0x2c0ff469U, 0xbf723f12U, 0xb2379b61U, 0xbf59b4f5U, 0xc91b1c3fU,
+  0xf0046d27U, 0x0000008dU,
+// 5**540 (i=20), start=380, end=420
+  0x525c9e11U, 0xf4e0eb41U, 0xebb2895dU, 0x5da512f9U, 0x7d9b29d4U, 0x452f4edcU,
+  0x0b90bc37U, 0x341777cbU, 0x63d269afU, 0x1da77929U, 0x0a5c1826U, 0x77991898U,
+  0x5aeddf86U, 0xf853a877U, 0x538c31ccU, 0xe84896daU, 0xb7a0010bU, 0x17ef4de5U,
+  0xa52a2adeU, 0x029fd81cU, 0x987ce701U, 0x27fefd77U, 0xdb46c66fU, 0x5d301900U,
+  0x496998c0U, 0xbb6598b9U, 0x5eebb607U, 0xe547354aU, 0xdf4a2f7eU, 0xf06c4955U,
+  0x96242ffaU, 0x1775fb27U, 0xbecc58ceU, 0xebf2a53bU, 0x3eaad82aU, 0xf41137baU,
+  0x573e6fbaU, 0xfb4866b8U, 0x54002148U, 0x00000039U,
+};
+// clang-format on
+
+// Returns a pointer to the big integer data for (5**27)**i.  i must be
+// between 1 and 20, inclusive.
+const uint32_t* LargePowerOfFiveData(int i) {
+  return kLargePowersOfFive + i * (i - 1);
+}
+
+// Returns the size of the big integer data for (5**27)**i, in words.  i must be
+// between 1 and 20, inclusive.
+int LargePowerOfFiveSize(int i) { return 2 * i; }
+}  // namespace
+
+const uint32_t kFiveToNth[14] = {
+    1,     5,      25,      125,     625,      3125,      15625,
+    78125, 390625, 1953125, 9765625, 48828125, 244140625, 1220703125,
+};
+
+const uint32_t kTenToNth[10] = {
+    1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000,
+};
+
+template <int max_words>
+int BigUnsigned<max_words>::ReadFloatMantissa(const ParsedFloat& fp,
+                                              int significant_digits) {
+  SetToZero();
+  assert(fp.type == FloatType::kNumber);
+
+  if (fp.subrange_begin == nullptr) {
+    // We already exactly parsed the mantissa, so no more work is necessary.
+    words_[0] = fp.mantissa & 0xffffffffu;
+    words_[1] = fp.mantissa >> 32;
+    if (words_[1]) {
+      size_ = 2;
+    } else if (words_[0]) {
+      size_ = 1;
+    }
+    return fp.exponent;
+  }
+  int exponent_adjust =
+      ReadDigits(fp.subrange_begin, fp.subrange_end, significant_digits);
+  return fp.literal_exponent + exponent_adjust;
+}
+
+template <int max_words>
+int BigUnsigned<max_words>::ReadDigits(const char* begin, const char* end,
+                                       int significant_digits) {
+  assert(significant_digits <= Digits10() + 1);
+  SetToZero();
+
+  bool after_decimal_point = false;
+  // Discard any leading zeroes before the decimal point
+  while (begin < end && *begin == '0') {
+    ++begin;
+  }
+  int dropped_digits = 0;
+  // Discard any trailing zeroes.  These may or may not be after the decimal
+  // point.
+  while (begin < end && *std::prev(end) == '0') {
+    --end;
+    ++dropped_digits;
+  }
+  if (begin < end && *std::prev(end) == '.') {
+    // If the std::string ends in '.', either before or after dropping zeroes, then
+    // drop the decimal point and look for more digits to drop.
+    dropped_digits = 0;
+    --end;
+    while (begin < end && *std::prev(end) == '0') {
+      --end;
+      ++dropped_digits;
+    }
+  } else if (dropped_digits) {
+    // We dropped digits, and aren't sure if they're before or after the decimal
+    // point.  Figure that out now.
+    const char* dp = std::find(begin, end, '.');
+    if (dp != end) {
+      // The dropped trailing digits were after the decimal point, so don't
+      // count them.
+      dropped_digits = 0;
+    }
+  }
+  // Any non-fraction digits we dropped need to be accounted for in our exponent
+  // adjustment.
+  int exponent_adjust = dropped_digits;
+
+  uint32_t queued = 0;
+  int digits_queued = 0;
+  for (; begin != end && significant_digits > 0; ++begin) {
+    if (*begin == '.') {
+      after_decimal_point = true;
+      continue;
+    }
+    if (after_decimal_point) {
+      // For each fractional digit we emit in our parsed integer, adjust our
+      // decimal exponent to compensate.
+      --exponent_adjust;
+    }
+    int digit = (*begin - '0');
+    --significant_digits;
+    if (significant_digits == 0 && std::next(begin) != end &&
+        (digit == 0 || digit == 5)) {
+      // If this is the very last significant digit, but insignificant digits
+      // remain, we know that the last of those remaining significant digits is
+      // nonzero.  (If it wasn't, we would have stripped it before we got here.)
+      // So if this final digit is a 0 or 5, adjust it upward by 1.
+      //
+      // This adjustment is what allows incredibly large mantissas ending in
+      // 500000...000000000001 to correctly round up, rather than to nearest.
+      ++digit;
+    }
+    queued = 10 * queued + digit;
+    ++digits_queued;
+    if (digits_queued == kMaxSmallPowerOfTen) {
+      MultiplyBy(kTenToNth[kMaxSmallPowerOfTen]);
+      AddWithCarry(0, queued);
+      queued = digits_queued = 0;
+    }
+  }
+  // Encode any remaining digits.
+  if (digits_queued) {
+    MultiplyBy(kTenToNth[digits_queued]);
+    AddWithCarry(0, queued);
+  }
+
+  // If any insignificant digits remain, we will drop them.  But if we have not
+  // yet read the decimal point, then we have to adjust the exponent to account
+  // for the dropped digits.
+  if (begin < end && !after_decimal_point) {
+    // This call to std::find will result in a pointer either to the decimal
+    // point, or to the end of our buffer if there was none.
+    //
+    // Either way, [begin, decimal_point) will contain the set of dropped digits
+    // that require an exponent adjustment.
+    const char* decimal_point = std::find(begin, end, '.');
+    exponent_adjust += (decimal_point - begin);
+  }
+  return exponent_adjust;
+}
+
+template <int max_words>
+/* static */ BigUnsigned<max_words> BigUnsigned<max_words>::FiveToTheNth(
+    int n) {
+  BigUnsigned answer(1u);
+
+  // Seed from the table of large powers, if possible.
+  bool first_pass = true;
+  while (n >= kLargePowerOfFiveStep) {
+    int big_power =
+        std::min(n / kLargePowerOfFiveStep, kLargestPowerOfFiveIndex);
+    if (first_pass) {
+      // just copy, rather than multiplying by 1
+      std::copy(
+          LargePowerOfFiveData(big_power),
+          LargePowerOfFiveData(big_power) + LargePowerOfFiveSize(big_power),
+          answer.words_);
+      answer.size_ = LargePowerOfFiveSize(big_power);
+      first_pass = false;
+    } else {
+      answer.MultiplyBy(LargePowerOfFiveSize(big_power),
+                        LargePowerOfFiveData(big_power));
+    }
+    n -= kLargePowerOfFiveStep * big_power;
+  }
+  answer.MultiplyByFiveToTheNth(n);
+  return answer;
+}
+
+template <int max_words>
+void BigUnsigned<max_words>::MultiplyStep(int original_size,
+                                          const uint32_t* other_words,
+                                          int other_size, int step) {
+  int this_i = std::min(original_size - 1, step);
+  int other_i = step - this_i;
+
+  uint64_t this_word = 0;
+  uint64_t carry = 0;
+  for (; this_i >= 0 && other_i < other_size; --this_i, ++other_i) {
+    uint64_t product = words_[this_i];
+    product *= other_words[other_i];
+    this_word += product;
+    carry += (this_word >> 32);
+    this_word &= 0xffffffff;
+  }
+  AddWithCarry(step + 1, carry);
+  words_[step] = this_word & 0xffffffff;
+  if (this_word > 0 && size_ <= step) {
+    size_ = step + 1;
+  }
+}
+
+template <int max_words>
+std::string BigUnsigned<max_words>::ToString() const {
+  BigUnsigned<max_words> copy = *this;
+  std::string result;
+  // Build result in reverse order
+  while (copy.size() > 0) {
+    int next_digit = copy.DivMod<10>();
+    result.push_back('0' + next_digit);
+  }
+  if (result.empty()) {
+    result.push_back('0');
+  }
+  std::reverse(result.begin(), result.end());
+  return result;
+}
+
+template class BigUnsigned<4>;
+template class BigUnsigned<84>;
+
+}  // namespace strings_internal
+}  // namespace absl
diff --git a/absl/strings/internal/charconv_bigint.h b/absl/strings/internal/charconv_bigint.h
new file mode 100644
index 0000000..7da9a7e
--- /dev/null
+++ b/absl/strings/internal/charconv_bigint.h
@@ -0,0 +1,419 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_INTERNAL_CHARCONV_BIGINT_H_
+#define ABSL_STRINGS_INTERNAL_CHARCONV_BIGINT_H_
+
+#include <algorithm>
+#include <cstdint>
+#include <iostream>
+#include <string>
+
+#include "absl/strings/ascii.h"
+#include "absl/strings/internal/charconv_parse.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+namespace strings_internal {
+
+// The largest power that 5 that can be raised to, and still fit in a uint32_t.
+constexpr int kMaxSmallPowerOfFive = 13;
+// The largest power that 10 that can be raised to, and still fit in a uint32_t.
+constexpr int kMaxSmallPowerOfTen = 9;
+
+extern const uint32_t kFiveToNth[kMaxSmallPowerOfFive + 1];
+extern const uint32_t kTenToNth[kMaxSmallPowerOfTen + 1];
+
+// Large, fixed-width unsigned integer.
+//
+// Exact rounding for decimal-to-binary floating point conversion requires very
+// large integer math, but a design goal of absl::from_chars is to avoid
+// allocating memory.  The integer precision needed for decimal-to-binary
+// conversions is large but bounded, so a huge fixed-width integer class
+// suffices.
+//
+// This is an intentionally limited big integer class.  Only needed operations
+// are implemented.  All storage lives in an array data member, and all
+// arithmetic is done in-place, to avoid requiring separate storage for operand
+// and result.
+//
+// This is an internal class.  Some methods live in the .cc file, and are
+// instantiated only for the values of max_words we need.
+template <int max_words>
+class BigUnsigned {
+ public:
+  static_assert(max_words == 4 || max_words == 84,
+                "unsupported max_words value");
+
+  BigUnsigned() : size_(0), words_{} {}
+  explicit constexpr BigUnsigned(uint64_t v)
+      : size_((v >> 32) ? 2 : v ? 1 : 0),
+        words_{static_cast<uint32_t>(v & 0xffffffffu),
+               static_cast<uint32_t>(v >> 32)} {}
+
+  // Constructs a BigUnsigned from the given string_view containing a decimal
+  // value.  If the input std::string is not a decimal integer, constructs a 0
+  // instead.
+  explicit BigUnsigned(absl::string_view sv) : size_(0), words_{} {
+    // Check for valid input, returning a 0 otherwise.  This is reasonable
+    // behavior only because this constructor is for unit tests.
+    if (std::find_if_not(sv.begin(), sv.end(), ascii_isdigit) != sv.end() ||
+        sv.empty()) {
+      return;
+    }
+    int exponent_adjust =
+        ReadDigits(sv.data(), sv.data() + sv.size(), Digits10() + 1);
+    if (exponent_adjust > 0) {
+      MultiplyByTenToTheNth(exponent_adjust);
+    }
+  }
+
+  // Loads the mantissa value of a previously-parsed float.
+  //
+  // Returns the associated decimal exponent.  The value of the parsed float is
+  // exactly *this * 10**exponent.
+  int ReadFloatMantissa(const ParsedFloat& fp, int significant_digits);
+
+  // Returns the number of decimal digits of precision this type provides.  All
+  // numbers with this many decimal digits or fewer are representable by this
+  // type.
+  //
+  // Analagous to std::numeric_limits<BigUnsigned>::digits10.
+  static constexpr int Digits10() {
+    // 9975007/1035508 is very slightly less than log10(2**32).
+    return static_cast<uint64_t>(max_words) * 9975007 / 1035508;
+  }
+
+  // Shifts left by the given number of bits.
+  void ShiftLeft(int count) {
+    if (count > 0) {
+      const int word_shift = count / 32;
+      if (word_shift >= max_words) {
+        SetToZero();
+        return;
+      }
+      size_ = (std::min)(size_ + word_shift, max_words);
+      count %= 32;
+      if (count == 0) {
+        std::copy_backward(words_, words_ + size_ - word_shift, words_ + size_);
+      } else {
+        for (int i = (std::min)(size_, max_words - 1); i > word_shift; --i) {
+          words_[i] = (words_[i - word_shift] << count) |
+                      (words_[i - word_shift - 1] >> (32 - count));
+        }
+        words_[word_shift] = words_[0] << count;
+        // Grow size_ if necessary.
+        if (size_ < max_words && words_[size_]) {
+          ++size_;
+        }
+      }
+      std::fill(words_, words_ + word_shift, 0u);
+    }
+  }
+
+
+  // Multiplies by v in-place.
+  void MultiplyBy(uint32_t v) {
+    if (size_ == 0 || v == 1) {
+      return;
+    }
+    if (v == 0) {
+      SetToZero();
+      return;
+    }
+    const uint64_t factor = v;
+    uint64_t window = 0;
+    for (int i = 0; i < size_; ++i) {
+      window += factor * words_[i];
+      words_[i] = window & 0xffffffff;
+      window >>= 32;
+    }
+    // If carry bits remain and there's space for them, grow size_.
+    if (window && size_ < max_words) {
+      words_[size_] = window & 0xffffffff;
+      ++size_;
+    }
+  }
+
+  void MultiplyBy(uint64_t v) {
+    uint32_t words[2];
+    words[0] = static_cast<uint32_t>(v);
+    words[1] = static_cast<uint32_t>(v >> 32);
+    if (words[1] == 0) {
+      MultiplyBy(words[0]);
+    } else {
+      MultiplyBy(2, words);
+    }
+  }
+
+  // Multiplies in place by 5 to the power of n.  n must be non-negative.
+  void MultiplyByFiveToTheNth(int n) {
+    while (n >= kMaxSmallPowerOfFive) {
+      MultiplyBy(kFiveToNth[kMaxSmallPowerOfFive]);
+      n -= kMaxSmallPowerOfFive;
+    }
+    if (n > 0) {
+      MultiplyBy(kFiveToNth[n]);
+    }
+  }
+
+  // Multiplies in place by 10 to the power of n.  n must be non-negative.
+  void MultiplyByTenToTheNth(int n) {
+    if (n > kMaxSmallPowerOfTen) {
+      // For large n, raise to a power of 5, then shift left by the same amount.
+      // (10**n == 5**n * 2**n.)  This requires fewer multiplications overall.
+      MultiplyByFiveToTheNth(n);
+      ShiftLeft(n);
+    } else if (n > 0) {
+      // We can do this more quickly for very small N by using a single
+      // multiplication.
+      MultiplyBy(kTenToNth[n]);
+    }
+  }
+
+  // Returns the value of 5**n, for non-negative n.  This implementation uses
+  // a lookup table, and is faster then seeding a BigUnsigned with 1 and calling
+  // MultiplyByFiveToTheNth().
+  static BigUnsigned FiveToTheNth(int n);
+
+  // Multiplies by another BigUnsigned, in-place.
+  template <int M>
+  void MultiplyBy(const BigUnsigned<M>& other) {
+    MultiplyBy(other.size(), other.words());
+  }
+
+  void SetToZero() {
+    std::fill(words_, words_ + size_, 0u);
+    size_ = 0;
+  }
+
+  // Returns the value of the nth word of this BigUnsigned.  This is
+  // range-checked, and returns 0 on out-of-bounds accesses.
+  uint32_t GetWord(int index) const {
+    if (index < 0 || index >= size_) {
+      return 0;
+    }
+    return words_[index];
+  }
+
+  // Returns this integer as a decimal std::string.  This is not used in the decimal-
+  // to-binary conversion; it is intended to aid in testing.
+  std::string ToString() const;
+
+  int size() const { return size_; }
+  const uint32_t* words() const { return words_; }
+
+ private:
+  // Reads the number between [begin, end), possibly containing a decimal point,
+  // into this BigUnsigned.
+  //
+  // Callers are required to ensure [begin, end) contains a valid number, with
+  // one or more decimal digits and at most one decimal point.  This routine
+  // will behave unpredictably if these preconditions are not met.
+  //
+  // Only the first `significant_digits` digits are read.  Digits beyond this
+  // limit are "sticky": If the final significant digit is 0 or 5, and if any
+  // dropped digit is nonzero, then that final significant digit is adjusted up
+  // to 1 or 6.  This adjustment allows for precise rounding.
+  //
+  // Returns `exponent_adjustment`, a power-of-ten exponent adjustment to
+  // account for the decimal point and for dropped significant digits.  After
+  // this function returns,
+  //   actual_value_of_parsed_string ~= *this * 10**exponent_adjustment.
+  int ReadDigits(const char* begin, const char* end, int significant_digits);
+
+  // Performs a step of big integer multiplication.  This computes the full
+  // (64-bit-wide) values that should be added at the given index (step), and
+  // adds to that location in-place.
+  //
+  // Because our math all occurs in place, we must multiply starting from the
+  // highest word working downward.  (This is a bit more expensive due to the
+  // extra carries involved.)
+  //
+  // This must be called in steps, for each word to be calculated, starting from
+  // the high end and working down to 0.  The first value of `step` should be
+  //   `std::min(original_size + other.size_ - 2, max_words - 1)`.
+  // The reason for this expression is that multiplying the i'th word from one
+  // multiplicand and the j'th word of another multiplicand creates a
+  // two-word-wide value to be stored at the (i+j)'th element.  The highest
+  // word indices we will access are `original_size - 1` from this object, and
+  // `other.size_ - 1` from our operand.  Therefore,
+  // `original_size + other.size_ - 2` is the first step we should calculate,
+  // but limited on an upper bound by max_words.
+
+  // Working from high-to-low ensures that we do not overwrite the portions of
+  // the initial value of *this which are still needed for later steps.
+  //
+  // Once called with step == 0, *this contains the result of the
+  // multiplication.
+  //
+  // `original_size` is the size_ of *this before the first call to
+  // MultiplyStep().  `other_words` and `other_size` are the contents of our
+  // operand.  `step` is the step to perform, as described above.
+  void MultiplyStep(int original_size, const uint32_t* other_words,
+                    int other_size, int step);
+
+  void MultiplyBy(int other_size, const uint32_t* other_words) {
+    const int original_size = size_;
+    const int first_step =
+        (std::min)(original_size + other_size - 2, max_words - 1);
+    for (int step = first_step; step >= 0; --step) {
+      MultiplyStep(original_size, other_words, other_size, step);
+    }
+  }
+
+  // Adds a 32-bit value to the index'th word, with carry.
+  void AddWithCarry(int index, uint32_t value) {
+    if (value) {
+      while (index < max_words && value > 0) {
+        words_[index] += value;
+        // carry if we overflowed in this word:
+        if (value > words_[index]) {
+          value = 1;
+          ++index;
+        } else {
+          value = 0;
+        }
+      }
+      size_ = (std::min)(max_words, (std::max)(index + 1, size_));
+    }
+  }
+
+  void AddWithCarry(int index, uint64_t value) {
+    if (value && index < max_words) {
+      uint32_t high = value >> 32;
+      uint32_t low = value & 0xffffffff;
+      words_[index] += low;
+      if (words_[index] < low) {
+        ++high;
+        if (high == 0) {
+          // Carry from the low word caused our high word to overflow.
+          // Short circuit here to do the right thing.
+          AddWithCarry(index + 2, static_cast<uint32_t>(1));
+          return;
+        }
+      }
+      if (high > 0) {
+        AddWithCarry(index + 1, high);
+      } else {
+        // Normally 32-bit AddWithCarry() sets size_, but since we don't call
+        // it when `high` is 0, do it ourselves here.
+        size_ = (std::min)(max_words, (std::max)(index + 1, size_));
+      }
+    }
+  }
+
+  // Divide this in place by a constant divisor.  Returns the remainder of the
+  // division.
+  template <uint32_t divisor>
+  uint32_t DivMod() {
+    uint64_t accumulator = 0;
+    for (int i = size_ - 1; i >= 0; --i) {
+      accumulator <<= 32;
+      accumulator += words_[i];
+      // accumulator / divisor will never overflow an int32_t in this loop
+      words_[i] = static_cast<uint32_t>(accumulator / divisor);
+      accumulator = accumulator % divisor;
+    }
+    while (size_ > 0 && words_[size_ - 1] == 0) {
+      --size_;
+    }
+    return static_cast<uint32_t>(accumulator);
+  }
+
+  // The number of elements in words_ that may carry significant values.
+  // All elements beyond this point are 0.
+  //
+  // When size_ is 0, this BigUnsigned stores the value 0.
+  // When size_ is nonzero, is *not* guaranteed that words_[size_ - 1] is
+  // nonzero.  This can occur due to overflow truncation.
+  // In particular, x.size_ != y.size_ does *not* imply x != y.
+  int size_;
+  uint32_t words_[max_words];
+};
+
+// Compares two big integer instances.
+//
+// Returns -1 if lhs < rhs, 0 if lhs == rhs, and 1 if lhs > rhs.
+template <int N, int M>
+int Compare(const BigUnsigned<N>& lhs, const BigUnsigned<M>& rhs) {
+  int limit = (std::max)(lhs.size(), rhs.size());
+  for (int i = limit - 1; i >= 0; --i) {
+    const uint32_t lhs_word = lhs.GetWord(i);
+    const uint32_t rhs_word = rhs.GetWord(i);
+    if (lhs_word < rhs_word) {
+      return -1;
+    } else if (lhs_word > rhs_word) {
+      return 1;
+    }
+  }
+  return 0;
+}
+
+template <int N, int M>
+bool operator==(const BigUnsigned<N>& lhs, const BigUnsigned<M>& rhs) {
+  int limit = (std::max)(lhs.size(), rhs.size());
+  for (int i = 0; i < limit; ++i) {
+    if (lhs.GetWord(i) != rhs.GetWord(i)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+template <int N, int M>
+bool operator!=(const BigUnsigned<N>& lhs, const BigUnsigned<M>& rhs) {
+  return !(lhs == rhs);
+}
+
+template <int N, int M>
+bool operator<(const BigUnsigned<N>& lhs, const BigUnsigned<M>& rhs) {
+  return Compare(lhs, rhs) == -1;
+}
+
+template <int N, int M>
+bool operator>(const BigUnsigned<N>& lhs, const BigUnsigned<M>& rhs) {
+  return rhs < lhs;
+}
+template <int N, int M>
+bool operator<=(const BigUnsigned<N>& lhs, const BigUnsigned<M>& rhs) {
+  return !(rhs < lhs);
+}
+template <int N, int M>
+bool operator>=(const BigUnsigned<N>& lhs, const BigUnsigned<M>& rhs) {
+  return !(lhs < rhs);
+}
+
+// Output operator for BigUnsigned, for testing purposes only.
+template <int N>
+std::ostream& operator<<(std::ostream& os, const BigUnsigned<N>& num) {
+  return os << num.ToString();
+}
+
+// Explicit instantiation declarations for the sizes of BigUnsigned that we
+// are using.
+//
+// For now, the choices of 4 and 84 are arbitrary; 4 is a small value that is
+// still bigger than an int128, and 84 is a large value we will want to use
+// in the from_chars implementation.
+//
+// Comments justifying the use of 84 belong in the from_chars implementation,
+// and will be added in a follow-up CL.
+extern template class BigUnsigned<4>;
+extern template class BigUnsigned<84>;
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_CHARCONV_BIGINT_H_
diff --git a/absl/strings/internal/charconv_bigint_test.cc b/absl/strings/internal/charconv_bigint_test.cc
new file mode 100644
index 0000000..745714a
--- /dev/null
+++ b/absl/strings/internal/charconv_bigint_test.cc
@@ -0,0 +1,203 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/charconv_bigint.h"
+
+#include <string>
+
+#include "gtest/gtest.h"
+
+namespace absl {
+namespace strings_internal {
+
+TEST(BigUnsigned, ShiftLeft) {
+  {
+    // Check that 3 * 2**100 is calculated correctly
+    BigUnsigned<4> num(3u);
+    num.ShiftLeft(100);
+    EXPECT_EQ(num, BigUnsigned<4>("3802951800684688204490109616128"));
+  }
+  {
+    // Test that overflow is truncated properly.
+    // 15 is 4 bits long, and BigUnsigned<4> is a 128-bit bigint.
+    // Shifting left by 125 bits should truncate off the high bit, so that
+    //   15 << 125 == 7 << 125
+    // after truncation.
+    BigUnsigned<4> a(15u);
+    BigUnsigned<4> b(7u);
+    BigUnsigned<4> c(3u);
+    a.ShiftLeft(125);
+    b.ShiftLeft(125);
+    c.ShiftLeft(125);
+    EXPECT_EQ(a, b);
+    EXPECT_NE(a, c);
+  }
+  {
+    // Same test, larger bigint:
+    BigUnsigned<84> a(15u);
+    BigUnsigned<84> b(7u);
+    BigUnsigned<84> c(3u);
+    a.ShiftLeft(84 * 32 - 3);
+    b.ShiftLeft(84 * 32 - 3);
+    c.ShiftLeft(84 * 32 - 3);
+    EXPECT_EQ(a, b);
+    EXPECT_NE(a, c);
+  }
+  {
+    // Check that incrementally shifting has the same result as doing it all at
+    // once (attempting to capture corner cases.)
+    const std::string seed = "1234567890123456789012345678901234567890";
+    BigUnsigned<84> a(seed);
+    for (int i = 1; i <= 84 * 32; ++i) {
+      a.ShiftLeft(1);
+      BigUnsigned<84> b(seed);
+      b.ShiftLeft(i);
+      EXPECT_EQ(a, b);
+    }
+    // And we should have fully rotated all bits off by now:
+    EXPECT_EQ(a, BigUnsigned<84>(0u));
+  }
+}
+
+TEST(BigUnsigned, MultiplyByUint32) {
+  const BigUnsigned<84> factorial_100(
+      "933262154439441526816992388562667004907159682643816214685929638952175999"
+      "932299156089414639761565182862536979208272237582511852109168640000000000"
+      "00000000000000");
+  BigUnsigned<84> a(1u);
+  for (uint32_t i = 1; i <= 100; ++i) {
+    a.MultiplyBy(i);
+  }
+  EXPECT_EQ(a, BigUnsigned<84>(factorial_100));
+}
+
+TEST(BigUnsigned, MultiplyByBigUnsigned) {
+  {
+    // Put the terms of factorial_200 into two bigints, and multiply them
+    // together.
+    const BigUnsigned<84> factorial_200(
+        "7886578673647905035523632139321850622951359776871732632947425332443594"
+        "4996340334292030428401198462390417721213891963883025764279024263710506"
+        "1926624952829931113462857270763317237396988943922445621451664240254033"
+        "2918641312274282948532775242424075739032403212574055795686602260319041"
+        "7032406235170085879617892222278962370389737472000000000000000000000000"
+        "0000000000000000000000000");
+    BigUnsigned<84> evens(1u);
+    BigUnsigned<84> odds(1u);
+    for (uint32_t i = 1; i < 200; i += 2) {
+      odds.MultiplyBy(i);
+      evens.MultiplyBy(i + 1);
+    }
+    evens.MultiplyBy(odds);
+    EXPECT_EQ(evens, factorial_200);
+  }
+  {
+    // Multiply various powers of 10 together.
+    for (int a = 0 ; a < 700; a += 25) {
+      SCOPED_TRACE(a);
+      BigUnsigned<84> a_value("3" + std::string(a, '0'));
+      for (int b = 0; b < (700 - a); b += 25) {
+        SCOPED_TRACE(b);
+        BigUnsigned<84> b_value("2" + std::string(b, '0'));
+        BigUnsigned<84> expected_product("6" + std::string(a + b, '0'));
+        b_value.MultiplyBy(a_value);
+        EXPECT_EQ(b_value, expected_product);
+      }
+    }
+  }
+}
+
+TEST(BigUnsigned, MultiplyByOverflow) {
+  {
+    // Check that multiplcation overflow predictably truncates.
+
+    // A big int with all bits on.
+    BigUnsigned<4> all_bits_on("340282366920938463463374607431768211455");
+    // Modulo 2**128, this is equal to -1.  Therefore the square of this,
+    // modulo 2**128, should be 1.
+    all_bits_on.MultiplyBy(all_bits_on);
+    EXPECT_EQ(all_bits_on, BigUnsigned<4>(1u));
+  }
+  {
+    // Try multiplying a large bigint by 2**50, and compare the result to
+    // shifting.
+    BigUnsigned<4> value_1("12345678901234567890123456789012345678");
+    BigUnsigned<4> value_2("12345678901234567890123456789012345678");
+    BigUnsigned<4> two_to_fiftieth(1u);
+    two_to_fiftieth.ShiftLeft(50);
+
+    value_1.ShiftLeft(50);
+    value_2.MultiplyBy(two_to_fiftieth);
+    EXPECT_EQ(value_1, value_2);
+  }
+}
+
+TEST(BigUnsigned, FiveToTheNth) {
+  {
+    // Sanity check that MultiplyByFiveToTheNth gives consistent answers, up to
+    // and including overflow.
+    for (int i = 0; i < 1160; ++i) {
+      SCOPED_TRACE(i);
+      BigUnsigned<84> value_1(123u);
+      BigUnsigned<84> value_2(123u);
+      value_1.MultiplyByFiveToTheNth(i);
+      for (int j = 0; j < i; j++) {
+        value_2.MultiplyBy(5u);
+      }
+      EXPECT_EQ(value_1, value_2);
+    }
+  }
+  {
+    // Check that the faster, table-lookup-based static method returns the same
+    // result that multiplying in-place would return, up to and including
+    // overflow.
+    for (int i = 0; i < 1160; ++i) {
+      SCOPED_TRACE(i);
+      BigUnsigned<84> value_1(1u);
+      value_1.MultiplyByFiveToTheNth(i);
+      BigUnsigned<84> value_2 = BigUnsigned<84>::FiveToTheNth(i);
+      EXPECT_EQ(value_1, value_2);
+    }
+  }
+}
+
+TEST(BigUnsigned, TenToTheNth) {
+  {
+    // Sanity check MultiplyByTenToTheNth.
+    for (int i = 0; i < 800; ++i) {
+      SCOPED_TRACE(i);
+      BigUnsigned<84> value_1(123u);
+      BigUnsigned<84> value_2(123u);
+      value_1.MultiplyByTenToTheNth(i);
+      for (int j = 0; j < i; j++) {
+        value_2.MultiplyBy(10u);
+      }
+      EXPECT_EQ(value_1, value_2);
+    }
+  }
+  {
+    // Alternate testing approach, taking advantage of the decimal parser.
+    for (int i = 0; i < 200; ++i) {
+      SCOPED_TRACE(i);
+      BigUnsigned<84> value_1(135u);
+      value_1.MultiplyByTenToTheNth(i);
+      BigUnsigned<84> value_2("135" + std::string(i, '0'));
+      EXPECT_EQ(value_1, value_2);
+    }
+  }
+}
+
+
+}  // namespace strings_internal
+}  // namespace absl
diff --git a/absl/strings/internal/charconv_parse.cc b/absl/strings/internal/charconv_parse.cc
new file mode 100644
index 0000000..f3c7232
--- /dev/null
+++ b/absl/strings/internal/charconv_parse.cc
@@ -0,0 +1,496 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/charconv_parse.h"
+#include "absl/strings/charconv.h"
+
+#include <cassert>
+#include <cstdint>
+#include <limits>
+
+#include "absl/strings/internal/memutil.h"
+
+namespace absl {
+namespace {
+
+// ParseFloat<10> will read the first 19 significant digits of the mantissa.
+// This number was chosen for multiple reasons.
+//
+// (a) First, for whatever integer type we choose to represent the mantissa, we
+// want to choose the largest possible number of decimal digits for that integer
+// type.  We are using uint64_t, which can express any 19-digit unsigned
+// integer.
+//
+// (b) Second, we need to parse enough digits that the binary value of any
+// mantissa we capture has more bits of resolution than the mantissa
+// representation in the target float.  Our algorithm requires at least 3 bits
+// of headway, but 19 decimal digits give a little more than that.
+//
+// The following static assertions verify the above comments:
+constexpr int kDecimalMantissaDigitsMax = 19;
+
+static_assert(std::numeric_limits<uint64_t>::digits10 ==
+                  kDecimalMantissaDigitsMax,
+              "(a) above");
+
+// IEEE doubles, which we assume in Abseil, have 53 binary bits of mantissa.
+static_assert(std::numeric_limits<double>::is_iec559, "IEEE double assumed");
+static_assert(std::numeric_limits<double>::radix == 2, "IEEE double fact");
+static_assert(std::numeric_limits<double>::digits == 53, "IEEE double fact");
+
+// The lowest valued 19-digit decimal mantissa we can read still contains
+// sufficient information to reconstruct a binary mantissa.
+static_assert(1000000000000000000u > (uint64_t(1) << (53 + 3)), "(b) above");
+
+// ParseFloat<16> will read the first 15 significant digits of the mantissa.
+//
+// Because a base-16-to-base-2 conversion can be done exactly, we do not need
+// to maximize the number of scanned hex digits to improve our conversion.  What
+// is required is to scan two more bits than the mantissa can represent, so that
+// we always round correctly.
+//
+// (One extra bit does not suffice to perform correct rounding, since a number
+// exactly halfway between two representable floats has unique rounding rules,
+// so we need to differentiate between a "halfway between" number and a "closer
+// to the larger value" number.)
+constexpr int kHexadecimalMantissaDigitsMax = 15;
+
+// The minimum number of significant bits that will be read from
+// kHexadecimalMantissaDigitsMax hex digits.  We must subtract by three, since
+// the most significant digit can be a "1", which only contributes a single
+// significant bit.
+constexpr int kGuaranteedHexadecimalMantissaBitPrecision =
+    4 * kHexadecimalMantissaDigitsMax - 3;
+
+static_assert(kGuaranteedHexadecimalMantissaBitPrecision >
+                  std::numeric_limits<double>::digits + 2,
+              "kHexadecimalMantissaDigitsMax too small");
+
+// We also impose a limit on the number of significant digits we will read from
+// an exponent, to avoid having to deal with integer overflow.  We use 9 for
+// this purpose.
+//
+// If we read a 9 digit exponent, the end result of the conversion will
+// necessarily be infinity or zero, depending on the sign of the exponent.
+// Therefore we can just drop extra digits on the floor without any extra
+// logic.
+constexpr int kDecimalExponentDigitsMax = 9;
+static_assert(std::numeric_limits<int>::digits10 >= kDecimalExponentDigitsMax,
+              "int type too small");
+
+// To avoid incredibly large inputs causing integer overflow for our exponent,
+// we impose an arbitrary but very large limit on the number of significant
+// digits we will accept.  The implementation refuses to match a string with
+// more consecutive significant mantissa digits than this.
+constexpr int kDecimalDigitLimit = 50000000;
+
+// Corresponding limit for hexadecimal digit inputs.  This is one fourth the
+// amount of kDecimalDigitLimit, since each dropped hexadecimal digit requires
+// a binary exponent adjustment of 4.
+constexpr int kHexadecimalDigitLimit = kDecimalDigitLimit / 4;
+
+// The largest exponent we can read is 999999999 (per
+// kDecimalExponentDigitsMax), and the largest exponent adjustment we can get
+// from dropped mantissa digits is 2 * kDecimalDigitLimit, and the sum of these
+// comfortably fits in an integer.
+//
+// We count kDecimalDigitLimit twice because there are independent limits for
+// numbers before and after the decimal point.  (In the case where there are no
+// significant digits before the decimal point, there are independent limits for
+// post-decimal-point leading zeroes and for significant digits.)
+static_assert(999999999 + 2 * kDecimalDigitLimit <
+                  std::numeric_limits<int>::max(),
+              "int type too small");
+static_assert(999999999 + 2 * (4 * kHexadecimalDigitLimit) <
+                  std::numeric_limits<int>::max(),
+              "int type too small");
+
+// Returns true if the provided bitfield allows parsing an exponent value
+// (e.g., "1.5e100").
+bool AllowExponent(chars_format flags) {
+  bool fixed = (flags & chars_format::fixed) == chars_format::fixed;
+  bool scientific =
+      (flags & chars_format::scientific) == chars_format::scientific;
+  return scientific || !fixed;
+}
+
+// Returns true if the provided bitfield requires an exponent value be present.
+bool RequireExponent(chars_format flags) {
+  bool fixed = (flags & chars_format::fixed) == chars_format::fixed;
+  bool scientific =
+      (flags & chars_format::scientific) == chars_format::scientific;
+  return scientific && !fixed;
+}
+
+const int8_t kAsciiToInt[256] = {
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 0,  1,  2,  3,  4,  5,  6,  7,  8,
+    9,  -1, -1, -1, -1, -1, -1, -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1};
+
+// Returns true if `ch` is a digit in the given base
+template <int base>
+bool IsDigit(char ch);
+
+// Converts a valid `ch` to its digit value in the given base.
+template <int base>
+unsigned ToDigit(char ch);
+
+// Returns true if `ch` is the exponent delimiter for the given base.
+template <int base>
+bool IsExponentCharacter(char ch);
+
+// Returns the maximum number of significant digits we will read for a float
+// in the given base.
+template <int base>
+constexpr int MantissaDigitsMax();
+
+// Returns the largest consecutive run of digits we will accept when parsing a
+// number in the given base.
+template <int base>
+constexpr int DigitLimit();
+
+// Returns the amount the exponent must be adjusted by for each dropped digit.
+// (For decimal this is 1, since the digits are in base 10 and the exponent base
+// is also 10, but for hexadecimal this is 4, since the digits are base 16 but
+// the exponent base is 2.)
+template <int base>
+constexpr int DigitMagnitude();
+
+template <>
+bool IsDigit<10>(char ch) {
+  return ch >= '0' && ch <= '9';
+}
+template <>
+bool IsDigit<16>(char ch) {
+  return kAsciiToInt[static_cast<unsigned char>(ch)] >= 0;
+}
+
+template <>
+unsigned ToDigit<10>(char ch) {
+  return ch - '0';
+}
+template <>
+unsigned ToDigit<16>(char ch) {
+  return kAsciiToInt[static_cast<unsigned char>(ch)];
+}
+
+template <>
+bool IsExponentCharacter<10>(char ch) {
+  return ch == 'e' || ch == 'E';
+}
+
+template <>
+bool IsExponentCharacter<16>(char ch) {
+  return ch == 'p' || ch == 'P';
+}
+
+template <>
+constexpr int MantissaDigitsMax<10>() {
+  return kDecimalMantissaDigitsMax;
+}
+template <>
+constexpr int MantissaDigitsMax<16>() {
+  return kHexadecimalMantissaDigitsMax;
+}
+
+template <>
+constexpr int DigitLimit<10>() {
+  return kDecimalDigitLimit;
+}
+template <>
+constexpr int DigitLimit<16>() {
+  return kHexadecimalDigitLimit;
+}
+
+template <>
+constexpr int DigitMagnitude<10>() {
+  return 1;
+}
+template <>
+constexpr int DigitMagnitude<16>() {
+  return 4;
+}
+
+// Reads decimal digits from [begin, end) into *out.  Returns the number of
+// digits consumed.
+//
+// After max_digits has been read, keeps consuming characters, but no longer
+// adjusts *out.  If a nonzero digit is dropped this way, *dropped_nonzero_digit
+// is set; otherwise, it is left unmodified.
+//
+// If no digits are matched, returns 0 and leaves *out unchanged.
+//
+// ConsumeDigits does not protect against overflow on *out; max_digits must
+// be chosen with respect to type T to avoid the possibility of overflow.
+template <int base, typename T>
+std::size_t ConsumeDigits(const char* begin, const char* end, int max_digits,
+                          T* out, bool* dropped_nonzero_digit) {
+  if (base == 10) {
+    assert(max_digits <= std::numeric_limits<T>::digits10);
+  } else if (base == 16) {
+    assert(max_digits * 4 <= std::numeric_limits<T>::digits);
+  }
+  const char* const original_begin = begin;
+  T accumulator = *out;
+  const char* significant_digits_end =
+      (end - begin > max_digits) ? begin + max_digits : end;
+  while (begin < significant_digits_end && IsDigit<base>(*begin)) {
+    // Do not guard against *out overflow; max_digits was chosen to avoid this.
+    // Do assert against it, to detect problems in debug builds.
+    auto digit = static_cast<T>(ToDigit<base>(*begin));
+    assert(accumulator * base >= accumulator);
+    accumulator *= base;
+    assert(accumulator + digit >= accumulator);
+    accumulator += digit;
+    ++begin;
+  }
+  bool dropped_nonzero = false;
+  while (begin < end && IsDigit<base>(*begin)) {
+    dropped_nonzero = dropped_nonzero || (*begin != '0');
+    ++begin;
+  }
+  if (dropped_nonzero && dropped_nonzero_digit != nullptr) {
+    *dropped_nonzero_digit = true;
+  }
+  *out = accumulator;
+  return begin - original_begin;
+}
+
+// Returns true if `v` is one of the chars allowed inside parentheses following
+// a NaN.
+bool IsNanChar(char v) {
+  return (v == '_') || (v >= '0' && v <= '9') || (v >= 'a' && v <= 'z') ||
+         (v >= 'A' && v <= 'Z');
+}
+
+// Checks the range [begin, end) for a strtod()-formatted infinity or NaN.  If
+// one is found, sets `out` appropriately and returns true.
+bool ParseInfinityOrNan(const char* begin, const char* end,
+                        strings_internal::ParsedFloat* out) {
+  if (end - begin < 3) {
+    return false;
+  }
+  switch (*begin) {
+    case 'i':
+    case 'I': {
+      // An infinity std::string consists of the characters "inf" or "infinity",
+      // case insensitive.
+      if (strings_internal::memcasecmp(begin + 1, "nf", 2) != 0) {
+        return false;
+      }
+      out->type = strings_internal::FloatType::kInfinity;
+      if (end - begin >= 8 &&
+          strings_internal::memcasecmp(begin + 3, "inity", 5) == 0) {
+        out->end = begin + 8;
+      } else {
+        out->end = begin + 3;
+      }
+      return true;
+    }
+    case 'n':
+    case 'N': {
+      // A NaN consists of the characters "nan", case insensitive, optionally
+      // followed by a parenthesized sequence of zero or more alphanumeric
+      // characters and/or underscores.
+      if (strings_internal::memcasecmp(begin + 1, "an", 2) != 0) {
+        return false;
+      }
+      out->type = strings_internal::FloatType::kNan;
+      out->end = begin + 3;
+      // NaN is allowed to be followed by a parenthesized std::string, consisting of
+      // only the characters [a-zA-Z0-9_].  Match that if it's present.
+      begin += 3;
+      if (begin < end && *begin == '(') {
+        const char* nan_begin = begin + 1;
+        while (nan_begin < end && IsNanChar(*nan_begin)) {
+          ++nan_begin;
+        }
+        if (nan_begin < end && *nan_begin == ')') {
+          // We found an extra NaN specifier range
+          out->subrange_begin = begin + 1;
+          out->subrange_end = nan_begin;
+          out->end = nan_begin + 1;
+        }
+      }
+      return true;
+    }
+    default:
+      return false;
+  }
+}
+}  // namespace
+
+namespace strings_internal {
+
+template <int base>
+strings_internal::ParsedFloat ParseFloat(const char* begin, const char* end,
+                                         chars_format format_flags) {
+  strings_internal::ParsedFloat result;
+
+  // Exit early if we're given an empty range.
+  if (begin == end) return result;
+
+  // Handle the infinity and NaN cases.
+  if (ParseInfinityOrNan(begin, end, &result)) {
+    return result;
+  }
+
+  const char* const mantissa_begin = begin;
+  while (begin < end && *begin == '0') {
+    ++begin;  // skip leading zeros
+  }
+  uint64_t mantissa = 0;
+
+  int exponent_adjustment = 0;
+  bool mantissa_is_inexact = false;
+  std::size_t pre_decimal_digits = ConsumeDigits<base>(
+      begin, end, MantissaDigitsMax<base>(), &mantissa, &mantissa_is_inexact);
+  begin += pre_decimal_digits;
+  int digits_left;
+  if (pre_decimal_digits >= DigitLimit<base>()) {
+    // refuse to parse pathological inputs
+    return result;
+  } else if (pre_decimal_digits > MantissaDigitsMax<base>()) {
+    // We dropped some non-fraction digits on the floor.  Adjust our exponent
+    // to compensate.
+    exponent_adjustment =
+        static_cast<int>(pre_decimal_digits - MantissaDigitsMax<base>());
+    digits_left = 0;
+  } else {
+    digits_left =
+        static_cast<int>(MantissaDigitsMax<base>() - pre_decimal_digits);
+  }
+  if (begin < end && *begin == '.') {
+    ++begin;
+    if (mantissa == 0) {
+      // If we haven't seen any nonzero digits yet, keep skipping zeros.  We
+      // have to adjust the exponent to reflect the changed place value.
+      const char* begin_zeros = begin;
+      while (begin < end && *begin == '0') {
+        ++begin;
+      }
+      std::size_t zeros_skipped = begin - begin_zeros;
+      if (zeros_skipped >= DigitLimit<base>()) {
+        // refuse to parse pathological inputs
+        return result;
+      }
+      exponent_adjustment -= static_cast<int>(zeros_skipped);
+    }
+    std::size_t post_decimal_digits = ConsumeDigits<base>(
+        begin, end, digits_left, &mantissa, &mantissa_is_inexact);
+    begin += post_decimal_digits;
+
+    // Since `mantissa` is an integer, each significant digit we read after
+    // the decimal point requires an adjustment to the exponent. "1.23e0" will
+    // be stored as `mantissa` == 123 and `exponent` == -2 (that is,
+    // "123e-2").
+    if (post_decimal_digits >= DigitLimit<base>()) {
+      // refuse to parse pathological inputs
+      return result;
+    } else if (post_decimal_digits > digits_left) {
+      exponent_adjustment -= digits_left;
+    } else {
+      exponent_adjustment -= post_decimal_digits;
+    }
+  }
+  // If we've found no mantissa whatsoever, this isn't a number.
+  if (mantissa_begin == begin) {
+    return result;
+  }
+  // A bare "." doesn't count as a mantissa either.
+  if (begin - mantissa_begin == 1 && *mantissa_begin == '.') {
+    return result;
+  }
+
+  if (mantissa_is_inexact) {
+    // We dropped significant digits on the floor.  Handle this appropriately.
+    if (base == 10) {
+      // If we truncated significant decimal digits, store the full range of the
+      // mantissa for future big integer math for exact rounding.
+      result.subrange_begin = mantissa_begin;
+      result.subrange_end = begin;
+    } else if (base == 16) {
+      // If we truncated hex digits, reflect this fact by setting the low
+      // ("sticky") bit.  This allows for correct rounding in all cases.
+      mantissa |= 1;
+    }
+  }
+  result.mantissa = mantissa;
+
+  const char* const exponent_begin = begin;
+  result.literal_exponent = 0;
+  bool found_exponent = false;
+  if (AllowExponent(format_flags) && begin < end &&
+      IsExponentCharacter<base>(*begin)) {
+    bool negative_exponent = false;
+    ++begin;
+    if (begin < end && *begin == '-') {
+      negative_exponent = true;
+      ++begin;
+    } else if (begin < end && *begin == '+') {
+      ++begin;
+    }
+    const char* const exponent_digits_begin = begin;
+    // Exponent is always expressed in decimal, even for hexadecimal floats.
+    begin += ConsumeDigits<10>(begin, end, kDecimalExponentDigitsMax,
+                               &result.literal_exponent, nullptr);
+    if (begin == exponent_digits_begin) {
+      // there were no digits where we expected an exponent.  We failed to read
+      // an exponent and should not consume the 'e' after all.  Rewind 'begin'.
+      found_exponent = false;
+      begin = exponent_begin;
+    } else {
+      found_exponent = true;
+      if (negative_exponent) {
+        result.literal_exponent = -result.literal_exponent;
+      }
+    }
+  }
+
+  if (!found_exponent && RequireExponent(format_flags)) {
+    // Provided flags required an exponent, but none was found.  This results
+    // in a failure to scan.
+    return result;
+  }
+
+  // Success!
+  result.type = strings_internal::FloatType::kNumber;
+  if (result.mantissa > 0) {
+    result.exponent = result.literal_exponent +
+                      (DigitMagnitude<base>() * exponent_adjustment);
+  } else {
+    result.exponent = 0;
+  }
+  result.end = begin;
+  return result;
+}
+
+template ParsedFloat ParseFloat<10>(const char* begin, const char* end,
+                                    chars_format format_flags);
+template ParsedFloat ParseFloat<16>(const char* begin, const char* end,
+                                    chars_format format_flags);
+
+}  // namespace strings_internal
+}  // namespace absl
diff --git a/absl/strings/internal/charconv_parse.h b/absl/strings/internal/charconv_parse.h
new file mode 100644
index 0000000..44d06b2
--- /dev/null
+++ b/absl/strings/internal/charconv_parse.h
@@ -0,0 +1,96 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_INTERNAL_CHARCONV_PARSE_H_
+#define ABSL_STRINGS_INTERNAL_CHARCONV_PARSE_H_
+
+#include <cstdint>
+
+#include "absl/strings/charconv.h"
+
+namespace absl {
+namespace strings_internal {
+
+// Enum indicating whether a parsed float is a number or special value.
+enum class FloatType { kNumber, kInfinity, kNan };
+
+// The decomposed parts of a parsed `float` or `double`.
+struct ParsedFloat {
+  // Representation of the parsed mantissa, with the decimal point adjusted to
+  // make it an integer.
+  //
+  // During decimal scanning, this contains 19 significant digits worth of
+  // mantissa value.  If digits beyond this point are found, they
+  // are truncated, and if any of these dropped digits are nonzero, then
+  // `mantissa` is inexact, and the full mantissa is stored in [subrange_begin,
+  // subrange_end).
+  //
+  // During hexadecimal scanning, this contains 15 significant hex digits worth
+  // of mantissa value.  Digits beyond this point are sticky -- they are
+  // truncated, but if any dropped digits are nonzero, the low bit of mantissa
+  // will be set.  (This allows for precise rounding, and avoids the need
+  // to store the full mantissa in [subrange_begin, subrange_end).)
+  uint64_t mantissa = 0;
+
+  // Floating point expontent.  This reflects any decimal point adjustments and
+  // any truncated digits from the mantissa.  The absolute value of the parsed
+  // number is represented by mantissa * (base ** exponent), where base==10 for
+  // decimal floats, and base==2 for hexadecimal floats.
+  int exponent = 0;
+
+  // The literal exponent value scanned from the input, or 0 if none was
+  // present.  This does not reflect any adjustments applied to mantissa.
+  int literal_exponent = 0;
+
+  // The type of number scanned.
+  FloatType type = FloatType::kNumber;
+
+  // When non-null, [subrange_begin, subrange_end) marks a range of characters
+  // that require further processing.  The meaning is dependent on float type.
+  // If type == kNumber and this is set, this is a "wide input": the input
+  // mantissa contained more than 19 digits.  The range contains the full
+  // mantissa.  It plus `literal_exponent` need to be examined to find the best
+  // floating point match.
+  // If type == kNan and this is set, the range marks the contents of a
+  // matched parenthesized character region after the NaN.
+  const char* subrange_begin = nullptr;
+  const char* subrange_end = nullptr;
+
+  // One-past-the-end of the successfully parsed region, or nullptr if no
+  // matching pattern was found.
+  const char* end = nullptr;
+};
+
+// Read the floating point number in the provided range, and populate
+// ParsedFloat accordingly.
+//
+// format_flags is a bitmask value specifying what patterns this API will match.
+// `scientific` and `fixed`  are honored per std::from_chars rules
+// ([utility.from.chars], C++17): if exactly one of these bits is set, then an
+// exponent is required, or dislallowed, respectively.
+//
+// Template parameter `base` must be either 10 or 16.  For base 16, a "0x" is
+// *not* consumed.  The `hex` bit from format_flags is ignored by ParseFloat.
+template <int base>
+ParsedFloat ParseFloat(const char* begin, const char* end,
+                       absl::chars_format format_flags);
+
+extern template ParsedFloat ParseFloat<10>(const char* begin, const char* end,
+                                           absl::chars_format format_flags);
+extern template ParsedFloat ParseFloat<16>(const char* begin, const char* end,
+                                           absl::chars_format format_flags);
+
+}  // namespace strings_internal
+}  // namespace absl
+#endif  // ABSL_STRINGS_INTERNAL_CHARCONV_PARSE_H_
diff --git a/absl/strings/internal/charconv_parse_test.cc b/absl/strings/internal/charconv_parse_test.cc
new file mode 100644
index 0000000..9511c98
--- /dev/null
+++ b/absl/strings/internal/charconv_parse_test.cc
@@ -0,0 +1,357 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/charconv_parse.h"
+
+#include <string>
+#include <utility>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/strings/str_cat.h"
+
+using absl::chars_format;
+using absl::strings_internal::FloatType;
+using absl::strings_internal::ParsedFloat;
+using absl::strings_internal::ParseFloat;
+
+namespace {
+
+// Check that a given string input is parsed to the expected mantissa and
+// exponent.
+//
+// Input string `s` must contain a '$' character.  It marks the end of the
+// characters that should be consumed by the match.  It is stripped from the
+// input to ParseFloat.
+//
+// If input string `s` contains '[' and ']' characters, these mark the region
+// of characters that should be marked as the "subrange".  For NaNs, this is
+// the location of the extended NaN string.  For numbers, this is the location
+// of the full, over-large mantissa.
+template <int base>
+void ExpectParsedFloat(std::string s, absl::chars_format format_flags,
+                       FloatType expected_type, uint64_t expected_mantissa,
+                       int expected_exponent,
+                       int expected_literal_exponent = -999) {
+  SCOPED_TRACE(s);
+
+  int begin_subrange = -1;
+  int end_subrange = -1;
+  // If s contains '[' and ']', then strip these characters and set the subrange
+  // indices appropriately.
+  std::string::size_type open_bracket_pos = s.find('[');
+  if (open_bracket_pos != std::string::npos) {
+    begin_subrange = static_cast<int>(open_bracket_pos);
+    s.replace(open_bracket_pos, 1, "");
+    std::string::size_type close_bracket_pos = s.find(']');
+    ABSL_RAW_CHECK(close_bracket_pos != absl::string_view::npos,
+                   "Test input contains [ without matching ]");
+    end_subrange = static_cast<int>(close_bracket_pos);
+    s.replace(close_bracket_pos, 1, "");
+  }
+  const std::string::size_type expected_characters_matched = s.find('$');
+  ABSL_RAW_CHECK(expected_characters_matched != std::string::npos,
+                 "Input std::string must contain $");
+  s.replace(expected_characters_matched, 1, "");
+
+  ParsedFloat parsed =
+      ParseFloat<base>(s.data(), s.data() + s.size(), format_flags);
+
+  EXPECT_NE(parsed.end, nullptr);
+  if (parsed.end == nullptr) {
+    return;  // The following tests are not useful if we fully failed to parse
+  }
+  EXPECT_EQ(parsed.type, expected_type);
+  if (begin_subrange == -1) {
+    EXPECT_EQ(parsed.subrange_begin, nullptr);
+    EXPECT_EQ(parsed.subrange_end, nullptr);
+  } else {
+    EXPECT_EQ(parsed.subrange_begin, s.data() + begin_subrange);
+    EXPECT_EQ(parsed.subrange_end, s.data() + end_subrange);
+  }
+  if (parsed.type == FloatType::kNumber) {
+    EXPECT_EQ(parsed.mantissa, expected_mantissa);
+    EXPECT_EQ(parsed.exponent, expected_exponent);
+    if (expected_literal_exponent != -999) {
+      EXPECT_EQ(parsed.literal_exponent, expected_literal_exponent);
+    }
+  }
+  auto characters_matched = static_cast<int>(parsed.end - s.data());
+  EXPECT_EQ(characters_matched, expected_characters_matched);
+}
+
+// Check that a given string input is parsed to the expected mantissa and
+// exponent.
+//
+// Input string `s` must contain a '$' character.  It marks the end of the
+// characters that were consumed by the match.
+template <int base>
+void ExpectNumber(std::string s, absl::chars_format format_flags,
+                  uint64_t expected_mantissa, int expected_exponent,
+                  int expected_literal_exponent = -999) {
+  ExpectParsedFloat<base>(std::move(s), format_flags, FloatType::kNumber,
+                          expected_mantissa, expected_exponent,
+                          expected_literal_exponent);
+}
+
+// Check that a given string input is parsed to the given special value.
+//
+// This tests against both number bases, since infinities and NaNs have
+// identical representations in both modes.
+void ExpectSpecial(const std::string& s, absl::chars_format format_flags,
+                   FloatType type) {
+  ExpectParsedFloat<10>(s, format_flags, type, 0, 0);
+  ExpectParsedFloat<16>(s, format_flags, type, 0, 0);
+}
+
+// Check that a given input string is not matched by Float.
+template <int base>
+void ExpectFailedParse(absl::string_view s, absl::chars_format format_flags) {
+  ParsedFloat parsed =
+      ParseFloat<base>(s.data(), s.data() + s.size(), format_flags);
+  EXPECT_EQ(parsed.end, nullptr);
+}
+
+TEST(ParseFloat, SimpleValue) {
+  // Test that various forms of floating point numbers all parse correctly.
+  ExpectNumber<10>("1.23456789e5$", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("1.23456789e+5$", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("1.23456789E5$", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("1.23456789e05$", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("123.456789e3$", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("0.000123456789e9$", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("123456.789$", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("123456789e-3$", chars_format::general, 123456789, -3);
+
+  ExpectNumber<16>("1.234abcdefp28$", chars_format::general, 0x1234abcdef, -8);
+  ExpectNumber<16>("1.234abcdefp+28$", chars_format::general, 0x1234abcdef, -8);
+  ExpectNumber<16>("1.234ABCDEFp28$", chars_format::general, 0x1234abcdef, -8);
+  ExpectNumber<16>("1.234AbCdEfP0028$", chars_format::general, 0x1234abcdef,
+                   -8);
+  ExpectNumber<16>("123.4abcdefp20$", chars_format::general, 0x1234abcdef, -8);
+  ExpectNumber<16>("0.0001234abcdefp44$", chars_format::general, 0x1234abcdef,
+                   -8);
+  ExpectNumber<16>("1234abcd.ef$", chars_format::general, 0x1234abcdef, -8);
+  ExpectNumber<16>("1234abcdefp-8$", chars_format::general, 0x1234abcdef, -8);
+
+  // ExpectNumber does not attempt to drop trailing zeroes.
+  ExpectNumber<10>("0001.2345678900e005$", chars_format::general, 12345678900,
+                   -5);
+  ExpectNumber<16>("0001.234abcdef000p28$", chars_format::general,
+                   0x1234abcdef000, -20);
+
+  // Ensure non-matching characters after a number are ignored, even when they
+  // look like potentially matching characters.
+  ExpectNumber<10>("1.23456789e5$   ", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("1.23456789e5$e5e5", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("1.23456789e5$.25", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("1.23456789e5$-", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("1.23456789e5$PUPPERS!!!", chars_format::general, 123456789,
+                   -3);
+  ExpectNumber<10>("123456.789$efghij", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("123456.789$e", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("123456.789$p5", chars_format::general, 123456789, -3);
+  ExpectNumber<10>("123456.789$.10", chars_format::general, 123456789, -3);
+
+  ExpectNumber<16>("1.234abcdefp28$   ", chars_format::general, 0x1234abcdef,
+                   -8);
+  ExpectNumber<16>("1.234abcdefp28$p28", chars_format::general, 0x1234abcdef,
+                   -8);
+  ExpectNumber<16>("1.234abcdefp28$.125", chars_format::general, 0x1234abcdef,
+                   -8);
+  ExpectNumber<16>("1.234abcdefp28$-", chars_format::general, 0x1234abcdef, -8);
+  ExpectNumber<16>("1.234abcdefp28$KITTEHS!!!", chars_format::general,
+                   0x1234abcdef, -8);
+  ExpectNumber<16>("1234abcd.ef$ghijk", chars_format::general, 0x1234abcdef,
+                   -8);
+  ExpectNumber<16>("1234abcd.ef$p", chars_format::general, 0x1234abcdef, -8);
+  ExpectNumber<16>("1234abcd.ef$.10", chars_format::general, 0x1234abcdef, -8);
+
+  // Ensure we can read a full resolution mantissa without overflow.
+  ExpectNumber<10>("9999999999999999999$", chars_format::general,
+                   9999999999999999999u, 0);
+  ExpectNumber<16>("fffffffffffffff$", chars_format::general,
+                   0xfffffffffffffffu, 0);
+
+  // Check that zero is consistently read.
+  ExpectNumber<10>("0$", chars_format::general, 0, 0);
+  ExpectNumber<16>("0$", chars_format::general, 0, 0);
+  ExpectNumber<10>("000000000000000000000000000000000000000$",
+                   chars_format::general, 0, 0);
+  ExpectNumber<16>("000000000000000000000000000000000000000$",
+                   chars_format::general, 0, 0);
+  ExpectNumber<10>("0000000000000000000000.000000000000000000$",
+                   chars_format::general, 0, 0);
+  ExpectNumber<16>("0000000000000000000000.000000000000000000$",
+                   chars_format::general, 0, 0);
+  ExpectNumber<10>("0.00000000000000000000000000000000e123456$",
+                   chars_format::general, 0, 0);
+  ExpectNumber<16>("0.00000000000000000000000000000000p123456$",
+                   chars_format::general, 0, 0);
+}
+
+TEST(ParseFloat, LargeDecimalMantissa) {
+  // After 19 significant decimal digits in the mantissa, ParsedFloat will
+  // truncate additional digits.  We need to test that:
+  //   1) the truncation to 19 digits happens
+  //   2) the returned exponent reflects the dropped significant digits
+  //   3) a correct literal_exponent is set
+  //
+  // If and only if a significant digit is found after 19 digits, then the
+  // entirety of the mantissa in case the exact value is needed to make a
+  // rounding decision.  The [ and ] characters below denote where such a
+  // subregion was marked by by ParseFloat.  They are not part of the input.
+
+  // Mark a capture group only if a dropped digit is significant (nonzero).
+  ExpectNumber<10>("100000000000000000000000000$", chars_format::general,
+                   1000000000000000000,
+                   /* adjusted exponent */ 8);
+
+  ExpectNumber<10>("123456789123456789100000000$", chars_format::general,
+                   1234567891234567891,
+                   /* adjusted exponent */ 8);
+
+  ExpectNumber<10>("[123456789123456789123456789]$", chars_format::general,
+                   1234567891234567891,
+                   /* adjusted exponent */ 8,
+                   /* literal exponent */ 0);
+
+  ExpectNumber<10>("[123456789123456789100000009]$", chars_format::general,
+                   1234567891234567891,
+                   /* adjusted exponent */ 8,
+                   /* literal exponent */ 0);
+
+  ExpectNumber<10>("[123456789123456789120000000]$", chars_format::general,
+                   1234567891234567891,
+                   /* adjusted exponent */ 8,
+                   /* literal exponent */ 0);
+
+  // Leading zeroes should not count towards the 19 significant digit limit
+  ExpectNumber<10>("[00000000123456789123456789123456789]$",
+                   chars_format::general, 1234567891234567891,
+                   /* adjusted exponent */ 8,
+                   /* literal exponent */ 0);
+
+  ExpectNumber<10>("00000000123456789123456789100000000$",
+                   chars_format::general, 1234567891234567891,
+                   /* adjusted exponent */ 8);
+
+  // Truncated digits after the decimal point should not cause a further
+  // exponent adjustment.
+  ExpectNumber<10>("1.234567891234567891e123$", chars_format::general,
+                   1234567891234567891, 105);
+  ExpectNumber<10>("[1.23456789123456789123456789]e123$", chars_format::general,
+                   1234567891234567891,
+                   /* adjusted exponent */ 105,
+                   /* literal exponent */ 123);
+
+  // Ensure we truncate, and not round.  (The from_chars algorithm we use
+  // depends on our guess missing low, if it misses, so we need the rounding
+  // error to be downward.)
+  ExpectNumber<10>("[1999999999999999999999]$", chars_format::general,
+                   1999999999999999999,
+                   /* adjusted exponent */ 3,
+                   /* literal exponent */ 0);
+}
+
+TEST(ParseFloat, LargeHexadecimalMantissa) {
+  // After 15 significant hex digits in the mantissa, ParsedFloat will treat
+  // additional digits as sticky,  We need to test that:
+  //   1) The truncation to 15 digits happens
+  //   2) The returned exponent reflects the dropped significant digits
+  //   3) If a nonzero digit is dropped, the low bit of mantissa is set.
+
+  ExpectNumber<16>("123456789abcdef123456789abcdef$", chars_format::general,
+                   0x123456789abcdef, 60);
+
+  // Leading zeroes should not count towards the 15 significant digit limit
+  ExpectNumber<16>("000000123456789abcdef123456789abcdef$",
+                   chars_format::general, 0x123456789abcdef, 60);
+
+  // Truncated digits after the radix point should not cause a further
+  // exponent adjustment.
+  ExpectNumber<16>("1.23456789abcdefp100$", chars_format::general,
+                   0x123456789abcdef, 44);
+  ExpectNumber<16>("1.23456789abcdef123456789abcdefp100$",
+                   chars_format::general, 0x123456789abcdef, 44);
+
+  // test sticky digit behavior.  The low bit should be set iff any dropped
+  // digit is nonzero.
+  ExpectNumber<16>("123456789abcdee123456789abcdee$", chars_format::general,
+                   0x123456789abcdef, 60);
+  ExpectNumber<16>("123456789abcdee000000000000001$", chars_format::general,
+                   0x123456789abcdef, 60);
+  ExpectNumber<16>("123456789abcdee000000000000000$", chars_format::general,
+                   0x123456789abcdee, 60);
+}
+
+TEST(ParseFloat, ScientificVsFixed) {
+  // In fixed mode, an exponent is never matched (but the remainder of the
+  // number will be matched.)
+  ExpectNumber<10>("1.23456789$e5", chars_format::fixed, 123456789, -8);
+  ExpectNumber<10>("123456.789$", chars_format::fixed, 123456789, -3);
+  ExpectNumber<16>("1.234abcdef$p28", chars_format::fixed, 0x1234abcdef, -36);
+  ExpectNumber<16>("1234abcd.ef$", chars_format::fixed, 0x1234abcdef, -8);
+
+  // In scientific mode, numbers don't match *unless* they have an exponent.
+  ExpectNumber<10>("1.23456789e5$", chars_format::scientific, 123456789, -3);
+  ExpectFailedParse<10>("-123456.789$", chars_format::scientific);
+  ExpectNumber<16>("1.234abcdefp28$", chars_format::scientific, 0x1234abcdef,
+                   -8);
+  ExpectFailedParse<16>("1234abcd.ef$", chars_format::scientific);
+}
+
+TEST(ParseFloat, Infinity) {
+  ExpectFailedParse<10>("in", chars_format::general);
+  ExpectFailedParse<16>("in", chars_format::general);
+  ExpectFailedParse<10>("inx", chars_format::general);
+  ExpectFailedParse<16>("inx", chars_format::general);
+  ExpectSpecial("inf$", chars_format::general, FloatType::kInfinity);
+  ExpectSpecial("Inf$", chars_format::general, FloatType::kInfinity);
+  ExpectSpecial("INF$", chars_format::general, FloatType::kInfinity);
+  ExpectSpecial("inf$inite", chars_format::general, FloatType::kInfinity);
+  ExpectSpecial("iNfInItY$", chars_format::general, FloatType::kInfinity);
+  ExpectSpecial("infinity$!!!", chars_format::general, FloatType::kInfinity);
+}
+
+TEST(ParseFloat, NaN) {
+  ExpectFailedParse<10>("na", chars_format::general);
+  ExpectFailedParse<16>("na", chars_format::general);
+  ExpectFailedParse<10>("nah", chars_format::general);
+  ExpectFailedParse<16>("nah", chars_format::general);
+  ExpectSpecial("nan$", chars_format::general, FloatType::kNan);
+  ExpectSpecial("NaN$", chars_format::general, FloatType::kNan);
+  ExpectSpecial("nAn$", chars_format::general, FloatType::kNan);
+  ExpectSpecial("NAN$", chars_format::general, FloatType::kNan);
+  ExpectSpecial("NaN$aNaNaNaNaBatman!", chars_format::general, FloatType::kNan);
+
+  // A parenthesized sequence of the characters [a-zA-Z0-9_] is allowed to
+  // appear after an NaN.  Check that this is allowed, and that the correct
+  // characters are grouped.
+  //
+  // (The characters [ and ] in the pattern below delimit the expected matched
+  // subgroup; they are not part of the input passed to ParseFloat.)
+  ExpectSpecial("nan([0xabcdef])$", chars_format::general, FloatType::kNan);
+  ExpectSpecial("nan([0xabcdef])$...", chars_format::general, FloatType::kNan);
+  ExpectSpecial("nan([0xabcdef])$)...", chars_format::general, FloatType::kNan);
+  ExpectSpecial("nan([])$", chars_format::general, FloatType::kNan);
+  ExpectSpecial("nan([aAzZ09_])$", chars_format::general, FloatType::kNan);
+  // If the subgroup contains illegal characters, don't match it at all.
+  ExpectSpecial("nan$(bad-char)", chars_format::general, FloatType::kNan);
+  // Also cope with a missing close paren.
+  ExpectSpecial("nan$(0xabcdef", chars_format::general, FloatType::kNan);
+}
+
+}  // namespace
diff --git a/absl/strings/internal/escaping_test_common.h b/absl/strings/internal/escaping_test_common.h
new file mode 100644
index 0000000..bd80303
--- /dev/null
+++ b/absl/strings/internal/escaping_test_common.h
@@ -0,0 +1,131 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This test contains common things needed by both escaping_test.cc and
+// escaping_benchmark.cc.
+
+#ifndef ABSL_STRINGS_INTERNAL_ESCAPING_TEST_COMMON_H_
+#define ABSL_STRINGS_INTERNAL_ESCAPING_TEST_COMMON_H_
+
+#include <array>
+#include "absl/strings/string_view.h"
+
+namespace absl {
+namespace strings_internal {
+
+struct base64_testcase {
+  absl::string_view plaintext;
+  absl::string_view cyphertext;
+};
+
+inline const std::array<base64_testcase, 5>& base64_strings() {
+  static const std::array<base64_testcase, 5> testcase{{
+      // Some google quotes
+      // Cyphertext created with "uuencode (GNU sharutils) 4.6.3"
+      // (Note that we're testing the websafe encoding, though, so if
+      // you add messages, be sure to run "tr -- '+/' '-_'" on the output)
+      { "I was always good at math and science, and I never realized "
+        "that was unusual or somehow undesirable. So one of the things "
+        "I care a lot about is helping to remove that stigma, "
+        "to show girls that you can be feminine, you can like the things "
+        "that girls like, but you can also be really good at technology. "
+        "You can be really good at building things."
+        " - Marissa Meyer, Newsweek, 2010-12-22" "\n",
+
+        "SSB3YXMgYWx3YXlzIGdvb2QgYXQgbWF0aCBhbmQgc2NpZW5jZSwgYW5kIEkg"
+        "bmV2ZXIgcmVhbGl6ZWQgdGhhdCB3YXMgdW51c3VhbCBvciBzb21laG93IHVu"
+        "ZGVzaXJhYmxlLiBTbyBvbmUgb2YgdGhlIHRoaW5ncyBJIGNhcmUgYSBsb3Qg"
+        "YWJvdXQgaXMgaGVscGluZyB0byByZW1vdmUgdGhhdCBzdGlnbWEsIHRvIHNo"
+        "b3cgZ2lybHMgdGhhdCB5b3UgY2FuIGJlIGZlbWluaW5lLCB5b3UgY2FuIGxp"
+        "a2UgdGhlIHRoaW5ncyB0aGF0IGdpcmxzIGxpa2UsIGJ1dCB5b3UgY2FuIGFs"
+        "c28gYmUgcmVhbGx5IGdvb2QgYXQgdGVjaG5vbG9neS4gWW91IGNhbiBiZSBy"
+        "ZWFsbHkgZ29vZCBhdCBidWlsZGluZyB0aGluZ3MuIC0gTWFyaXNzYSBNZXll"
+        "ciwgTmV3c3dlZWssIDIwMTAtMTItMjIK" },
+
+      { "Typical first year for a new cluster: "
+        "~0.5 overheating "
+        "~1 PDU failure "
+        "~1 rack-move "
+        "~1 network rewiring "
+        "~20 rack failures "
+        "~5 racks go wonky "
+        "~8 network maintenances "
+        "~12 router reloads "
+        "~3 router failures "
+        "~dozens of minor 30-second blips for dns "
+        "~1000 individual machine failures "
+        "~thousands of hard drive failures "
+        "slow disks, bad memory, misconfigured machines, flaky machines, etc."
+        " - Jeff Dean, The Joys of Real Hardware" "\n",
+
+        "VHlwaWNhbCBmaXJzdCB5ZWFyIGZvciBhIG5ldyBjbHVzdGVyOiB-MC41IG92"
+        "ZXJoZWF0aW5nIH4xIFBEVSBmYWlsdXJlIH4xIHJhY2stbW92ZSB-MSBuZXR3"
+        "b3JrIHJld2lyaW5nIH4yMCByYWNrIGZhaWx1cmVzIH41IHJhY2tzIGdvIHdv"
+        "bmt5IH44IG5ldHdvcmsgbWFpbnRlbmFuY2VzIH4xMiByb3V0ZXIgcmVsb2Fk"
+        "cyB-MyByb3V0ZXIgZmFpbHVyZXMgfmRvemVucyBvZiBtaW5vciAzMC1zZWNv"
+        "bmQgYmxpcHMgZm9yIGRucyB-MTAwMCBpbmRpdmlkdWFsIG1hY2hpbmUgZmFp"
+        "bHVyZXMgfnRob3VzYW5kcyBvZiBoYXJkIGRyaXZlIGZhaWx1cmVzIHNsb3cg"
+        "ZGlza3MsIGJhZCBtZW1vcnksIG1pc2NvbmZpZ3VyZWQgbWFjaGluZXMsIGZs"
+        "YWt5IG1hY2hpbmVzLCBldGMuIC0gSmVmZiBEZWFuLCBUaGUgSm95cyBvZiBS"
+        "ZWFsIEhhcmR3YXJlCg" },
+
+      { "I'm the head of the webspam team at Google.  "
+        "That means that if you type your name into Google and get porn back, "
+        "it's my fault. Unless you're a porn star, in which case porn is a "
+        "completely reasonable response."
+        " - Matt Cutts, Google Plus" "\n",
+
+        "SSdtIHRoZSBoZWFkIG9mIHRoZSB3ZWJzcGFtIHRlYW0gYXQgR29vZ2xlLiAg"
+        "VGhhdCBtZWFucyB0aGF0IGlmIHlvdSB0eXBlIHlvdXIgbmFtZSBpbnRvIEdv"
+        "b2dsZSBhbmQgZ2V0IHBvcm4gYmFjaywgaXQncyBteSBmYXVsdC4gVW5sZXNz"
+        "IHlvdSdyZSBhIHBvcm4gc3RhciwgaW4gd2hpY2ggY2FzZSBwb3JuIGlzIGEg"
+        "Y29tcGxldGVseSByZWFzb25hYmxlIHJlc3BvbnNlLiAtIE1hdHQgQ3V0dHMs"
+        "IEdvb2dsZSBQbHVzCg" },
+
+      { "It will still be a long time before machines approach human "
+        "intelligence. "
+        "But luckily, machines don't actually have to be intelligent; "
+        "they just have to fake it. Access to a wealth of information, "
+        "combined with a rudimentary decision-making capacity, "
+        "can often be almost as useful. Of course, the results are better yet "
+        "when coupled with intelligence. A reference librarian with access to "
+        "a good search engine is a formidable tool."
+        " - Craig Silverstein, Siemens Pictures of the Future, Spring 2004"
+        "\n",
+
+        "SXQgd2lsbCBzdGlsbCBiZSBhIGxvbmcgdGltZSBiZWZvcmUgbWFjaGluZXMg"
+        "YXBwcm9hY2ggaHVtYW4gaW50ZWxsaWdlbmNlLiBCdXQgbHVja2lseSwgbWFj"
+        "aGluZXMgZG9uJ3QgYWN0dWFsbHkgaGF2ZSB0byBiZSBpbnRlbGxpZ2VudDsg"
+        "dGhleSBqdXN0IGhhdmUgdG8gZmFrZSBpdC4gQWNjZXNzIHRvIGEgd2VhbHRo"
+        "IG9mIGluZm9ybWF0aW9uLCBjb21iaW5lZCB3aXRoIGEgcnVkaW1lbnRhcnkg"
+        "ZGVjaXNpb24tbWFraW5nIGNhcGFjaXR5LCBjYW4gb2Z0ZW4gYmUgYWxtb3N0"
+        "IGFzIHVzZWZ1bC4gT2YgY291cnNlLCB0aGUgcmVzdWx0cyBhcmUgYmV0dGVy"
+        "IHlldCB3aGVuIGNvdXBsZWQgd2l0aCBpbnRlbGxpZ2VuY2UuIEEgcmVmZXJl"
+        "bmNlIGxpYnJhcmlhbiB3aXRoIGFjY2VzcyB0byBhIGdvb2Qgc2VhcmNoIGVu"
+        "Z2luZSBpcyBhIGZvcm1pZGFibGUgdG9vbC4gLSBDcmFpZyBTaWx2ZXJzdGVp"
+        "biwgU2llbWVucyBQaWN0dXJlcyBvZiB0aGUgRnV0dXJlLCBTcHJpbmcgMjAw"
+        "NAo" },
+
+      // Degenerate edge case
+      { "",
+        "" },
+  }};
+
+  return testcase;
+}
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_ESCAPING_TEST_COMMON_H_
diff --git a/absl/strings/internal/memutil.cc b/absl/strings/internal/memutil.cc
new file mode 100644
index 0000000..77aa63c
--- /dev/null
+++ b/absl/strings/internal/memutil.cc
@@ -0,0 +1,110 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/memutil.h"
+
+#include <cstdlib>
+
+namespace absl {
+namespace strings_internal {
+
+int memcasecmp(const char* s1, const char* s2, size_t len) {
+  const unsigned char* us1 = reinterpret_cast<const unsigned char*>(s1);
+  const unsigned char* us2 = reinterpret_cast<const unsigned char*>(s2);
+
+  for (size_t i = 0; i < len; i++) {
+    const int diff =
+        int{static_cast<unsigned char>(absl::ascii_tolower(us1[i]))} -
+        int{static_cast<unsigned char>(absl::ascii_tolower(us2[i]))};
+    if (diff != 0) return diff;
+  }
+  return 0;
+}
+
+char* memdup(const char* s, size_t slen) {
+  void* copy;
+  if ((copy = malloc(slen)) == nullptr) return nullptr;
+  memcpy(copy, s, slen);
+  return reinterpret_cast<char*>(copy);
+}
+
+char* memrchr(const char* s, int c, size_t slen) {
+  for (const char* e = s + slen - 1; e >= s; e--) {
+    if (*e == c) return const_cast<char*>(e);
+  }
+  return nullptr;
+}
+
+size_t memspn(const char* s, size_t slen, const char* accept) {
+  const char* p = s;
+  const char* spanp;
+  char c, sc;
+
+cont:
+  c = *p++;
+  if (slen-- == 0) return p - 1 - s;
+  for (spanp = accept; (sc = *spanp++) != '\0';)
+    if (sc == c) goto cont;
+  return p - 1 - s;
+}
+
+size_t memcspn(const char* s, size_t slen, const char* reject) {
+  const char* p = s;
+  const char* spanp;
+  char c, sc;
+
+  while (slen-- != 0) {
+    c = *p++;
+    for (spanp = reject; (sc = *spanp++) != '\0';)
+      if (sc == c) return p - 1 - s;
+  }
+  return p - s;
+}
+
+char* mempbrk(const char* s, size_t slen, const char* accept) {
+  const char* scanp;
+  int sc;
+
+  for (; slen; ++s, --slen) {
+    for (scanp = accept; (sc = *scanp++) != '\0';)
+      if (sc == *s) return const_cast<char*>(s);
+  }
+  return nullptr;
+}
+
+// This is significantly faster for case-sensitive matches with very
+// few possible matches.  See unit test for benchmarks.
+const char* memmatch(const char* phaystack, size_t haylen, const char* pneedle,
+                     size_t neelen) {
+  if (0 == neelen) {
+    return phaystack;  // even if haylen is 0
+  }
+  if (haylen < neelen) return nullptr;
+
+  const char* match;
+  const char* hayend = phaystack + haylen - neelen + 1;
+  // A static cast is used here to work around the fact that memchr returns
+  // a void* on Posix-compliant systems and const void* on Windows.
+  while ((match = static_cast<const char*>(
+              memchr(phaystack, pneedle[0], hayend - phaystack)))) {
+    if (memcmp(match, pneedle, neelen) == 0)
+      return match;
+    else
+      phaystack = match + 1;
+  }
+  return nullptr;
+}
+
+}  // namespace strings_internal
+}  // namespace absl
diff --git a/absl/strings/internal/memutil.h b/absl/strings/internal/memutil.h
new file mode 100644
index 0000000..7c071a8
--- /dev/null
+++ b/absl/strings/internal/memutil.h
@@ -0,0 +1,146 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// These routines provide mem versions of standard C string routines,
+// such as strpbrk.  They function exactly the same as the str versions,
+// so if you wonder what they are, replace the word "mem" by
+// "str" and check out the man page.  I could return void*, as the
+// strutil.h mem*() routines tend to do, but I return char* instead
+// since this is by far the most common way these functions are called.
+//
+// The difference between the mem and str versions is the mem version
+// takes a pointer and a length, rather than a '\0'-terminated string.
+// The memcase* routines defined here assume the locale is "C"
+// (they use absl::ascii_tolower instead of tolower).
+//
+// These routines are based on the BSD library.
+//
+// Here's a list of routines from string.h, and their mem analogues.
+// Functions in lowercase are defined in string.h; those in UPPERCASE
+// are defined here:
+//
+// strlen                  --
+// strcat strncat          MEMCAT
+// strcpy strncpy          memcpy
+// --                      memccpy   (very cool function, btw)
+// --                      memmove
+// --                      memset
+// strcmp strncmp          memcmp
+// strcasecmp strncasecmp  MEMCASECMP
+// strchr                  memchr
+// strcoll                 --
+// strxfrm                 --
+// strdup strndup          MEMDUP
+// strrchr                 MEMRCHR
+// strspn                  MEMSPN
+// strcspn                 MEMCSPN
+// strpbrk                 MEMPBRK
+// strstr                  MEMSTR MEMMEM
+// (g)strcasestr           MEMCASESTR MEMCASEMEM
+// strtok                  --
+// strprefix               MEMPREFIX      (strprefix is from strutil.h)
+// strcaseprefix           MEMCASEPREFIX  (strcaseprefix is from strutil.h)
+// strsuffix               MEMSUFFIX      (strsuffix is from strutil.h)
+// strcasesuffix           MEMCASESUFFIX  (strcasesuffix is from strutil.h)
+// --                      MEMIS
+// --                      MEMCASEIS
+// strcount                MEMCOUNT       (strcount is from strutil.h)
+
+#ifndef ABSL_STRINGS_INTERNAL_MEMUTIL_H_
+#define ABSL_STRINGS_INTERNAL_MEMUTIL_H_
+
+#include <cstddef>
+#include <cstring>
+
+#include "absl/base/port.h"  // disable some warnings on Windows
+#include "absl/strings/ascii.h"  // for absl::ascii_tolower
+
+namespace absl {
+namespace strings_internal {
+
+inline char* memcat(char* dest, size_t destlen, const char* src,
+                    size_t srclen) {
+  return reinterpret_cast<char*>(memcpy(dest + destlen, src, srclen));
+}
+
+int memcasecmp(const char* s1, const char* s2, size_t len);
+char* memdup(const char* s, size_t slen);
+char* memrchr(const char* s, int c, size_t slen);
+size_t memspn(const char* s, size_t slen, const char* accept);
+size_t memcspn(const char* s, size_t slen, const char* reject);
+char* mempbrk(const char* s, size_t slen, const char* accept);
+
+// This is for internal use only.  Don't call this directly
+template <bool case_sensitive>
+const char* int_memmatch(const char* haystack, size_t haylen,
+                         const char* needle, size_t neelen) {
+  if (0 == neelen) {
+    return haystack;  // even if haylen is 0
+  }
+  const char* hayend = haystack + haylen;
+  const char* needlestart = needle;
+  const char* needleend = needlestart + neelen;
+
+  for (; haystack < hayend; ++haystack) {
+    char hay = case_sensitive
+                   ? *haystack
+                   : absl::ascii_tolower(static_cast<unsigned char>(*haystack));
+    char nee = case_sensitive
+                   ? *needle
+                   : absl::ascii_tolower(static_cast<unsigned char>(*needle));
+    if (hay == nee) {
+      if (++needle == needleend) {
+        return haystack + 1 - neelen;
+      }
+    } else if (needle != needlestart) {
+      // must back up haystack in case a prefix matched (find "aab" in "aaab")
+      haystack -= needle - needlestart;  // for loop will advance one more
+      needle = needlestart;
+    }
+  }
+  return nullptr;
+}
+
+// These are the guys you can call directly
+inline const char* memstr(const char* phaystack, size_t haylen,
+                          const char* pneedle) {
+  return int_memmatch<true>(phaystack, haylen, pneedle, strlen(pneedle));
+}
+
+inline const char* memcasestr(const char* phaystack, size_t haylen,
+                              const char* pneedle) {
+  return int_memmatch<false>(phaystack, haylen, pneedle, strlen(pneedle));
+}
+
+inline const char* memmem(const char* phaystack, size_t haylen,
+                          const char* pneedle, size_t needlelen) {
+  return int_memmatch<true>(phaystack, haylen, pneedle, needlelen);
+}
+
+inline const char* memcasemem(const char* phaystack, size_t haylen,
+                              const char* pneedle, size_t needlelen) {
+  return int_memmatch<false>(phaystack, haylen, pneedle, needlelen);
+}
+
+// This is significantly faster for case-sensitive matches with very
+// few possible matches.  See unit test for benchmarks.
+const char* memmatch(const char* phaystack, size_t haylen, const char* pneedle,
+                     size_t neelen);
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_MEMUTIL_H_
diff --git a/absl/strings/internal/memutil_benchmark.cc b/absl/strings/internal/memutil_benchmark.cc
new file mode 100644
index 0000000..dc95c3e
--- /dev/null
+++ b/absl/strings/internal/memutil_benchmark.cc
@@ -0,0 +1,323 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/memutil.h"
+
+#include <algorithm>
+#include <cstdlib>
+
+#include "benchmark/benchmark.h"
+#include "absl/strings/ascii.h"
+
+// We fill the haystack with aaaaaaaaaaaaaaaaaa...aaaab.
+// That gives us:
+// - an easy search: 'b'
+// - a medium search: 'ab'.  That means every letter is a possible match.
+// - a pathological search: 'aaaaaa.......aaaaab' (half as many a's as haytack)
+// We benchmark case-sensitive and case-insensitive versions of
+// three memmem implementations:
+// - memmem() from memutil.h
+// - search() from STL
+// - memmatch(), a custom implementation using memchr and memcmp.
+// Here are sample results:
+//
+// Run on (12 X 3800 MHz CPU s)
+// CPU Caches:
+//   L1 Data 32K (x6)
+//   L1 Instruction 32K (x6)
+//   L2 Unified 256K (x6)
+//   L3 Unified 15360K (x1)
+// ----------------------------------------------------------------
+// Benchmark                           Time          CPU Iterations
+// ----------------------------------------------------------------
+// BM_Memmem                        3583 ns      3582 ns     196469  2.59966GB/s
+// BM_MemmemMedium                 13743 ns     13742 ns      50901  693.986MB/s
+// BM_MemmemPathological        13695030 ns  13693977 ns         51  713.133kB/s
+// BM_Memcasemem                    3299 ns      3299 ns     212942  2.82309GB/s
+// BM_MemcasememMedium             16407 ns     16406 ns      42170  581.309MB/s
+// BM_MemcasememPathological    17267745 ns  17266030 ns         41  565.598kB/s
+// BM_Search                        1610 ns      1609 ns     431321  5.78672GB/s
+// BM_SearchMedium                 11111 ns     11110 ns      63001  858.414MB/s
+// BM_SearchPathological        12117390 ns  12116397 ns         58  805.984kB/s
+// BM_Searchcase                    3081 ns      3081 ns     229949  3.02313GB/s
+// BM_SearchcaseMedium             16003 ns     16001 ns      44170  595.998MB/s
+// BM_SearchcasePathological    15823413 ns  15821909 ns         44  617.222kB/s
+// BM_Memmatch                       197 ns       197 ns    3584225  47.2951GB/s
+// BM_MemmatchMedium               52333 ns     52329 ns      13280  182.244MB/s
+// BM_MemmatchPathological        659799 ns    659727 ns       1058  14.4556MB/s
+// BM_Memcasematch                  5460 ns      5460 ns     127606  1.70586GB/s
+// BM_MemcasematchMedium           32861 ns     32857 ns      21258  290.248MB/s
+// BM_MemcasematchPathological  15154243 ns  15153089 ns         46  644.464kB/s
+// BM_MemmemStartup                    5 ns         5 ns  150821500
+// BM_SearchStartup                    5 ns         5 ns  150644203
+// BM_MemmatchStartup                  7 ns         7 ns   97068802
+//
+// Conclusions:
+//
+// The following recommendations are based on the sample results above. However,
+// we have found that the performance of STL search can vary significantly
+// depending on compiler and standard library implementation. We recommend you
+// run the benchmarks for yourself on relevant platforms.
+//
+// If you need case-insensitive, STL search is slightly better than memmem for
+// all cases.
+//
+// Case-sensitive is more subtle:
+// Custom memmatch is _very_ fast at scanning, so if you have very few possible
+// matches in your haystack, that's the way to go. Performance drops
+// significantly with more matches.
+//
+// STL search is slightly faster than memmem in the medium and pathological
+// benchmarks. However, the performance of memmem is currently more dependable
+// across platforms and build configurations.
+
+namespace {
+
+constexpr int kHaystackSize = 10000;
+constexpr int64_t kHaystackSize64 = kHaystackSize;
+const char* MakeHaystack() {
+  char* haystack = new char[kHaystackSize];
+  for (int i = 0; i < kHaystackSize - 1; ++i) haystack[i] = 'a';
+  haystack[kHaystackSize - 1] = 'b';
+  return haystack;
+}
+const char* const kHaystack = MakeHaystack();
+
+void BM_Memmem(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        absl::strings_internal::memmem(kHaystack, kHaystackSize, "b", 1));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_Memmem);
+
+void BM_MemmemMedium(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        absl::strings_internal::memmem(kHaystack, kHaystackSize, "ab", 2));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_MemmemMedium);
+
+void BM_MemmemPathological(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(absl::strings_internal::memmem(
+        kHaystack, kHaystackSize, kHaystack + kHaystackSize / 2,
+        kHaystackSize - kHaystackSize / 2));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_MemmemPathological);
+
+void BM_Memcasemem(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        absl::strings_internal::memcasemem(kHaystack, kHaystackSize, "b", 1));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_Memcasemem);
+
+void BM_MemcasememMedium(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        absl::strings_internal::memcasemem(kHaystack, kHaystackSize, "ab", 2));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_MemcasememMedium);
+
+void BM_MemcasememPathological(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(absl::strings_internal::memcasemem(
+        kHaystack, kHaystackSize, kHaystack + kHaystackSize / 2,
+        kHaystackSize - kHaystackSize / 2));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_MemcasememPathological);
+
+bool case_eq(const char a, const char b) {
+  return absl::ascii_tolower(a) == absl::ascii_tolower(b);
+}
+
+void BM_Search(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
+                                         kHaystack + kHaystackSize - 1,
+                                         kHaystack + kHaystackSize));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_Search);
+
+void BM_SearchMedium(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
+                                         kHaystack + kHaystackSize - 2,
+                                         kHaystack + kHaystackSize));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_SearchMedium);
+
+void BM_SearchPathological(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
+                                         kHaystack + kHaystackSize / 2,
+                                         kHaystack + kHaystackSize));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_SearchPathological);
+
+void BM_Searchcase(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
+                                         kHaystack + kHaystackSize - 1,
+                                         kHaystack + kHaystackSize, case_eq));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_Searchcase);
+
+void BM_SearchcaseMedium(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
+                                         kHaystack + kHaystackSize - 2,
+                                         kHaystack + kHaystackSize, case_eq));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_SearchcaseMedium);
+
+void BM_SearchcasePathological(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(std::search(kHaystack, kHaystack + kHaystackSize,
+                                         kHaystack + kHaystackSize / 2,
+                                         kHaystack + kHaystackSize, case_eq));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_SearchcasePathological);
+
+char* memcasechr(const char* s, int c, size_t slen) {
+  c = absl::ascii_tolower(c);
+  for (; slen; ++s, --slen) {
+    if (absl::ascii_tolower(*s) == c) return const_cast<char*>(s);
+  }
+  return nullptr;
+}
+
+const char* memcasematch(const char* phaystack, size_t haylen,
+                         const char* pneedle, size_t neelen) {
+  if (0 == neelen) {
+    return phaystack;  // even if haylen is 0
+  }
+  if (haylen < neelen) return nullptr;
+
+  const char* match;
+  const char* hayend = phaystack + haylen - neelen + 1;
+  while ((match = static_cast<char*>(
+              memcasechr(phaystack, pneedle[0], hayend - phaystack)))) {
+    if (absl::strings_internal::memcasecmp(match, pneedle, neelen) == 0)
+      return match;
+    else
+      phaystack = match + 1;
+  }
+  return nullptr;
+}
+
+void BM_Memmatch(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        absl::strings_internal::memmatch(kHaystack, kHaystackSize, "b", 1));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_Memmatch);
+
+void BM_MemmatchMedium(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        absl::strings_internal::memmatch(kHaystack, kHaystackSize, "ab", 2));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_MemmatchMedium);
+
+void BM_MemmatchPathological(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(absl::strings_internal::memmatch(
+        kHaystack, kHaystackSize, kHaystack + kHaystackSize / 2,
+        kHaystackSize - kHaystackSize / 2));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_MemmatchPathological);
+
+void BM_Memcasematch(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(memcasematch(kHaystack, kHaystackSize, "b", 1));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_Memcasematch);
+
+void BM_MemcasematchMedium(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(memcasematch(kHaystack, kHaystackSize, "ab", 2));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_MemcasematchMedium);
+
+void BM_MemcasematchPathological(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(memcasematch(kHaystack, kHaystackSize,
+                                          kHaystack + kHaystackSize / 2,
+                                          kHaystackSize - kHaystackSize / 2));
+  }
+  state.SetBytesProcessed(kHaystackSize64 * state.iterations());
+}
+BENCHMARK(BM_MemcasematchPathological);
+
+void BM_MemmemStartup(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(absl::strings_internal::memmem(
+        kHaystack + kHaystackSize - 10, 10, kHaystack + kHaystackSize - 1, 1));
+  }
+}
+BENCHMARK(BM_MemmemStartup);
+
+void BM_SearchStartup(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        std::search(kHaystack + kHaystackSize - 10, kHaystack + kHaystackSize,
+                    kHaystack + kHaystackSize - 1, kHaystack + kHaystackSize));
+  }
+}
+BENCHMARK(BM_SearchStartup);
+
+void BM_MemmatchStartup(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(absl::strings_internal::memmatch(
+        kHaystack + kHaystackSize - 10, 10, kHaystack + kHaystackSize - 1, 1));
+  }
+}
+BENCHMARK(BM_MemmatchStartup);
+
+}  // namespace
diff --git a/absl/strings/internal/memutil_test.cc b/absl/strings/internal/memutil_test.cc
new file mode 100644
index 0000000..d8681dd
--- /dev/null
+++ b/absl/strings/internal/memutil_test.cc
@@ -0,0 +1,179 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Unit test for memutil.cc
+
+#include "absl/strings/internal/memutil.h"
+
+#include <cstdlib>
+
+#include "gtest/gtest.h"
+#include "absl/strings/ascii.h"
+
+namespace {
+
+static char* memcasechr(const char* s, int c, size_t slen) {
+  c = absl::ascii_tolower(c);
+  for (; slen; ++s, --slen) {
+    if (absl::ascii_tolower(*s) == c) return const_cast<char*>(s);
+  }
+  return nullptr;
+}
+
+static const char* memcasematch(const char* phaystack, size_t haylen,
+                                const char* pneedle, size_t neelen) {
+  if (0 == neelen) {
+    return phaystack;  // even if haylen is 0
+  }
+  if (haylen < neelen) return nullptr;
+
+  const char* match;
+  const char* hayend = phaystack + haylen - neelen + 1;
+  while ((match = static_cast<char*>(
+              memcasechr(phaystack, pneedle[0], hayend - phaystack)))) {
+    if (absl::strings_internal::memcasecmp(match, pneedle, neelen) == 0)
+      return match;
+    else
+      phaystack = match + 1;
+  }
+  return nullptr;
+}
+
+TEST(MemUtilTest, AllTests) {
+  // check memutil functions
+  char a[1000];
+  absl::strings_internal::memcat(a, 0, "hello", sizeof("hello") - 1);
+  absl::strings_internal::memcat(a, 5, " there", sizeof(" there") - 1);
+
+  EXPECT_EQ(absl::strings_internal::memcasecmp(a, "heLLO there",
+                                               sizeof("hello there") - 1),
+            0);
+  EXPECT_EQ(absl::strings_internal::memcasecmp(a, "heLLO therf",
+                                               sizeof("hello there") - 1),
+            -1);
+  EXPECT_EQ(absl::strings_internal::memcasecmp(a, "heLLO therf",
+                                               sizeof("hello there") - 2),
+            0);
+  EXPECT_EQ(absl::strings_internal::memcasecmp(a, "whatever", 0), 0);
+
+  char* p = absl::strings_internal::memdup("hello", 5);
+  free(p);
+
+  p = absl::strings_internal::memrchr("hello there", 'e',
+                                      sizeof("hello there") - 1);
+  EXPECT_TRUE(p && p[-1] == 'r');
+  p = absl::strings_internal::memrchr("hello there", 'e',
+                                      sizeof("hello there") - 2);
+  EXPECT_TRUE(p && p[-1] == 'h');
+  p = absl::strings_internal::memrchr("hello there", 'u',
+                                      sizeof("hello there") - 1);
+  EXPECT_TRUE(p == nullptr);
+
+  int len = absl::strings_internal::memspn("hello there",
+                                           sizeof("hello there") - 1, "hole");
+  EXPECT_EQ(len, sizeof("hello") - 1);
+  len = absl::strings_internal::memspn("hello there", sizeof("hello there") - 1,
+                                       "u");
+  EXPECT_EQ(len, 0);
+  len = absl::strings_internal::memspn("hello there", sizeof("hello there") - 1,
+                                       "");
+  EXPECT_EQ(len, 0);
+  len = absl::strings_internal::memspn("hello there", sizeof("hello there") - 1,
+                                       "trole h");
+  EXPECT_EQ(len, sizeof("hello there") - 1);
+  len = absl::strings_internal::memspn("hello there!",
+                                       sizeof("hello there!") - 1, "trole h");
+  EXPECT_EQ(len, sizeof("hello there") - 1);
+  len = absl::strings_internal::memspn("hello there!",
+                                       sizeof("hello there!") - 2, "trole h!");
+  EXPECT_EQ(len, sizeof("hello there!") - 2);
+
+  len = absl::strings_internal::memcspn("hello there",
+                                        sizeof("hello there") - 1, "leho");
+  EXPECT_EQ(len, 0);
+  len = absl::strings_internal::memcspn("hello there",
+                                        sizeof("hello there") - 1, "u");
+  EXPECT_EQ(len, sizeof("hello there") - 1);
+  len = absl::strings_internal::memcspn("hello there",
+                                        sizeof("hello there") - 1, "");
+  EXPECT_EQ(len, sizeof("hello there") - 1);
+  len = absl::strings_internal::memcspn("hello there",
+                                        sizeof("hello there") - 1, " ");
+  EXPECT_EQ(len, 5);
+
+  p = absl::strings_internal::mempbrk("hello there", sizeof("hello there") - 1,
+                                      "leho");
+  EXPECT_TRUE(p && p[1] == 'e' && p[2] == 'l');
+  p = absl::strings_internal::mempbrk("hello there", sizeof("hello there") - 1,
+                                      "nu");
+  EXPECT_TRUE(p == nullptr);
+  p = absl::strings_internal::mempbrk("hello there!",
+                                      sizeof("hello there!") - 2, "!");
+  EXPECT_TRUE(p == nullptr);
+  p = absl::strings_internal::mempbrk("hello there", sizeof("hello there") - 1,
+                                      " t ");
+  EXPECT_TRUE(p && p[-1] == 'o' && p[1] == 't');
+
+  {
+    const char kHaystack[] = "0123456789";
+    EXPECT_EQ(absl::strings_internal::memmem(kHaystack, 0, "", 0), kHaystack);
+    EXPECT_EQ(absl::strings_internal::memmem(kHaystack, 10, "012", 3),
+              kHaystack);
+    EXPECT_EQ(absl::strings_internal::memmem(kHaystack, 10, "0xx", 1),
+              kHaystack);
+    EXPECT_EQ(absl::strings_internal::memmem(kHaystack, 10, "789", 3),
+              kHaystack + 7);
+    EXPECT_EQ(absl::strings_internal::memmem(kHaystack, 10, "9xx", 1),
+              kHaystack + 9);
+    EXPECT_TRUE(absl::strings_internal::memmem(kHaystack, 10, "9xx", 3) ==
+                nullptr);
+    EXPECT_TRUE(absl::strings_internal::memmem(kHaystack, 10, "xxx", 1) ==
+                nullptr);
+  }
+  {
+    const char kHaystack[] = "aBcDeFgHiJ";
+    EXPECT_EQ(absl::strings_internal::memcasemem(kHaystack, 0, "", 0),
+              kHaystack);
+    EXPECT_EQ(absl::strings_internal::memcasemem(kHaystack, 10, "Abc", 3),
+              kHaystack);
+    EXPECT_EQ(absl::strings_internal::memcasemem(kHaystack, 10, "Axx", 1),
+              kHaystack);
+    EXPECT_EQ(absl::strings_internal::memcasemem(kHaystack, 10, "hIj", 3),
+              kHaystack + 7);
+    EXPECT_EQ(absl::strings_internal::memcasemem(kHaystack, 10, "jxx", 1),
+              kHaystack + 9);
+    EXPECT_TRUE(absl::strings_internal::memcasemem(kHaystack, 10, "jxx", 3) ==
+                nullptr);
+    EXPECT_TRUE(absl::strings_internal::memcasemem(kHaystack, 10, "xxx", 1) ==
+                nullptr);
+  }
+  {
+    const char kHaystack[] = "0123456789";
+    EXPECT_EQ(absl::strings_internal::memmatch(kHaystack, 0, "", 0), kHaystack);
+    EXPECT_EQ(absl::strings_internal::memmatch(kHaystack, 10, "012", 3),
+              kHaystack);
+    EXPECT_EQ(absl::strings_internal::memmatch(kHaystack, 10, "0xx", 1),
+              kHaystack);
+    EXPECT_EQ(absl::strings_internal::memmatch(kHaystack, 10, "789", 3),
+              kHaystack + 7);
+    EXPECT_EQ(absl::strings_internal::memmatch(kHaystack, 10, "9xx", 1),
+              kHaystack + 9);
+    EXPECT_TRUE(absl::strings_internal::memmatch(kHaystack, 10, "9xx", 3) ==
+                nullptr);
+    EXPECT_TRUE(absl::strings_internal::memmatch(kHaystack, 10, "xxx", 1) ==
+                nullptr);
+  }
+}
+
+}  // namespace
diff --git a/absl/strings/internal/numbers_test_common.h b/absl/strings/internal/numbers_test_common.h
new file mode 100644
index 0000000..2824720
--- /dev/null
+++ b/absl/strings/internal/numbers_test_common.h
@@ -0,0 +1,179 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This file contains common things needed by numbers_test.cc,
+// numbers_legacy_test.cc and numbers_benchmark.cc.
+
+#ifndef ABSL_STRINGS_INTERNAL_NUMBERS_TEST_COMMON_H_
+#define ABSL_STRINGS_INTERNAL_NUMBERS_TEST_COMMON_H_
+
+#include <array>
+#include <cstdint>
+#include <limits>
+#include <string>
+
+namespace absl {
+namespace strings_internal {
+
+template <typename IntType>
+inline bool Itoa(IntType value, int base, std::string* destination) {
+  destination->clear();
+  if (base <= 1 || base > 36) {
+    return false;
+  }
+
+  if (value == 0) {
+    destination->push_back('0');
+    return true;
+  }
+
+  bool negative = value < 0;
+  while (value != 0) {
+    const IntType next_value = value / base;
+    // Can't use std::abs here because of problems when IntType is unsigned.
+    int remainder = value > next_value * base ? value - next_value * base
+                                              : next_value * base - value;
+    char c = remainder < 10 ? '0' + remainder : 'A' + remainder - 10;
+    destination->insert(0, 1, c);
+    value = next_value;
+  }
+
+  if (negative) {
+    destination->insert(0, 1, '-');
+  }
+  return true;
+}
+
+struct uint32_test_case {
+  const char* str;
+  bool expect_ok;
+  int base;  // base to pass to the conversion function
+  uint32_t expected;
+};
+
+inline const std::array<uint32_test_case, 27>& strtouint32_test_cases() {
+  static const std::array<uint32_test_case, 27> test_cases{{
+      {"0xffffffff", true, 16, (std::numeric_limits<uint32_t>::max)()},
+      {"0x34234324", true, 16, 0x34234324},
+      {"34234324", true, 16, 0x34234324},
+      {"0", true, 16, 0},
+      {" \t\n 0xffffffff", true, 16, (std::numeric_limits<uint32_t>::max)()},
+      {" \f\v 46", true, 10, 46},  // must accept weird whitespace
+      {" \t\n 72717222", true, 8, 072717222},
+      {" \t\n 072717222", true, 8, 072717222},
+      {" \t\n 072717228", false, 8, 07271722},
+      {"0", true, 0, 0},
+
+      // Base-10 version.
+      {"34234324", true, 0, 34234324},
+      {"4294967295", true, 0, (std::numeric_limits<uint32_t>::max)()},
+      {"34234324 \n\t", true, 10, 34234324},
+
+      // Unusual base
+      {"0", true, 3, 0},
+      {"2", true, 3, 2},
+      {"11", true, 3, 4},
+
+      // Invalid uints.
+      {"", false, 0, 0},
+      {"  ", false, 0, 0},
+      {"abc", false, 0, 0},  // would be valid hex, but prefix is missing
+      {"34234324a", false, 0, 34234324},
+      {"34234.3", false, 0, 34234},
+      {"-1", false, 0, 0},
+      {"   -123", false, 0, 0},
+      {" \t\n -123", false, 0, 0},
+
+      // Out of bounds.
+      {"4294967296", false, 0, (std::numeric_limits<uint32_t>::max)()},
+      {"0x100000000", false, 0, (std::numeric_limits<uint32_t>::max)()},
+      {nullptr, false, 0, 0},
+  }};
+  return test_cases;
+}
+
+struct uint64_test_case {
+  const char* str;
+  bool expect_ok;
+  int base;
+  uint64_t expected;
+};
+
+inline const std::array<uint64_test_case, 34>& strtouint64_test_cases() {
+  static const std::array<uint64_test_case, 34> test_cases{{
+      {"0x3423432448783446", true, 16, int64_t{0x3423432448783446}},
+      {"3423432448783446", true, 16, int64_t{0x3423432448783446}},
+
+      {"0", true, 16, 0},
+      {"000", true, 0, 0},
+      {"0", true, 0, 0},
+      {" \t\n 0xffffffffffffffff", true, 16,
+       (std::numeric_limits<uint64_t>::max)()},
+
+      {"012345670123456701234", true, 8, int64_t{012345670123456701234}},
+      {"12345670123456701234", true, 8, int64_t{012345670123456701234}},
+
+      {"12845670123456701234", false, 8, 0},
+
+      // Base-10 version.
+      {"34234324487834466", true, 0, int64_t{34234324487834466}},
+
+      {" \t\n 18446744073709551615", true, 0,
+       (std::numeric_limits<uint64_t>::max)()},
+
+      {"34234324487834466 \n\t ", true, 0, int64_t{34234324487834466}},
+
+      {" \f\v 46", true, 10, 46},  // must accept weird whitespace
+
+      // Unusual base
+      {"0", true, 3, 0},
+      {"2", true, 3, 2},
+      {"11", true, 3, 4},
+
+      {"0", true, 0, 0},
+
+      // Invalid uints.
+      {"", false, 0, 0},
+      {"  ", false, 0, 0},
+      {"abc", false, 0, 0},
+      {"34234324487834466a", false, 0, 0},
+      {"34234487834466.3", false, 0, 0},
+      {"-1", false, 0, 0},
+      {"   -123", false, 0, 0},
+      {" \t\n -123", false, 0, 0},
+
+      // Out of bounds.
+      {"18446744073709551616", false, 10, 0},
+      {"18446744073709551616", false, 0, 0},
+      {"0x10000000000000000", false, 16,
+       (std::numeric_limits<uint64_t>::max)()},
+      {"0X10000000000000000", false, 16,
+       (std::numeric_limits<uint64_t>::max)()},  // 0X versus 0x.
+      {"0x10000000000000000", false, 0, (std::numeric_limits<uint64_t>::max)()},
+      {"0X10000000000000000", false, 0,
+       (std::numeric_limits<uint64_t>::max)()},  // 0X versus 0x.
+
+      {"0x1234", true, 16, 0x1234},
+
+      // Base-10 std::string version.
+      {"1234", true, 0, 1234},
+      {nullptr, false, 0, 0},
+  }};
+  return test_cases;
+}
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_NUMBERS_TEST_COMMON_H_
diff --git a/absl/strings/internal/ostringstream.cc b/absl/strings/internal/ostringstream.cc
new file mode 100644
index 0000000..d0f0f84
--- /dev/null
+++ b/absl/strings/internal/ostringstream.cc
@@ -0,0 +1,34 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/ostringstream.h"
+
+namespace absl {
+namespace strings_internal {
+
+OStringStream::Buf::int_type OStringStream::overflow(int c) {
+  assert(s_);
+  if (!Buf::traits_type::eq_int_type(c, Buf::traits_type::eof()))
+    s_->push_back(static_cast<char>(c));
+  return 1;
+}
+
+std::streamsize OStringStream::xsputn(const char* s, std::streamsize n) {
+  assert(s_);
+  s_->append(s, n);
+  return n;
+}
+
+}  // namespace strings_internal
+}  // namespace absl
diff --git a/absl/strings/internal/ostringstream.h b/absl/strings/internal/ostringstream.h
new file mode 100644
index 0000000..2079201
--- /dev/null
+++ b/absl/strings/internal/ostringstream.h
@@ -0,0 +1,87 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
+#define ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
+
+#include <cassert>
+#include <ostream>
+#include <streambuf>
+#include <string>
+
+#include "absl/base/port.h"
+
+namespace absl {
+namespace strings_internal {
+
+// The same as std::ostringstream but appends to a user-specified std::string,
+// and is faster. It is ~70% faster to create, ~50% faster to write to, and
+// completely free to extract the result std::string.
+//
+//   std::string s;
+//   OStringStream strm(&s);
+//   strm << 42 << ' ' << 3.14;  // appends to `s`
+//
+// The stream object doesn't have to be named. Starting from C++11 operator<<
+// works with rvalues of std::ostream.
+//
+//   std::string s;
+//   OStringStream(&s) << 42 << ' ' << 3.14;  // appends to `s`
+//
+// OStringStream is faster to create than std::ostringstream but it's still
+// relatively slow. Avoid creating multiple streams where a single stream will
+// do.
+//
+// Creates unnecessary instances of OStringStream: slow.
+//
+//   std::string s;
+//   OStringStream(&s) << 42;
+//   OStringStream(&s) << ' ';
+//   OStringStream(&s) << 3.14;
+//
+// Creates a single instance of OStringStream and reuses it: fast.
+//
+//   std::string s;
+//   OStringStream strm(&s);
+//   strm << 42;
+//   strm << ' ';
+//   strm << 3.14;
+//
+// Note: flush() has no effect. No reason to call it.
+class OStringStream : private std::basic_streambuf<char>, public std::ostream {
+ public:
+  // The argument can be null, in which case you'll need to call str(p) with a
+  // non-null argument before you can write to the stream.
+  //
+  // The destructor of OStringStream doesn't use the std::string. It's OK to
+  // destroy the std::string before the stream.
+  explicit OStringStream(std::string* s) : std::ostream(this), s_(s) {}
+
+  std::string* str() { return s_; }
+  const std::string* str() const { return s_; }
+  void str(std::string* s) { s_ = s; }
+
+ private:
+  using Buf = std::basic_streambuf<char>;
+
+  Buf::int_type overflow(int c) override;
+  std::streamsize xsputn(const char* s, std::streamsize n) override;
+
+  std::string* s_;
+};
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
diff --git a/absl/strings/internal/ostringstream_benchmark.cc b/absl/strings/internal/ostringstream_benchmark.cc
new file mode 100644
index 0000000..5979f18
--- /dev/null
+++ b/absl/strings/internal/ostringstream_benchmark.cc
@@ -0,0 +1,106 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/ostringstream.h"
+
+#include <sstream>
+#include <string>
+
+#include "benchmark/benchmark.h"
+
+namespace {
+
+enum StringType {
+  kNone,
+  kStdString,
+};
+
+// Benchmarks for std::ostringstream.
+template <StringType kOutput>
+void BM_StdStream(benchmark::State& state) {
+  const int num_writes = state.range(0);
+  const int bytes_per_write = state.range(1);
+  const std::string payload(bytes_per_write, 'x');
+  for (auto _ : state) {
+    std::ostringstream strm;
+    benchmark::DoNotOptimize(strm);
+    for (int i = 0; i != num_writes; ++i) {
+      strm << payload;
+    }
+    switch (kOutput) {
+      case kNone: {
+        break;
+      }
+      case kStdString: {
+        std::string s = strm.str();
+        benchmark::DoNotOptimize(s);
+        break;
+      }
+    }
+  }
+}
+
+// Create the stream, optionally write to it, then destroy it.
+BENCHMARK_TEMPLATE(BM_StdStream, kNone)
+    ->ArgPair(0, 0)
+    ->ArgPair(1, 16)   // 16 bytes is small enough for SSO
+    ->ArgPair(1, 256)  // 256 bytes requires heap allocation
+    ->ArgPair(1024, 256);
+// Create the stream, write to it, get std::string out, then destroy.
+BENCHMARK_TEMPLATE(BM_StdStream, kStdString)
+    ->ArgPair(1, 16)   // 16 bytes is small enough for SSO
+    ->ArgPair(1, 256)  // 256 bytes requires heap allocation
+    ->ArgPair(1024, 256);
+
+// Benchmarks for OStringStream.
+template <StringType kOutput>
+void BM_CustomStream(benchmark::State& state) {
+  const int num_writes = state.range(0);
+  const int bytes_per_write = state.range(1);
+  const std::string payload(bytes_per_write, 'x');
+  for (auto _ : state) {
+    std::string out;
+    absl::strings_internal::OStringStream strm(&out);
+    benchmark::DoNotOptimize(strm);
+    for (int i = 0; i != num_writes; ++i) {
+      strm << payload;
+    }
+    switch (kOutput) {
+      case kNone: {
+        break;
+      }
+      case kStdString: {
+        std::string s = out;
+        benchmark::DoNotOptimize(s);
+        break;
+      }
+    }
+  }
+}
+
+// Create the stream, optionally write to it, then destroy it.
+BENCHMARK_TEMPLATE(BM_CustomStream, kNone)
+    ->ArgPair(0, 0)
+    ->ArgPair(1, 16)   // 16 bytes is small enough for SSO
+    ->ArgPair(1, 256)  // 256 bytes requires heap allocation
+    ->ArgPair(1024, 256);
+// Create the stream, write to it, get std::string out, then destroy.
+// It's not useful in practice to extract std::string from OStringStream; we
+// measure it for completeness.
+BENCHMARK_TEMPLATE(BM_CustomStream, kStdString)
+    ->ArgPair(1, 16)   // 16 bytes is small enough for SSO
+    ->ArgPair(1, 256)  // 256 bytes requires heap allocation
+    ->ArgPair(1024, 256);
+
+}  // namespace
diff --git a/absl/strings/internal/ostringstream_test.cc b/absl/strings/internal/ostringstream_test.cc
new file mode 100644
index 0000000..2879e50
--- /dev/null
+++ b/absl/strings/internal/ostringstream_test.cc
@@ -0,0 +1,102 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/ostringstream.h"
+
+#include <memory>
+#include <ostream>
+#include <string>
+#include <type_traits>
+
+#include "gtest/gtest.h"
+
+namespace {
+
+TEST(OStringStream, IsOStream) {
+  static_assert(
+      std::is_base_of<std::ostream, absl::strings_internal::OStringStream>(),
+      "");
+}
+
+TEST(OStringStream, ConstructDestroy) {
+  {
+    absl::strings_internal::OStringStream strm(nullptr);
+    EXPECT_EQ(nullptr, strm.str());
+  }
+  {
+    std::string s = "abc";
+    {
+      absl::strings_internal::OStringStream strm(&s);
+      EXPECT_EQ(&s, strm.str());
+    }
+    EXPECT_EQ("abc", s);
+  }
+  {
+    std::unique_ptr<std::string> s(new std::string);
+    absl::strings_internal::OStringStream strm(s.get());
+    s.reset();
+  }
+}
+
+TEST(OStringStream, Str) {
+  std::string s1;
+  absl::strings_internal::OStringStream strm(&s1);
+  const absl::strings_internal::OStringStream& c_strm(strm);
+
+  static_assert(std::is_same<decltype(strm.str()), std::string*>(), "");
+  static_assert(std::is_same<decltype(c_strm.str()), const std::string*>(), "");
+
+  EXPECT_EQ(&s1, strm.str());
+  EXPECT_EQ(&s1, c_strm.str());
+
+  strm.str(&s1);
+  EXPECT_EQ(&s1, strm.str());
+  EXPECT_EQ(&s1, c_strm.str());
+
+  std::string s2;
+  strm.str(&s2);
+  EXPECT_EQ(&s2, strm.str());
+  EXPECT_EQ(&s2, c_strm.str());
+
+  strm.str(nullptr);
+  EXPECT_EQ(nullptr, strm.str());
+  EXPECT_EQ(nullptr, c_strm.str());
+}
+
+TEST(OStreamStream, WriteToLValue) {
+  std::string s = "abc";
+  {
+    absl::strings_internal::OStringStream strm(&s);
+    EXPECT_EQ("abc", s);
+    strm << "";
+    EXPECT_EQ("abc", s);
+    strm << 42;
+    EXPECT_EQ("abc42", s);
+    strm << 'x' << 'y';
+    EXPECT_EQ("abc42xy", s);
+  }
+  EXPECT_EQ("abc42xy", s);
+}
+
+TEST(OStreamStream, WriteToRValue) {
+  std::string s = "abc";
+  absl::strings_internal::OStringStream(&s) << "";
+  EXPECT_EQ("abc", s);
+  absl::strings_internal::OStringStream(&s) << 42;
+  EXPECT_EQ("abc42", s);
+  absl::strings_internal::OStringStream(&s) << 'x' << 'y';
+  EXPECT_EQ("abc42xy", s);
+}
+
+}  // namespace
diff --git a/absl/strings/internal/pow10_helper.cc b/absl/strings/internal/pow10_helper.cc
new file mode 100644
index 0000000..03ed8d0
--- /dev/null
+++ b/absl/strings/internal/pow10_helper.cc
@@ -0,0 +1,120 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/pow10_helper.h"
+
+#include <cmath>
+
+namespace absl {
+namespace strings_internal {
+
+namespace {
+
+// The exact value of 1e23 falls precisely halfway between two representable
+// doubles. Furthermore, the rounding rules we prefer (break ties by rounding
+// to the nearest even) dictate in this case that the number should be rounded
+// down, but this is not completely specified for floating-point literals in
+// C++. (It just says to use the default rounding mode of the standard
+// library.) We ensure the result we want by using a number that has an
+// unambiguous correctly rounded answer.
+constexpr double k1e23 = 9999999999999999e7;
+
+constexpr double kPowersOfTen[] = {
+    0.0,    1e-323, 1e-322, 1e-321, 1e-320, 1e-319, 1e-318, 1e-317, 1e-316,
+    1e-315, 1e-314, 1e-313, 1e-312, 1e-311, 1e-310, 1e-309, 1e-308, 1e-307,
+    1e-306, 1e-305, 1e-304, 1e-303, 1e-302, 1e-301, 1e-300, 1e-299, 1e-298,
+    1e-297, 1e-296, 1e-295, 1e-294, 1e-293, 1e-292, 1e-291, 1e-290, 1e-289,
+    1e-288, 1e-287, 1e-286, 1e-285, 1e-284, 1e-283, 1e-282, 1e-281, 1e-280,
+    1e-279, 1e-278, 1e-277, 1e-276, 1e-275, 1e-274, 1e-273, 1e-272, 1e-271,
+    1e-270, 1e-269, 1e-268, 1e-267, 1e-266, 1e-265, 1e-264, 1e-263, 1e-262,
+    1e-261, 1e-260, 1e-259, 1e-258, 1e-257, 1e-256, 1e-255, 1e-254, 1e-253,
+    1e-252, 1e-251, 1e-250, 1e-249, 1e-248, 1e-247, 1e-246, 1e-245, 1e-244,
+    1e-243, 1e-242, 1e-241, 1e-240, 1e-239, 1e-238, 1e-237, 1e-236, 1e-235,
+    1e-234, 1e-233, 1e-232, 1e-231, 1e-230, 1e-229, 1e-228, 1e-227, 1e-226,
+    1e-225, 1e-224, 1e-223, 1e-222, 1e-221, 1e-220, 1e-219, 1e-218, 1e-217,
+    1e-216, 1e-215, 1e-214, 1e-213, 1e-212, 1e-211, 1e-210, 1e-209, 1e-208,
+    1e-207, 1e-206, 1e-205, 1e-204, 1e-203, 1e-202, 1e-201, 1e-200, 1e-199,
+    1e-198, 1e-197, 1e-196, 1e-195, 1e-194, 1e-193, 1e-192, 1e-191, 1e-190,
+    1e-189, 1e-188, 1e-187, 1e-186, 1e-185, 1e-184, 1e-183, 1e-182, 1e-181,
+    1e-180, 1e-179, 1e-178, 1e-177, 1e-176, 1e-175, 1e-174, 1e-173, 1e-172,
+    1e-171, 1e-170, 1e-169, 1e-168, 1e-167, 1e-166, 1e-165, 1e-164, 1e-163,
+    1e-162, 1e-161, 1e-160, 1e-159, 1e-158, 1e-157, 1e-156, 1e-155, 1e-154,
+    1e-153, 1e-152, 1e-151, 1e-150, 1e-149, 1e-148, 1e-147, 1e-146, 1e-145,
+    1e-144, 1e-143, 1e-142, 1e-141, 1e-140, 1e-139, 1e-138, 1e-137, 1e-136,
+    1e-135, 1e-134, 1e-133, 1e-132, 1e-131, 1e-130, 1e-129, 1e-128, 1e-127,
+    1e-126, 1e-125, 1e-124, 1e-123, 1e-122, 1e-121, 1e-120, 1e-119, 1e-118,
+    1e-117, 1e-116, 1e-115, 1e-114, 1e-113, 1e-112, 1e-111, 1e-110, 1e-109,
+    1e-108, 1e-107, 1e-106, 1e-105, 1e-104, 1e-103, 1e-102, 1e-101, 1e-100,
+    1e-99,  1e-98,  1e-97,  1e-96,  1e-95,  1e-94,  1e-93,  1e-92,  1e-91,
+    1e-90,  1e-89,  1e-88,  1e-87,  1e-86,  1e-85,  1e-84,  1e-83,  1e-82,
+    1e-81,  1e-80,  1e-79,  1e-78,  1e-77,  1e-76,  1e-75,  1e-74,  1e-73,
+    1e-72,  1e-71,  1e-70,  1e-69,  1e-68,  1e-67,  1e-66,  1e-65,  1e-64,
+    1e-63,  1e-62,  1e-61,  1e-60,  1e-59,  1e-58,  1e-57,  1e-56,  1e-55,
+    1e-54,  1e-53,  1e-52,  1e-51,  1e-50,  1e-49,  1e-48,  1e-47,  1e-46,
+    1e-45,  1e-44,  1e-43,  1e-42,  1e-41,  1e-40,  1e-39,  1e-38,  1e-37,
+    1e-36,  1e-35,  1e-34,  1e-33,  1e-32,  1e-31,  1e-30,  1e-29,  1e-28,
+    1e-27,  1e-26,  1e-25,  1e-24,  1e-23,  1e-22,  1e-21,  1e-20,  1e-19,
+    1e-18,  1e-17,  1e-16,  1e-15,  1e-14,  1e-13,  1e-12,  1e-11,  1e-10,
+    1e-9,   1e-8,   1e-7,   1e-6,   1e-5,   1e-4,   1e-3,   1e-2,   1e-1,
+    1e+0,   1e+1,   1e+2,   1e+3,   1e+4,   1e+5,   1e+6,   1e+7,   1e+8,
+    1e+9,   1e+10,  1e+11,  1e+12,  1e+13,  1e+14,  1e+15,  1e+16,  1e+17,
+    1e+18,  1e+19,  1e+20,  1e+21,  1e+22,  k1e23,  1e+24,  1e+25,  1e+26,
+    1e+27,  1e+28,  1e+29,  1e+30,  1e+31,  1e+32,  1e+33,  1e+34,  1e+35,
+    1e+36,  1e+37,  1e+38,  1e+39,  1e+40,  1e+41,  1e+42,  1e+43,  1e+44,
+    1e+45,  1e+46,  1e+47,  1e+48,  1e+49,  1e+50,  1e+51,  1e+52,  1e+53,
+    1e+54,  1e+55,  1e+56,  1e+57,  1e+58,  1e+59,  1e+60,  1e+61,  1e+62,
+    1e+63,  1e+64,  1e+65,  1e+66,  1e+67,  1e+68,  1e+69,  1e+70,  1e+71,
+    1e+72,  1e+73,  1e+74,  1e+75,  1e+76,  1e+77,  1e+78,  1e+79,  1e+80,
+    1e+81,  1e+82,  1e+83,  1e+84,  1e+85,  1e+86,  1e+87,  1e+88,  1e+89,
+    1e+90,  1e+91,  1e+92,  1e+93,  1e+94,  1e+95,  1e+96,  1e+97,  1e+98,
+    1e+99,  1e+100, 1e+101, 1e+102, 1e+103, 1e+104, 1e+105, 1e+106, 1e+107,
+    1e+108, 1e+109, 1e+110, 1e+111, 1e+112, 1e+113, 1e+114, 1e+115, 1e+116,
+    1e+117, 1e+118, 1e+119, 1e+120, 1e+121, 1e+122, 1e+123, 1e+124, 1e+125,
+    1e+126, 1e+127, 1e+128, 1e+129, 1e+130, 1e+131, 1e+132, 1e+133, 1e+134,
+    1e+135, 1e+136, 1e+137, 1e+138, 1e+139, 1e+140, 1e+141, 1e+142, 1e+143,
+    1e+144, 1e+145, 1e+146, 1e+147, 1e+148, 1e+149, 1e+150, 1e+151, 1e+152,
+    1e+153, 1e+154, 1e+155, 1e+156, 1e+157, 1e+158, 1e+159, 1e+160, 1e+161,
+    1e+162, 1e+163, 1e+164, 1e+165, 1e+166, 1e+167, 1e+168, 1e+169, 1e+170,
+    1e+171, 1e+172, 1e+173, 1e+174, 1e+175, 1e+176, 1e+177, 1e+178, 1e+179,
+    1e+180, 1e+181, 1e+182, 1e+183, 1e+184, 1e+185, 1e+186, 1e+187, 1e+188,
+    1e+189, 1e+190, 1e+191, 1e+192, 1e+193, 1e+194, 1e+195, 1e+196, 1e+197,
+    1e+198, 1e+199, 1e+200, 1e+201, 1e+202, 1e+203, 1e+204, 1e+205, 1e+206,
+    1e+207, 1e+208, 1e+209, 1e+210, 1e+211, 1e+212, 1e+213, 1e+214, 1e+215,
+    1e+216, 1e+217, 1e+218, 1e+219, 1e+220, 1e+221, 1e+222, 1e+223, 1e+224,
+    1e+225, 1e+226, 1e+227, 1e+228, 1e+229, 1e+230, 1e+231, 1e+232, 1e+233,
+    1e+234, 1e+235, 1e+236, 1e+237, 1e+238, 1e+239, 1e+240, 1e+241, 1e+242,
+    1e+243, 1e+244, 1e+245, 1e+246, 1e+247, 1e+248, 1e+249, 1e+250, 1e+251,
+    1e+252, 1e+253, 1e+254, 1e+255, 1e+256, 1e+257, 1e+258, 1e+259, 1e+260,
+    1e+261, 1e+262, 1e+263, 1e+264, 1e+265, 1e+266, 1e+267, 1e+268, 1e+269,
+    1e+270, 1e+271, 1e+272, 1e+273, 1e+274, 1e+275, 1e+276, 1e+277, 1e+278,
+    1e+279, 1e+280, 1e+281, 1e+282, 1e+283, 1e+284, 1e+285, 1e+286, 1e+287,
+    1e+288, 1e+289, 1e+290, 1e+291, 1e+292, 1e+293, 1e+294, 1e+295, 1e+296,
+    1e+297, 1e+298, 1e+299, 1e+300, 1e+301, 1e+302, 1e+303, 1e+304, 1e+305,
+    1e+306, 1e+307, 1e+308,
+};
+
+}  // namespace
+
+double Pow10(int exp) {
+  if (exp < -324) {
+    return 0.0;
+  } else if (exp > 308) {
+    return INFINITY;
+  } else {
+    return kPowersOfTen[exp + 324];
+  }
+}
+
+}  // namespace strings_internal
+}  // namespace absl
diff --git a/absl/strings/internal/pow10_helper.h b/absl/strings/internal/pow10_helper.h
new file mode 100644
index 0000000..9d1aa71
--- /dev/null
+++ b/absl/strings/internal/pow10_helper.h
@@ -0,0 +1,36 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This test helper library contains a table of powers of 10, to guarantee
+// precise values are computed across the full range of doubles. We can't rely
+// on the pow() function, because not all standard libraries ship a version
+// that is precise.
+#ifndef ABSL_STRINGS_INTERNAL_POW10_HELPER_H_
+#define ABSL_STRINGS_INTERNAL_POW10_HELPER_H_
+
+#include <vector>
+
+namespace absl {
+namespace strings_internal {
+
+// Computes the precise value of 10^exp. (I.e. the nearest representable
+// double to the exact value, rounding to nearest-even in the (single) case of
+// being exactly halfway between.)
+double Pow10(int exp);
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_POW10_HELPER_H_
diff --git a/absl/strings/internal/pow10_helper_test.cc b/absl/strings/internal/pow10_helper_test.cc
new file mode 100644
index 0000000..a4a68b5
--- /dev/null
+++ b/absl/strings/internal/pow10_helper_test.cc
@@ -0,0 +1,120 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/pow10_helper.h"
+
+#include <cmath>
+
+#include "gtest/gtest.h"
+#include "absl/strings/str_format.h"
+
+namespace absl {
+namespace strings_internal {
+
+namespace {
+
+struct TestCase {
+  int power;           // Testing Pow10(power)
+  uint64_t significand;  // Raw bits of the expected value
+  int radix;           // significand is adjusted by 2^radix
+};
+
+TEST(Pow10HelperTest, Works) {
+  // The logic in pow10_helper.cc is so simple that theoretically we don't even
+  // need a test. However, we're paranoid and believe that there may be
+  // compilers that don't round floating-point literals correctly, even though
+  // it is specified by the standard. We check various edge cases, just to be
+  // sure.
+  constexpr TestCase kTestCases[] = {
+      // Subnormals
+      {-323, 0x2, -1074},
+      {-322, 0x14, -1074},
+      {-321, 0xca, -1074},
+      {-320, 0x7e8, -1074},
+      {-319, 0x4f10, -1074},
+      {-318, 0x316a2, -1074},
+      {-317, 0x1ee257, -1074},
+      {-316, 0x134d761, -1074},
+      {-315, 0xc1069cd, -1074},
+      {-314, 0x78a42205, -1074},
+      {-313, 0x4b6695433, -1074},
+      {-312, 0x2f201d49fb, -1074},
+      {-311, 0x1d74124e3d1, -1074},
+      {-310, 0x12688b70e62b, -1074},
+      {-309, 0xb8157268fdaf, -1074},
+      {-308, 0x730d67819e8d2, -1074},
+      // Values that are very close to rounding the other way.
+      // Comment shows difference of significand from the true value.
+      {-307, 0x11fa182c40c60d, -1072},  // -.4588
+      {-290, 0x18f2b061aea072, -1016},  //  .4854
+      {-276, 0x11BA03F5B21000, -969},   //  .4709
+      {-259, 0x1899C2F6732210, -913},   //  .4830
+      {-252, 0x1D53844EE47DD1, -890},   // -.4743
+      {-227, 0x1E5297287C2F45, -807},   // -.4708
+      {-198, 0x1322E220A5B17E, -710},   // -.4714
+      {-195, 0x12B010D3E1CF56, -700},   //  .4928
+      {-192, 0x123FF06EEA847A, -690},   //  .4968
+      {-163, 0x1708D0F84D3DE7, -594},   // -.4977
+      {-145, 0x13FAAC3E3FA1F3, -534},   // -.4785
+      {-111, 0x133D4032C2C7F5, -421},   //  .4774
+      {-106, 0x1D5B561574765B, -405},   // -.4869
+      {-104, 0x16EF5B40C2FC77, -398},   // -.4741
+      {-88, 0x197683DF2F268D, -345},    // -.4738
+      {-86, 0x13E497065CD61F, -338},    //  .4736
+      {-76, 0x17288E1271F513, -305},    // -.4761
+      {-63, 0x1A53FC9631D10D, -262},    //  .4929
+      {-30, 0x14484BFEEBC2A0, -152},    //  .4758
+      {-21, 0x12E3B40A0E9B4F, -122},    // -.4916
+      {-5, 0x14F8B588E368F1, -69},      //  .4829
+      {23, 0x152D02C7E14AF6, 24},       // -.5000 (exactly, round-to-even)
+      {29, 0x1431E0FAE6D721, 44},       // -.4870
+      {34, 0x1ED09BEAD87C03, 60},       // -.4721
+      {70, 0x172EBAD6DDC73D, 180},      //  .4733
+      {105, 0x1BE7ABD3781ECA, 296},     // -.4850
+      {126, 0x17A2ECC414A03F, 366},     // -.4999
+      {130, 0x1CDA62055B2D9E, 379},     //  .4855
+      {165, 0x115D847AD00087, 496},     // -.4913
+      {172, 0x14B378469B6732, 519},     //  .4818
+      {187, 0x1262DFEEBBB0F9, 569},     // -.4805
+      {210, 0x18557F31326BBB, 645},     // -.4992
+      {212, 0x1302CB5E6F642A, 652},     // -.4838
+      {215, 0x1290BA9A38C7D1, 662},     // -.4881
+      {236, 0x1F736F9B3494E9, 731},     //  .4707
+      {244, 0x176EC98994F489, 758},     //  .4924
+      {250, 0x1658E3AB795204, 778},     // -.4963
+      {252, 0x117571DDF6C814, 785},     //  .4873
+      {254, 0x1B4781EAD1989E, 791},     // -.4887
+      {260, 0x1A03FDE214CAF1, 811},     //  .4784
+      {284, 0x1585041B2C477F, 891},     //  .4798
+      {304, 0x1D2A1BE4048F90, 957},     // -.4987
+      // Out-of-range values
+      {-324, 0x0, 0},
+      {-325, 0x0, 0},
+      {-326, 0x0, 0},
+      {309, 1, 2000},
+      {310, 1, 2000},
+      {311, 1, 2000},
+  };
+  for (const TestCase& test_case : kTestCases) {
+    EXPECT_EQ(Pow10(test_case.power),
+              std::ldexp(test_case.significand, test_case.radix))
+        << absl::StrFormat("Failure for Pow10(%d): %a vs %a", test_case.power,
+                           Pow10(test_case.power),
+                           std::ldexp(test_case.significand, test_case.radix));
+  }
+}
+
+}  // namespace
+}  // namespace strings_internal
+}  // namespace absl
diff --git a/absl/strings/internal/resize_uninitialized.h b/absl/strings/internal/resize_uninitialized.h
new file mode 100644
index 0000000..469962b
--- /dev/null
+++ b/absl/strings/internal/resize_uninitialized.h
@@ -0,0 +1,72 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_
+#define ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_
+
+#include <string>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/port.h"
+#include "absl/meta/type_traits.h"  //  for void_t
+
+namespace absl {
+namespace strings_internal {
+
+// Is a subclass of true_type or false_type, depending on whether or not
+// T has a __resize_default_init member.
+template <typename string_type, typename = void>
+struct ResizeUninitializedTraits {
+  using HasMember = std::false_type;
+  static void Resize(string_type* s, size_t new_size) { s->resize(new_size); }
+};
+
+// __resize_default_init is provided by libc++ >= 8.0 and by Google's internal
+// ::string implementation.
+template <typename string_type>
+struct ResizeUninitializedTraits<
+    string_type, absl::void_t<decltype(std::declval<string_type&>()
+                                           .__resize_default_init(237))> > {
+  using HasMember = std::true_type;
+  static void Resize(string_type* s, size_t new_size) {
+    s->__resize_default_init(new_size);
+  }
+};
+
+// Returns true if the std::string implementation supports a resize where
+// the new characters added to the std::string are left untouched.
+//
+// (A better name might be "STLStringSupportsUninitializedResize", alluding to
+// the previous function.)
+template <typename string_type>
+inline constexpr bool STLStringSupportsNontrashingResize(string_type*) {
+  return ResizeUninitializedTraits<string_type>::HasMember::value;
+}
+
+// Like str->resize(new_size), except any new characters added to "*str" as a
+// result of resizing may be left uninitialized, rather than being filled with
+// '0' bytes. Typically used when code is then going to overwrite the backing
+// store of the std::string with known data.
+template <typename string_type, typename = void>
+inline void STLStringResizeUninitialized(string_type* s, size_t new_size) {
+  ResizeUninitializedTraits<string_type>::Resize(s, new_size);
+}
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_
diff --git a/absl/strings/internal/resize_uninitialized_test.cc b/absl/strings/internal/resize_uninitialized_test.cc
new file mode 100644
index 0000000..c5be0b1
--- /dev/null
+++ b/absl/strings/internal/resize_uninitialized_test.cc
@@ -0,0 +1,68 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/resize_uninitialized.h"
+
+#include "gtest/gtest.h"
+
+namespace {
+
+int resize_call_count = 0;
+
+struct resizable_string {
+  void resize(size_t) { resize_call_count += 1; }
+};
+
+int resize_default_init_call_count = 0;
+
+struct resize_default_init_string {
+  void resize(size_t) { resize_call_count += 1; }
+  void __resize_default_init(size_t) { resize_default_init_call_count += 1; }
+};
+
+TEST(ResizeUninit, WithAndWithout) {
+  resize_call_count = 0;
+  resize_default_init_call_count = 0;
+  {
+    resizable_string rs;
+
+    EXPECT_EQ(resize_call_count, 0);
+    EXPECT_EQ(resize_default_init_call_count, 0);
+    EXPECT_FALSE(
+        absl::strings_internal::STLStringSupportsNontrashingResize(&rs));
+    EXPECT_EQ(resize_call_count, 0);
+    EXPECT_EQ(resize_default_init_call_count, 0);
+    absl::strings_internal::STLStringResizeUninitialized(&rs, 237);
+    EXPECT_EQ(resize_call_count, 1);
+    EXPECT_EQ(resize_default_init_call_count, 0);
+  }
+
+  resize_call_count = 0;
+  resize_default_init_call_count = 0;
+  {
+    resize_default_init_string rus;
+
+    EXPECT_EQ(resize_call_count, 0);
+    EXPECT_EQ(resize_default_init_call_count, 0);
+    EXPECT_TRUE(
+        absl::strings_internal::STLStringSupportsNontrashingResize(&rus));
+    EXPECT_EQ(resize_call_count, 0);
+    EXPECT_EQ(resize_default_init_call_count, 0);
+    absl::strings_internal::STLStringResizeUninitialized(&rus, 237);
+    EXPECT_EQ(resize_call_count, 0);
+    EXPECT_EQ(resize_default_init_call_count, 1);
+  }
+}
+
+}  // namespace
diff --git a/absl/strings/internal/stl_type_traits.h b/absl/strings/internal/stl_type_traits.h
new file mode 100644
index 0000000..202ab37
--- /dev/null
+++ b/absl/strings/internal/stl_type_traits.h
@@ -0,0 +1,246 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// Thie file provides the IsStrictlyBaseOfAndConvertibleToSTLContainer type
+// trait metafunction to assist in working with the _GLIBCXX_DEBUG debug
+// wrappers of STL containers.
+//
+// DO NOT INCLUDE THIS FILE DIRECTLY. Use this file by including
+// absl/strings/str_split.h.
+//
+// IWYU pragma: private, include "absl/strings/str_split.h"
+
+#ifndef ABSL_STRINGS_INTERNAL_STL_TYPE_TRAITS_H_
+#define ABSL_STRINGS_INTERNAL_STL_TYPE_TRAITS_H_
+
+#include <array>
+#include <bitset>
+#include <deque>
+#include <forward_list>
+#include <list>
+#include <map>
+#include <set>
+#include <type_traits>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+namespace strings_internal {
+
+template <typename C, template <typename...> class T>
+struct IsSpecializationImpl : std::false_type {};
+template <template <typename...> class T, typename... Args>
+struct IsSpecializationImpl<T<Args...>, T> : std::true_type {};
+template <typename C, template <typename...> class T>
+using IsSpecialization = IsSpecializationImpl<absl::decay_t<C>, T>;
+
+template <typename C>
+struct IsArrayImpl : std::false_type {};
+template <template <typename, size_t> class A, typename T, size_t N>
+struct IsArrayImpl<A<T, N>> : std::is_same<A<T, N>, std::array<T, N>> {};
+template <typename C>
+using IsArray = IsArrayImpl<absl::decay_t<C>>;
+
+template <typename C>
+struct IsBitsetImpl : std::false_type {};
+template <template <size_t> class B, size_t N>
+struct IsBitsetImpl<B<N>> : std::is_same<B<N>, std::bitset<N>> {};
+template <typename C>
+using IsBitset = IsBitsetImpl<absl::decay_t<C>>;
+
+template <typename C>
+struct IsSTLContainer
+    : absl::disjunction<
+          IsArray<C>, IsBitset<C>, IsSpecialization<C, std::deque>,
+          IsSpecialization<C, std::forward_list>,
+          IsSpecialization<C, std::list>, IsSpecialization<C, std::map>,
+          IsSpecialization<C, std::multimap>, IsSpecialization<C, std::set>,
+          IsSpecialization<C, std::multiset>,
+          IsSpecialization<C, std::unordered_map>,
+          IsSpecialization<C, std::unordered_multimap>,
+          IsSpecialization<C, std::unordered_set>,
+          IsSpecialization<C, std::unordered_multiset>,
+          IsSpecialization<C, std::vector>> {};
+
+template <typename C, template <typename...> class T, typename = void>
+struct IsBaseOfSpecializationImpl : std::false_type {};
+// IsBaseOfSpecializationImpl needs multiple partial specializations to SFINAE
+// on the existence of container dependent types and plug them into the STL
+// template.
+template <typename C, template <typename, typename> class T>
+struct IsBaseOfSpecializationImpl<
+    C, T, absl::void_t<typename C::value_type, typename C::allocator_type>>
+    : std::is_base_of<C,
+                      T<typename C::value_type, typename C::allocator_type>> {};
+template <typename C, template <typename, typename, typename> class T>
+struct IsBaseOfSpecializationImpl<
+    C, T,
+    absl::void_t<typename C::key_type, typename C::key_compare,
+                 typename C::allocator_type>>
+    : std::is_base_of<C, T<typename C::key_type, typename C::key_compare,
+                           typename C::allocator_type>> {};
+template <typename C, template <typename, typename, typename, typename> class T>
+struct IsBaseOfSpecializationImpl<
+    C, T,
+    absl::void_t<typename C::key_type, typename C::mapped_type,
+                 typename C::key_compare, typename C::allocator_type>>
+    : std::is_base_of<C,
+                      T<typename C::key_type, typename C::mapped_type,
+                        typename C::key_compare, typename C::allocator_type>> {
+};
+template <typename C, template <typename, typename, typename, typename> class T>
+struct IsBaseOfSpecializationImpl<
+    C, T,
+    absl::void_t<typename C::key_type, typename C::hasher,
+                 typename C::key_equal, typename C::allocator_type>>
+    : std::is_base_of<C, T<typename C::key_type, typename C::hasher,
+                           typename C::key_equal, typename C::allocator_type>> {
+};
+template <typename C,
+          template <typename, typename, typename, typename, typename> class T>
+struct IsBaseOfSpecializationImpl<
+    C, T,
+    absl::void_t<typename C::key_type, typename C::mapped_type,
+                 typename C::hasher, typename C::key_equal,
+                 typename C::allocator_type>>
+    : std::is_base_of<C, T<typename C::key_type, typename C::mapped_type,
+                           typename C::hasher, typename C::key_equal,
+                           typename C::allocator_type>> {};
+template <typename C, template <typename...> class T>
+using IsBaseOfSpecialization = IsBaseOfSpecializationImpl<absl::decay_t<C>, T>;
+
+template <typename C>
+struct IsBaseOfArrayImpl : std::false_type {};
+template <template <typename, size_t> class A, typename T, size_t N>
+struct IsBaseOfArrayImpl<A<T, N>> : std::is_base_of<A<T, N>, std::array<T, N>> {
+};
+template <typename C>
+using IsBaseOfArray = IsBaseOfArrayImpl<absl::decay_t<C>>;
+
+template <typename C>
+struct IsBaseOfBitsetImpl : std::false_type {};
+template <template <size_t> class B, size_t N>
+struct IsBaseOfBitsetImpl<B<N>> : std::is_base_of<B<N>, std::bitset<N>> {};
+template <typename C>
+using IsBaseOfBitset = IsBaseOfBitsetImpl<absl::decay_t<C>>;
+
+template <typename C>
+struct IsBaseOfSTLContainer
+    : absl::disjunction<IsBaseOfArray<C>, IsBaseOfBitset<C>,
+                        IsBaseOfSpecialization<C, std::deque>,
+                        IsBaseOfSpecialization<C, std::forward_list>,
+                        IsBaseOfSpecialization<C, std::list>,
+                        IsBaseOfSpecialization<C, std::map>,
+                        IsBaseOfSpecialization<C, std::multimap>,
+                        IsBaseOfSpecialization<C, std::set>,
+                        IsBaseOfSpecialization<C, std::multiset>,
+                        IsBaseOfSpecialization<C, std::unordered_map>,
+                        IsBaseOfSpecialization<C, std::unordered_multimap>,
+                        IsBaseOfSpecialization<C, std::unordered_set>,
+                        IsBaseOfSpecialization<C, std::unordered_multiset>,
+                        IsBaseOfSpecialization<C, std::vector>> {};
+
+template <typename C, template <typename...> class T, typename = void>
+struct IsConvertibleToSpecializationImpl : std::false_type {};
+// IsConvertibleToSpecializationImpl needs multiple partial specializations to
+// SFINAE on the existence of container dependent types and plug them into the
+// STL template.
+template <typename C, template <typename, typename> class T>
+struct IsConvertibleToSpecializationImpl<
+    C, T, absl::void_t<typename C::value_type, typename C::allocator_type>>
+    : std::is_convertible<
+          C, T<typename C::value_type, typename C::allocator_type>> {};
+template <typename C, template <typename, typename, typename> class T>
+struct IsConvertibleToSpecializationImpl<
+    C, T,
+    absl::void_t<typename C::key_type, typename C::key_compare,
+                 typename C::allocator_type>>
+    : std::is_convertible<C, T<typename C::key_type, typename C::key_compare,
+                               typename C::allocator_type>> {};
+template <typename C, template <typename, typename, typename, typename> class T>
+struct IsConvertibleToSpecializationImpl<
+    C, T,
+    absl::void_t<typename C::key_type, typename C::mapped_type,
+                 typename C::key_compare, typename C::allocator_type>>
+    : std::is_convertible<
+          C, T<typename C::key_type, typename C::mapped_type,
+               typename C::key_compare, typename C::allocator_type>> {};
+template <typename C, template <typename, typename, typename, typename> class T>
+struct IsConvertibleToSpecializationImpl<
+    C, T,
+    absl::void_t<typename C::key_type, typename C::hasher,
+                 typename C::key_equal, typename C::allocator_type>>
+    : std::is_convertible<
+          C, T<typename C::key_type, typename C::hasher, typename C::key_equal,
+               typename C::allocator_type>> {};
+template <typename C,
+          template <typename, typename, typename, typename, typename> class T>
+struct IsConvertibleToSpecializationImpl<
+    C, T,
+    absl::void_t<typename C::key_type, typename C::mapped_type,
+                 typename C::hasher, typename C::key_equal,
+                 typename C::allocator_type>>
+    : std::is_convertible<C, T<typename C::key_type, typename C::mapped_type,
+                               typename C::hasher, typename C::key_equal,
+                               typename C::allocator_type>> {};
+template <typename C, template <typename...> class T>
+using IsConvertibleToSpecialization =
+    IsConvertibleToSpecializationImpl<absl::decay_t<C>, T>;
+
+template <typename C>
+struct IsConvertibleToArrayImpl : std::false_type {};
+template <template <typename, size_t> class A, typename T, size_t N>
+struct IsConvertibleToArrayImpl<A<T, N>>
+    : std::is_convertible<A<T, N>, std::array<T, N>> {};
+template <typename C>
+using IsConvertibleToArray = IsConvertibleToArrayImpl<absl::decay_t<C>>;
+
+template <typename C>
+struct IsConvertibleToBitsetImpl : std::false_type {};
+template <template <size_t> class B, size_t N>
+struct IsConvertibleToBitsetImpl<B<N>>
+    : std::is_convertible<B<N>, std::bitset<N>> {};
+template <typename C>
+using IsConvertibleToBitset = IsConvertibleToBitsetImpl<absl::decay_t<C>>;
+
+template <typename C>
+struct IsConvertibleToSTLContainer
+    : absl::disjunction<
+          IsConvertibleToArray<C>, IsConvertibleToBitset<C>,
+          IsConvertibleToSpecialization<C, std::deque>,
+          IsConvertibleToSpecialization<C, std::forward_list>,
+          IsConvertibleToSpecialization<C, std::list>,
+          IsConvertibleToSpecialization<C, std::map>,
+          IsConvertibleToSpecialization<C, std::multimap>,
+          IsConvertibleToSpecialization<C, std::set>,
+          IsConvertibleToSpecialization<C, std::multiset>,
+          IsConvertibleToSpecialization<C, std::unordered_map>,
+          IsConvertibleToSpecialization<C, std::unordered_multimap>,
+          IsConvertibleToSpecialization<C, std::unordered_set>,
+          IsConvertibleToSpecialization<C, std::unordered_multiset>,
+          IsConvertibleToSpecialization<C, std::vector>> {};
+
+template <typename C>
+struct IsStrictlyBaseOfAndConvertibleToSTLContainer
+    : absl::conjunction<absl::negation<IsSTLContainer<C>>,
+                        IsBaseOfSTLContainer<C>,
+                        IsConvertibleToSTLContainer<C>> {};
+
+}  // namespace strings_internal
+}  // namespace absl
+#endif  // ABSL_STRINGS_INTERNAL_STL_TYPE_TRAITS_H_
diff --git a/absl/strings/internal/str_format/arg.cc b/absl/strings/internal/str_format/arg.cc
new file mode 100644
index 0000000..b40be8f
--- /dev/null
+++ b/absl/strings/internal/str_format/arg.cc
@@ -0,0 +1,377 @@
+//
+// POSIX spec:
+//   http://pubs.opengroup.org/onlinepubs/009695399/functions/fprintf.html
+//
+#include "absl/strings/internal/str_format/arg.h"
+
+#include <cassert>
+#include <cerrno>
+#include <cstdlib>
+#include <string>
+#include <type_traits>
+
+#include "absl/base/port.h"
+#include "absl/strings/internal/str_format/float_conversion.h"
+
+namespace absl {
+namespace str_format_internal {
+namespace {
+
+const char kDigit[2][32] = { "0123456789abcdef", "0123456789ABCDEF" };
+
+// Reduce *capacity by s.size(), clipped to a 0 minimum.
+void ReducePadding(string_view s, size_t *capacity) {
+  *capacity = Excess(s.size(), *capacity);
+}
+
+// Reduce *capacity by n, clipped to a 0 minimum.
+void ReducePadding(size_t n, size_t *capacity) {
+  *capacity = Excess(n, *capacity);
+}
+
+template <typename T>
+struct MakeUnsigned : std::make_unsigned<T> {};
+template <>
+struct MakeUnsigned<absl::uint128> {
+  using type = absl::uint128;
+};
+
+template <typename T>
+struct IsSigned : std::is_signed<T> {};
+template <>
+struct IsSigned<absl::uint128> : std::false_type {};
+
+class ConvertedIntInfo {
+ public:
+  template <typename T>
+  ConvertedIntInfo(T v, ConversionChar conv) {
+    using Unsigned = typename MakeUnsigned<T>::type;
+    auto u = static_cast<Unsigned>(v);
+    if (IsNeg(v)) {
+      is_neg_ = true;
+      u = Unsigned{} - u;
+    } else {
+      is_neg_ = false;
+    }
+    UnsignedToStringRight(u, conv);
+  }
+
+  string_view digits() const {
+    return {end() - size_, static_cast<size_t>(size_)};
+  }
+  bool is_neg() const { return is_neg_; }
+
+ private:
+  template <typename T, bool IsSigned>
+  struct IsNegImpl {
+    static bool Eval(T v) { return v < 0; }
+  };
+  template <typename T>
+  struct IsNegImpl<T, false> {
+    static bool Eval(T) {
+      return false;
+    }
+  };
+
+  template <typename T>
+  bool IsNeg(T v) {
+    return IsNegImpl<T, IsSigned<T>::value>::Eval(v);
+  }
+
+  template <typename T>
+  void UnsignedToStringRight(T u, ConversionChar conv) {
+    char *p = end();
+    switch (conv.radix()) {
+      default:
+      case 10:
+        for (; u; u /= 10)
+          *--p = static_cast<char>('0' + static_cast<size_t>(u % 10));
+        break;
+      case 8:
+        for (; u; u /= 8)
+          *--p = static_cast<char>('0' + static_cast<size_t>(u % 8));
+        break;
+      case 16: {
+        const char *digits = kDigit[conv.upper() ? 1 : 0];
+        for (; u; u /= 16) *--p = digits[static_cast<size_t>(u % 16)];
+        break;
+      }
+    }
+    size_ = static_cast<int>(end() - p);
+  }
+
+  const char *end() const { return storage_ + sizeof(storage_); }
+  char *end() { return storage_ + sizeof(storage_); }
+
+  bool is_neg_;
+  int size_;
+  // Max size: 128 bit value as octal -> 43 digits
+  char storage_[128 / 3 + 1];
+};
+
+// Note: 'o' conversions do not have a base indicator, it's just that
+// the '#' flag is specified to modify the precision for 'o' conversions.
+string_view BaseIndicator(const ConvertedIntInfo &info,
+                          const ConversionSpec conv) {
+  bool alt = conv.flags().alt;
+  int radix = conv.conv().radix();
+  if (conv.conv().id() == ConversionChar::p)
+    alt = true;  // always show 0x for %p.
+  // From the POSIX description of '#' flag:
+  //   "For x or X conversion specifiers, a non-zero result shall have
+  //   0x (or 0X) prefixed to it."
+  if (alt && radix == 16 && !info.digits().empty()) {
+    if (conv.conv().upper()) return "0X";
+    return "0x";
+  }
+  return {};
+}
+
+string_view SignColumn(bool neg, const ConversionSpec conv) {
+  if (conv.conv().is_signed()) {
+    if (neg) return "-";
+    if (conv.flags().show_pos) return "+";
+    if (conv.flags().sign_col) return " ";
+  }
+  return {};
+}
+
+bool ConvertCharImpl(unsigned char v, const ConversionSpec conv,
+                     FormatSinkImpl *sink) {
+  size_t fill = 0;
+  if (conv.width() >= 0) fill = conv.width();
+  ReducePadding(1, &fill);
+  if (!conv.flags().left) sink->Append(fill, ' ');
+  sink->Append(1, v);
+  if (conv.flags().left) sink->Append(fill, ' ');
+  return true;
+}
+
+bool ConvertIntImplInner(const ConvertedIntInfo &info,
+                         const ConversionSpec conv, FormatSinkImpl *sink) {
+  // Print as a sequence of Substrings:
+  //   [left_spaces][sign][base_indicator][zeroes][formatted][right_spaces]
+  size_t fill = 0;
+  if (conv.width() >= 0) fill = conv.width();
+
+  string_view formatted = info.digits();
+  ReducePadding(formatted, &fill);
+
+  string_view sign = SignColumn(info.is_neg(), conv);
+  ReducePadding(sign, &fill);
+
+  string_view base_indicator = BaseIndicator(info, conv);
+  ReducePadding(base_indicator, &fill);
+
+  int precision = conv.precision();
+  bool precision_specified = precision >= 0;
+  if (!precision_specified)
+    precision = 1;
+
+  if (conv.flags().alt && conv.conv().id() == ConversionChar::o) {
+    // From POSIX description of the '#' (alt) flag:
+    //   "For o conversion, it increases the precision (if necessary) to
+    //   force the first digit of the result to be zero."
+    if (formatted.empty() || *formatted.begin() != '0') {
+      int needed = static_cast<int>(formatted.size()) + 1;
+      precision = std::max(precision, needed);
+    }
+  }
+
+  size_t num_zeroes = Excess(formatted.size(), precision);
+  ReducePadding(num_zeroes, &fill);
+
+  size_t num_left_spaces = !conv.flags().left ? fill : 0;
+  size_t num_right_spaces = conv.flags().left ? fill : 0;
+
+  // From POSIX description of the '0' (zero) flag:
+  //   "For d, i, o, u, x, and X conversion specifiers, if a precision
+  //   is specified, the '0' flag is ignored."
+  if (!precision_specified && conv.flags().zero) {
+    num_zeroes += num_left_spaces;
+    num_left_spaces = 0;
+  }
+
+  sink->Append(num_left_spaces, ' ');
+  sink->Append(sign);
+  sink->Append(base_indicator);
+  sink->Append(num_zeroes, '0');
+  sink->Append(formatted);
+  sink->Append(num_right_spaces, ' ');
+  return true;
+}
+
+template <typename T>
+bool ConvertIntImplInner(T v, const ConversionSpec conv, FormatSinkImpl *sink) {
+  ConvertedIntInfo info(v, conv.conv());
+  if (conv.flags().basic && conv.conv().id() != ConversionChar::p) {
+    if (info.is_neg()) sink->Append(1, '-');
+    if (info.digits().empty()) {
+      sink->Append(1, '0');
+    } else {
+      sink->Append(info.digits());
+    }
+    return true;
+  }
+  return ConvertIntImplInner(info, conv, sink);
+}
+
+template <typename T>
+bool ConvertIntArg(T v, const ConversionSpec conv, FormatSinkImpl *sink) {
+  if (conv.conv().is_float()) {
+    return FormatConvertImpl(static_cast<double>(v), conv, sink).value;
+  }
+  if (conv.conv().id() == ConversionChar::c)
+    return ConvertCharImpl(static_cast<unsigned char>(v), conv, sink);
+  if (!conv.conv().is_integral())
+    return false;
+  if (!conv.conv().is_signed() && IsSigned<T>::value) {
+    using U = typename MakeUnsigned<T>::type;
+    return FormatConvertImpl(static_cast<U>(v), conv, sink).value;
+  }
+  return ConvertIntImplInner(v, conv, sink);
+}
+
+template <typename T>
+bool ConvertFloatArg(T v, const ConversionSpec conv, FormatSinkImpl *sink) {
+  return conv.conv().is_float() && ConvertFloatImpl(v, conv, sink);
+}
+
+inline bool ConvertStringArg(string_view v, const ConversionSpec conv,
+                             FormatSinkImpl *sink) {
+  if (conv.conv().id() != ConversionChar::s)
+    return false;
+  if (conv.flags().basic) {
+    sink->Append(v);
+    return true;
+  }
+  return sink->PutPaddedString(v, conv.width(), conv.precision(),
+                               conv.flags().left);
+}
+
+}  // namespace
+
+// ==================== Strings ====================
+ConvertResult<Conv::s> FormatConvertImpl(const std::string &v,
+                                         const ConversionSpec conv,
+                                         FormatSinkImpl *sink) {
+  return {ConvertStringArg(v, conv, sink)};
+}
+
+ConvertResult<Conv::s> FormatConvertImpl(string_view v,
+                                         const ConversionSpec conv,
+                                         FormatSinkImpl *sink) {
+  return {ConvertStringArg(v, conv, sink)};
+}
+
+ConvertResult<Conv::s | Conv::p> FormatConvertImpl(const char *v,
+                                                   const ConversionSpec conv,
+                                                   FormatSinkImpl *sink) {
+  if (conv.conv().id() == ConversionChar::p)
+    return {FormatConvertImpl(VoidPtr(v), conv, sink).value};
+  size_t len;
+  if (v == nullptr) {
+    len = 0;
+  } else if (conv.precision() < 0) {
+    len = std::strlen(v);
+  } else {
+    // If precision is set, we look for the null terminator on the valid range.
+    len = std::find(v, v + conv.precision(), '\0') - v;
+  }
+  return {ConvertStringArg(string_view(v, len), conv, sink)};
+}
+
+// ==================== Raw pointers ====================
+ConvertResult<Conv::p> FormatConvertImpl(VoidPtr v, const ConversionSpec conv,
+                                         FormatSinkImpl *sink) {
+  if (conv.conv().id() != ConversionChar::p)
+    return {false};
+  if (!v.value) {
+    sink->Append("(nil)");
+    return {true};
+  }
+  return {ConvertIntImplInner(v.value, conv, sink)};
+}
+
+// ==================== Floats ====================
+FloatingConvertResult FormatConvertImpl(float v, const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertFloatArg(v, conv, sink)};
+}
+FloatingConvertResult FormatConvertImpl(double v, const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertFloatArg(v, conv, sink)};
+}
+FloatingConvertResult FormatConvertImpl(long double v,
+                                        const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertFloatArg(v, conv, sink)};
+}
+
+// ==================== Chars ====================
+IntegralConvertResult FormatConvertImpl(char v, const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+IntegralConvertResult FormatConvertImpl(signed char v,
+                                        const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+IntegralConvertResult FormatConvertImpl(unsigned char v,
+                                        const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+
+// ==================== Ints ====================
+IntegralConvertResult FormatConvertImpl(short v,  // NOLINT
+                                        const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+IntegralConvertResult FormatConvertImpl(unsigned short v,  // NOLINT
+                                        const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+IntegralConvertResult FormatConvertImpl(int v, const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+IntegralConvertResult FormatConvertImpl(unsigned v, const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+IntegralConvertResult FormatConvertImpl(long v,  // NOLINT
+                                        const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+IntegralConvertResult FormatConvertImpl(unsigned long v,  // NOLINT
+                                        const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+IntegralConvertResult FormatConvertImpl(long long v,  // NOLINT
+                                        const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+IntegralConvertResult FormatConvertImpl(unsigned long long v,  // NOLINT
+                                        const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+IntegralConvertResult FormatConvertImpl(absl::uint128 v,
+                                        const ConversionSpec conv,
+                                        FormatSinkImpl *sink) {
+  return {ConvertIntArg(v, conv, sink)};
+}
+
+ABSL_INTERNAL_FORMAT_DISPATCH_OVERLOADS_EXPAND_();
+
+
+}  // namespace str_format_internal
+
+}  // namespace absl
diff --git a/absl/strings/internal/str_format/arg.h b/absl/strings/internal/str_format/arg.h
new file mode 100644
index 0000000..5cb3a14
--- /dev/null
+++ b/absl/strings/internal/str_format/arg.h
@@ -0,0 +1,424 @@
+#ifndef ABSL_STRINGS_INTERNAL_STR_FORMAT_ARG_H_
+#define ABSL_STRINGS_INTERNAL_STR_FORMAT_ARG_H_
+
+#include <string.h>
+#include <wchar.h>
+
+#include <cstdio>
+#include <iomanip>
+#include <limits>
+#include <memory>
+#include <sstream>
+#include <string>
+#include <type_traits>
+
+#include "absl/base/port.h"
+#include "absl/meta/type_traits.h"
+#include "absl/numeric/int128.h"
+#include "absl/strings/internal/str_format/extension.h"
+#include "absl/strings/string_view.h"
+
+class Cord;
+class CordReader;
+
+namespace absl {
+
+class FormatCountCapture;
+class FormatSink;
+
+namespace str_format_internal {
+
+template <typename T, typename = void>
+struct HasUserDefinedConvert : std::false_type {};
+
+template <typename T>
+struct HasUserDefinedConvert<
+    T, void_t<decltype(AbslFormatConvert(
+           std::declval<const T&>(), std::declval<ConversionSpec>(),
+           std::declval<FormatSink*>()))>> : std::true_type {};
+
+template <typename T>
+class StreamedWrapper;
+
+// If 'v' can be converted (in the printf sense) according to 'conv',
+// then convert it, appending to `sink` and return `true`.
+// Otherwise fail and return `false`.
+
+// Raw pointers.
+struct VoidPtr {
+  VoidPtr() = default;
+  template <typename T,
+            decltype(reinterpret_cast<uintptr_t>(std::declval<T*>())) = 0>
+  VoidPtr(T* ptr)  // NOLINT
+      : value(ptr ? reinterpret_cast<uintptr_t>(ptr) : 0) {}
+  uintptr_t value;
+};
+ConvertResult<Conv::p> FormatConvertImpl(VoidPtr v, ConversionSpec conv,
+                                         FormatSinkImpl* sink);
+
+// Strings.
+ConvertResult<Conv::s> FormatConvertImpl(const std::string& v,
+                                         ConversionSpec conv,
+                                         FormatSinkImpl* sink);
+ConvertResult<Conv::s> FormatConvertImpl(string_view v, ConversionSpec conv,
+                                         FormatSinkImpl* sink);
+ConvertResult<Conv::s | Conv::p> FormatConvertImpl(const char* v,
+                                                   ConversionSpec conv,
+                                                   FormatSinkImpl* sink);
+template <class AbslCord,
+          typename std::enable_if<
+              std::is_same<AbslCord, ::Cord>::value>::type* = nullptr,
+          class AbslCordReader = ::CordReader>
+ConvertResult<Conv::s> FormatConvertImpl(const AbslCord& value,
+                                         ConversionSpec conv,
+                                         FormatSinkImpl* sink) {
+  if (conv.conv().id() != ConversionChar::s) return {false};
+
+  bool is_left = conv.flags().left;
+  size_t space_remaining = 0;
+
+  int width = conv.width();
+  if (width >= 0) space_remaining = width;
+
+  size_t to_write = value.size();
+
+  int precision = conv.precision();
+  if (precision >= 0)
+    to_write = (std::min)(to_write, static_cast<size_t>(precision));
+
+  space_remaining = Excess(to_write, space_remaining);
+
+  if (space_remaining > 0 && !is_left) sink->Append(space_remaining, ' ');
+
+  string_view piece;
+  for (AbslCordReader reader(value);
+       to_write > 0 && reader.ReadFragment(&piece); to_write -= piece.size()) {
+    if (piece.size() > to_write) piece.remove_suffix(piece.size() - to_write);
+    sink->Append(piece);
+  }
+
+  if (space_remaining > 0 && is_left) sink->Append(space_remaining, ' ');
+  return {true};
+}
+
+using IntegralConvertResult =
+    ConvertResult<Conv::c | Conv::numeric | Conv::star>;
+using FloatingConvertResult = ConvertResult<Conv::floating>;
+
+// Floats.
+FloatingConvertResult FormatConvertImpl(float v, ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+FloatingConvertResult FormatConvertImpl(double v, ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+FloatingConvertResult FormatConvertImpl(long double v, ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+
+// Chars.
+IntegralConvertResult FormatConvertImpl(char v, ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+IntegralConvertResult FormatConvertImpl(signed char v, ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+IntegralConvertResult FormatConvertImpl(unsigned char v, ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+
+// Ints.
+IntegralConvertResult FormatConvertImpl(short v,  // NOLINT
+                                        ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+IntegralConvertResult FormatConvertImpl(unsigned short v,  // NOLINT
+                                        ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+IntegralConvertResult FormatConvertImpl(int v, ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+IntegralConvertResult FormatConvertImpl(unsigned v, ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+IntegralConvertResult FormatConvertImpl(long v,  // NOLINT
+                                        ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+IntegralConvertResult FormatConvertImpl(unsigned long v,  // NOLINT
+                                        ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+IntegralConvertResult FormatConvertImpl(long long v,  // NOLINT
+                                        ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+IntegralConvertResult FormatConvertImpl(unsigned long long v,  // NOLINT
+                                        ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+IntegralConvertResult FormatConvertImpl(uint128 v, ConversionSpec conv,
+                                        FormatSinkImpl* sink);
+template <typename T, enable_if_t<std::is_same<T, bool>::value, int> = 0>
+IntegralConvertResult FormatConvertImpl(T v, ConversionSpec conv,
+                                        FormatSinkImpl* sink) {
+  return FormatConvertImpl(static_cast<int>(v), conv, sink);
+}
+
+// We provide this function to help the checker, but it is never defined.
+// FormatArgImpl will use the underlying Convert functions instead.
+template <typename T>
+typename std::enable_if<std::is_enum<T>::value &&
+                            !HasUserDefinedConvert<T>::value,
+                        IntegralConvertResult>::type
+FormatConvertImpl(T v, ConversionSpec conv, FormatSinkImpl* sink);
+
+template <typename T>
+ConvertResult<Conv::s> FormatConvertImpl(const StreamedWrapper<T>& v,
+                                         ConversionSpec conv,
+                                         FormatSinkImpl* out) {
+  std::ostringstream oss;
+  oss << v.v_;
+  if (!oss) return {false};
+  return str_format_internal::FormatConvertImpl(oss.str(), conv, out);
+}
+
+// Use templates and dependent types to delay evaluation of the function
+// until after FormatCountCapture is fully defined.
+struct FormatCountCaptureHelper {
+  template <class T = int>
+  static ConvertResult<Conv::n> ConvertHelper(const FormatCountCapture& v,
+                                              ConversionSpec conv,
+                                              FormatSinkImpl* sink) {
+    const absl::enable_if_t<sizeof(T) != 0, FormatCountCapture>& v2 = v;
+
+    if (conv.conv().id() != str_format_internal::ConversionChar::n)
+      return {false};
+    *v2.p_ = static_cast<int>(sink->size());
+    return {true};
+  }
+};
+
+template <class T = int>
+ConvertResult<Conv::n> FormatConvertImpl(const FormatCountCapture& v,
+                                         ConversionSpec conv,
+                                         FormatSinkImpl* sink) {
+  return FormatCountCaptureHelper::ConvertHelper(v, conv, sink);
+}
+
+// Helper friend struct to hide implementation details from the public API of
+// FormatArgImpl.
+struct FormatArgImplFriend {
+  template <typename Arg>
+  static bool ToInt(Arg arg, int* out) {
+    // A value initialized ConversionSpec has a `none` conv, which tells the
+    // dispatcher to run the `int` conversion.
+    return arg.dispatcher_(arg.data_, {}, out);
+  }
+
+  template <typename Arg>
+  static bool Convert(Arg arg, str_format_internal::ConversionSpec conv,
+                      FormatSinkImpl* out) {
+    return arg.dispatcher_(arg.data_, conv, out);
+  }
+
+  template <typename Arg>
+  static typename Arg::Dispatcher GetVTablePtrForTest(Arg arg) {
+    return arg.dispatcher_;
+  }
+};
+
+// A type-erased handle to a format argument.
+class FormatArgImpl {
+ private:
+  enum { kInlinedSpace = 8 };
+
+  using VoidPtr = str_format_internal::VoidPtr;
+
+  union Data {
+    const void* ptr;
+    const volatile void* volatile_ptr;
+    char buf[kInlinedSpace];
+  };
+
+  using Dispatcher = bool (*)(Data, ConversionSpec, void* out);
+
+  template <typename T>
+  struct store_by_value
+      : std::integral_constant<bool, (sizeof(T) <= kInlinedSpace) &&
+                                         (std::is_integral<T>::value ||
+                                          std::is_floating_point<T>::value ||
+                                          std::is_pointer<T>::value ||
+                                          std::is_same<VoidPtr, T>::value)> {};
+
+  enum StoragePolicy { ByPointer, ByVolatilePointer, ByValue };
+  template <typename T>
+  struct storage_policy
+      : std::integral_constant<StoragePolicy,
+                               (std::is_volatile<T>::value
+                                    ? ByVolatilePointer
+                                    : (store_by_value<T>::value ? ByValue
+                                                                : ByPointer))> {
+  };
+
+  // To reduce the number of vtables we will decay values before hand.
+  // Anything with a user-defined Convert will get its own vtable.
+  // For everything else:
+  //   - Decay char* and char arrays into `const char*`
+  //   - Decay any other pointer to `const void*`
+  //   - Decay all enums to their underlying type.
+  //   - Decay function pointers to void*.
+  template <typename T, typename = void>
+  struct DecayType {
+    static constexpr bool kHasUserDefined =
+        str_format_internal::HasUserDefinedConvert<T>::value;
+    using type = typename std::conditional<
+        !kHasUserDefined && std::is_convertible<T, const char*>::value,
+        const char*,
+        typename std::conditional<!kHasUserDefined &&
+                                      std::is_convertible<T, VoidPtr>::value,
+                                  VoidPtr, const T&>::type>::type;
+  };
+  template <typename T>
+  struct DecayType<T,
+                   typename std::enable_if<
+                       !str_format_internal::HasUserDefinedConvert<T>::value &&
+                       std::is_enum<T>::value>::type> {
+    using type = typename std::underlying_type<T>::type;
+  };
+
+ public:
+  template <typename T>
+  explicit FormatArgImpl(const T& value) {
+    using D = typename DecayType<T>::type;
+    static_assert(
+        std::is_same<D, const T&>::value || storage_policy<D>::value == ByValue,
+        "Decayed types must be stored by value");
+    Init(static_cast<D>(value));
+  }
+
+ private:
+  friend struct str_format_internal::FormatArgImplFriend;
+  template <typename T, StoragePolicy = storage_policy<T>::value>
+  struct Manager;
+
+  template <typename T>
+  struct Manager<T, ByPointer> {
+    static Data SetValue(const T& value) {
+      Data data;
+      data.ptr = std::addressof(value);
+      return data;
+    }
+
+    static const T& Value(Data arg) { return *static_cast<const T*>(arg.ptr); }
+  };
+
+  template <typename T>
+  struct Manager<T, ByVolatilePointer> {
+    static Data SetValue(const T& value) {
+      Data data;
+      data.volatile_ptr = &value;
+      return data;
+    }
+
+    static const T& Value(Data arg) {
+      return *static_cast<const T*>(arg.volatile_ptr);
+    }
+  };
+
+  template <typename T>
+  struct Manager<T, ByValue> {
+    static Data SetValue(const T& value) {
+      Data data;
+      memcpy(data.buf, &value, sizeof(value));
+      return data;
+    }
+
+    static T Value(Data arg) {
+      T value;
+      memcpy(&value, arg.buf, sizeof(T));
+      return value;
+    }
+  };
+
+  template <typename T>
+  void Init(const T& value) {
+    data_ = Manager<T>::SetValue(value);
+    dispatcher_ = &Dispatch<T>;
+  }
+
+  template <typename T>
+  static int ToIntVal(const T& val) {
+    using CommonType = typename std::conditional<std::is_signed<T>::value,
+                                                 int64_t, uint64_t>::type;
+    if (static_cast<CommonType>(val) >
+        static_cast<CommonType>((std::numeric_limits<int>::max)())) {
+      return (std::numeric_limits<int>::max)();
+    } else if (std::is_signed<T>::value &&
+               static_cast<CommonType>(val) <
+                   static_cast<CommonType>((std::numeric_limits<int>::min)())) {
+      return (std::numeric_limits<int>::min)();
+    }
+    return static_cast<int>(val);
+  }
+
+  template <typename T>
+  static bool ToInt(Data arg, int* out, std::true_type /* is_integral */,
+                    std::false_type) {
+    *out = ToIntVal(Manager<T>::Value(arg));
+    return true;
+  }
+
+  template <typename T>
+  static bool ToInt(Data arg, int* out, std::false_type,
+                    std::true_type /* is_enum */) {
+    *out = ToIntVal(static_cast<typename std::underlying_type<T>::type>(
+        Manager<T>::Value(arg)));
+    return true;
+  }
+
+  template <typename T>
+  static bool ToInt(Data, int*, std::false_type, std::false_type) {
+    return false;
+  }
+
+  template <typename T>
+  static bool Dispatch(Data arg, ConversionSpec spec, void* out) {
+    // A `none` conv indicates that we want the `int` conversion.
+    if (ABSL_PREDICT_FALSE(spec.conv().id() == ConversionChar::none)) {
+      return ToInt<T>(arg, static_cast<int*>(out), std::is_integral<T>(),
+                      std::is_enum<T>());
+    }
+
+    return str_format_internal::FormatConvertImpl(
+               Manager<T>::Value(arg), spec, static_cast<FormatSinkImpl*>(out))
+        .value;
+  }
+
+  Data data_;
+  Dispatcher dispatcher_;
+};
+
+#define ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(T, E) \
+  E template bool FormatArgImpl::Dispatch<T>(Data, ConversionSpec, void*)
+
+#define ABSL_INTERNAL_FORMAT_DISPATCH_OVERLOADS_EXPAND_(...)                   \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(str_format_internal::VoidPtr,     \
+                                             __VA_ARGS__);                     \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(bool, __VA_ARGS__);               \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(char, __VA_ARGS__);               \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(signed char, __VA_ARGS__);        \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(unsigned char, __VA_ARGS__);      \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(short, __VA_ARGS__); /* NOLINT */ \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(unsigned short,      /* NOLINT */ \
+                                             __VA_ARGS__);                     \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(int, __VA_ARGS__);                \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(unsigned int, __VA_ARGS__);       \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(long, __VA_ARGS__); /* NOLINT */  \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(unsigned long,      /* NOLINT */  \
+                                             __VA_ARGS__);                     \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(long long, /* NOLINT */           \
+                                             __VA_ARGS__);                     \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(unsigned long long, /* NOLINT */  \
+                                             __VA_ARGS__);                     \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(uint128, __VA_ARGS__);            \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(float, __VA_ARGS__);              \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(double, __VA_ARGS__);             \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(long double, __VA_ARGS__);        \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(const char*, __VA_ARGS__);        \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(std::string, __VA_ARGS__);        \
+  ABSL_INTERNAL_FORMAT_DISPATCH_INSTANTIATE_(string_view, __VA_ARGS__)
+
+ABSL_INTERNAL_FORMAT_DISPATCH_OVERLOADS_EXPAND_(extern);
+
+}  // namespace str_format_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_STR_FORMAT_ARG_H_
diff --git a/absl/strings/internal/str_format/arg_test.cc b/absl/strings/internal/str_format/arg_test.cc
new file mode 100644
index 0000000..3421fac
--- /dev/null
+++ b/absl/strings/internal/str_format/arg_test.cc
@@ -0,0 +1,111 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+#include "absl/strings/internal/str_format/arg.h"
+
+#include <ostream>
+#include <string>
+#include "gtest/gtest.h"
+#include "absl/strings/str_format.h"
+
+namespace absl {
+namespace str_format_internal {
+namespace {
+
+class FormatArgImplTest : public ::testing::Test {
+ public:
+  enum Color { kRed, kGreen, kBlue };
+
+  static const char *hi() { return "hi"; }
+};
+
+TEST_F(FormatArgImplTest, ToInt) {
+  int out = 0;
+  EXPECT_TRUE(FormatArgImplFriend::ToInt(FormatArgImpl(1), &out));
+  EXPECT_EQ(1, out);
+  EXPECT_TRUE(FormatArgImplFriend::ToInt(FormatArgImpl(-1), &out));
+  EXPECT_EQ(-1, out);
+  EXPECT_TRUE(
+      FormatArgImplFriend::ToInt(FormatArgImpl(static_cast<char>(64)), &out));
+  EXPECT_EQ(64, out);
+  EXPECT_TRUE(FormatArgImplFriend::ToInt(
+      FormatArgImpl(static_cast<unsigned long long>(123456)), &out));  // NOLINT
+  EXPECT_EQ(123456, out);
+  EXPECT_TRUE(FormatArgImplFriend::ToInt(
+      FormatArgImpl(static_cast<unsigned long long>(  // NOLINT
+                        std::numeric_limits<int>::max()) +
+                    1),
+      &out));
+  EXPECT_EQ(std::numeric_limits<int>::max(), out);
+  EXPECT_TRUE(FormatArgImplFriend::ToInt(
+      FormatArgImpl(static_cast<long long>(  // NOLINT
+                        std::numeric_limits<int>::min()) -
+                    10),
+      &out));
+  EXPECT_EQ(std::numeric_limits<int>::min(), out);
+  EXPECT_TRUE(FormatArgImplFriend::ToInt(FormatArgImpl(false), &out));
+  EXPECT_EQ(0, out);
+  EXPECT_TRUE(FormatArgImplFriend::ToInt(FormatArgImpl(true), &out));
+  EXPECT_EQ(1, out);
+  EXPECT_FALSE(FormatArgImplFriend::ToInt(FormatArgImpl(2.2), &out));
+  EXPECT_FALSE(FormatArgImplFriend::ToInt(FormatArgImpl(3.2f), &out));
+  EXPECT_FALSE(FormatArgImplFriend::ToInt(
+      FormatArgImpl(static_cast<int *>(nullptr)), &out));
+  EXPECT_FALSE(FormatArgImplFriend::ToInt(FormatArgImpl(hi()), &out));
+  EXPECT_FALSE(FormatArgImplFriend::ToInt(FormatArgImpl("hi"), &out));
+  EXPECT_TRUE(FormatArgImplFriend::ToInt(FormatArgImpl(kBlue), &out));
+  EXPECT_EQ(2, out);
+}
+
+extern const char kMyArray[];
+
+TEST_F(FormatArgImplTest, CharArraysDecayToCharPtr) {
+  const char* a = "";
+  EXPECT_EQ(FormatArgImplFriend::GetVTablePtrForTest(FormatArgImpl(a)),
+            FormatArgImplFriend::GetVTablePtrForTest(FormatArgImpl("")));
+  EXPECT_EQ(FormatArgImplFriend::GetVTablePtrForTest(FormatArgImpl(a)),
+            FormatArgImplFriend::GetVTablePtrForTest(FormatArgImpl("A")));
+  EXPECT_EQ(FormatArgImplFriend::GetVTablePtrForTest(FormatArgImpl(a)),
+            FormatArgImplFriend::GetVTablePtrForTest(FormatArgImpl("ABC")));
+  EXPECT_EQ(FormatArgImplFriend::GetVTablePtrForTest(FormatArgImpl(a)),
+            FormatArgImplFriend::GetVTablePtrForTest(FormatArgImpl(kMyArray)));
+}
+
+TEST_F(FormatArgImplTest, OtherPtrDecayToVoidPtr) {
+  auto expected = FormatArgImplFriend::GetVTablePtrForTest(
+      FormatArgImpl(static_cast<void *>(nullptr)));
+  EXPECT_EQ(FormatArgImplFriend::GetVTablePtrForTest(
+                FormatArgImpl(static_cast<int *>(nullptr))),
+            expected);
+  EXPECT_EQ(FormatArgImplFriend::GetVTablePtrForTest(
+                FormatArgImpl(static_cast<volatile int *>(nullptr))),
+            expected);
+
+  auto p = static_cast<void (*)()>([] {});
+  EXPECT_EQ(FormatArgImplFriend::GetVTablePtrForTest(FormatArgImpl(p)),
+            expected);
+}
+
+TEST_F(FormatArgImplTest, WorksWithCharArraysOfUnknownSize) {
+  std::string s;
+  FormatSinkImpl sink(&s);
+  ConversionSpec conv;
+  conv.set_conv(ConversionChar::FromChar('s'));
+  conv.set_flags(Flags());
+  conv.set_width(-1);
+  conv.set_precision(-1);
+  EXPECT_TRUE(
+      FormatArgImplFriend::Convert(FormatArgImpl(kMyArray), conv, &sink));
+  sink.Flush();
+  EXPECT_EQ("ABCDE", s);
+}
+const char kMyArray[] = "ABCDE";
+
+}  // namespace
+}  // namespace str_format_internal
+}  // namespace absl
diff --git a/absl/strings/internal/str_format/bind.cc b/absl/strings/internal/str_format/bind.cc
new file mode 100644
index 0000000..a31859e
--- /dev/null
+++ b/absl/strings/internal/str_format/bind.cc
@@ -0,0 +1,230 @@
+#include "absl/strings/internal/str_format/bind.h"
+
+#include <cerrno>
+#include <limits>
+#include <sstream>
+#include <string>
+
+namespace absl {
+namespace str_format_internal {
+
+namespace {
+
+inline bool BindFromPosition(int position, int* value,
+                             absl::Span<const FormatArgImpl> pack) {
+  assert(position > 0);
+  if (static_cast<size_t>(position) > pack.size()) {
+    return false;
+  }
+  // -1 because positions are 1-based
+  return FormatArgImplFriend::ToInt(pack[position - 1], value);
+}
+
+class ArgContext {
+ public:
+  explicit ArgContext(absl::Span<const FormatArgImpl> pack) : pack_(pack) {}
+
+  // Fill 'bound' with the results of applying the context's argument pack
+  // to the specified 'unbound'. We synthesize a BoundConversion by
+  // lining up a UnboundConversion with a user argument. We also
+  // resolve any '*' specifiers for width and precision, so after
+  // this call, 'bound' has all the information it needs to be formatted.
+  // Returns false on failure.
+  bool Bind(const UnboundConversion* unbound, BoundConversion* bound);
+
+ private:
+  absl::Span<const FormatArgImpl> pack_;
+};
+
+inline bool ArgContext::Bind(const UnboundConversion* unbound,
+                             BoundConversion* bound) {
+  const FormatArgImpl* arg = nullptr;
+  int arg_position = unbound->arg_position;
+  if (static_cast<size_t>(arg_position - 1) >= pack_.size()) return false;
+  arg = &pack_[arg_position - 1];  // 1-based
+
+  if (!unbound->flags.basic) {
+    int width = unbound->width.value();
+    bool force_left = false;
+    if (unbound->width.is_from_arg()) {
+      if (!BindFromPosition(unbound->width.get_from_arg(), &width, pack_))
+        return false;
+      if (width < 0) {
+        // "A negative field width is taken as a '-' flag followed by a
+        // positive field width."
+        force_left = true;
+        // Make sure we don't overflow the width when negating it.
+        width = -std::max(width, -std::numeric_limits<int>::max());
+      }
+    }
+
+    int precision = unbound->precision.value();
+    if (unbound->precision.is_from_arg()) {
+      if (!BindFromPosition(unbound->precision.get_from_arg(), &precision,
+                            pack_))
+        return false;
+    }
+
+    bound->set_width(width);
+    bound->set_precision(precision);
+    bound->set_flags(unbound->flags);
+    if (force_left)
+      bound->set_left(true);
+  } else {
+    bound->set_flags(unbound->flags);
+    bound->set_width(-1);
+    bound->set_precision(-1);
+  }
+
+  bound->set_length_mod(unbound->length_mod);
+  bound->set_conv(unbound->conv);
+  bound->set_arg(arg);
+  return true;
+}
+
+template <typename Converter>
+class ConverterConsumer {
+ public:
+  ConverterConsumer(Converter converter, absl::Span<const FormatArgImpl> pack)
+      : converter_(converter), arg_context_(pack) {}
+
+  bool Append(string_view s) {
+    converter_.Append(s);
+    return true;
+  }
+  bool ConvertOne(const UnboundConversion& conv, string_view conv_string) {
+    BoundConversion bound;
+    if (!arg_context_.Bind(&conv, &bound)) return false;
+    return converter_.ConvertOne(bound, conv_string);
+  }
+
+ private:
+  Converter converter_;
+  ArgContext arg_context_;
+};
+
+template <typename Converter>
+bool ConvertAll(const UntypedFormatSpecImpl format,
+                absl::Span<const FormatArgImpl> args, Converter converter) {
+  if (format.has_parsed_conversion()) {
+    return format.parsed_conversion()->ProcessFormat(
+        ConverterConsumer<Converter>(converter, args));
+  } else {
+    return ParseFormatString(format.str(),
+                             ConverterConsumer<Converter>(converter, args));
+  }
+}
+
+class DefaultConverter {
+ public:
+  explicit DefaultConverter(FormatSinkImpl* sink) : sink_(sink) {}
+
+  void Append(string_view s) const { sink_->Append(s); }
+
+  bool ConvertOne(const BoundConversion& bound, string_view /*conv*/) const {
+    return FormatArgImplFriend::Convert(*bound.arg(), bound, sink_);
+  }
+
+ private:
+  FormatSinkImpl* sink_;
+};
+
+class SummarizingConverter {
+ public:
+  explicit SummarizingConverter(FormatSinkImpl* sink) : sink_(sink) {}
+
+  void Append(string_view s) const { sink_->Append(s); }
+
+  bool ConvertOne(const BoundConversion& bound, string_view /*conv*/) const {
+    UntypedFormatSpecImpl spec("%d");
+
+    std::ostringstream ss;
+    ss << "{" << Streamable(spec, {*bound.arg()}) << ":" << bound.flags();
+    if (bound.width() >= 0) ss << bound.width();
+    if (bound.precision() >= 0) ss << "." << bound.precision();
+    ss << bound.length_mod() << bound.conv() << "}";
+    Append(ss.str());
+    return true;
+  }
+
+ private:
+  FormatSinkImpl* sink_;
+};
+
+}  // namespace
+
+bool BindWithPack(const UnboundConversion* props,
+                  absl::Span<const FormatArgImpl> pack,
+                  BoundConversion* bound) {
+  return ArgContext(pack).Bind(props, bound);
+}
+
+std::string Summarize(const UntypedFormatSpecImpl format,
+                      absl::Span<const FormatArgImpl> args) {
+  typedef SummarizingConverter Converter;
+  std::string out;
+  {
+    // inner block to destroy sink before returning out. It ensures a last
+    // flush.
+    FormatSinkImpl sink(&out);
+    if (!ConvertAll(format, args, Converter(&sink))) {
+      return "";
+    }
+  }
+  return out;
+}
+
+bool FormatUntyped(FormatRawSinkImpl raw_sink,
+                   const UntypedFormatSpecImpl format,
+                   absl::Span<const FormatArgImpl> args) {
+  FormatSinkImpl sink(raw_sink);
+  using Converter = DefaultConverter;
+  return ConvertAll(format, args, Converter(&sink));
+}
+
+std::ostream& Streamable::Print(std::ostream& os) const {
+  if (!FormatUntyped(&os, format_, args_)) os.setstate(std::ios::failbit);
+  return os;
+}
+
+std::string& AppendPack(std::string* out, const UntypedFormatSpecImpl format,
+                        absl::Span<const FormatArgImpl> args) {
+  size_t orig = out->size();
+  if (ABSL_PREDICT_FALSE(!FormatUntyped(out, format, args))) {
+    out->erase(orig);
+  }
+  return *out;
+}
+
+int FprintF(std::FILE* output, const UntypedFormatSpecImpl format,
+            absl::Span<const FormatArgImpl> args) {
+  FILERawSink sink(output);
+  if (!FormatUntyped(&sink, format, args)) {
+    errno = EINVAL;
+    return -1;
+  }
+  if (sink.error()) {
+    errno = sink.error();
+    return -1;
+  }
+  if (sink.count() > std::numeric_limits<int>::max()) {
+    errno = EFBIG;
+    return -1;
+  }
+  return static_cast<int>(sink.count());
+}
+
+int SnprintF(char* output, size_t size, const UntypedFormatSpecImpl format,
+             absl::Span<const FormatArgImpl> args) {
+  BufferRawSink sink(output, size ? size - 1 : 0);
+  if (!FormatUntyped(&sink, format, args)) {
+    errno = EINVAL;
+    return -1;
+  }
+  size_t total = sink.total_written();
+  if (size) output[std::min(total, size - 1)] = 0;
+  return static_cast<int>(total);
+}
+
+}  // namespace str_format_internal
+}  // namespace absl
diff --git a/absl/strings/internal/str_format/bind.h b/absl/strings/internal/str_format/bind.h
new file mode 100644
index 0000000..7df140a
--- /dev/null
+++ b/absl/strings/internal/str_format/bind.h
@@ -0,0 +1,211 @@
+#ifndef ABSL_STRINGS_INTERNAL_STR_FORMAT_BIND_H_
+#define ABSL_STRINGS_INTERNAL_STR_FORMAT_BIND_H_
+
+#include <array>
+#include <cstdio>
+#include <sstream>
+#include <string>
+
+#include "absl/base/port.h"
+#include "absl/strings/internal/str_format/arg.h"
+#include "absl/strings/internal/str_format/checker.h"
+#include "absl/strings/internal/str_format/parser.h"
+#include "absl/types/span.h"
+
+namespace absl {
+
+class UntypedFormatSpec;
+
+namespace str_format_internal {
+
+class BoundConversion : public ConversionSpec {
+ public:
+  const FormatArgImpl* arg() const { return arg_; }
+  void set_arg(const FormatArgImpl* a) { arg_ = a; }
+
+ private:
+  const FormatArgImpl* arg_;
+};
+
+// This is the type-erased class that the implementation uses.
+class UntypedFormatSpecImpl {
+ public:
+  UntypedFormatSpecImpl() = delete;
+
+  explicit UntypedFormatSpecImpl(string_view s)
+      : data_(s.data()), size_(s.size()) {}
+  explicit UntypedFormatSpecImpl(
+      const str_format_internal::ParsedFormatBase* pc)
+      : data_(pc), size_(~size_t{}) {}
+
+  bool has_parsed_conversion() const { return size_ == ~size_t{}; }
+
+  string_view str() const {
+    assert(!has_parsed_conversion());
+    return string_view(static_cast<const char*>(data_), size_);
+  }
+  const str_format_internal::ParsedFormatBase* parsed_conversion() const {
+    assert(has_parsed_conversion());
+    return static_cast<const str_format_internal::ParsedFormatBase*>(data_);
+  }
+
+  template <typename T>
+  static const UntypedFormatSpecImpl& Extract(const T& s) {
+    return s.spec_;
+  }
+
+ private:
+  const void* data_;
+  size_t size_;
+};
+
+template <typename T, typename...>
+struct MakeDependent {
+  using type = T;
+};
+
+// Implicitly convertible from `const char*`, `string_view`, and the
+// `ExtendedParsedFormat` type. This abstraction allows all format functions to
+// operate on any without providing too many overloads.
+template <typename... Args>
+class FormatSpecTemplate
+    : public MakeDependent<UntypedFormatSpec, Args...>::type {
+  using Base = typename MakeDependent<UntypedFormatSpec, Args...>::type;
+
+ public:
+#if ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+  // Honeypot overload for when the std::string is not constexpr.
+  // We use the 'unavailable' attribute to give a better compiler error than
+  // just 'method is deleted'.
+  FormatSpecTemplate(...)  // NOLINT
+      __attribute__((unavailable("Format std::string is not constexpr.")));
+
+  // Honeypot overload for when the format is constexpr and invalid.
+  // We use the 'unavailable' attribute to give a better compiler error than
+  // just 'method is deleted'.
+  // To avoid checking the format twice, we just check that the format is
+  // constexpr. If is it valid, then the overload below will kick in.
+  // We add the template here to make this overload have lower priority.
+  template <typename = void>
+  FormatSpecTemplate(const char* s)  // NOLINT
+      __attribute__((
+          enable_if(str_format_internal::EnsureConstexpr(s), "constexpr trap"),
+          unavailable(
+              "Format specified does not match the arguments passed.")));
+
+  template <typename T = void>
+  FormatSpecTemplate(string_view s)  // NOLINT
+      __attribute__((enable_if(str_format_internal::EnsureConstexpr(s),
+                               "constexpr trap"))) {
+    static_assert(sizeof(T*) == 0,
+                  "Format specified does not match the arguments passed.");
+  }
+
+  // Good format overload.
+  FormatSpecTemplate(const char* s)  // NOLINT
+      __attribute__((enable_if(ValidFormatImpl<ArgumentToConv<Args>()...>(s),
+                               "bad format trap")))
+      : Base(s) {}
+
+  FormatSpecTemplate(string_view s)  // NOLINT
+      __attribute__((enable_if(ValidFormatImpl<ArgumentToConv<Args>()...>(s),
+                               "bad format trap")))
+      : Base(s) {}
+
+#else  // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+  FormatSpecTemplate(const char* s) : Base(s) {}  // NOLINT
+  FormatSpecTemplate(string_view s) : Base(s) {}  // NOLINT
+
+#endif  // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+  template <Conv... C, typename = typename std::enable_if<
+                           sizeof...(C) == sizeof...(Args) &&
+                           AllOf(Contains(ArgumentToConv<Args>(),
+                                          C)...)>::type>
+  FormatSpecTemplate(const ExtendedParsedFormat<C...>& pc)  // NOLINT
+      : Base(&pc) {}
+};
+
+template <typename... Args>
+struct FormatSpecDeductionBarrier {
+  using type = FormatSpecTemplate<Args...>;
+};
+
+class Streamable {
+ public:
+  Streamable(const UntypedFormatSpecImpl& format,
+             absl::Span<const FormatArgImpl> args)
+      : format_(format) {
+    if (args.size() <= ABSL_ARRAYSIZE(few_args_)) {
+      for (size_t i = 0; i < args.size(); ++i) {
+        few_args_[i] = args[i];
+      }
+      args_ = absl::MakeSpan(few_args_, args.size());
+    } else {
+      many_args_.assign(args.begin(), args.end());
+      args_ = many_args_;
+    }
+  }
+
+  std::ostream& Print(std::ostream& os) const;
+
+  friend std::ostream& operator<<(std::ostream& os, const Streamable& l) {
+    return l.Print(os);
+  }
+
+ private:
+  const UntypedFormatSpecImpl& format_;
+  absl::Span<const FormatArgImpl> args_;
+  // if args_.size() is 4 or less:
+  FormatArgImpl few_args_[4] = {FormatArgImpl(0), FormatArgImpl(0),
+                                FormatArgImpl(0), FormatArgImpl(0)};
+  // if args_.size() is more than 4:
+  std::vector<FormatArgImpl> many_args_;
+};
+
+// for testing
+std::string Summarize(UntypedFormatSpecImpl format,
+                      absl::Span<const FormatArgImpl> args);
+bool BindWithPack(const UnboundConversion* props,
+                  absl::Span<const FormatArgImpl> pack, BoundConversion* bound);
+
+bool FormatUntyped(FormatRawSinkImpl raw_sink,
+                   UntypedFormatSpecImpl format,
+                   absl::Span<const FormatArgImpl> args);
+
+std::string& AppendPack(std::string* out, UntypedFormatSpecImpl format,
+                        absl::Span<const FormatArgImpl> args);
+
+inline std::string FormatPack(const UntypedFormatSpecImpl format,
+                              absl::Span<const FormatArgImpl> args) {
+  std::string out;
+  AppendPack(&out, format, args);
+  return out;
+}
+
+int FprintF(std::FILE* output, UntypedFormatSpecImpl format,
+            absl::Span<const FormatArgImpl> args);
+int SnprintF(char* output, size_t size, UntypedFormatSpecImpl format,
+             absl::Span<const FormatArgImpl> args);
+
+// Returned by Streamed(v). Converts via '%s' to the std::string created
+// by std::ostream << v.
+template <typename T>
+class StreamedWrapper {
+ public:
+  explicit StreamedWrapper(const T& v) : v_(v) { }
+
+ private:
+  template <typename S>
+  friend ConvertResult<Conv::s> FormatConvertImpl(const StreamedWrapper<S>& v,
+                                                  ConversionSpec conv,
+                                                  FormatSinkImpl* out);
+  const T& v_;
+};
+
+}  // namespace str_format_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_STR_FORMAT_BIND_H_
diff --git a/absl/strings/internal/str_format/bind_test.cc b/absl/strings/internal/str_format/bind_test.cc
new file mode 100644
index 0000000..2574801
--- /dev/null
+++ b/absl/strings/internal/str_format/bind_test.cc
@@ -0,0 +1,141 @@
+#include "absl/strings/internal/str_format/bind.h"
+
+#include <string.h>
+#include <limits>
+
+#include "gtest/gtest.h"
+
+namespace absl {
+namespace str_format_internal {
+namespace {
+
+class FormatBindTest : public ::testing::Test {
+ public:
+  bool Extract(const char *s, UnboundConversion *props, int *next) const {
+    return ConsumeUnboundConversion(s, s + strlen(s), props, next) ==
+           s + strlen(s);
+  }
+};
+
+TEST_F(FormatBindTest, BindSingle) {
+  struct Expectation {
+    int line;
+    const char *fmt;
+    int ok_phases;
+    const FormatArgImpl *arg;
+    int width;
+    int precision;
+    int next_arg;
+  };
+  const int no = -1;
+  const int ia[] = { 10, 20, 30, 40};
+  const FormatArgImpl args[] = {FormatArgImpl(ia[0]), FormatArgImpl(ia[1]),
+                                FormatArgImpl(ia[2]), FormatArgImpl(ia[3])};
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmissing-field-initializers"
+  const Expectation kExpect[] = {
+    {__LINE__, "d",          2, &args[0], no, no, 2},
+    {__LINE__, "4d",         2, &args[0],  4, no, 2},
+    {__LINE__, ".5d",        2, &args[0], no,  5, 2},
+    {__LINE__, "4.5d",       2, &args[0],  4,  5, 2},
+    {__LINE__, "*d",         2, &args[1], 10, no, 3},
+    {__LINE__, ".*d",        2, &args[1], no, 10, 3},
+    {__LINE__, "*.*d",       2, &args[2], 10, 20, 4},
+    {__LINE__, "1$d",        2, &args[0], no, no, 0},
+    {__LINE__, "2$d",        2, &args[1], no, no, 0},
+    {__LINE__, "3$d",        2, &args[2], no, no, 0},
+    {__LINE__, "4$d",        2, &args[3], no, no, 0},
+    {__LINE__, "2$*1$d",     2, &args[1], 10, no, 0},
+    {__LINE__, "2$*2$d",     2, &args[1], 20, no, 0},
+    {__LINE__, "2$*3$d",     2, &args[1], 30, no, 0},
+    {__LINE__, "2$.*1$d",    2, &args[1], no, 10, 0},
+    {__LINE__, "2$.*2$d",    2, &args[1], no, 20, 0},
+    {__LINE__, "2$.*3$d",    2, &args[1], no, 30, 0},
+    {__LINE__, "2$*3$.*1$d", 2, &args[1], 30, 10, 0},
+    {__LINE__, "2$*2$.*2$d", 2, &args[1], 20, 20, 0},
+    {__LINE__, "2$*1$.*3$d", 2, &args[1], 10, 30, 0},
+    {__LINE__, "2$*3$.*1$d", 2, &args[1], 30, 10, 0},
+    {__LINE__, "1$*d",       0},  // indexed, then positional
+    {__LINE__, "*2$d",       0},  // positional, then indexed
+    {__LINE__, "6$d",        1},  // arg position out of bounds
+    {__LINE__, "1$6$d",      0},  // width position incorrectly specified
+    {__LINE__, "1$.6$d",     0},  // precision position incorrectly specified
+    {__LINE__, "1$*6$d",     1},  // width position out of bounds
+    {__LINE__, "1$.*6$d",    1},  // precision position out of bounds
+  };
+#pragma GCC diagnostic pop
+  for (const Expectation &e : kExpect) {
+    SCOPED_TRACE(e.line);
+    SCOPED_TRACE(e.fmt);
+    UnboundConversion props;
+    BoundConversion bound;
+    int ok_phases = 0;
+    int next = 0;
+    if (Extract(e.fmt, &props, &next)) {
+      ++ok_phases;
+      if (BindWithPack(&props, args, &bound)) {
+        ++ok_phases;
+      }
+    }
+    EXPECT_EQ(e.ok_phases, ok_phases);
+    if (e.ok_phases < 2) continue;
+    if (e.arg != nullptr) {
+      EXPECT_EQ(e.arg, bound.arg());
+    }
+    EXPECT_EQ(e.width, bound.width());
+    EXPECT_EQ(e.precision, bound.precision());
+  }
+}
+
+TEST_F(FormatBindTest, WidthUnderflowRegression) {
+  UnboundConversion props;
+  BoundConversion bound;
+  int next = 0;
+  const int args_i[] = {std::numeric_limits<int>::min(), 17};
+  const FormatArgImpl args[] = {FormatArgImpl(args_i[0]),
+                                FormatArgImpl(args_i[1])};
+  ASSERT_TRUE(Extract("*d", &props, &next));
+  ASSERT_TRUE(BindWithPack(&props, args, &bound));
+
+  EXPECT_EQ(bound.width(), std::numeric_limits<int>::max());
+  EXPECT_EQ(bound.arg(), args + 1);
+}
+
+TEST_F(FormatBindTest, FormatPack) {
+  struct Expectation {
+    int line;
+    const char *fmt;
+    const char *summary;
+  };
+  const int ia[] = { 10, 20, 30, 40, -10 };
+  const FormatArgImpl args[] = {FormatArgImpl(ia[0]), FormatArgImpl(ia[1]),
+                                FormatArgImpl(ia[2]), FormatArgImpl(ia[3]),
+                                FormatArgImpl(ia[4])};
+  const Expectation kExpect[] = {
+    {__LINE__, "a%4db%dc", "a{10:4d}b{20:d}c"},
+    {__LINE__, "a%.4db%dc", "a{10:.4d}b{20:d}c"},
+    {__LINE__, "a%4.5db%dc", "a{10:4.5d}b{20:d}c"},
+    {__LINE__, "a%db%4.5dc", "a{10:d}b{20:4.5d}c"},
+    {__LINE__, "a%db%*.*dc", "a{10:d}b{40:20.30d}c"},
+    {__LINE__, "a%.*fb", "a{20:.10f}b"},
+    {__LINE__, "a%1$db%2$*3$.*4$dc", "a{10:d}b{20:30.40d}c"},
+    {__LINE__, "a%4$db%3$*2$.*1$dc", "a{40:d}b{30:20.10d}c"},
+    {__LINE__, "a%04ldb", "a{10:04ld}b"},
+    {__LINE__, "a%-#04lldb", "a{10:-#04lld}b"},
+    {__LINE__, "a%1$*5$db", "a{10:-10d}b"},
+    {__LINE__, "a%1$.*5$db", "a{10:d}b"},
+  };
+  for (const Expectation &e : kExpect) {
+    absl::string_view fmt = e.fmt;
+    SCOPED_TRACE(e.line);
+    SCOPED_TRACE(e.fmt);
+    UntypedFormatSpecImpl format(fmt);
+    EXPECT_EQ(e.summary,
+              str_format_internal::Summarize(format, absl::MakeSpan(args)))
+        << "line:" << e.line;
+  }
+}
+
+}  // namespace
+}  // namespace str_format_internal
+}  // namespace absl
diff --git a/absl/strings/internal/str_format/checker.h b/absl/strings/internal/str_format/checker.h
new file mode 100644
index 0000000..8b594f2
--- /dev/null
+++ b/absl/strings/internal/str_format/checker.h
@@ -0,0 +1,325 @@
+#ifndef ABSL_STRINGS_INTERNAL_STR_FORMAT_CHECKER_H_
+#define ABSL_STRINGS_INTERNAL_STR_FORMAT_CHECKER_H_
+
+#include "absl/strings/internal/str_format/arg.h"
+#include "absl/strings/internal/str_format/extension.h"
+
+// Compile time check support for entry points.
+
+#ifndef ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+#if defined(__clang__) && !defined(__native_client__)
+#if __has_attribute(enable_if)
+#define ABSL_INTERNAL_ENABLE_FORMAT_CHECKER 1
+#endif  // __has_attribute(enable_if)
+#endif  // defined(__clang__) && !defined(__native_client__)
+#endif  // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+namespace absl {
+namespace str_format_internal {
+
+constexpr bool AllOf() { return true; }
+
+template <typename... T>
+constexpr bool AllOf(bool b, T... t) {
+  return b && AllOf(t...);
+}
+
+template <typename Arg>
+constexpr Conv ArgumentToConv() {
+  return decltype(str_format_internal::FormatConvertImpl(
+      std::declval<const Arg&>(), std::declval<const ConversionSpec&>(),
+      std::declval<FormatSinkImpl*>()))::kConv;
+}
+
+#if ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+constexpr bool ContainsChar(const char* chars, char c) {
+  return *chars == c || (*chars && ContainsChar(chars + 1, c));
+}
+
+// A constexpr compatible list of Convs.
+struct ConvList {
+  const Conv* array;
+  int count;
+
+  // We do the bound check here to avoid having to do it on the callers.
+  // Returning an empty Conv has the same effect as short circuiting because it
+  // will never match any conversion.
+  constexpr Conv operator[](int i) const {
+    return i < count ? array[i] : Conv{};
+  }
+
+  constexpr ConvList without_front() const {
+    return count != 0 ? ConvList{array + 1, count - 1} : *this;
+  }
+};
+
+template <size_t count>
+struct ConvListT {
+  // Make sure the array has size > 0.
+  Conv list[count ? count : 1];
+};
+
+constexpr char GetChar(string_view str, size_t index) {
+  return index < str.size() ? str[index] : char{};
+}
+
+constexpr string_view ConsumeFront(string_view str, size_t len = 1) {
+  return len <= str.size() ? string_view(str.data() + len, str.size() - len)
+                           : string_view();
+}
+
+constexpr string_view ConsumeAnyOf(string_view format, const char* chars) {
+  return ContainsChar(chars, GetChar(format, 0))
+             ? ConsumeAnyOf(ConsumeFront(format), chars)
+             : format;
+}
+
+constexpr bool IsDigit(char c) { return c >= '0' && c <= '9'; }
+
+// Helper class for the ParseDigits function.
+// It encapsulates the two return values we need there.
+struct Integer {
+  string_view format;
+  int value;
+
+  // If the next character is a '$', consume it.
+  // Otherwise, make `this` an invalid positional argument.
+  constexpr Integer ConsumePositionalDollar() const {
+    return GetChar(format, 0) == '$' ? Integer{ConsumeFront(format), value}
+                                     : Integer{format, 0};
+  }
+};
+
+constexpr Integer ParseDigits(string_view format, int value = 0) {
+  return IsDigit(GetChar(format, 0))
+             ? ParseDigits(ConsumeFront(format),
+                           10 * value + GetChar(format, 0) - '0')
+             : Integer{format, value};
+}
+
+// Parse digits for a positional argument.
+// The parsing also consumes the '$'.
+constexpr Integer ParsePositional(string_view format) {
+  return ParseDigits(format).ConsumePositionalDollar();
+}
+
+// Parses a single conversion specifier.
+// See ConvParser::Run() for post conditions.
+class ConvParser {
+  constexpr ConvParser SetFormat(string_view format) const {
+    return ConvParser(format, args_, error_, arg_position_, is_positional_);
+  }
+
+  constexpr ConvParser SetArgs(ConvList args) const {
+    return ConvParser(format_, args, error_, arg_position_, is_positional_);
+  }
+
+  constexpr ConvParser SetError(bool error) const {
+    return ConvParser(format_, args_, error_ || error, arg_position_,
+                      is_positional_);
+  }
+
+  constexpr ConvParser SetArgPosition(int arg_position) const {
+    return ConvParser(format_, args_, error_, arg_position, is_positional_);
+  }
+
+  // Consumes the next arg and verifies that it matches `conv`.
+  // `error_` is set if there is no next arg or if it doesn't match `conv`.
+  constexpr ConvParser ConsumeNextArg(char conv) const {
+    return SetArgs(args_.without_front()).SetError(!Contains(args_[0], conv));
+  }
+
+  // Verify that positional argument `i.value` matches `conv`.
+  // `error_` is set if `i.value` is not a valid argument or if it doesn't
+  // match.
+  constexpr ConvParser VerifyPositional(Integer i, char conv) const {
+    return SetFormat(i.format).SetError(!Contains(args_[i.value - 1], conv));
+  }
+
+  // Parse the position of the arg and store it in `arg_position_`.
+  constexpr ConvParser ParseArgPosition(Integer arg) const {
+    return SetFormat(arg.format).SetArgPosition(arg.value);
+  }
+
+  // Consume the flags.
+  constexpr ConvParser ParseFlags() const {
+    return SetFormat(ConsumeAnyOf(format_, "-+ #0"));
+  }
+
+  // Consume the width.
+  // If it is '*', we verify that it matches `args_`. `error_` is set if it
+  // doesn't match.
+  constexpr ConvParser ParseWidth() const {
+    return IsDigit(GetChar(format_, 0))
+               ? SetFormat(ParseDigits(format_).format)
+               : GetChar(format_, 0) == '*'
+                     ? is_positional_
+                           ? VerifyPositional(
+                                 ParsePositional(ConsumeFront(format_)), '*')
+                           : SetFormat(ConsumeFront(format_))
+                                 .ConsumeNextArg('*')
+                     : *this;
+  }
+
+  // Consume the precision.
+  // If it is '*', we verify that it matches `args_`. `error_` is set if it
+  // doesn't match.
+  constexpr ConvParser ParsePrecision() const {
+    return GetChar(format_, 0) != '.'
+               ? *this
+               : GetChar(format_, 1) == '*'
+                     ? is_positional_
+                           ? VerifyPositional(
+                                 ParsePositional(ConsumeFront(format_, 2)), '*')
+                           : SetFormat(ConsumeFront(format_, 2))
+                                 .ConsumeNextArg('*')
+                     : SetFormat(ParseDigits(ConsumeFront(format_)).format);
+  }
+
+  // Consume the length characters.
+  constexpr ConvParser ParseLength() const {
+    return SetFormat(ConsumeAnyOf(format_, "lLhjztq"));
+  }
+
+  // Consume the conversion character and verify that it matches `args_`.
+  // `error_` is set if it doesn't match.
+  constexpr ConvParser ParseConversion() const {
+    return is_positional_
+               ? VerifyPositional({ConsumeFront(format_), arg_position_},
+                                  GetChar(format_, 0))
+               : ConsumeNextArg(GetChar(format_, 0))
+                     .SetFormat(ConsumeFront(format_));
+  }
+
+  constexpr ConvParser(string_view format, ConvList args, bool error,
+                       int arg_position, bool is_positional)
+      : format_(format),
+        args_(args),
+        error_(error),
+        arg_position_(arg_position),
+        is_positional_(is_positional) {}
+
+ public:
+  constexpr ConvParser(string_view format, ConvList args, bool is_positional)
+      : format_(format),
+        args_(args),
+        error_(false),
+        arg_position_(0),
+        is_positional_(is_positional) {}
+
+  // Consume the whole conversion specifier.
+  // `format()` will be set to the character after the conversion character.
+  // `error()` will be set if any of the arguments do not match.
+  constexpr ConvParser Run() const {
+    return (is_positional_ ? ParseArgPosition(ParsePositional(format_)) : *this)
+        .ParseFlags()
+        .ParseWidth()
+        .ParsePrecision()
+        .ParseLength()
+        .ParseConversion();
+  }
+
+  constexpr string_view format() const { return format_; }
+  constexpr ConvList args() const { return args_; }
+  constexpr bool error() const { return error_; }
+  constexpr bool is_positional() const { return is_positional_; }
+
+ private:
+  string_view format_;
+  // Current list of arguments. If we are not in positional mode we will consume
+  // from the front.
+  ConvList args_;
+  bool error_;
+  // Holds the argument position of the conversion character, if we are in
+  // positional mode. Otherwise, it is unspecified.
+  int arg_position_;
+  // Whether we are in positional mode.
+  // It changes the behavior of '*' and where to find the converted argument.
+  bool is_positional_;
+};
+
+// Parses a whole format expression.
+// See FormatParser::Run().
+class FormatParser {
+  static constexpr bool FoundPercent(string_view format) {
+    return format.empty() ||
+           (GetChar(format, 0) == '%' && GetChar(format, 1) != '%');
+  }
+
+  // We use an inner function to increase the recursion limit.
+  // The inner function consumes up to `limit` characters on every run.
+  // This increases the limit from 512 to ~512*limit.
+  static constexpr string_view ConsumeNonPercentInner(string_view format,
+                                                      int limit = 20) {
+    return FoundPercent(format) || !limit
+               ? format
+               : ConsumeNonPercentInner(
+                     ConsumeFront(format, GetChar(format, 0) == '%' &&
+                                                  GetChar(format, 1) == '%'
+                                              ? 2
+                                              : 1),
+                     limit - 1);
+  }
+
+  // Consume characters until the next conversion spec %.
+  // It skips %%.
+  static constexpr string_view ConsumeNonPercent(string_view format) {
+    return FoundPercent(format)
+               ? format
+               : ConsumeNonPercent(ConsumeNonPercentInner(format));
+  }
+
+  static constexpr bool IsPositional(string_view format) {
+    return IsDigit(GetChar(format, 0)) ? IsPositional(ConsumeFront(format))
+                                       : GetChar(format, 0) == '$';
+  }
+
+  constexpr bool RunImpl(bool is_positional) const {
+    // In non-positional mode we require all arguments to be consumed.
+    // In positional mode just reaching the end of the format without errors is
+    // enough.
+    return (format_.empty() && (is_positional || args_.count == 0)) ||
+           (!format_.empty() &&
+            ValidateArg(
+                ConvParser(ConsumeFront(format_), args_, is_positional).Run()));
+  }
+
+  constexpr bool ValidateArg(ConvParser conv) const {
+    return !conv.error() && FormatParser(conv.format(), conv.args())
+                                .RunImpl(conv.is_positional());
+  }
+
+ public:
+  constexpr FormatParser(string_view format, ConvList args)
+      : format_(ConsumeNonPercent(format)), args_(args) {}
+
+  // Runs the parser for `format` and `args`.
+  // It verifies that the format is valid and that all conversion specifiers
+  // match the arguments passed.
+  // In non-positional mode it also verfies that all arguments are consumed.
+  constexpr bool Run() const {
+    return RunImpl(!format_.empty() && IsPositional(ConsumeFront(format_)));
+  }
+
+ private:
+  string_view format_;
+  // Current list of arguments.
+  // If we are not in positional mode we will consume from the front and will
+  // have to be empty in the end.
+  ConvList args_;
+};
+
+template <Conv... C>
+constexpr bool ValidFormatImpl(string_view format) {
+  return FormatParser(format,
+                      {ConvListT<sizeof...(C)>{{C...}}.list, sizeof...(C)})
+      .Run();
+}
+
+#endif  // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+}  // namespace str_format_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_STR_FORMAT_CHECKER_H_
diff --git a/absl/strings/internal/str_format/checker_test.cc b/absl/strings/internal/str_format/checker_test.cc
new file mode 100644
index 0000000..c1d8c76
--- /dev/null
+++ b/absl/strings/internal/str_format/checker_test.cc
@@ -0,0 +1,150 @@
+#include <string>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/strings/str_format.h"
+
+namespace absl {
+namespace str_format_internal {
+namespace {
+
+std::string ConvToString(Conv conv) {
+  std::string out;
+#define CONV_SET_CASE(c) \
+  if (Contains(conv, Conv::c)) out += #c;
+  ABSL_CONVERSION_CHARS_EXPAND_(CONV_SET_CASE, )
+#undef CONV_SET_CASE
+  if (Contains(conv, Conv::star)) out += "*";
+  return out;
+}
+
+TEST(StrFormatChecker, ArgumentToConv) {
+  Conv conv = ArgumentToConv<std::string>();
+  EXPECT_EQ(ConvToString(conv), "s");
+
+  conv = ArgumentToConv<const char*>();
+  EXPECT_EQ(ConvToString(conv), "sp");
+
+  conv = ArgumentToConv<double>();
+  EXPECT_EQ(ConvToString(conv), "fFeEgGaA");
+
+  conv = ArgumentToConv<int>();
+  EXPECT_EQ(ConvToString(conv), "cdiouxXfFeEgGaA*");
+
+  conv = ArgumentToConv<std::string*>();
+  EXPECT_EQ(ConvToString(conv), "p");
+}
+
+#if ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+struct Case {
+  bool result;
+  const char* format;
+};
+
+template <typename... Args>
+constexpr Case ValidFormat(const char* format) {
+  return {ValidFormatImpl<ArgumentToConv<Args>()...>(format), format};
+}
+
+TEST(StrFormatChecker, ValidFormat) {
+  // We want to make sure these expressions are constexpr and they have the
+  // expected value.
+  // If they are not constexpr the attribute will just ignore them and not give
+  // a compile time error.
+  enum e {};
+  enum class e2 {};
+  constexpr Case trues[] = {
+      ValidFormat<>("abc"),  //
+
+      ValidFormat<e>("%d"),                             //
+      ValidFormat<e2>("%d"),                            //
+      ValidFormat<int>("%% %d"),                        //
+      ValidFormat<int>("%ld"),                          //
+      ValidFormat<int>("%lld"),                         //
+      ValidFormat<std::string>("%s"),                   //
+      ValidFormat<std::string>("%10s"),                 //
+      ValidFormat<int>("%.10x"),                        //
+      ValidFormat<int, int>("%*.3x"),                   //
+      ValidFormat<int>("%1.d"),                         //
+      ValidFormat<int>("%.d"),                          //
+      ValidFormat<int, double>("%d %g"),                //
+      ValidFormat<int, std::string>("%*s"),             //
+      ValidFormat<int, double>("%.*f"),                 //
+      ValidFormat<void (*)(), volatile int*>("%p %p"),  //
+      ValidFormat<string_view, const char*, double, void*>(
+          "string_view=%s const char*=%s double=%f void*=%p)"),
+
+      ValidFormat<int>("%% %1$d"),               //
+      ValidFormat<int>("%1$ld"),                 //
+      ValidFormat<int>("%1$lld"),                //
+      ValidFormat<std::string>("%1$s"),          //
+      ValidFormat<std::string>("%1$10s"),        //
+      ValidFormat<int>("%1$.10x"),               //
+      ValidFormat<int>("%1$*1$.*1$d"),           //
+      ValidFormat<int, int>("%1$*2$.3x"),        //
+      ValidFormat<int>("%1$1.d"),                //
+      ValidFormat<int>("%1$.d"),                 //
+      ValidFormat<double, int>("%2$d %1$g"),     //
+      ValidFormat<int, std::string>("%2$*1$s"),  //
+      ValidFormat<int, double>("%2$.*1$f"),      //
+      ValidFormat<void*, string_view, const char*, double>(
+          "string_view=%2$s const char*=%3$s double=%4$f void*=%1$p "
+          "repeat=%3$s)")};
+
+  for (Case c : trues) {
+    EXPECT_TRUE(c.result) << c.format;
+  }
+
+  constexpr Case falses[] = {
+      ValidFormat<int>(""),  //
+
+      ValidFormat<e>("%s"),                  //
+      ValidFormat<e2>("%s"),                 //
+      ValidFormat<>("%s"),                   //
+      ValidFormat<>("%r"),                   //
+      ValidFormat<int>("%s"),                //
+      ValidFormat<int>("%.1.d"),             //
+      ValidFormat<int>("%*1d"),              //
+      ValidFormat<int>("%1-d"),              //
+      ValidFormat<std::string, int>("%*s"),  //
+      ValidFormat<int>("%*d"),               //
+      ValidFormat<std::string>("%p"),        //
+      ValidFormat<int (*)(int)>("%d"),       //
+
+      ValidFormat<>("%3$d"),                     //
+      ValidFormat<>("%1$r"),                     //
+      ValidFormat<int>("%1$s"),                  //
+      ValidFormat<int>("%1$.1.d"),               //
+      ValidFormat<int>("%1$*2$1d"),              //
+      ValidFormat<int>("%1$1-d"),                //
+      ValidFormat<std::string, int>("%2$*1$s"),  //
+      ValidFormat<std::string>("%1$p"),
+
+      ValidFormat<int, int>("%d %2$d"),  //
+  };
+
+  for (Case c : falses) {
+    EXPECT_FALSE(c.result) << c.format;
+  }
+}
+
+TEST(StrFormatChecker, LongFormat) {
+#define CHARS_X_40 "1234567890123456789012345678901234567890"
+#define CHARS_X_400                                                            \
+  CHARS_X_40 CHARS_X_40 CHARS_X_40 CHARS_X_40 CHARS_X_40 CHARS_X_40 CHARS_X_40 \
+      CHARS_X_40 CHARS_X_40 CHARS_X_40
+#define CHARS_X_4000                                                      \
+  CHARS_X_400 CHARS_X_400 CHARS_X_400 CHARS_X_400 CHARS_X_400 CHARS_X_400 \
+      CHARS_X_400 CHARS_X_400 CHARS_X_400 CHARS_X_400
+  constexpr char long_format[] =
+      CHARS_X_4000 "%d" CHARS_X_4000 "%s" CHARS_X_4000;
+  constexpr bool is_valid = ValidFormat<int, std::string>(long_format).result;
+  EXPECT_TRUE(is_valid);
+}
+
+#endif  // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+}  // namespace
+}  // namespace str_format_internal
+}  // namespace absl
diff --git a/absl/strings/internal/str_format/convert_test.cc b/absl/strings/internal/str_format/convert_test.cc
new file mode 100644
index 0000000..814ccf4
--- /dev/null
+++ b/absl/strings/internal/str_format/convert_test.cc
@@ -0,0 +1,590 @@
+#include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <cctype>
+#include <cmath>
+#include <string>
+
+#include "gtest/gtest.h"
+#include "absl/strings/internal/str_format/bind.h"
+
+namespace absl {
+namespace str_format_internal {
+namespace {
+
+template <typename T, size_t N>
+size_t ArraySize(T (&)[N]) {
+  return N;
+}
+
+std::string LengthModFor(float) { return ""; }
+std::string LengthModFor(double) { return ""; }
+std::string LengthModFor(long double) { return "L"; }
+std::string LengthModFor(char) { return "hh"; }
+std::string LengthModFor(signed char) { return "hh"; }
+std::string LengthModFor(unsigned char) { return "hh"; }
+std::string LengthModFor(short) { return "h"; }           // NOLINT
+std::string LengthModFor(unsigned short) { return "h"; }  // NOLINT
+std::string LengthModFor(int) { return ""; }
+std::string LengthModFor(unsigned) { return ""; }
+std::string LengthModFor(long) { return "l"; }                 // NOLINT
+std::string LengthModFor(unsigned long) { return "l"; }        // NOLINT
+std::string LengthModFor(long long) { return "ll"; }           // NOLINT
+std::string LengthModFor(unsigned long long) { return "ll"; }  // NOLINT
+
+std::string EscCharImpl(int v) {
+  if (std::isprint(static_cast<unsigned char>(v))) {
+    return std::string(1, static_cast<char>(v));
+  }
+  char buf[64];
+  int n = snprintf(buf, sizeof(buf), "\\%#.2x",
+                   static_cast<unsigned>(v & 0xff));
+  assert(n > 0 && n < sizeof(buf));
+  return std::string(buf, n);
+}
+
+std::string Esc(char v) { return EscCharImpl(v); }
+std::string Esc(signed char v) { return EscCharImpl(v); }
+std::string Esc(unsigned char v) { return EscCharImpl(v); }
+
+template <typename T>
+std::string Esc(const T &v) {
+  std::ostringstream oss;
+  oss << v;
+  return oss.str();
+}
+
+void StrAppend(std::string *dst, const char *format, va_list ap) {
+  // First try with a small fixed size buffer
+  static const int kSpaceLength = 1024;
+  char space[kSpaceLength];
+
+  // It's possible for methods that use a va_list to invalidate
+  // the data in it upon use.  The fix is to make a copy
+  // of the structure before using it and use that copy instead.
+  va_list backup_ap;
+  va_copy(backup_ap, ap);
+  int result = vsnprintf(space, kSpaceLength, format, backup_ap);
+  va_end(backup_ap);
+  if (result < kSpaceLength) {
+    if (result >= 0) {
+      // Normal case -- everything fit.
+      dst->append(space, result);
+      return;
+    }
+    if (result < 0) {
+      // Just an error.
+      return;
+    }
+  }
+
+  // Increase the buffer size to the size requested by vsnprintf,
+  // plus one for the closing \0.
+  int length = result + 1;
+  char *buf = new char[length];
+
+  // Restore the va_list before we use it again
+  va_copy(backup_ap, ap);
+  result = vsnprintf(buf, length, format, backup_ap);
+  va_end(backup_ap);
+
+  if (result >= 0 && result < length) {
+    // It fit
+    dst->append(buf, result);
+  }
+  delete[] buf;
+}
+
+std::string StrPrint(const char *format, ...) {
+  va_list ap;
+  va_start(ap, format);
+  std::string result;
+  StrAppend(&result, format, ap);
+  va_end(ap);
+  return result;
+}
+
+class FormatConvertTest : public ::testing::Test { };
+
+template <typename T>
+void TestStringConvert(const T& str) {
+  const FormatArgImpl args[] = {FormatArgImpl(str)};
+  struct Expectation {
+    const char *out;
+    const char *fmt;
+  };
+  const Expectation kExpect[] = {
+    {"hello",  "%1$s"      },
+    {"",       "%1$.s"     },
+    {"",       "%1$.0s"    },
+    {"h",      "%1$.1s"    },
+    {"he",     "%1$.2s"    },
+    {"hello",  "%1$.10s"   },
+    {" hello", "%1$6s"     },
+    {"   he",  "%1$5.2s"   },
+    {"he   ",  "%1$-5.2s"  },
+    {"hello ", "%1$-6.10s" },
+  };
+  for (const Expectation &e : kExpect) {
+    UntypedFormatSpecImpl format(e.fmt);
+    EXPECT_EQ(e.out, FormatPack(format, absl::MakeSpan(args)));
+  }
+}
+
+TEST_F(FormatConvertTest, BasicString) {
+  TestStringConvert("hello");  // As char array.
+  TestStringConvert(static_cast<const char*>("hello"));
+  TestStringConvert(std::string("hello"));
+  TestStringConvert(string_view("hello"));
+}
+
+TEST_F(FormatConvertTest, NullString) {
+  const char* p = nullptr;
+  UntypedFormatSpecImpl format("%s");
+  EXPECT_EQ("", FormatPack(format, {FormatArgImpl(p)}));
+}
+
+TEST_F(FormatConvertTest, StringPrecision) {
+  // We cap at the precision.
+  char c = 'a';
+  const char* p = &c;
+  UntypedFormatSpecImpl format("%.1s");
+  EXPECT_EQ("a", FormatPack(format, {FormatArgImpl(p)}));
+
+  // We cap at the nul terminator.
+  p = "ABC";
+  UntypedFormatSpecImpl format2("%.10s");
+  EXPECT_EQ("ABC", FormatPack(format2, {FormatArgImpl(p)}));
+}
+
+TEST_F(FormatConvertTest, Pointer) {
+#ifdef _MSC_VER
+  // MSVC's printf implementation prints pointers differently. We can't easily
+  // compare our implementation to theirs.
+  return;
+#endif
+  static int x = 0;
+  const int *xp = &x;
+  char c = 'h';
+  char *mcp = &c;
+  const char *cp = "hi";
+  const char *cnil = nullptr;
+  const int *inil = nullptr;
+  using VoidF = void (*)();
+  VoidF fp = [] {}, fnil = nullptr;
+  volatile char vc;
+  volatile char* vcp = &vc;
+  volatile char* vcnil = nullptr;
+  const FormatArgImpl args[] = {
+      FormatArgImpl(xp),   FormatArgImpl(cp),  FormatArgImpl(inil),
+      FormatArgImpl(cnil), FormatArgImpl(mcp), FormatArgImpl(fp),
+      FormatArgImpl(fnil), FormatArgImpl(vcp), FormatArgImpl(vcnil),
+  };
+  struct Expectation {
+    std::string out;
+    const char *fmt;
+  };
+  const Expectation kExpect[] = {
+      {StrPrint("%p", &x), "%p"},
+      {StrPrint("%20p", &x), "%20p"},
+      {StrPrint("%.1p", &x), "%.1p"},
+      {StrPrint("%.20p", &x), "%.20p"},
+      {StrPrint("%30.20p", &x), "%30.20p"},
+
+      {StrPrint("%-p", &x), "%-p"},
+      {StrPrint("%-20p", &x), "%-20p"},
+      {StrPrint("%-.1p", &x), "%-.1p"},
+      {StrPrint("%.20p", &x), "%.20p"},
+      {StrPrint("%-30.20p", &x), "%-30.20p"},
+
+      {StrPrint("%p", cp), "%2$p"},   // const char*
+      {"(nil)", "%3$p"},              // null const char *
+      {"(nil)", "%4$p"},              // null const int *
+      {StrPrint("%p", mcp), "%5$p"},  // nonconst char*
+
+      {StrPrint("%p", fp), "%6$p"},   // function pointer
+      {StrPrint("%p", vcp), "%8$p"},  // function pointer
+
+#ifndef __APPLE__
+      // Apple's printf differs here (0x0 vs. nil)
+      {StrPrint("%p", fnil), "%7$p"},   // null function pointer
+      {StrPrint("%p", vcnil), "%9$p"},  // null function pointer
+#endif
+  };
+  for (const Expectation &e : kExpect) {
+    UntypedFormatSpecImpl format(e.fmt);
+    EXPECT_EQ(e.out, FormatPack(format, absl::MakeSpan(args))) << e.fmt;
+  }
+}
+
+struct Cardinal {
+  enum Pos { k1 = 1, k2 = 2, k3 = 3 };
+  enum Neg { kM1 = -1, kM2 = -2, kM3 = -3 };
+};
+
+TEST_F(FormatConvertTest, Enum) {
+  const Cardinal::Pos k3 = Cardinal::k3;
+  const Cardinal::Neg km3 = Cardinal::kM3;
+  const FormatArgImpl args[] = {FormatArgImpl(k3), FormatArgImpl(km3)};
+  UntypedFormatSpecImpl format("%1$d");
+  UntypedFormatSpecImpl format2("%2$d");
+  EXPECT_EQ("3", FormatPack(format, absl::MakeSpan(args)));
+  EXPECT_EQ("-3", FormatPack(format2, absl::MakeSpan(args)));
+}
+
+template <typename T>
+class TypedFormatConvertTest : public FormatConvertTest { };
+
+TYPED_TEST_SUITE_P(TypedFormatConvertTest);
+
+std::vector<std::string> AllFlagCombinations() {
+  const char kFlags[] = {'-', '#', '0', '+', ' '};
+  std::vector<std::string> result;
+  for (size_t fsi = 0; fsi < (1ull << ArraySize(kFlags)); ++fsi) {
+    std::string flag_set;
+    for (size_t fi = 0; fi < ArraySize(kFlags); ++fi)
+      if (fsi & (1ull << fi))
+        flag_set += kFlags[fi];
+    result.push_back(flag_set);
+  }
+  return result;
+}
+
+TYPED_TEST_P(TypedFormatConvertTest, AllIntsWithFlags) {
+  typedef TypeParam T;
+  typedef typename std::make_unsigned<T>::type UnsignedT;
+  using remove_volatile_t = typename std::remove_volatile<T>::type;
+  const T kMin = std::numeric_limits<remove_volatile_t>::min();
+  const T kMax = std::numeric_limits<remove_volatile_t>::max();
+  const T kVals[] = {
+      remove_volatile_t(1),
+      remove_volatile_t(2),
+      remove_volatile_t(3),
+      remove_volatile_t(123),
+      remove_volatile_t(-1),
+      remove_volatile_t(-2),
+      remove_volatile_t(-3),
+      remove_volatile_t(-123),
+      remove_volatile_t(0),
+      kMax - remove_volatile_t(1),
+      kMax,
+      kMin + remove_volatile_t(1),
+      kMin,
+  };
+  const char kConvChars[] = {'d', 'i', 'u', 'o', 'x', 'X'};
+  const std::string kWid[] = {"", "4", "10"};
+  const std::string kPrec[] = {"", ".", ".0", ".4", ".10"};
+
+  const std::vector<std::string> flag_sets = AllFlagCombinations();
+
+  for (size_t vi = 0; vi < ArraySize(kVals); ++vi) {
+    const T val = kVals[vi];
+    SCOPED_TRACE(Esc(val));
+    const FormatArgImpl args[] = {FormatArgImpl(val)};
+    for (size_t ci = 0; ci < ArraySize(kConvChars); ++ci) {
+      const char conv_char = kConvChars[ci];
+      for (size_t fsi = 0; fsi < flag_sets.size(); ++fsi) {
+        const std::string &flag_set = flag_sets[fsi];
+        for (size_t wi = 0; wi < ArraySize(kWid); ++wi) {
+          const std::string &wid = kWid[wi];
+          for (size_t pi = 0; pi < ArraySize(kPrec); ++pi) {
+            const std::string &prec = kPrec[pi];
+
+            const bool is_signed_conv = (conv_char == 'd' || conv_char == 'i');
+            const bool is_unsigned_to_signed =
+                !std::is_signed<T>::value && is_signed_conv;
+            // Don't consider sign-related flags '+' and ' ' when doing
+            // unsigned to signed conversions.
+            if (is_unsigned_to_signed &&
+                flag_set.find_first_of("+ ") != std::string::npos) {
+              continue;
+            }
+
+            std::string new_fmt("%");
+            new_fmt += flag_set;
+            new_fmt += wid;
+            new_fmt += prec;
+            // old and new always agree up to here.
+            std::string old_fmt = new_fmt;
+            new_fmt += conv_char;
+            std::string old_result;
+            if (is_unsigned_to_signed) {
+              // don't expect agreement on unsigned formatted as signed,
+              // as printf can't do that conversion properly. For those
+              // cases, we do expect agreement with printf with a "%u"
+              // and the unsigned equivalent of 'val'.
+              UnsignedT uval = val;
+              old_fmt += LengthModFor(uval);
+              old_fmt += "u";
+              old_result = StrPrint(old_fmt.c_str(), uval);
+            } else {
+              old_fmt += LengthModFor(val);
+              old_fmt += conv_char;
+              old_result = StrPrint(old_fmt.c_str(), val);
+            }
+
+            SCOPED_TRACE(std::string() + " old_fmt: \"" + old_fmt +
+                         "\"'"
+                         " new_fmt: \"" +
+                         new_fmt + "\"");
+            UntypedFormatSpecImpl format(new_fmt);
+            EXPECT_EQ(old_result, FormatPack(format, absl::MakeSpan(args)));
+          }
+        }
+      }
+    }
+  }
+}
+
+TYPED_TEST_P(TypedFormatConvertTest, Char) {
+  typedef TypeParam T;
+  using remove_volatile_t = typename std::remove_volatile<T>::type;
+  static const T kMin = std::numeric_limits<remove_volatile_t>::min();
+  static const T kMax = std::numeric_limits<remove_volatile_t>::max();
+  T kVals[] = {
+    remove_volatile_t(1), remove_volatile_t(2), remove_volatile_t(10),
+    remove_volatile_t(-1), remove_volatile_t(-2), remove_volatile_t(-10),
+    remove_volatile_t(0),
+    kMin + remove_volatile_t(1), kMin,
+    kMax - remove_volatile_t(1), kMax
+  };
+  for (const T &c : kVals) {
+    const FormatArgImpl args[] = {FormatArgImpl(c)};
+    UntypedFormatSpecImpl format("%c");
+    EXPECT_EQ(StrPrint("%c", c), FormatPack(format, absl::MakeSpan(args)));
+  }
+}
+
+REGISTER_TYPED_TEST_CASE_P(TypedFormatConvertTest, AllIntsWithFlags, Char);
+
+typedef ::testing::Types<
+    int, unsigned, volatile int,
+    short, unsigned short,
+    long, unsigned long,
+    long long, unsigned long long,
+    signed char, unsigned char, char>
+    AllIntTypes;
+INSTANTIATE_TYPED_TEST_CASE_P(TypedFormatConvertTestWithAllIntTypes,
+                              TypedFormatConvertTest, AllIntTypes);
+
+TEST_F(FormatConvertTest, VectorBool) {
+  // Make sure vector<bool>'s values behave as bools.
+  std::vector<bool> v = {true, false};
+  const std::vector<bool> cv = {true, false};
+  EXPECT_EQ("1,0,1,0",
+            FormatPack(UntypedFormatSpecImpl("%d,%d,%d,%d"),
+                       absl::Span<const FormatArgImpl>(
+                           {FormatArgImpl(v[0]), FormatArgImpl(v[1]),
+                            FormatArgImpl(cv[0]), FormatArgImpl(cv[1])})));
+}
+
+TEST_F(FormatConvertTest, Uint128) {
+  absl::uint128 v = static_cast<absl::uint128>(0x1234567890abcdef) * 1979;
+  absl::uint128 max = absl::Uint128Max();
+  const FormatArgImpl args[] = {FormatArgImpl(v), FormatArgImpl(max)};
+
+  struct Case {
+    const char* format;
+    const char* expected;
+  } cases[] = {
+      {"%1$d", "2595989796776606496405"},
+      {"%1$30d", "        2595989796776606496405"},
+      {"%1$-30d", "2595989796776606496405        "},
+      {"%1$u", "2595989796776606496405"},
+      {"%1$x", "8cba9876066020f695"},
+      {"%2$d", "340282366920938463463374607431768211455"},
+      {"%2$u", "340282366920938463463374607431768211455"},
+      {"%2$x", "ffffffffffffffffffffffffffffffff"},
+  };
+
+  for (auto c : cases) {
+    UntypedFormatSpecImpl format(c.format);
+    EXPECT_EQ(c.expected, FormatPack(format, absl::MakeSpan(args)));
+  }
+}
+
+TEST_F(FormatConvertTest, Float) {
+#ifdef _MSC_VER
+  // MSVC has a different rounding policy than us so we can't test our
+  // implementation against the native one there.
+  return;
+#endif  // _MSC_VER
+
+  const char *const kFormats[] = {
+      "%",  "%.3",  "%8.5",   "%9",   "%.60", "%.30",   "%03",    "%+",
+      "% ", "%-10", "%#15.3", "%#.0", "%.0",  "%1$*2$", "%1$.*2$"};
+
+  std::vector<double> doubles = {0.0,
+                                 -0.0,
+                                 .99999999999999,
+                                 99999999999999.,
+                                 std::numeric_limits<double>::max(),
+                                 -std::numeric_limits<double>::max(),
+                                 std::numeric_limits<double>::min(),
+                                 -std::numeric_limits<double>::min(),
+                                 std::numeric_limits<double>::lowest(),
+                                 -std::numeric_limits<double>::lowest(),
+                                 std::numeric_limits<double>::epsilon(),
+                                 std::numeric_limits<double>::epsilon() + 1,
+                                 std::numeric_limits<double>::infinity(),
+                                 -std::numeric_limits<double>::infinity()};
+
+#ifndef __APPLE__
+  // Apple formats NaN differently (+nan) vs. (nan)
+  doubles.push_back(std::nan(""));
+#endif
+
+  // Some regression tests.
+  doubles.push_back(0.99999999999999989);
+
+  if (std::numeric_limits<double>::has_denorm != std::denorm_absent) {
+    doubles.push_back(std::numeric_limits<double>::denorm_min());
+    doubles.push_back(-std::numeric_limits<double>::denorm_min());
+  }
+
+  for (double base :
+       {1., 12., 123., 1234., 12345., 123456., 1234567., 12345678., 123456789.,
+        1234567890., 12345678901., 123456789012., 1234567890123.}) {
+    for (int exp = -123; exp <= 123; ++exp) {
+      for (int sign : {1, -1}) {
+        doubles.push_back(sign * std::ldexp(base, exp));
+      }
+    }
+  }
+
+  for (const char *fmt : kFormats) {
+    for (char f : {'f', 'F',  //
+                   'g', 'G',  //
+                   'a', 'A',  //
+                   'e', 'E'}) {
+      std::string fmt_str = std::string(fmt) + f;
+      for (double d : doubles) {
+        int i = -10;
+        FormatArgImpl args[2] = {FormatArgImpl(d), FormatArgImpl(i)};
+        UntypedFormatSpecImpl format(fmt_str);
+        // We use ASSERT_EQ here because failures are usually correlated and a
+        // bug would print way too many failed expectations causing the test to
+        // time out.
+        ASSERT_EQ(StrPrint(fmt_str.c_str(), d, i),
+                  FormatPack(format, absl::MakeSpan(args)))
+            << fmt_str << " " << StrPrint("%.18g", d) << " "
+            << StrPrint("%.999f", d);
+      }
+    }
+  }
+}
+
+TEST_F(FormatConvertTest, LongDouble) {
+  const char *const kFormats[] = {"%",    "%.3", "%8.5", "%9",
+                                  "%.60", "%+",  "% ",   "%-10"};
+
+  // This value is not representable in double, but it is in long double that
+  // uses the extended format.
+  // This is to verify that we are not truncating the value mistakenly through a
+  // double.
+  long double very_precise = 10000000000000000.25L;
+
+  std::vector<long double> doubles = {
+      0.0,
+      -0.0,
+      very_precise,
+      1 / very_precise,
+      std::numeric_limits<long double>::max(),
+      -std::numeric_limits<long double>::max(),
+      std::numeric_limits<long double>::min(),
+      -std::numeric_limits<long double>::min(),
+      std::numeric_limits<long double>::infinity(),
+      -std::numeric_limits<long double>::infinity()};
+
+  for (const char *fmt : kFormats) {
+    for (char f : {'f', 'F',  //
+                   'g', 'G',  //
+                   'a', 'A',  //
+                   'e', 'E'}) {
+      std::string fmt_str = std::string(fmt) + 'L' + f;
+      for (auto d : doubles) {
+        FormatArgImpl arg(d);
+        UntypedFormatSpecImpl format(fmt_str);
+        // We use ASSERT_EQ here because failures are usually correlated and a
+        // bug would print way too many failed expectations causing the test to
+        // time out.
+        ASSERT_EQ(StrPrint(fmt_str.c_str(), d),
+                  FormatPack(format, {&arg, 1}))
+            << fmt_str << " " << StrPrint("%.18Lg", d) << " "
+            << StrPrint("%.999Lf", d);
+      }
+    }
+  }
+}
+
+TEST_F(FormatConvertTest, IntAsFloat) {
+  const int kMin = std::numeric_limits<int>::min();
+  const int kMax = std::numeric_limits<int>::max();
+  const int ia[] = {
+    1, 2, 3, 123,
+    -1, -2, -3, -123,
+    0, kMax - 1, kMax, kMin + 1, kMin };
+  for (const int fx : ia) {
+    SCOPED_TRACE(fx);
+    const FormatArgImpl args[] = {FormatArgImpl(fx)};
+    struct Expectation {
+      int line;
+      std::string out;
+      const char *fmt;
+    };
+    const double dx = static_cast<double>(fx);
+    const Expectation kExpect[] = {
+      { __LINE__, StrPrint("%f", dx), "%f" },
+      { __LINE__, StrPrint("%12f", dx), "%12f" },
+      { __LINE__, StrPrint("%.12f", dx), "%.12f" },
+      { __LINE__, StrPrint("%12a", dx), "%12a" },
+      { __LINE__, StrPrint("%.12a", dx), "%.12a" },
+    };
+    for (const Expectation &e : kExpect) {
+      SCOPED_TRACE(e.line);
+      SCOPED_TRACE(e.fmt);
+      UntypedFormatSpecImpl format(e.fmt);
+      EXPECT_EQ(e.out, FormatPack(format, absl::MakeSpan(args)));
+    }
+  }
+}
+
+template <typename T>
+bool FormatFails(const char* test_format, T value) {
+  std::string format_string = std::string("<<") + test_format + ">>";
+  UntypedFormatSpecImpl format(format_string);
+
+  int one = 1;
+  const FormatArgImpl args[] = {FormatArgImpl(value), FormatArgImpl(one)};
+  EXPECT_EQ(FormatPack(format, absl::MakeSpan(args)), "")
+      << "format=" << test_format << " value=" << value;
+  return FormatPack(format, absl::MakeSpan(args)).empty();
+}
+
+TEST_F(FormatConvertTest, ExpectedFailures) {
+  // Int input
+  EXPECT_TRUE(FormatFails("%p", 1));
+  EXPECT_TRUE(FormatFails("%s", 1));
+  EXPECT_TRUE(FormatFails("%n", 1));
+
+  // Double input
+  EXPECT_TRUE(FormatFails("%p", 1.));
+  EXPECT_TRUE(FormatFails("%s", 1.));
+  EXPECT_TRUE(FormatFails("%n", 1.));
+  EXPECT_TRUE(FormatFails("%c", 1.));
+  EXPECT_TRUE(FormatFails("%d", 1.));
+  EXPECT_TRUE(FormatFails("%x", 1.));
+  EXPECT_TRUE(FormatFails("%*d", 1.));
+
+  // String input
+  EXPECT_TRUE(FormatFails("%n", ""));
+  EXPECT_TRUE(FormatFails("%c", ""));
+  EXPECT_TRUE(FormatFails("%d", ""));
+  EXPECT_TRUE(FormatFails("%x", ""));
+  EXPECT_TRUE(FormatFails("%f", ""));
+  EXPECT_TRUE(FormatFails("%*d", ""));
+}
+
+}  // namespace
+}  // namespace str_format_internal
+}  // namespace absl
diff --git a/absl/strings/internal/str_format/extension.cc b/absl/strings/internal/str_format/extension.cc
new file mode 100644
index 0000000..d7f5815
--- /dev/null
+++ b/absl/strings/internal/str_format/extension.cc
@@ -0,0 +1,84 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/str_format/extension.h"
+
+#include <errno.h>
+#include <algorithm>
+#include <string>
+
+namespace absl {
+namespace str_format_internal {
+namespace {
+// clang-format off
+#define ABSL_LENGTH_MODS_EXPAND_ \
+  X_VAL(h) X_SEP \
+  X_VAL(hh) X_SEP \
+  X_VAL(l) X_SEP \
+  X_VAL(ll) X_SEP \
+  X_VAL(L) X_SEP \
+  X_VAL(j) X_SEP \
+  X_VAL(z) X_SEP \
+  X_VAL(t) X_SEP \
+  X_VAL(q)
+// clang-format on
+}  // namespace
+
+const LengthMod::Spec LengthMod::kSpecs[] = {
+#define X_VAL(id) { LengthMod::id, #id, strlen(#id) }
+#define X_SEP ,
+    ABSL_LENGTH_MODS_EXPAND_, {LengthMod::none, "", 0}
+#undef X_VAL
+#undef X_SEP
+};
+
+const ConversionChar::Spec ConversionChar::kSpecs[] = {
+#define X_VAL(id) { ConversionChar::id, #id[0] }
+#define X_SEP ,
+    ABSL_CONVERSION_CHARS_EXPAND_(X_VAL, X_SEP),
+    {ConversionChar::none, '\0'},
+#undef X_VAL
+#undef X_SEP
+};
+
+std::string Flags::ToString() const {
+  std::string s;
+  s.append(left     ? "-" : "");
+  s.append(show_pos ? "+" : "");
+  s.append(sign_col ? " " : "");
+  s.append(alt      ? "#" : "");
+  s.append(zero     ? "0" : "");
+  return s;
+}
+
+const size_t LengthMod::kNumValues;
+
+const size_t ConversionChar::kNumValues;
+
+bool FormatSinkImpl::PutPaddedString(string_view v, int w, int p, bool l) {
+  size_t space_remaining = 0;
+  if (w >= 0) space_remaining = w;
+  size_t n = v.size();
+  if (p >= 0) n = std::min(n, static_cast<size_t>(p));
+  string_view shown(v.data(), n);
+  space_remaining = Excess(shown.size(), space_remaining);
+  if (!l) Append(space_remaining, ' ');
+  Append(shown);
+  if (l) Append(space_remaining, ' ');
+  return true;
+}
+
+}  // namespace str_format_internal
+}  // namespace absl
diff --git a/absl/strings/internal/str_format/extension.h b/absl/strings/internal/str_format/extension.h
new file mode 100644
index 0000000..eb81f8a
--- /dev/null
+++ b/absl/strings/internal/str_format/extension.h
@@ -0,0 +1,411 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#ifndef ABSL_STRINGS_INTERNAL_STR_FORMAT_EXTENSION_H_
+#define ABSL_STRINGS_INTERNAL_STR_FORMAT_EXTENSION_H_
+
+#include <limits.h>
+#include <cstddef>
+#include <cstring>
+#include <ostream>
+
+#include "absl/base/port.h"
+#include "absl/strings/internal/str_format/output.h"
+#include "absl/strings/string_view.h"
+
+class Cord;
+
+namespace absl {
+
+namespace str_format_internal {
+
+class FormatRawSinkImpl {
+ public:
+  // Implicitly convert from any type that provides the hook function as
+  // described above.
+  template <typename T, decltype(str_format_internal::InvokeFlush(
+                            std::declval<T*>(), string_view()))* = nullptr>
+  FormatRawSinkImpl(T* raw)  // NOLINT
+      : sink_(raw), write_(&FormatRawSinkImpl::Flush<T>) {}
+
+  void Write(string_view s) { write_(sink_, s); }
+
+  template <typename T>
+  static FormatRawSinkImpl Extract(T s) {
+    return s.sink_;
+  }
+
+ private:
+  template <typename T>
+  static void Flush(void* r, string_view s) {
+    str_format_internal::InvokeFlush(static_cast<T*>(r), s);
+  }
+
+  void* sink_;
+  void (*write_)(void*, string_view);
+};
+
+// An abstraction to which conversions write their string data.
+class FormatSinkImpl {
+ public:
+  explicit FormatSinkImpl(FormatRawSinkImpl raw) : raw_(raw) {}
+
+  ~FormatSinkImpl() { Flush(); }
+
+  void Flush() {
+    raw_.Write(string_view(buf_, pos_ - buf_));
+    pos_ = buf_;
+  }
+
+  void Append(size_t n, char c) {
+    if (n == 0) return;
+    size_ += n;
+    auto raw_append = [&](size_t count) {
+      memset(pos_, c, count);
+      pos_ += count;
+    };
+    while (n > Avail()) {
+      n -= Avail();
+      if (Avail() > 0) {
+        raw_append(Avail());
+      }
+      Flush();
+    }
+    raw_append(n);
+  }
+
+  void Append(string_view v) {
+    size_t n = v.size();
+    if (n == 0) return;
+    size_ += n;
+    if (n >= Avail()) {
+      Flush();
+      raw_.Write(v);
+      return;
+    }
+    memcpy(pos_, v.data(), n);
+    pos_ += n;
+  }
+
+  size_t size() const { return size_; }
+
+  // Put 'v' to 'sink' with specified width, precision, and left flag.
+  bool PutPaddedString(string_view v, int w, int p, bool l);
+
+  template <typename T>
+  T Wrap() {
+    return T(this);
+  }
+
+  template <typename T>
+  static FormatSinkImpl* Extract(T* s) {
+    return s->sink_;
+  }
+
+ private:
+  size_t Avail() const { return buf_ + sizeof(buf_) - pos_; }
+
+  FormatRawSinkImpl raw_;
+  size_t size_ = 0;
+  char* pos_ = buf_;
+  char buf_[1024];
+};
+
+struct Flags {
+  bool basic : 1;     // fastest conversion: no flags, width, or precision
+  bool left : 1;      // "-"
+  bool show_pos : 1;  // "+"
+  bool sign_col : 1;  // " "
+  bool alt : 1;       // "#"
+  bool zero : 1;      // "0"
+  std::string ToString() const;
+  friend std::ostream& operator<<(std::ostream& os, const Flags& v) {
+    return os << v.ToString();
+  }
+};
+
+struct LengthMod {
+ public:
+  enum Id : uint8_t {
+    h, hh, l, ll, L, j, z, t, q, none
+  };
+  static const size_t kNumValues = none + 1;
+
+  LengthMod() : id_(none) {}
+
+  // Index into the opaque array of LengthMod enums.
+  // Requires: i < kNumValues
+  static LengthMod FromIndex(size_t i) {
+    return LengthMod(kSpecs[i].value);
+  }
+
+  static LengthMod FromId(Id id) { return LengthMod(id); }
+
+  // The length modifier std::string associated with a specified LengthMod.
+  string_view name() const {
+    const Spec& spec = kSpecs[id_];
+    return {spec.name, spec.name_length};
+  }
+
+  Id id() const { return id_; }
+
+  friend bool operator==(const LengthMod& a, const LengthMod& b) {
+    return a.id() == b.id();
+  }
+  friend bool operator!=(const LengthMod& a, const LengthMod& b) {
+    return !(a == b);
+  }
+  friend std::ostream& operator<<(std::ostream& os, const LengthMod& v) {
+    return os << v.name();
+  }
+
+ private:
+  struct Spec {
+    Id value;
+    const char *name;
+    size_t name_length;
+  };
+  static const Spec kSpecs[];
+
+  explicit LengthMod(Id id) : id_(id) {}
+
+  Id id_;
+};
+
+// clang-format off
+#define ABSL_CONVERSION_CHARS_EXPAND_(X_VAL, X_SEP) \
+  /* text */ \
+  X_VAL(c) X_SEP X_VAL(C) X_SEP X_VAL(s) X_SEP X_VAL(S) X_SEP \
+  /* ints */ \
+  X_VAL(d) X_SEP X_VAL(i) X_SEP X_VAL(o) X_SEP \
+  X_VAL(u) X_SEP X_VAL(x) X_SEP X_VAL(X) X_SEP \
+  /* floats */ \
+  X_VAL(f) X_SEP X_VAL(F) X_SEP X_VAL(e) X_SEP X_VAL(E) X_SEP \
+  X_VAL(g) X_SEP X_VAL(G) X_SEP X_VAL(a) X_SEP X_VAL(A) X_SEP \
+  /* misc */ \
+  X_VAL(n) X_SEP X_VAL(p)
+// clang-format on
+
+struct ConversionChar {
+ public:
+  enum Id : uint8_t {
+    c, C, s, S,              // text
+    d, i, o, u, x, X,        // int
+    f, F, e, E, g, G, a, A,  // float
+    n, p,                    // misc
+    none
+  };
+  static const size_t kNumValues = none + 1;
+
+  ConversionChar() : id_(none) {}
+
+ public:
+  // Index into the opaque array of ConversionChar enums.
+  // Requires: i < kNumValues
+  static ConversionChar FromIndex(size_t i) {
+    return ConversionChar(kSpecs[i].value);
+  }
+
+  static ConversionChar FromChar(char c) {
+    ConversionChar::Id out_id = ConversionChar::none;
+    switch (c) {
+#define X_VAL(id)                \
+  case #id[0]:                   \
+    out_id = ConversionChar::id; \
+    break;
+      ABSL_CONVERSION_CHARS_EXPAND_(X_VAL, )
+#undef X_VAL
+      default:
+        break;
+    }
+    return ConversionChar(out_id);
+  }
+
+  static ConversionChar FromId(Id id) { return ConversionChar(id); }
+  Id id() const { return id_; }
+
+  int radix() const {
+    switch (id()) {
+      case x: case X: case a: case A: case p: return 16;
+      case o: return 8;
+      default: return 10;
+    }
+  }
+
+  bool upper() const {
+    switch (id()) {
+      case X: case F: case E: case G: case A: return true;
+      default: return false;
+    }
+  }
+
+  bool is_signed() const {
+    switch (id()) {
+      case d: case i: return true;
+      default: return false;
+    }
+  }
+
+  bool is_integral() const {
+    switch (id()) {
+      case d: case i: case u: case o: case x: case X:
+        return true;
+      default: return false;
+    }
+  }
+
+  bool is_float() const {
+    switch (id()) {
+      case a: case e: case f: case g: case A: case E: case F: case G:
+        return true;
+      default: return false;
+    }
+  }
+
+  bool IsValid() const { return id() != none; }
+
+  // The associated char.
+  char Char() const { return kSpecs[id_].name; }
+
+  friend bool operator==(const ConversionChar& a, const ConversionChar& b) {
+    return a.id() == b.id();
+  }
+  friend bool operator!=(const ConversionChar& a, const ConversionChar& b) {
+    return !(a == b);
+  }
+  friend std::ostream& operator<<(std::ostream& os, const ConversionChar& v) {
+    char c = v.Char();
+    if (!c) c = '?';
+    return os << c;
+  }
+
+ private:
+  struct Spec {
+    Id value;
+    char name;
+  };
+  static const Spec kSpecs[];
+
+  explicit ConversionChar(Id id) : id_(id) {}
+
+  Id id_;
+};
+
+class ConversionSpec {
+ public:
+  Flags flags() const { return flags_; }
+  LengthMod length_mod() const { return length_mod_; }
+  ConversionChar conv() const {
+    // Keep this field first in the struct . It generates better code when
+    // accessing it when ConversionSpec is passed by value in registers.
+    static_assert(offsetof(ConversionSpec, conv_) == 0, "");
+    return conv_;
+  }
+
+  // Returns the specified width. If width is unspecfied, it returns a negative
+  // value.
+  int width() const { return width_; }
+  // Returns the specified precision. If precision is unspecfied, it returns a
+  // negative value.
+  int precision() const { return precision_; }
+
+  void set_flags(Flags f) { flags_ = f; }
+  void set_length_mod(LengthMod lm) { length_mod_ = lm; }
+  void set_conv(ConversionChar c) { conv_ = c; }
+  void set_width(int w) { width_ = w; }
+  void set_precision(int p) { precision_ = p; }
+  void set_left(bool b) { flags_.left = b; }
+
+ private:
+  ConversionChar conv_;
+  Flags flags_;
+  LengthMod length_mod_;
+  int width_;
+  int precision_;
+};
+
+constexpr uint64_t ConversionCharToConvValue(char conv) {
+  return
+#define CONV_SET_CASE(c) \
+  conv == #c[0] ? (uint64_t{1} << (1 + ConversionChar::Id::c)):
+      ABSL_CONVERSION_CHARS_EXPAND_(CONV_SET_CASE, )
+#undef CONV_SET_CASE
+                  conv == '*'
+          ? 1
+          : 0;
+}
+
+enum class Conv : uint64_t {
+#define CONV_SET_CASE(c) c = ConversionCharToConvValue(#c[0]),
+  ABSL_CONVERSION_CHARS_EXPAND_(CONV_SET_CASE, )
+#undef CONV_SET_CASE
+
+  // Used for width/precision '*' specification.
+  star = ConversionCharToConvValue('*'),
+
+  // Some predefined values:
+  integral = d | i | u | o | x | X,
+  floating = a | e | f | g | A | E | F | G,
+  numeric = integral | floating,
+  string = s,
+  pointer = p
+};
+
+// Type safe OR operator.
+// We need this for two reasons:
+//  1. operator| on enums makes them decay to integers and the result is an
+//     integer. We need the result to stay as an enum.
+//  2. We use "enum class" which would not work even if we accepted the decay.
+constexpr Conv operator|(Conv a, Conv b) {
+  return Conv(static_cast<uint64_t>(a) | static_cast<uint64_t>(b));
+}
+
+// Get a conversion with a single character in it.
+constexpr Conv ConversionCharToConv(char c) {
+  return Conv(ConversionCharToConvValue(c));
+}
+
+// Checks whether `c` exists in `set`.
+constexpr bool Contains(Conv set, char c) {
+  return (static_cast<uint64_t>(set) & ConversionCharToConvValue(c)) != 0;
+}
+
+// Checks whether all the characters in `c` are contained in `set`
+constexpr bool Contains(Conv set, Conv c) {
+  return (static_cast<uint64_t>(set) & static_cast<uint64_t>(c)) ==
+         static_cast<uint64_t>(c);
+}
+
+// Return type of the AbslFormatConvert() functions.
+// The Conv template parameter is used to inform the framework of what
+// conversion characters are supported by that AbslFormatConvert routine.
+template <Conv C>
+struct ConvertResult {
+  static constexpr Conv kConv = C;
+  bool value;
+};
+template <Conv C>
+constexpr Conv ConvertResult<C>::kConv;
+
+// Return capacity - used, clipped to a minimum of 0.
+inline size_t Excess(size_t used, size_t capacity) {
+  return used < capacity ? capacity - used : 0;
+}
+
+}  // namespace str_format_internal
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_STR_FORMAT_EXTENSION_H_
diff --git a/absl/strings/internal/str_format/extension_test.cc b/absl/strings/internal/str_format/extension_test.cc
new file mode 100644
index 0000000..4e23fef
--- /dev/null
+++ b/absl/strings/internal/str_format/extension_test.cc
@@ -0,0 +1,66 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "absl/strings/internal/str_format/extension.h"
+
+#include <random>
+#include <string>
+
+#include "absl/strings/str_format.h"
+
+#include "gtest/gtest.h"
+
+namespace {
+
+std::string MakeRandomString(size_t len) {
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  std::uniform_int_distribution<> dis('a', 'z');
+  std::string s(len, '0');
+  for (char& c : s) {
+    c = dis(gen);
+  }
+  return s;
+}
+
+TEST(FormatExtensionTest, SinkAppendSubstring) {
+  for (size_t chunk_size : {1, 10, 100, 1000, 10000}) {
+    std::string expected, actual;
+    absl::str_format_internal::FormatSinkImpl sink(&actual);
+    for (size_t chunks = 0; chunks < 10; ++chunks) {
+      std::string rand = MakeRandomString(chunk_size);
+      expected += rand;
+      sink.Append(rand);
+    }
+    sink.Flush();
+    EXPECT_EQ(actual, expected);
+  }
+}
+
+TEST(FormatExtensionTest, SinkAppendChars) {
+  for (size_t chunk_size : {1, 10, 100, 1000, 10000}) {
+    std::string expected, actual;
+    absl::str_format_internal::FormatSinkImpl sink(&actual);
+    for (size_t chunks = 0; chunks < 10; ++chunks) {
+      std::string rand = MakeRandomString(1);
+      expected.append(chunk_size, rand[0]);
+      sink.Append(chunk_size, rand[0]);
+    }
+    sink.Flush();
+    EXPECT_EQ(actual, expected);
+  }
+}
+}  // namespace
diff --git a/absl/strings/internal/str_format/float_conversion.cc b/absl/strings/internal/str_format/float_conversion.cc
new file mode 100644
index 0000000..9236acd
--- /dev/null
+++ b/absl/strings/internal/str_format/float_conversion.cc
@@ -0,0 +1,485 @@
+#include "absl/strings/internal/str_format/float_conversion.h"
+
+#include <string.h>
+#include <algorithm>
+#include <cassert>
+#include <cmath>
+#include <string>
+
+#include "absl/base/config.h"
+
+namespace absl {
+namespace str_format_internal {
+
+namespace {
+
+char *CopyStringTo(string_view v, char *out) {
+  std::memcpy(out, v.data(), v.size());
+  return out + v.size();
+}
+
+template <typename Float>
+bool FallbackToSnprintf(const Float v, const ConversionSpec &conv,
+                        FormatSinkImpl *sink) {
+  int w = conv.width() >= 0 ? conv.width() : 0;
+  int p = conv.precision() >= 0 ? conv.precision() : -1;
+  char fmt[32];
+  {
+    char *fp = fmt;
+    *fp++ = '%';
+    fp = CopyStringTo(conv.flags().ToString(), fp);
+    fp = CopyStringTo("*.*", fp);
+    if (std::is_same<long double, Float>()) {
+      *fp++ = 'L';
+    }
+    *fp++ = conv.conv().Char();
+    *fp = 0;
+    assert(fp < fmt + sizeof(fmt));
+  }
+  std::string space(512, '\0');
+  string_view result;
+  while (true) {
+    int n = snprintf(&space[0], space.size(), fmt, w, p, v);
+    if (n < 0) return false;
+    if (static_cast<size_t>(n) < space.size()) {
+      result = string_view(space.data(), n);
+      break;
+    }
+    space.resize(n + 1);
+  }
+  sink->Append(result);
+  return true;
+}
+
+// 128-bits in decimal: ceil(128*log(2)/log(10))
+//   or std::numeric_limits<__uint128_t>::digits10
+constexpr int kMaxFixedPrecision = 39;
+
+constexpr int kBufferLength = /*sign*/ 1 +
+                              /*integer*/ kMaxFixedPrecision +
+                              /*point*/ 1 +
+                              /*fraction*/ kMaxFixedPrecision +
+                              /*exponent e+123*/ 5;
+
+struct Buffer {
+  void push_front(char c) {
+    assert(begin > data);
+    *--begin = c;
+  }
+  void push_back(char c) {
+    assert(end < data + sizeof(data));
+    *end++ = c;
+  }
+  void pop_back() {
+    assert(begin < end);
+    --end;
+  }
+
+  char &back() {
+    assert(begin < end);
+    return end[-1];
+  }
+
+  char last_digit() const { return end[-1] == '.' ? end[-2] : end[-1]; }
+
+  int size() const { return static_cast<int>(end - begin); }
+
+  char data[kBufferLength];
+  char *begin;
+  char *end;
+};
+
+enum class FormatStyle { Fixed, Precision };
+
+// If the value is Inf or Nan, print it and return true.
+// Otherwise, return false.
+template <typename Float>
+bool ConvertNonNumericFloats(char sign_char, Float v,
+                             const ConversionSpec &conv, FormatSinkImpl *sink) {
+  char text[4], *ptr = text;
+  if (sign_char) *ptr++ = sign_char;
+  if (std::isnan(v)) {
+    ptr = std::copy_n(conv.conv().upper() ? "NAN" : "nan", 3, ptr);
+  } else if (std::isinf(v)) {
+    ptr = std::copy_n(conv.conv().upper() ? "INF" : "inf", 3, ptr);
+  } else {
+    return false;
+  }
+
+  return sink->PutPaddedString(string_view(text, ptr - text), conv.width(), -1,
+                               conv.flags().left);
+}
+
+// Round up the last digit of the value.
+// It will carry over and potentially overflow. 'exp' will be adjusted in that
+// case.
+template <FormatStyle mode>
+void RoundUp(Buffer *buffer, int *exp) {
+  char *p = &buffer->back();
+  while (p >= buffer->begin && (*p == '9' || *p == '.')) {
+    if (*p == '9') *p = '0';
+    --p;
+  }
+
+  if (p < buffer->begin) {
+    *p = '1';
+    buffer->begin = p;
+    if (mode == FormatStyle::Precision) {
+      std::swap(p[1], p[2]);  // move the .
+      ++*exp;
+      buffer->pop_back();
+    }
+  } else {
+    ++*p;
+  }
+}
+
+void PrintExponent(int exp, char e, Buffer *out) {
+  out->push_back(e);
+  if (exp < 0) {
+    out->push_back('-');
+    exp = -exp;
+  } else {
+    out->push_back('+');
+  }
+  // Exponent digits.
+  if (exp > 99) {
+    out->push_back(exp / 100 + '0');
+    out->push_back(exp / 10 % 10 + '0');
+    out->push_back(exp % 10 + '0');
+  } else {
+    out->push_back(exp / 10 + '0');
+    out->push_back(exp % 10 + '0');
+  }
+}
+
+template <typename Float, typename Int>
+constexpr bool CanFitMantissa() {
+  return
+#if defined(__clang__) && !defined(__SSE3__)
+      // Workaround for clang bug: https://bugs.llvm.org/show_bug.cgi?id=38289
+      // Casting from long double to uint64_t is miscompiled and drops bits.
+      (!std::is_same<Float, long double>::value ||
+       !std::is_same<Int, uint64_t>::value) &&
+#endif
+      std::numeric_limits<Float>::digits <= std::numeric_limits<Int>::digits;
+}
+
+template <typename Float>
+struct Decomposed {
+  Float mantissa;
+  int exponent;
+};
+
+// Decompose the double into an integer mantissa and an exponent.
+template <typename Float>
+Decomposed<Float> Decompose(Float v) {
+  int exp;
+  Float m = std::frexp(v, &exp);
+  m = std::ldexp(m, std::numeric_limits<Float>::digits);
+  exp -= std::numeric_limits<Float>::digits;
+  return {m, exp};
+}
+
+// Print 'digits' as decimal.
+// In Fixed mode, we add a '.' at the end.
+// In Precision mode, we add a '.' after the first digit.
+template <FormatStyle mode, typename Int>
+int PrintIntegralDigits(Int digits, Buffer *out) {
+  int printed = 0;
+  if (digits) {
+    for (; digits; digits /= 10) out->push_front(digits % 10 + '0');
+    printed = out->size();
+    if (mode == FormatStyle::Precision) {
+      out->push_front(*out->begin);
+      out->begin[1] = '.';
+    } else {
+      out->push_back('.');
+    }
+  } else if (mode == FormatStyle::Fixed) {
+    out->push_front('0');
+    out->push_back('.');
+    printed = 1;
+  }
+  return printed;
+}
+
+// Back out 'extra_digits' digits and round up if necessary.
+bool RemoveExtraPrecision(int extra_digits, bool has_leftover_value,
+                          Buffer *out, int *exp_out) {
+  if (extra_digits <= 0) return false;
+
+  // Back out the extra digits
+  out->end -= extra_digits;
+
+  bool needs_to_round_up = [&] {
+    // We look at the digit just past the end.
+    // There must be 'extra_digits' extra valid digits after end.
+    if (*out->end > '5') return true;
+    if (*out->end < '5') return false;
+    if (has_leftover_value || std::any_of(out->end + 1, out->end + extra_digits,
+                                          [](char c) { return c != '0'; }))
+      return true;
+
+    // Ends in ...50*, round to even.
+    return out->last_digit() % 2 == 1;
+  }();
+
+  if (needs_to_round_up) {
+    RoundUp<FormatStyle::Precision>(out, exp_out);
+  }
+  return true;
+}
+
+// Print the value into the buffer.
+// This will not include the exponent, which will be returned in 'exp_out' for
+// Precision mode.
+template <typename Int, typename Float, FormatStyle mode>
+bool FloatToBufferImpl(Int int_mantissa, int exp, int precision, Buffer *out,
+                       int *exp_out) {
+  assert((CanFitMantissa<Float, Int>()));
+
+  const int int_bits = std::numeric_limits<Int>::digits;
+
+  // In precision mode, we start printing one char to the right because it will
+  // also include the '.'
+  // In fixed mode we put the dot afterwards on the right.
+  out->begin = out->end =
+      out->data + 1 + kMaxFixedPrecision + (mode == FormatStyle::Precision);
+
+  if (exp >= 0) {
+    if (std::numeric_limits<Float>::digits + exp > int_bits) {
+      // The value will overflow the Int
+      return false;
+    }
+    int digits_printed = PrintIntegralDigits<mode>(int_mantissa << exp, out);
+    int digits_to_zero_pad = precision;
+    if (mode == FormatStyle::Precision) {
+      *exp_out = digits_printed - 1;
+      digits_to_zero_pad -= digits_printed - 1;
+      if (RemoveExtraPrecision(-digits_to_zero_pad, false, out, exp_out)) {
+        return true;
+      }
+    }
+    for (; digits_to_zero_pad-- > 0;) out->push_back('0');
+    return true;
+  }
+
+  exp = -exp;
+  // We need at least 4 empty bits for the next decimal digit.
+  // We will multiply by 10.
+  if (exp > int_bits - 4) return false;
+
+  const Int mask = (Int{1} << exp) - 1;
+
+  // Print the integral part first.
+  int digits_printed = PrintIntegralDigits<mode>(int_mantissa >> exp, out);
+  int_mantissa &= mask;
+
+  int fractional_count = precision;
+  if (mode == FormatStyle::Precision) {
+    if (digits_printed == 0) {
+      // Find the first non-zero digit, when in Precision mode.
+      *exp_out = 0;
+      if (int_mantissa) {
+        while (int_mantissa <= mask) {
+          int_mantissa *= 10;
+          --*exp_out;
+        }
+      }
+      out->push_front(static_cast<char>(int_mantissa >> exp) + '0');
+      out->push_back('.');
+      int_mantissa &= mask;
+    } else {
+      // We already have a digit, and a '.'
+      *exp_out = digits_printed - 1;
+      fractional_count -= *exp_out;
+      if (RemoveExtraPrecision(-fractional_count, int_mantissa != 0, out,
+                               exp_out)) {
+        // If we had enough digits, return right away.
+        // The code below will try to round again otherwise.
+        return true;
+      }
+    }
+  }
+
+  auto get_next_digit = [&] {
+    int_mantissa *= 10;
+    int digit = static_cast<int>(int_mantissa >> exp);
+    int_mantissa &= mask;
+    return digit;
+  };
+
+  // Print fractional_count more digits, if available.
+  for (; fractional_count > 0; --fractional_count) {
+    out->push_back(get_next_digit() + '0');
+  }
+
+  int next_digit = get_next_digit();
+  if (next_digit > 5 ||
+      (next_digit == 5 && (int_mantissa || out->last_digit() % 2 == 1))) {
+    RoundUp<mode>(out, exp_out);
+  }
+
+  return true;
+}
+
+template <FormatStyle mode, typename Float>
+bool FloatToBuffer(Decomposed<Float> decomposed, int precision, Buffer *out,
+                   int *exp) {
+  if (precision > kMaxFixedPrecision) return false;
+
+  // Try with uint64_t.
+  if (CanFitMantissa<Float, std::uint64_t>() &&
+      FloatToBufferImpl<std::uint64_t, Float, mode>(
+          static_cast<std::uint64_t>(decomposed.mantissa),
+          static_cast<std::uint64_t>(decomposed.exponent), precision, out, exp))
+    return true;
+
+#if defined(ABSL_HAVE_INTRINSIC_INT128)
+  // If that is not enough, try with __uint128_t.
+  return CanFitMantissa<Float, __uint128_t>() &&
+         FloatToBufferImpl<__uint128_t, Float, mode>(
+             static_cast<__uint128_t>(decomposed.mantissa),
+             static_cast<__uint128_t>(decomposed.exponent), precision, out,
+             exp);
+#endif
+  return false;
+}
+
+void WriteBufferToSink(char sign_char, string_view str,
+                       const ConversionSpec &conv, FormatSinkImpl *sink) {
+  int left_spaces = 0, zeros = 0, right_spaces = 0;
+  int missing_chars =
+      conv.width() >= 0 ? std::max(conv.width() - static_cast<int>(str.size()) -
+                                       static_cast<int>(sign_char != 0),
+                                   0)
+                        : 0;
+  if (conv.flags().left) {
+    right_spaces = missing_chars;
+  } else if (conv.flags().zero) {
+    zeros = missing_chars;
+  } else {
+    left_spaces = missing_chars;
+  }
+
+  sink->Append(left_spaces, ' ');
+  if (sign_char) sink->Append(1, sign_char);
+  sink->Append(zeros, '0');
+  sink->Append(str);
+  sink->Append(right_spaces, ' ');
+}
+
+template <typename Float>
+bool FloatToSink(const Float v, const ConversionSpec &conv,
+                 FormatSinkImpl *sink) {
+  // Print the sign or the sign column.
+  Float abs_v = v;
+  char sign_char = 0;
+  if (std::signbit(abs_v)) {
+    sign_char = '-';
+    abs_v = -abs_v;
+  } else if (conv.flags().show_pos) {
+    sign_char = '+';
+  } else if (conv.flags().sign_col) {
+    sign_char = ' ';
+  }
+
+  // Print nan/inf.
+  if (ConvertNonNumericFloats(sign_char, abs_v, conv, sink)) {
+    return true;
+  }
+
+  int precision = conv.precision() < 0 ? 6 : conv.precision();
+
+  int exp = 0;
+
+  auto decomposed = Decompose(abs_v);
+
+  Buffer buffer;
+
+  switch (conv.conv().id()) {
+    case ConversionChar::f:
+    case ConversionChar::F:
+      if (!FloatToBuffer<FormatStyle::Fixed>(decomposed, precision, &buffer,
+                                             nullptr)) {
+        return FallbackToSnprintf(v, conv, sink);
+      }
+      if (!conv.flags().alt && buffer.back() == '.') buffer.pop_back();
+      break;
+
+    case ConversionChar::e:
+    case ConversionChar::E:
+      if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
+                                                 &exp)) {
+        return FallbackToSnprintf(v, conv, sink);
+      }
+      if (!conv.flags().alt && buffer.back() == '.') buffer.pop_back();
+      PrintExponent(exp, conv.conv().upper() ? 'E' : 'e', &buffer);
+      break;
+
+    case ConversionChar::g:
+    case ConversionChar::G:
+      precision = std::max(0, precision - 1);
+      if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
+                                                 &exp)) {
+        return FallbackToSnprintf(v, conv, sink);
+      }
+      if (precision + 1 > exp && exp >= -4) {
+        if (exp < 0) {
+          // Have 1.23456, needs 0.00123456
+          // Move the first digit
+          buffer.begin[1] = *buffer.begin;
+          // Add some zeros
+          for (; exp < -1; ++exp) *buffer.begin-- = '0';
+          *buffer.begin-- = '.';
+          *buffer.begin = '0';
+        } else if (exp > 0) {
+          // Have 1.23456, needs 1234.56
+          // Move the '.' exp positions to the right.
+          std::rotate(buffer.begin + 1, buffer.begin + 2,
+                      buffer.begin + exp + 2);
+        }
+        exp = 0;
+      }
+      if (!conv.flags().alt) {
+        while (buffer.back() == '0') buffer.pop_back();
+        if (buffer.back() == '.') buffer.pop_back();
+      }
+      if (exp) PrintExponent(exp, conv.conv().upper() ? 'E' : 'e', &buffer);
+      break;
+
+    case ConversionChar::a:
+    case ConversionChar::A:
+      return FallbackToSnprintf(v, conv, sink);
+
+    default:
+      return false;
+  }
+
+  WriteBufferToSink(sign_char,
+                    string_view(buffer.begin, buffer.end - buffer.begin), conv,
+                    sink);
+
+  return true;
+}
+
+}  // namespace
+
+bool ConvertFloatImpl(long double v, const ConversionSpec &conv,
+                      FormatSinkImpl *sink) {
+  return FloatToSink(v, conv, sink);
+}
+
+bool ConvertFloatImpl(float v, const ConversionSpec &conv,
+                      FormatSinkImpl *sink) {
+  return FloatToSink(v, conv, sink);
+}
+
+bool ConvertFloatImpl(double v, const ConversionSpec &conv,
+                      FormatSinkImpl *sink) {
+  return FloatToSink(v, conv, sink);
+}
+
+}  // namespace str_format_internal
+}  // namespace absl
diff --git a/absl/strings/internal/str_format/float_conversion.h b/absl/strings/internal/str_format/float_conversion.h
new file mode 100644
index 0000000..8ba5566
--- /dev/null
+++ b/absl/strings/internal/str_format/float_conversion.h
@@ -0,0 +1,21 @@
+#ifndef ABSL_STRINGS_INTERNAL_STR_FORMAT_FLOAT_CONVERSION_H_
+#define ABSL_STRINGS_INTERNAL_STR_FORMAT_FLOAT_CONVERSION_H_
+
+#include "absl/strings/internal/str_format/extension.h"
+
+namespace absl {
+namespace str_format_internal {
+
+bool ConvertFloatImpl(float v, const ConversionSpec &conv,
+                      FormatSinkImpl *sink);
+
+bool ConvertFloatImpl(double v, const ConversionSpec &conv,
+                      FormatSinkImpl *sink);
+
+bool ConvertFloatImpl(long double v, const ConversionSpec &conv,
+                      FormatSinkImpl *sink);
+
+}  // namespace str_format_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_STR_FORMAT_FLOAT_CONVERSION_H_
diff --git a/absl/strings/internal/str_format/output.cc b/absl/strings/internal/str_format/output.cc
new file mode 100644
index 0000000..38987b6
--- /dev/null
+++ b/absl/strings/internal/str_format/output.cc
@@ -0,0 +1,70 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/str_format/output.h"
+
+#include <errno.h>
+#include <cstring>
+
+namespace absl {
+namespace str_format_internal {
+
+namespace {
+struct ClearErrnoGuard {
+  ClearErrnoGuard() : old_value(errno) { errno = 0; }
+  ~ClearErrnoGuard() {
+    if (!errno) errno = old_value;
+  }
+  int old_value;
+};
+}  // namespace
+
+void BufferRawSink::Write(string_view v) {
+  size_t to_write = std::min(v.size(), size_);
+  std::memcpy(buffer_, v.data(), to_write);
+  buffer_ += to_write;
+  size_ -= to_write;
+  total_written_ += v.size();
+}
+
+void FILERawSink::Write(string_view v) {
+  while (!v.empty() && !error_) {
+    // Reset errno to zero in case the libc implementation doesn't set errno
+    // when a failure occurs.
+    ClearErrnoGuard guard;
+
+    if (size_t result = std::fwrite(v.data(), 1, v.size(), output_)) {
+      // Some progress was made.
+      count_ += result;
+      v.remove_prefix(result);
+    } else {
+      if (errno == EINTR) {
+        continue;
+      } else if (errno) {
+        error_ = errno;
+      } else if (std::ferror(output_)) {
+        // Non-POSIX compliant libc implementations may not set errno, so we
+        // have check the streams error indicator.
+        error_ = EBADF;
+      } else {
+        // We're likely on a non-POSIX system that encountered EINTR but had no
+        // way of reporting it.
+        continue;
+      }
+    }
+  }
+}
+
+}  // namespace str_format_internal
+}  // namespace absl
diff --git a/absl/strings/internal/str_format/output.h b/absl/strings/internal/str_format/output.h
new file mode 100644
index 0000000..42da641
--- /dev/null
+++ b/absl/strings/internal/str_format/output.h
@@ -0,0 +1,101 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Output extension hooks for the Format library.
+// `internal::InvokeFlush` calls the appropriate flush function for the
+// specified output argument.
+// `BufferRawSink` is a simple output sink for a char buffer. Used by SnprintF.
+// `FILERawSink` is a std::FILE* based sink. Used by PrintF and FprintF.
+
+#ifndef ABSL_STRINGS_INTERNAL_STR_FORMAT_OUTPUT_H_
+#define ABSL_STRINGS_INTERNAL_STR_FORMAT_OUTPUT_H_
+
+#include <cstdio>
+#include <ostream>
+#include <string>
+
+#include "absl/base/port.h"
+#include "absl/strings/string_view.h"
+
+class Cord;
+
+namespace absl {
+namespace str_format_internal {
+
+// RawSink implementation that writes into a char* buffer.
+// It will not overflow the buffer, but will keep the total count of chars
+// that would have been written.
+class BufferRawSink {
+ public:
+  BufferRawSink(char* buffer, size_t size) : buffer_(buffer), size_(size) {}
+
+  size_t total_written() const { return total_written_; }
+  void Write(string_view v);
+
+ private:
+  char* buffer_;
+  size_t size_;
+  size_t total_written_ = 0;
+};
+
+// RawSink implementation that writes into a FILE*.
+// It keeps track of the total number of bytes written and any error encountered
+// during the writes.
+class FILERawSink {
+ public:
+  explicit FILERawSink(std::FILE* output) : output_(output) {}
+
+  void Write(string_view v);
+
+  size_t count() const { return count_; }
+  int error() const { return error_; }
+
+ private:
+  std::FILE* output_;
+  int error_ = 0;
+  size_t count_ = 0;
+};
+
+// Provide RawSink integration with common types from the STL.
+inline void AbslFormatFlush(std::string* out, string_view s) {
+  out->append(s.data(), s.size());
+}
+inline void AbslFormatFlush(std::ostream* out, string_view s) {
+  out->write(s.data(), s.size());
+}
+
+template <class AbslCord, typename = typename std::enable_if<
+                              std::is_same<AbslCord, ::Cord>::value>::type>
+inline void AbslFormatFlush(AbslCord* out, string_view s) {
+  out->Append(s);
+}
+
+inline void AbslFormatFlush(FILERawSink* sink, string_view v) {
+  sink->Write(v);
+}
+
+inline void AbslFormatFlush(BufferRawSink* sink, string_view v) {
+  sink->Write(v);
+}
+
+template <typename T>
+auto InvokeFlush(T* out, string_view s)
+    -> decltype(str_format_internal::AbslFormatFlush(out, s)) {
+  str_format_internal::AbslFormatFlush(out, s);
+}
+
+}  // namespace str_format_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_STR_FORMAT_OUTPUT_H_
diff --git a/absl/strings/internal/str_format/output_test.cc b/absl/strings/internal/str_format/output_test.cc
new file mode 100644
index 0000000..6e04abe
--- /dev/null
+++ b/absl/strings/internal/str_format/output_test.cc
@@ -0,0 +1,71 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/str_format/output.h"
+
+#include <sstream>
+#include <string>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+namespace absl {
+namespace {
+
+TEST(InvokeFlush, String) {
+  std::string str = "ABC";
+  str_format_internal::InvokeFlush(&str, "DEF");
+  EXPECT_EQ(str, "ABCDEF");
+}
+
+TEST(InvokeFlush, Stream) {
+  std::stringstream str;
+  str << "ABC";
+  str_format_internal::InvokeFlush(&str, "DEF");
+  EXPECT_EQ(str.str(), "ABCDEF");
+}
+
+TEST(BufferRawSink, Limits) {
+  char buf[16];
+  {
+    std::fill(std::begin(buf), std::end(buf), 'x');
+    str_format_internal::BufferRawSink bufsink(buf, sizeof(buf) - 1);
+    str_format_internal::InvokeFlush(&bufsink, "Hello World237");
+    EXPECT_EQ(std::string(buf, sizeof(buf)), "Hello World237xx");
+  }
+  {
+    std::fill(std::begin(buf), std::end(buf), 'x');
+    str_format_internal::BufferRawSink bufsink(buf, sizeof(buf) - 1);
+    str_format_internal::InvokeFlush(&bufsink, "Hello World237237");
+    EXPECT_EQ(std::string(buf, sizeof(buf)), "Hello World2372x");
+  }
+  {
+    std::fill(std::begin(buf), std::end(buf), 'x');
+    str_format_internal::BufferRawSink bufsink(buf, sizeof(buf) - 1);
+    str_format_internal::InvokeFlush(&bufsink, "Hello World");
+    str_format_internal::InvokeFlush(&bufsink, "237");
+    EXPECT_EQ(std::string(buf, sizeof(buf)), "Hello World237xx");
+  }
+  {
+    std::fill(std::begin(buf), std::end(buf), 'x');
+    str_format_internal::BufferRawSink bufsink(buf, sizeof(buf) - 1);
+    str_format_internal::InvokeFlush(&bufsink, "Hello World");
+    str_format_internal::InvokeFlush(&bufsink, "237237");
+    EXPECT_EQ(std::string(buf, sizeof(buf)), "Hello World2372x");
+  }
+}
+
+}  // namespace
+}  // namespace absl
+
diff --git a/absl/strings/internal/str_format/parser.cc b/absl/strings/internal/str_format/parser.cc
new file mode 100644
index 0000000..9ef5615
--- /dev/null
+++ b/absl/strings/internal/str_format/parser.cc
@@ -0,0 +1,303 @@
+#include "absl/strings/internal/str_format/parser.h"
+
+#include <assert.h>
+#include <string.h>
+#include <wchar.h>
+#include <cctype>
+#include <cstdint>
+
+#include <algorithm>
+#include <initializer_list>
+#include <limits>
+#include <ostream>
+#include <string>
+#include <unordered_set>
+
+namespace absl {
+namespace str_format_internal {
+
+using CC = ConversionChar::Id;
+using LM = LengthMod::Id;
+ABSL_CONST_INIT const ConvTag kTags[256] = {
+    {},    {},    {},    {},    {},    {},    {},    {},     // 00-07
+    {},    {},    {},    {},    {},    {},    {},    {},     // 08-0f
+    {},    {},    {},    {},    {},    {},    {},    {},     // 10-17
+    {},    {},    {},    {},    {},    {},    {},    {},     // 18-1f
+    {},    {},    {},    {},    {},    {},    {},    {},     // 20-27
+    {},    {},    {},    {},    {},    {},    {},    {},     // 28-2f
+    {},    {},    {},    {},    {},    {},    {},    {},     // 30-37
+    {},    {},    {},    {},    {},    {},    {},    {},     // 38-3f
+    {},    CC::A, {},    CC::C, {},    CC::E, CC::F, CC::G,  // @ABCDEFG
+    {},    {},    {},    {},    LM::L, {},    {},    {},     // HIJKLMNO
+    {},    {},    {},    CC::S, {},    {},    {},    {},     // PQRSTUVW
+    CC::X, {},    {},    {},    {},    {},    {},    {},     // XYZ[\]^_
+    {},    CC::a, {},    CC::c, CC::d, CC::e, CC::f, CC::g,  // `abcdefg
+    LM::h, CC::i, LM::j, {},    LM::l, {},    CC::n, CC::o,  // hijklmno
+    CC::p, LM::q, {},    CC::s, LM::t, CC::u, {},    {},     // pqrstuvw
+    CC::x, {},    LM::z, {},    {},    {},    {},    {},     // xyz{|}!
+    {},    {},    {},    {},    {},    {},    {},    {},     // 80-87
+    {},    {},    {},    {},    {},    {},    {},    {},     // 88-8f
+    {},    {},    {},    {},    {},    {},    {},    {},     // 90-97
+    {},    {},    {},    {},    {},    {},    {},    {},     // 98-9f
+    {},    {},    {},    {},    {},    {},    {},    {},     // a0-a7
+    {},    {},    {},    {},    {},    {},    {},    {},     // a8-af
+    {},    {},    {},    {},    {},    {},    {},    {},     // b0-b7
+    {},    {},    {},    {},    {},    {},    {},    {},     // b8-bf
+    {},    {},    {},    {},    {},    {},    {},    {},     // c0-c7
+    {},    {},    {},    {},    {},    {},    {},    {},     // c8-cf
+    {},    {},    {},    {},    {},    {},    {},    {},     // d0-d7
+    {},    {},    {},    {},    {},    {},    {},    {},     // d8-df
+    {},    {},    {},    {},    {},    {},    {},    {},     // e0-e7
+    {},    {},    {},    {},    {},    {},    {},    {},     // e8-ef
+    {},    {},    {},    {},    {},    {},    {},    {},     // f0-f7
+    {},    {},    {},    {},    {},    {},    {},    {},     // f8-ff
+};
+
+namespace {
+
+bool CheckFastPathSetting(const UnboundConversion& conv) {
+  bool should_be_basic = !conv.flags.left &&      //
+                         !conv.flags.show_pos &&  //
+                         !conv.flags.sign_col &&  //
+                         !conv.flags.alt &&       //
+                         !conv.flags.zero &&      //
+                         (conv.width.value() == -1) &&
+                         (conv.precision.value() == -1);
+  if (should_be_basic != conv.flags.basic) {
+    fprintf(stderr,
+            "basic=%d left=%d show_pos=%d sign_col=%d alt=%d zero=%d "
+            "width=%d precision=%d\n",
+            conv.flags.basic, conv.flags.left, conv.flags.show_pos,
+            conv.flags.sign_col, conv.flags.alt, conv.flags.zero,
+            conv.width.value(), conv.precision.value());
+  }
+  return should_be_basic == conv.flags.basic;
+}
+
+template <bool is_positional>
+const char *ConsumeConversion(const char *pos, const char *const end,
+                              UnboundConversion *conv, int *next_arg) {
+  const char* const original_pos = pos;
+  char c;
+  // Read the next char into `c` and update `pos`. Returns false if there are
+  // no more chars to read.
+#define ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR()          \
+  do {                                                  \
+    if (ABSL_PREDICT_FALSE(pos == end)) return nullptr; \
+    c = *pos++;                                         \
+  } while (0)
+
+  const auto parse_digits = [&] {
+    int digits = c - '0';
+    // We do not want to overflow `digits` so we consume at most digits10
+    // digits. If there are more digits the parsing will fail later on when the
+    // digit doesn't match the expected characters.
+    int num_digits = std::numeric_limits<int>::digits10;
+    for (;;) {
+      if (ABSL_PREDICT_FALSE(pos == end)) break;
+      c = *pos++;
+      if (!std::isdigit(c)) break;
+      --num_digits;
+      if (ABSL_PREDICT_FALSE(!num_digits)) break;
+      digits = 10 * digits + c - '0';
+    }
+    return digits;
+  };
+
+  if (is_positional) {
+    ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+    if (ABSL_PREDICT_FALSE(c < '1' || c > '9')) return nullptr;
+    conv->arg_position = parse_digits();
+    assert(conv->arg_position > 0);
+    if (ABSL_PREDICT_FALSE(c != '$')) return nullptr;
+  }
+
+  ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+
+  // We should start with the basic flag on.
+  assert(conv->flags.basic);
+
+  // Any non alpha character makes this conversion not basic.
+  // This includes flags (-+ #0), width (1-9, *) or precision (.).
+  // All conversion characters and length modifiers are alpha characters.
+  if (c < 'A') {
+    conv->flags.basic = false;
+
+    for (; c <= '0';) {
+      // FIXME: We might be able to speed this up reusing the lookup table from
+      // above. It might require changing Flags to be a plain integer where we
+      // can |= a value.
+      switch (c) {
+        case '-':
+          conv->flags.left = true;
+          break;
+        case '+':
+          conv->flags.show_pos = true;
+          break;
+        case ' ':
+          conv->flags.sign_col = true;
+          break;
+        case '#':
+          conv->flags.alt = true;
+          break;
+        case '0':
+          conv->flags.zero = true;
+          break;
+        default:
+          goto flags_done;
+      }
+      ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+    }
+flags_done:
+
+    if (c <= '9') {
+      if (c >= '0') {
+        int maybe_width = parse_digits();
+        if (!is_positional && c == '$') {
+          if (ABSL_PREDICT_FALSE(*next_arg != 0)) return nullptr;
+          // Positional conversion.
+          *next_arg = -1;
+          conv->flags = Flags();
+          conv->flags.basic = true;
+          return ConsumeConversion<true>(original_pos, end, conv, next_arg);
+        }
+        conv->width.set_value(maybe_width);
+      } else if (c == '*') {
+        ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+        if (is_positional) {
+          if (ABSL_PREDICT_FALSE(c < '1' || c > '9')) return nullptr;
+          conv->width.set_from_arg(parse_digits());
+          if (ABSL_PREDICT_FALSE(c != '$')) return nullptr;
+          ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+        } else {
+          conv->width.set_from_arg(++*next_arg);
+        }
+      }
+    }
+
+    if (c == '.') {
+      ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+      if (std::isdigit(c)) {
+        conv->precision.set_value(parse_digits());
+      } else if (c == '*') {
+        ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+        if (is_positional) {
+          if (ABSL_PREDICT_FALSE(c < '1' || c > '9')) return nullptr;
+          conv->precision.set_from_arg(parse_digits());
+          if (c != '$') return nullptr;
+          ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+        } else {
+          conv->precision.set_from_arg(++*next_arg);
+        }
+      } else {
+        conv->precision.set_value(0);
+      }
+    }
+  }
+
+  auto tag = GetTagForChar(c);
+
+  if (ABSL_PREDICT_FALSE(!tag.is_conv())) {
+    if (ABSL_PREDICT_FALSE(!tag.is_length())) return nullptr;
+
+    // It is a length modifier.
+    using str_format_internal::LengthMod;
+    LengthMod length_mod = tag.as_length();
+    ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+    if (c == 'h' && length_mod.id() == LengthMod::h) {
+      conv->length_mod = LengthMod::FromId(LengthMod::hh);
+      ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+    } else if (c == 'l' && length_mod.id() == LengthMod::l) {
+      conv->length_mod = LengthMod::FromId(LengthMod::ll);
+      ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
+    } else {
+      conv->length_mod = length_mod;
+    }
+    tag = GetTagForChar(c);
+    if (ABSL_PREDICT_FALSE(!tag.is_conv())) return nullptr;
+  }
+
+  assert(CheckFastPathSetting(*conv));
+  (void)(&CheckFastPathSetting);
+
+  conv->conv = tag.as_conv();
+  if (!is_positional) conv->arg_position = ++*next_arg;
+  return pos;
+}
+
+}  // namespace
+
+const char *ConsumeUnboundConversion(const char *p, const char *end,
+                                     UnboundConversion *conv, int *next_arg) {
+  if (*next_arg < 0) return ConsumeConversion<true>(p, end, conv, next_arg);
+  return ConsumeConversion<false>(p, end, conv, next_arg);
+}
+
+struct ParsedFormatBase::ParsedFormatConsumer {
+  explicit ParsedFormatConsumer(ParsedFormatBase *parsedformat)
+      : parsed(parsedformat), data_pos(parsedformat->data_.get()) {}
+
+  bool Append(string_view s) {
+    if (s.empty()) return true;
+
+    size_t text_end = AppendText(s);
+
+    if (!parsed->items_.empty() && !parsed->items_.back().is_conversion) {
+      // Let's extend the existing text run.
+      parsed->items_.back().text_end = text_end;
+    } else {
+      // Let's make a new text run.
+      parsed->items_.push_back({false, text_end, {}});
+    }
+    return true;
+  }
+
+  bool ConvertOne(const UnboundConversion &conv, string_view s) {
+    size_t text_end = AppendText(s);
+    parsed->items_.push_back({true, text_end, conv});
+    return true;
+  }
+
+  size_t AppendText(string_view s) {
+    memcpy(data_pos, s.data(), s.size());
+    data_pos += s.size();
+    return static_cast<size_t>(data_pos - parsed->data_.get());
+  }
+
+  ParsedFormatBase *parsed;
+  char* data_pos;
+};
+
+ParsedFormatBase::ParsedFormatBase(string_view format, bool allow_ignored,
+                                   std::initializer_list<Conv> convs)
+    : data_(format.empty() ? nullptr : new char[format.size()]) {
+  has_error_ = !ParseFormatString(format, ParsedFormatConsumer(this)) ||
+               !MatchesConversions(allow_ignored, convs);
+}
+
+bool ParsedFormatBase::MatchesConversions(
+    bool allow_ignored, std::initializer_list<Conv> convs) const {
+  std::unordered_set<int> used;
+  auto add_if_valid_conv = [&](int pos, char c) {
+      if (static_cast<size_t>(pos) > convs.size() ||
+          !Contains(convs.begin()[pos - 1], c))
+        return false;
+      used.insert(pos);
+      return true;
+  };
+  for (const ConversionItem &item : items_) {
+    if (!item.is_conversion) continue;
+    auto &conv = item.conv;
+    if (conv.precision.is_from_arg() &&
+        !add_if_valid_conv(conv.precision.get_from_arg(), '*'))
+      return false;
+    if (conv.width.is_from_arg() &&
+        !add_if_valid_conv(conv.width.get_from_arg(), '*'))
+      return false;
+    if (!add_if_valid_conv(conv.arg_position, conv.conv.Char())) return false;
+  }
+  return used.size() == convs.size() || allow_ignored;
+}
+
+}  // namespace str_format_internal
+}  // namespace absl
diff --git a/absl/strings/internal/str_format/parser.h b/absl/strings/internal/str_format/parser.h
new file mode 100644
index 0000000..b7614a0
--- /dev/null
+++ b/absl/strings/internal/str_format/parser.h
@@ -0,0 +1,322 @@
+#ifndef ABSL_STRINGS_INTERNAL_STR_FORMAT_PARSER_H_
+#define ABSL_STRINGS_INTERNAL_STR_FORMAT_PARSER_H_
+
+#include <limits.h>
+#include <stddef.h>
+#include <stdlib.h>
+
+#include <cassert>
+#include <initializer_list>
+#include <iosfwd>
+#include <iterator>
+#include <memory>
+#include <vector>
+
+#include "absl/strings/internal/str_format/checker.h"
+#include "absl/strings/internal/str_format/extension.h"
+
+namespace absl {
+namespace str_format_internal {
+
+// The analyzed properties of a single specified conversion.
+struct UnboundConversion {
+  UnboundConversion()
+      : flags() /* This is required to zero all the fields of flags. */ {
+    flags.basic = true;
+  }
+
+  class InputValue {
+   public:
+    void set_value(int value) {
+      assert(value >= 0);
+      value_ = value;
+    }
+    int value() const { return value_; }
+
+    // Marks the value as "from arg". aka the '*' format.
+    // Requires `value >= 1`.
+    // When set, is_from_arg() return true and get_from_arg() returns the
+    // original value.
+    // `value()`'s return value is unspecfied in this state.
+    void set_from_arg(int value) {
+      assert(value > 0);
+      value_ = -value - 1;
+    }
+    bool is_from_arg() const { return value_ < -1; }
+    int get_from_arg() const {
+      assert(is_from_arg());
+      return -value_ - 1;
+    }
+
+   private:
+    int value_ = -1;
+  };
+
+  // No need to initialize. It will always be set in the parser.
+  int arg_position;
+
+  InputValue width;
+  InputValue precision;
+
+  Flags flags;
+  LengthMod length_mod;
+  ConversionChar conv;
+};
+
+// Consume conversion spec prefix (not including '%') of [p, end) if valid.
+// Examples of valid specs would be e.g.: "s", "d", "-12.6f".
+// If valid, it returns the first character following the conversion spec,
+// and the spec part is broken down and returned in 'conv'.
+// If invalid, returns nullptr.
+const char* ConsumeUnboundConversion(const char* p, const char* end,
+                                     UnboundConversion* conv, int* next_arg);
+
+// Helper tag class for the table below.
+// It allows fast `char -> ConversionChar/LengthMod` checking and conversions.
+class ConvTag {
+ public:
+  constexpr ConvTag(ConversionChar::Id id) : tag_(id) {}  // NOLINT
+  // We invert the length modifiers to make them negative so that we can easily
+  // test for them.
+  constexpr ConvTag(LengthMod::Id id) : tag_(~id) {}  // NOLINT
+  // Everything else is -128, which is negative to make is_conv() simpler.
+  constexpr ConvTag() : tag_(-128) {}
+
+  bool is_conv() const { return tag_ >= 0; }
+  bool is_length() const { return tag_ < 0 && tag_ != -128; }
+  ConversionChar as_conv() const {
+    assert(is_conv());
+    return ConversionChar::FromId(static_cast<ConversionChar::Id>(tag_));
+  }
+  LengthMod as_length() const {
+    assert(is_length());
+    return LengthMod::FromId(static_cast<LengthMod::Id>(~tag_));
+  }
+
+ private:
+  std::int8_t tag_;
+};
+
+extern const ConvTag kTags[256];
+// Keep a single table for all the conversion chars and length modifiers.
+inline ConvTag GetTagForChar(char c) {
+  return kTags[static_cast<unsigned char>(c)];
+}
+
+// Parse the format string provided in 'src' and pass the identified items into
+// 'consumer'.
+// Text runs will be passed by calling
+//   Consumer::Append(string_view);
+// ConversionItems will be passed by calling
+//   Consumer::ConvertOne(UnboundConversion, string_view);
+// In the case of ConvertOne, the string_view that is passed is the
+// portion of the format string corresponding to the conversion, not including
+// the leading %. On success, it returns true. On failure, it stops and returns
+// false.
+template <typename Consumer>
+bool ParseFormatString(string_view src, Consumer consumer) {
+  int next_arg = 0;
+  const char* p = src.data();
+  const char* const end = p + src.size();
+  while (p != end) {
+    const char* percent = static_cast<const char*>(memchr(p, '%', end - p));
+    if (!percent) {
+      // We found the last substring.
+      return consumer.Append(string_view(p, end - p));
+    }
+    // We found a percent, so push the text run then process the percent.
+    if (ABSL_PREDICT_FALSE(!consumer.Append(string_view(p, percent - p)))) {
+      return false;
+    }
+    if (ABSL_PREDICT_FALSE(percent + 1 >= end)) return false;
+
+    auto tag = GetTagForChar(percent[1]);
+    if (tag.is_conv()) {
+      if (ABSL_PREDICT_FALSE(next_arg < 0)) {
+        // This indicates an error in the format std::string.
+        // The only way to get `next_arg < 0` here is to have a positional
+        // argument first which sets next_arg to -1 and then a non-positional
+        // argument.
+        return false;
+      }
+      p = percent + 2;
+
+      // Keep this case separate from the one below.
+      // ConvertOne is more efficient when the compiler can see that the `basic`
+      // flag is set.
+      UnboundConversion conv;
+      conv.conv = tag.as_conv();
+      conv.arg_position = ++next_arg;
+      if (ABSL_PREDICT_FALSE(
+              !consumer.ConvertOne(conv, string_view(percent + 1, 1)))) {
+        return false;
+      }
+    } else if (percent[1] != '%') {
+      UnboundConversion conv;
+      p = ConsumeUnboundConversion(percent + 1, end, &conv, &next_arg);
+      if (ABSL_PREDICT_FALSE(p == nullptr)) return false;
+      if (ABSL_PREDICT_FALSE(!consumer.ConvertOne(
+          conv, string_view(percent + 1, p - (percent + 1))))) {
+        return false;
+      }
+    } else {
+      if (ABSL_PREDICT_FALSE(!consumer.Append("%"))) return false;
+      p = percent + 2;
+      continue;
+    }
+  }
+  return true;
+}
+
+// Always returns true, or fails to compile in a constexpr context if s does not
+// point to a constexpr char array.
+constexpr bool EnsureConstexpr(string_view s) {
+  return s.empty() || s[0] == s[0];
+}
+
+class ParsedFormatBase {
+ public:
+  explicit ParsedFormatBase(string_view format, bool allow_ignored,
+                            std::initializer_list<Conv> convs);
+
+  ParsedFormatBase(const ParsedFormatBase& other) { *this = other; }
+
+  ParsedFormatBase(ParsedFormatBase&& other) { *this = std::move(other); }
+
+  ParsedFormatBase& operator=(const ParsedFormatBase& other) {
+    if (this == &other) return *this;
+    has_error_ = other.has_error_;
+    items_ = other.items_;
+    size_t text_size = items_.empty() ? 0 : items_.back().text_end;
+    data_.reset(new char[text_size]);
+    memcpy(data_.get(), other.data_.get(), text_size);
+    return *this;
+  }
+
+  ParsedFormatBase& operator=(ParsedFormatBase&& other) {
+    if (this == &other) return *this;
+    has_error_ = other.has_error_;
+    data_ = std::move(other.data_);
+    items_ = std::move(other.items_);
+    // Reset the vector to make sure the invariants hold.
+    other.items_.clear();
+    return *this;
+  }
+
+  template <typename Consumer>
+  bool ProcessFormat(Consumer consumer) const {
+    const char* const base = data_.get();
+    string_view text(base, 0);
+    for (const auto& item : items_) {
+      const char* const end = text.data() + text.size();
+      text = string_view(end, (base + item.text_end) - end);
+      if (item.is_conversion) {
+        if (!consumer.ConvertOne(item.conv, text)) return false;
+      } else {
+        if (!consumer.Append(text)) return false;
+      }
+    }
+    return !has_error_;
+  }
+
+  bool has_error() const { return has_error_; }
+
+ private:
+  // Returns whether the conversions match and if !allow_ignored it verifies
+  // that all conversions are used by the format.
+  bool MatchesConversions(bool allow_ignored,
+                          std::initializer_list<Conv> convs) const;
+
+  struct ParsedFormatConsumer;
+
+  struct ConversionItem {
+    bool is_conversion;
+    // Points to the past-the-end location of this element in the data_ array.
+    size_t text_end;
+    UnboundConversion conv;
+  };
+
+  bool has_error_;
+  std::unique_ptr<char[]> data_;
+  std::vector<ConversionItem> items_;
+};
+
+
+// A value type representing a preparsed format.  These can be created, copied
+// around, and reused to speed up formatting loops.
+// The user must specify through the template arguments the conversion
+// characters used in the format. This will be checked at compile time.
+//
+// This class uses Conv enum values to specify each argument.
+// This allows for more flexibility as you can specify multiple possible
+// conversion characters for each argument.
+// ParsedFormat<char...> is a simplified alias for when the user only
+// needs to specify a single conversion character for each argument.
+//
+// Example:
+//   // Extended format supports multiple characters per argument:
+//   using MyFormat = ExtendedParsedFormat<Conv::d | Conv::x>;
+//   MyFormat GetFormat(bool use_hex) {
+//     if (use_hex) return MyFormat("foo %x bar");
+//     return MyFormat("foo %d bar");
+//   }
+//   // 'format' can be used with any value that supports 'd' and 'x',
+//   // like `int`.
+//   auto format = GetFormat(use_hex);
+//   value = StringF(format, i);
+//
+// This class also supports runtime format checking with the ::New() and
+// ::NewAllowIgnored() factory functions.
+// This is the only API that allows the user to pass a runtime specified format
+// string. These factory functions will return NULL if the format does not match
+// the conversions requested by the user.
+template <str_format_internal::Conv... C>
+class ExtendedParsedFormat : public str_format_internal::ParsedFormatBase {
+ public:
+  explicit ExtendedParsedFormat(string_view format)
+#if ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+      __attribute__((
+          enable_if(str_format_internal::EnsureConstexpr(format),
+                    "Format std::string is not constexpr."),
+          enable_if(str_format_internal::ValidFormatImpl<C...>(format),
+                    "Format specified does not match the template arguments.")))
+#endif  // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+      : ExtendedParsedFormat(format, false) {
+  }
+
+  // ExtendedParsedFormat factory function.
+  // The user still has to specify the conversion characters, but they will not
+  // be checked at compile time. Instead, it will be checked at runtime.
+  // This delays the checking to runtime, but allows the user to pass
+  // dynamically sourced formats.
+  // It returns NULL if the format does not match the conversion characters.
+  // The user is responsible for checking the return value before using it.
+  //
+  // The 'New' variant will check that all the specified arguments are being
+  // consumed by the format and return NULL if any argument is being ignored.
+  // The 'NewAllowIgnored' variant will not verify this and will allow formats
+  // that ignore arguments.
+  static std::unique_ptr<ExtendedParsedFormat> New(string_view format) {
+    return New(format, false);
+  }
+  static std::unique_ptr<ExtendedParsedFormat> NewAllowIgnored(
+      string_view format) {
+    return New(format, true);
+  }
+
+ private:
+  static std::unique_ptr<ExtendedParsedFormat> New(string_view format,
+                                                   bool allow_ignored) {
+    std::unique_ptr<ExtendedParsedFormat> conv(
+        new ExtendedParsedFormat(format, allow_ignored));
+    if (conv->has_error()) return nullptr;
+    return conv;
+  }
+
+  ExtendedParsedFormat(string_view s, bool allow_ignored)
+      : ParsedFormatBase(s, allow_ignored, {C...}) {}
+};
+}  // namespace str_format_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_STR_FORMAT_PARSER_H_
diff --git a/absl/strings/internal/str_format/parser_test.cc b/absl/strings/internal/str_format/parser_test.cc
new file mode 100644
index 0000000..6d356093
--- /dev/null
+++ b/absl/strings/internal/str_format/parser_test.cc
@@ -0,0 +1,392 @@
+#include "absl/strings/internal/str_format/parser.h"
+
+#include <string.h>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/macros.h"
+
+namespace absl {
+namespace str_format_internal {
+
+namespace {
+
+using testing::Pair;
+
+TEST(LengthModTest, Names) {
+  struct Expectation {
+    int line;
+    LengthMod::Id id;
+    const char *name;
+  };
+  const Expectation kExpect[] = {
+    {__LINE__, LengthMod::none, ""  },
+    {__LINE__, LengthMod::h,    "h" },
+    {__LINE__, LengthMod::hh,   "hh"},
+    {__LINE__, LengthMod::l,    "l" },
+    {__LINE__, LengthMod::ll,   "ll"},
+    {__LINE__, LengthMod::L,    "L" },
+    {__LINE__, LengthMod::j,    "j" },
+    {__LINE__, LengthMod::z,    "z" },
+    {__LINE__, LengthMod::t,    "t" },
+    {__LINE__, LengthMod::q,    "q" },
+  };
+  EXPECT_EQ(ABSL_ARRAYSIZE(kExpect), LengthMod::kNumValues);
+  for (auto e : kExpect) {
+    SCOPED_TRACE(e.line);
+    LengthMod mod = LengthMod::FromId(e.id);
+    EXPECT_EQ(e.id, mod.id());
+    EXPECT_EQ(e.name, mod.name());
+  }
+}
+
+TEST(ConversionCharTest, Names) {
+  struct Expectation {
+    ConversionChar::Id id;
+    char name;
+  };
+  // clang-format off
+  const Expectation kExpect[] = {
+#define X(c) {ConversionChar::c, #c[0]}
+    X(c), X(C), X(s), X(S),                          // text
+    X(d), X(i), X(o), X(u), X(x), X(X),              // int
+    X(f), X(F), X(e), X(E), X(g), X(G), X(a), X(A),  // float
+    X(n), X(p),                                      // misc
+#undef X
+    {ConversionChar::none, '\0'},
+  };
+  // clang-format on
+  EXPECT_EQ(ABSL_ARRAYSIZE(kExpect), ConversionChar::kNumValues);
+  for (auto e : kExpect) {
+    SCOPED_TRACE(e.name);
+    ConversionChar v = ConversionChar::FromId(e.id);
+    EXPECT_EQ(e.id, v.id());
+    EXPECT_EQ(e.name, v.Char());
+  }
+}
+
+class ConsumeUnboundConversionTest : public ::testing::Test {
+ public:
+  std::pair<string_view, string_view> Consume(string_view src) {
+    int next = 0;
+    o = UnboundConversion();  // refresh
+    const char* p = ConsumeUnboundConversion(
+        src.data(), src.data() + src.size(), &o, &next);
+    if (!p) return {{}, src};
+    return {string_view(src.data(), p - src.data()),
+            string_view(p, src.data() + src.size() - p)};
+  }
+
+  bool Run(const char *fmt, bool force_positional = false) {
+    int next = force_positional ? -1 : 0;
+    o = UnboundConversion();  // refresh
+    return ConsumeUnboundConversion(fmt, fmt + strlen(fmt), &o, &next) ==
+           fmt + strlen(fmt);
+  }
+  UnboundConversion o;
+};
+
+TEST_F(ConsumeUnboundConversionTest, ConsumeSpecification) {
+  struct Expectation {
+    int line;
+    string_view src;
+    string_view out;
+    string_view src_post;
+  };
+  const Expectation kExpect[] = {
+    {__LINE__, "",     "",     ""  },
+    {__LINE__, "b",    "",     "b" },  // 'b' is invalid
+    {__LINE__, "ba",   "",     "ba"},  // 'b' is invalid
+    {__LINE__, "l",    "",     "l" },  // just length mod isn't okay
+    {__LINE__, "d",    "d",    ""  },  // basic
+    {__LINE__, "d ",   "d",    " " },  // leave suffix
+    {__LINE__, "dd",   "d",    "d" },  // don't be greedy
+    {__LINE__, "d9",   "d",    "9" },  // leave non-space suffix
+    {__LINE__, "dzz",  "d",    "zz"},  // length mod as suffix
+    {__LINE__, "1$*2$d", "1$*2$d", ""  },  // arg indexing and * allowed.
+    {__LINE__, "0-14.3hhd", "0-14.3hhd", ""},  // precision, width
+    {__LINE__, " 0-+#14.3hhd", " 0-+#14.3hhd", ""},  // flags
+  };
+  for (const auto& e : kExpect) {
+    SCOPED_TRACE(e.line);
+    EXPECT_THAT(Consume(e.src), Pair(e.out, e.src_post));
+  }
+}
+
+TEST_F(ConsumeUnboundConversionTest, BasicConversion) {
+  EXPECT_FALSE(Run(""));
+  EXPECT_FALSE(Run("z"));
+
+  EXPECT_FALSE(Run("dd"));  // no excess allowed
+
+  EXPECT_TRUE(Run("d"));
+  EXPECT_EQ('d', o.conv.Char());
+  EXPECT_FALSE(o.width.is_from_arg());
+  EXPECT_LT(o.width.value(), 0);
+  EXPECT_FALSE(o.precision.is_from_arg());
+  EXPECT_LT(o.precision.value(), 0);
+  EXPECT_EQ(1, o.arg_position);
+  EXPECT_EQ(LengthMod::none, o.length_mod.id());
+}
+
+TEST_F(ConsumeUnboundConversionTest, ArgPosition) {
+  EXPECT_TRUE(Run("d"));
+  EXPECT_EQ(1, o.arg_position);
+  EXPECT_TRUE(Run("3$d"));
+  EXPECT_EQ(3, o.arg_position);
+  EXPECT_TRUE(Run("1$d"));
+  EXPECT_EQ(1, o.arg_position);
+  EXPECT_TRUE(Run("1$d", true));
+  EXPECT_EQ(1, o.arg_position);
+  EXPECT_TRUE(Run("123$d"));
+  EXPECT_EQ(123, o.arg_position);
+  EXPECT_TRUE(Run("123$d", true));
+  EXPECT_EQ(123, o.arg_position);
+  EXPECT_TRUE(Run("10$d"));
+  EXPECT_EQ(10, o.arg_position);
+  EXPECT_TRUE(Run("10$d", true));
+  EXPECT_EQ(10, o.arg_position);
+
+  // Position can't be zero.
+  EXPECT_FALSE(Run("0$d"));
+  EXPECT_FALSE(Run("0$d", true));
+  EXPECT_FALSE(Run("1$*0$d"));
+  EXPECT_FALSE(Run("1$.*0$d"));
+
+  // Position can't start with a zero digit at all. That is not a 'decimal'.
+  EXPECT_FALSE(Run("01$p"));
+  EXPECT_FALSE(Run("01$p", true));
+  EXPECT_FALSE(Run("1$*01$p"));
+  EXPECT_FALSE(Run("1$.*01$p"));
+}
+
+TEST_F(ConsumeUnboundConversionTest, WidthAndPrecision) {
+  EXPECT_TRUE(Run("14d"));
+  EXPECT_EQ('d', o.conv.Char());
+  EXPECT_FALSE(o.width.is_from_arg());
+  EXPECT_EQ(14, o.width.value());
+  EXPECT_FALSE(o.precision.is_from_arg());
+  EXPECT_LT(o.precision.value(), 0);
+
+  EXPECT_TRUE(Run("14.d"));
+  EXPECT_FALSE(o.width.is_from_arg());
+  EXPECT_FALSE(o.precision.is_from_arg());
+  EXPECT_EQ(14, o.width.value());
+  EXPECT_EQ(0, o.precision.value());
+
+  EXPECT_TRUE(Run(".d"));
+  EXPECT_FALSE(o.width.is_from_arg());
+  EXPECT_LT(o.width.value(), 0);
+  EXPECT_FALSE(o.precision.is_from_arg());
+  EXPECT_EQ(0, o.precision.value());
+
+  EXPECT_TRUE(Run(".5d"));
+  EXPECT_FALSE(o.width.is_from_arg());
+  EXPECT_LT(o.width.value(), 0);
+  EXPECT_FALSE(o.precision.is_from_arg());
+  EXPECT_EQ(5, o.precision.value());
+
+  EXPECT_TRUE(Run(".0d"));
+  EXPECT_FALSE(o.width.is_from_arg());
+  EXPECT_LT(o.width.value(), 0);
+  EXPECT_FALSE(o.precision.is_from_arg());
+  EXPECT_EQ(0, o.precision.value());
+
+  EXPECT_TRUE(Run("14.5d"));
+  EXPECT_FALSE(o.width.is_from_arg());
+  EXPECT_FALSE(o.precision.is_from_arg());
+  EXPECT_EQ(14, o.width.value());
+  EXPECT_EQ(5, o.precision.value());
+
+  EXPECT_TRUE(Run("*.*d"));
+  EXPECT_TRUE(o.width.is_from_arg());
+  EXPECT_EQ(1, o.width.get_from_arg());
+  EXPECT_TRUE(o.precision.is_from_arg());
+  EXPECT_EQ(2, o.precision.get_from_arg());
+  EXPECT_EQ(3, o.arg_position);
+
+  EXPECT_TRUE(Run("*d"));
+  EXPECT_TRUE(o.width.is_from_arg());
+  EXPECT_EQ(1, o.width.get_from_arg());
+  EXPECT_FALSE(o.precision.is_from_arg());
+  EXPECT_LT(o.precision.value(), 0);
+  EXPECT_EQ(2, o.arg_position);
+
+  EXPECT_TRUE(Run(".*d"));
+  EXPECT_FALSE(o.width.is_from_arg());
+  EXPECT_LT(o.width.value(), 0);
+  EXPECT_TRUE(o.precision.is_from_arg());
+  EXPECT_EQ(1, o.precision.get_from_arg());
+  EXPECT_EQ(2, o.arg_position);
+
+  // mixed implicit and explicit: didn't specify arg position.
+  EXPECT_FALSE(Run("*23$.*34$d"));
+
+  EXPECT_TRUE(Run("12$*23$.*34$d"));
+  EXPECT_EQ(12, o.arg_position);
+  EXPECT_TRUE(o.width.is_from_arg());
+  EXPECT_EQ(23, o.width.get_from_arg());
+  EXPECT_TRUE(o.precision.is_from_arg());
+  EXPECT_EQ(34, o.precision.get_from_arg());
+
+  EXPECT_TRUE(Run("2$*5$.*9$d"));
+  EXPECT_EQ(2, o.arg_position);
+  EXPECT_TRUE(o.width.is_from_arg());
+  EXPECT_EQ(5, o.width.get_from_arg());
+  EXPECT_TRUE(o.precision.is_from_arg());
+  EXPECT_EQ(9, o.precision.get_from_arg());
+
+  EXPECT_FALSE(Run(".*0$d")) << "no arg 0";
+
+  // Large values
+  EXPECT_TRUE(Run("999999999.999999999d"));
+  EXPECT_FALSE(o.width.is_from_arg());
+  EXPECT_EQ(999999999, o.width.value());
+  EXPECT_FALSE(o.precision.is_from_arg());
+  EXPECT_EQ(999999999, o.precision.value());
+
+  EXPECT_FALSE(Run("1000000000.999999999d"));
+  EXPECT_FALSE(Run("999999999.1000000000d"));
+  EXPECT_FALSE(Run("9999999999d"));
+  EXPECT_FALSE(Run(".9999999999d"));
+}
+
+TEST_F(ConsumeUnboundConversionTest, Flags) {
+  static const char kAllFlags[] = "-+ #0";
+  static const int kNumFlags = ABSL_ARRAYSIZE(kAllFlags) - 1;
+  for (int rev = 0; rev < 2; ++rev) {
+    for (int i = 0; i < 1 << kNumFlags; ++i) {
+      std::string fmt;
+      for (int k = 0; k < kNumFlags; ++k)
+        if ((i >> k) & 1) fmt += kAllFlags[k];
+      // flag order shouldn't matter
+      if (rev == 1) { std::reverse(fmt.begin(), fmt.end()); }
+      fmt += 'd';
+      SCOPED_TRACE(fmt);
+      EXPECT_TRUE(Run(fmt.c_str()));
+      EXPECT_EQ(fmt.find('-') == std::string::npos, !o.flags.left);
+      EXPECT_EQ(fmt.find('+') == std::string::npos, !o.flags.show_pos);
+      EXPECT_EQ(fmt.find(' ') == std::string::npos, !o.flags.sign_col);
+      EXPECT_EQ(fmt.find('#') == std::string::npos, !o.flags.alt);
+      EXPECT_EQ(fmt.find('0') == std::string::npos, !o.flags.zero);
+    }
+  }
+}
+
+TEST_F(ConsumeUnboundConversionTest, BasicFlag) {
+  // Flag is on
+  for (const char* fmt : {"d", "llx", "G", "1$X"}) {
+    SCOPED_TRACE(fmt);
+    EXPECT_TRUE(Run(fmt));
+    EXPECT_TRUE(o.flags.basic);
+  }
+
+  // Flag is off
+  for (const char* fmt : {"3d", ".llx", "-G", "1$#X"}) {
+    SCOPED_TRACE(fmt);
+    EXPECT_TRUE(Run(fmt));
+    EXPECT_FALSE(o.flags.basic);
+  }
+}
+
+struct SummarizeConsumer {
+  std::string* out;
+  explicit SummarizeConsumer(std::string* out) : out(out) {}
+
+  bool Append(string_view s) {
+    *out += "[" + std::string(s) + "]";
+    return true;
+  }
+
+  bool ConvertOne(const UnboundConversion& conv, string_view s) {
+    *out += "{";
+    *out += std::string(s);
+    *out += ":";
+    *out += std::to_string(conv.arg_position) + "$";
+    if (conv.width.is_from_arg()) {
+      *out += std::to_string(conv.width.get_from_arg()) + "$*";
+    }
+    if (conv.precision.is_from_arg()) {
+      *out += "." + std::to_string(conv.precision.get_from_arg()) + "$*";
+    }
+    *out += conv.conv.Char();
+    *out += "}";
+    return true;
+  }
+};
+
+std::string SummarizeParsedFormat(const ParsedFormatBase& pc) {
+  std::string out;
+  if (!pc.ProcessFormat(SummarizeConsumer(&out))) out += "!";
+  return out;
+}
+
+class ParsedFormatTest : public testing::Test {};
+
+TEST_F(ParsedFormatTest, ValueSemantics) {
+  ParsedFormatBase p1({}, true, {});  // empty format
+  EXPECT_EQ("", SummarizeParsedFormat(p1));
+
+  ParsedFormatBase p2 = p1;  // copy construct (empty)
+  EXPECT_EQ(SummarizeParsedFormat(p1), SummarizeParsedFormat(p2));
+
+  p1 = ParsedFormatBase("hello%s", true, {Conv::s});  // move assign
+  EXPECT_EQ("[hello]{s:1$s}", SummarizeParsedFormat(p1));
+
+  ParsedFormatBase p3 = p1;  // copy construct (nonempty)
+  EXPECT_EQ(SummarizeParsedFormat(p1), SummarizeParsedFormat(p3));
+
+  using std::swap;
+  swap(p1, p2);
+  EXPECT_EQ("", SummarizeParsedFormat(p1));
+  EXPECT_EQ("[hello]{s:1$s}", SummarizeParsedFormat(p2));
+  swap(p1, p2);  // undo
+
+  p2 = p1;  // copy assign
+  EXPECT_EQ(SummarizeParsedFormat(p1), SummarizeParsedFormat(p2));
+}
+
+struct ExpectParse {
+  const char* in;
+  std::initializer_list<Conv> conv_set;
+  const char* out;
+};
+
+TEST_F(ParsedFormatTest, Parsing) {
+  // Parse should be equivalent to that obtained by ConversionParseIterator.
+  // No need to retest the parsing edge cases here.
+  const ExpectParse kExpect[] = {
+      {"", {}, ""},
+      {"ab", {}, "[ab]"},
+      {"a%d", {Conv::d}, "[a]{d:1$d}"},
+      {"a%+d", {Conv::d}, "[a]{+d:1$d}"},
+      {"a% d", {Conv::d}, "[a]{ d:1$d}"},
+      {"a%b %d", {}, "[a]!"},  // stop after error
+  };
+  for (const auto& e : kExpect) {
+    SCOPED_TRACE(e.in);
+    EXPECT_EQ(e.out,
+              SummarizeParsedFormat(ParsedFormatBase(e.in, false, e.conv_set)));
+  }
+}
+
+TEST_F(ParsedFormatTest, ParsingFlagOrder) {
+  const ExpectParse kExpect[] = {
+      {"a%+ 0d", {Conv::d}, "[a]{+ 0d:1$d}"},
+      {"a%+0 d", {Conv::d}, "[a]{+0 d:1$d}"},
+      {"a%0+ d", {Conv::d}, "[a]{0+ d:1$d}"},
+      {"a% +0d", {Conv::d}, "[a]{ +0d:1$d}"},
+      {"a%0 +d", {Conv::d}, "[a]{0 +d:1$d}"},
+      {"a% 0+d", {Conv::d}, "[a]{ 0+d:1$d}"},
+      {"a%+   0+d", {Conv::d}, "[a]{+   0+d:1$d}"},
+  };
+  for (const auto& e : kExpect) {
+    SCOPED_TRACE(e.in);
+    EXPECT_EQ(e.out,
+              SummarizeParsedFormat(ParsedFormatBase(e.in, false, e.conv_set)));
+  }
+}
+
+}  // namespace
+}  // namespace str_format_internal
+}  // namespace absl
diff --git a/absl/strings/internal/str_join_internal.h b/absl/strings/internal/str_join_internal.h
new file mode 100644
index 0000000..7c35f4d
--- /dev/null
+++ b/absl/strings/internal/str_join_internal.h
@@ -0,0 +1,312 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// This file declares INTERNAL parts of the Join API that are inlined/templated
+// or otherwise need to be available at compile time. The main abstractions
+// defined in this file are:
+//
+//   - A handful of default Formatters
+//   - JoinAlgorithm() overloads
+//   - JoinRange() overloads
+//   - JoinTuple()
+//
+// DO NOT INCLUDE THIS FILE DIRECTLY. Use this file by including
+// absl/strings/str_join.h
+//
+// IWYU pragma: private, include "absl/strings/str_join.h"
+
+#ifndef ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_
+#define ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_
+
+#include <cstring>
+#include <iterator>
+#include <memory>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+#include "absl/strings/internal/ostringstream.h"
+#include "absl/strings/internal/resize_uninitialized.h"
+#include "absl/strings/str_cat.h"
+
+namespace absl {
+namespace strings_internal {
+
+//
+// Formatter objects
+//
+// The following are implementation classes for standard Formatter objects. The
+// factory functions that users will call to create and use these formatters are
+// defined and documented in strings/join.h.
+//
+
+// The default formatter. Converts alpha-numeric types to strings.
+struct AlphaNumFormatterImpl {
+  // This template is needed in order to support passing in a dereferenced
+  // vector<bool>::iterator
+  template <typename T>
+  void operator()(std::string* out, const T& t) const {
+    StrAppend(out, AlphaNum(t));
+  }
+
+  void operator()(std::string* out, const AlphaNum& t) const {
+    StrAppend(out, t);
+  }
+};
+
+// A type that's used to overload the JoinAlgorithm() function (defined below)
+// for ranges that do not require additional formatting (e.g., a range of
+// strings).
+
+struct NoFormatter : public AlphaNumFormatterImpl {};
+
+// Formats types to strings using the << operator.
+class StreamFormatterImpl {
+ public:
+  // The method isn't const because it mutates state. Making it const will
+  // render StreamFormatterImpl thread-hostile.
+  template <typename T>
+  void operator()(std::string* out, const T& t) {
+    // The stream is created lazily to avoid paying the relatively high cost
+    // of its construction when joining an empty range.
+    if (strm_) {
+      strm_->clear();  // clear the bad, fail and eof bits in case they were set
+      strm_->str(out);
+    } else {
+      strm_.reset(new strings_internal::OStringStream(out));
+    }
+    *strm_ << t;
+  }
+
+ private:
+  std::unique_ptr<strings_internal::OStringStream> strm_;
+};
+
+// Formats a std::pair<>. The 'first' member is formatted using f1_ and the
+// 'second' member is formatted using f2_. sep_ is the separator.
+template <typename F1, typename F2>
+class PairFormatterImpl {
+ public:
+  PairFormatterImpl(F1 f1, absl::string_view sep, F2 f2)
+      : f1_(std::move(f1)), sep_(sep), f2_(std::move(f2)) {}
+
+  template <typename T>
+  void operator()(std::string* out, const T& p) {
+    f1_(out, p.first);
+    out->append(sep_);
+    f2_(out, p.second);
+  }
+
+  template <typename T>
+  void operator()(std::string* out, const T& p) const {
+    f1_(out, p.first);
+    out->append(sep_);
+    f2_(out, p.second);
+  }
+
+ private:
+  F1 f1_;
+  std::string sep_;
+  F2 f2_;
+};
+
+// Wraps another formatter and dereferences the argument to operator() then
+// passes the dereferenced argument to the wrapped formatter. This can be
+// useful, for example, to join a std::vector<int*>.
+template <typename Formatter>
+class DereferenceFormatterImpl {
+ public:
+  DereferenceFormatterImpl() : f_() {}
+  explicit DereferenceFormatterImpl(Formatter&& f)
+      : f_(std::forward<Formatter>(f)) {}
+
+  template <typename T>
+  void operator()(std::string* out, const T& t) {
+    f_(out, *t);
+  }
+
+  template <typename T>
+  void operator()(std::string* out, const T& t) const {
+    f_(out, *t);
+  }
+
+ private:
+  Formatter f_;
+};
+
+// DefaultFormatter<T> is a traits class that selects a default Formatter to use
+// for the given type T. The ::Type member names the Formatter to use. This is
+// used by the strings::Join() functions that do NOT take a Formatter argument,
+// in which case a default Formatter must be chosen.
+//
+// AlphaNumFormatterImpl is the default in the base template, followed by
+// specializations for other types.
+template <typename ValueType>
+struct DefaultFormatter {
+  typedef AlphaNumFormatterImpl Type;
+};
+template <>
+struct DefaultFormatter<const char*> {
+  typedef AlphaNumFormatterImpl Type;
+};
+template <>
+struct DefaultFormatter<char*> {
+  typedef AlphaNumFormatterImpl Type;
+};
+template <>
+struct DefaultFormatter<std::string> {
+  typedef NoFormatter Type;
+};
+template <>
+struct DefaultFormatter<absl::string_view> {
+  typedef NoFormatter Type;
+};
+template <typename ValueType>
+struct DefaultFormatter<ValueType*> {
+  typedef DereferenceFormatterImpl<typename DefaultFormatter<ValueType>::Type>
+      Type;
+};
+
+template <typename ValueType>
+struct DefaultFormatter<std::unique_ptr<ValueType>>
+    : public DefaultFormatter<ValueType*> {};
+
+//
+// JoinAlgorithm() functions
+//
+
+// The main joining algorithm. This simply joins the elements in the given
+// iterator range, each separated by the given separator, into an output string,
+// and formats each element using the provided Formatter object.
+template <typename Iterator, typename Formatter>
+std::string JoinAlgorithm(Iterator start, Iterator end, absl::string_view s,
+                          Formatter&& f) {
+  std::string result;
+  absl::string_view sep("");
+  for (Iterator it = start; it != end; ++it) {
+    result.append(sep.data(), sep.size());
+    f(&result, *it);
+    sep = s;
+  }
+  return result;
+}
+
+// A joining algorithm that's optimized for a forward iterator range of
+// string-like objects that do not need any additional formatting. This is to
+// optimize the common case of joining, say, a std::vector<string> or a
+// std::vector<absl::string_view>.
+//
+// This is an overload of the previous JoinAlgorithm() function. Here the
+// Formatter argument is of type NoFormatter. Since NoFormatter is an internal
+// type, this overload is only invoked when strings::Join() is called with a
+// range of string-like objects (e.g., std::string, absl::string_view), and an
+// explicit Formatter argument was NOT specified.
+//
+// The optimization is that the needed space will be reserved in the output
+// string to avoid the need to resize while appending. To do this, the iterator
+// range will be traversed twice: once to calculate the total needed size, and
+// then again to copy the elements and delimiters to the output string.
+template <typename Iterator,
+          typename = typename std::enable_if<std::is_convertible<
+              typename std::iterator_traits<Iterator>::iterator_category,
+              std::forward_iterator_tag>::value>::type>
+std::string JoinAlgorithm(Iterator start, Iterator end, absl::string_view s,
+                          NoFormatter) {
+  std::string result;
+  if (start != end) {
+    // Sums size
+    size_t result_size = start->size();
+    for (Iterator it = start; ++it != end;) {
+      result_size += s.size();
+      result_size += it->size();
+    }
+
+    if (result_size > 0) {
+      STLStringResizeUninitialized(&result, result_size);
+
+      // Joins strings
+      char* result_buf = &*result.begin();
+      memcpy(result_buf, start->data(), start->size());
+      result_buf += start->size();
+      for (Iterator it = start; ++it != end;) {
+        memcpy(result_buf, s.data(), s.size());
+        result_buf += s.size();
+        memcpy(result_buf, it->data(), it->size());
+        result_buf += it->size();
+      }
+    }
+  }
+
+  return result;
+}
+
+// JoinTupleLoop implements a loop over the elements of a std::tuple, which
+// are heterogeneous. The primary template matches the tuple interior case. It
+// continues the iteration after appending a separator (for nonzero indices)
+// and formatting an element of the tuple. The specialization for the I=N case
+// matches the end-of-tuple, and terminates the iteration.
+template <size_t I, size_t N>
+struct JoinTupleLoop {
+  template <typename Tup, typename Formatter>
+  void operator()(std::string* out, const Tup& tup, absl::string_view sep,
+                  Formatter&& fmt) {
+    if (I > 0) out->append(sep.data(), sep.size());
+    fmt(out, std::get<I>(tup));
+    JoinTupleLoop<I + 1, N>()(out, tup, sep, fmt);
+  }
+};
+template <size_t N>
+struct JoinTupleLoop<N, N> {
+  template <typename Tup, typename Formatter>
+  void operator()(std::string*, const Tup&, absl::string_view, Formatter&&) {}
+};
+
+template <typename... T, typename Formatter>
+std::string JoinAlgorithm(const std::tuple<T...>& tup, absl::string_view sep,
+                          Formatter&& fmt) {
+  std::string result;
+  JoinTupleLoop<0, sizeof...(T)>()(&result, tup, sep, fmt);
+  return result;
+}
+
+template <typename Iterator>
+std::string JoinRange(Iterator first, Iterator last,
+                      absl::string_view separator) {
+  // No formatter was explicitly given, so a default must be chosen.
+  typedef typename std::iterator_traits<Iterator>::value_type ValueType;
+  typedef typename DefaultFormatter<ValueType>::Type Formatter;
+  return JoinAlgorithm(first, last, separator, Formatter());
+}
+
+template <typename Range, typename Formatter>
+std::string JoinRange(const Range& range, absl::string_view separator,
+                      Formatter&& fmt) {
+  using std::begin;
+  using std::end;
+  return JoinAlgorithm(begin(range), end(range), separator, fmt);
+}
+
+template <typename Range>
+std::string JoinRange(const Range& range, absl::string_view separator) {
+  using std::begin;
+  using std::end;
+  return JoinRange(begin(range), end(range), separator);
+}
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_
diff --git a/absl/strings/internal/str_split_internal.h b/absl/strings/internal/str_split_internal.h
new file mode 100644
index 0000000..52f6222
--- /dev/null
+++ b/absl/strings/internal/str_split_internal.h
@@ -0,0 +1,453 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// This file declares INTERNAL parts of the Split API that are inline/templated
+// or otherwise need to be available at compile time. The main abstractions
+// defined in here are
+//
+//   - ConvertibleToStringView
+//   - SplitIterator<>
+//   - Splitter<>
+//
+// DO NOT INCLUDE THIS FILE DIRECTLY. Use this file by including
+// absl/strings/str_split.h.
+//
+// IWYU pragma: private, include "absl/strings/str_split.h"
+
+#ifndef ABSL_STRINGS_INTERNAL_STR_SPLIT_INTERNAL_H_
+#define ABSL_STRINGS_INTERNAL_STR_SPLIT_INTERNAL_H_
+
+#include <array>
+#include <initializer_list>
+#include <iterator>
+#include <map>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+#include "absl/meta/type_traits.h"
+#include "absl/strings/string_view.h"
+
+#ifdef _GLIBCXX_DEBUG
+#include "absl/strings/internal/stl_type_traits.h"
+#endif  // _GLIBCXX_DEBUG
+
+namespace absl {
+namespace strings_internal {
+
+// This class is implicitly constructible from everything that absl::string_view
+// is implicitly constructible from. If it's constructed from a temporary
+// string, the data is moved into a data member so its lifetime matches that of
+// the ConvertibleToStringView instance.
+class ConvertibleToStringView {
+ public:
+  ConvertibleToStringView(const char* s)  // NOLINT(runtime/explicit)
+      : value_(s) {}
+  ConvertibleToStringView(char* s) : value_(s) {}  // NOLINT(runtime/explicit)
+  ConvertibleToStringView(absl::string_view s)     // NOLINT(runtime/explicit)
+      : value_(s) {}
+  ConvertibleToStringView(const std::string& s)  // NOLINT(runtime/explicit)
+      : value_(s) {}
+
+  // Matches rvalue strings and moves their data to a member.
+ConvertibleToStringView(std::string&& s)  // NOLINT(runtime/explicit)
+    : copy_(std::move(s)), value_(copy_) {}
+
+  ConvertibleToStringView(const ConvertibleToStringView& other)
+      : copy_(other.copy_),
+        value_(other.IsSelfReferential() ? copy_ : other.value_) {}
+
+  ConvertibleToStringView(ConvertibleToStringView&& other) {
+    StealMembers(std::move(other));
+  }
+
+  ConvertibleToStringView& operator=(ConvertibleToStringView other) {
+    StealMembers(std::move(other));
+    return *this;
+  }
+
+  absl::string_view value() const { return value_; }
+
+ private:
+  // Returns true if ctsp's value refers to its internal copy_ member.
+  bool IsSelfReferential() const { return value_.data() == copy_.data(); }
+
+  void StealMembers(ConvertibleToStringView&& other) {
+    if (other.IsSelfReferential()) {
+      copy_ = std::move(other.copy_);
+      value_ = copy_;
+      other.value_ = other.copy_;
+    } else {
+      value_ = other.value_;
+    }
+  }
+
+  // Holds the data moved from temporary std::string arguments. Declared first
+  // so that 'value' can refer to 'copy_'.
+  std::string copy_;
+  absl::string_view value_;
+};
+
+// An iterator that enumerates the parts of a string from a Splitter. The text
+// to be split, the Delimiter, and the Predicate are all taken from the given
+// Splitter object. Iterators may only be compared if they refer to the same
+// Splitter instance.
+//
+// This class is NOT part of the public splitting API.
+template <typename Splitter>
+class SplitIterator {
+ public:
+  using iterator_category = std::input_iterator_tag;
+  using value_type = absl::string_view;
+  using difference_type = ptrdiff_t;
+  using pointer = const value_type*;
+  using reference = const value_type&;
+
+  enum State { kInitState, kLastState, kEndState };
+  SplitIterator(State state, const Splitter* splitter)
+      : pos_(0),
+        state_(state),
+        splitter_(splitter),
+        delimiter_(splitter->delimiter()),
+        predicate_(splitter->predicate()) {
+    // Hack to maintain backward compatibility. This one block makes it so an
+    // empty absl::string_view whose .data() happens to be nullptr behaves
+    // *differently* from an otherwise empty absl::string_view whose .data() is
+    // not nullptr. This is an undesirable difference in general, but this
+    // behavior is maintained to avoid breaking existing code that happens to
+    // depend on this old behavior/bug. Perhaps it will be fixed one day. The
+    // difference in behavior is as follows:
+    //   Split(absl::string_view(""), '-');  // {""}
+    //   Split(absl::string_view(), '-');    // {}
+    if (splitter_->text().data() == nullptr) {
+      state_ = kEndState;
+      pos_ = splitter_->text().size();
+      return;
+    }
+
+    if (state_ == kEndState) {
+      pos_ = splitter_->text().size();
+    } else {
+      ++(*this);
+    }
+  }
+
+  bool at_end() const { return state_ == kEndState; }
+
+  reference operator*() const { return curr_; }
+  pointer operator->() const { return &curr_; }
+
+  SplitIterator& operator++() {
+    do {
+      if (state_ == kLastState) {
+        state_ = kEndState;
+        return *this;
+      }
+      const absl::string_view text = splitter_->text();
+      const absl::string_view d = delimiter_.Find(text, pos_);
+      if (d.data() == text.data() + text.size()) state_ = kLastState;
+      curr_ = text.substr(pos_, d.data() - (text.data() + pos_));
+      pos_ += curr_.size() + d.size();
+    } while (!predicate_(curr_));
+    return *this;
+  }
+
+  SplitIterator operator++(int) {
+    SplitIterator old(*this);
+    ++(*this);
+    return old;
+  }
+
+  friend bool operator==(const SplitIterator& a, const SplitIterator& b) {
+    return a.state_ == b.state_ && a.pos_ == b.pos_;
+  }
+
+  friend bool operator!=(const SplitIterator& a, const SplitIterator& b) {
+    return !(a == b);
+  }
+
+ private:
+  size_t pos_;
+  State state_;
+  absl::string_view curr_;
+  const Splitter* splitter_;
+  typename Splitter::DelimiterType delimiter_;
+  typename Splitter::PredicateType predicate_;
+};
+
+// HasMappedType<T>::value is true iff there exists a type T::mapped_type.
+template <typename T, typename = void>
+struct HasMappedType : std::false_type {};
+template <typename T>
+struct HasMappedType<T, absl::void_t<typename T::mapped_type>>
+    : std::true_type {};
+
+// HasValueType<T>::value is true iff there exists a type T::value_type.
+template <typename T, typename = void>
+struct HasValueType : std::false_type {};
+template <typename T>
+struct HasValueType<T, absl::void_t<typename T::value_type>> : std::true_type {
+};
+
+// HasConstIterator<T>::value is true iff there exists a type T::const_iterator.
+template <typename T, typename = void>
+struct HasConstIterator : std::false_type {};
+template <typename T>
+struct HasConstIterator<T, absl::void_t<typename T::const_iterator>>
+    : std::true_type {};
+
+// IsInitializerList<T>::value is true iff T is an std::initializer_list. More
+// details below in Splitter<> where this is used.
+std::false_type IsInitializerListDispatch(...);  // default: No
+template <typename T>
+std::true_type IsInitializerListDispatch(std::initializer_list<T>*);
+template <typename T>
+struct IsInitializerList
+    : decltype(IsInitializerListDispatch(static_cast<T*>(nullptr))) {};
+
+// A SplitterIsConvertibleTo<C>::type alias exists iff the specified condition
+// is true for type 'C'.
+//
+// Restricts conversion to container-like types (by testing for the presence of
+// a const_iterator member type) and also to disable conversion to an
+// std::initializer_list (which also has a const_iterator). Otherwise, code
+// compiled in C++11 will get an error due to ambiguous conversion paths (in
+// C++11 std::vector<T>::operator= is overloaded to take either a std::vector<T>
+// or an std::initializer_list<T>).
+
+template <typename C, bool has_value_type, bool has_mapped_type>
+struct SplitterIsConvertibleToImpl : std::false_type {};
+
+template <typename C>
+struct SplitterIsConvertibleToImpl<C, true, false>
+    : std::is_constructible<typename C::value_type, absl::string_view> {};
+
+template <typename C>
+struct SplitterIsConvertibleToImpl<C, true, true>
+    : absl::conjunction<
+          std::is_constructible<typename C::key_type, absl::string_view>,
+          std::is_constructible<typename C::mapped_type, absl::string_view>> {};
+
+template <typename C>
+struct SplitterIsConvertibleTo
+    : SplitterIsConvertibleToImpl<
+          C,
+#ifdef _GLIBCXX_DEBUG
+          !IsStrictlyBaseOfAndConvertibleToSTLContainer<C>::value &&
+#endif  // _GLIBCXX_DEBUG
+              !IsInitializerList<
+                  typename std::remove_reference<C>::type>::value &&
+              HasValueType<C>::value && HasConstIterator<C>::value,
+          HasMappedType<C>::value> {
+};
+
+// This class implements the range that is returned by absl::StrSplit(). This
+// class has templated conversion operators that allow it to be implicitly
+// converted to a variety of types that the caller may have specified on the
+// left-hand side of an assignment.
+//
+// The main interface for interacting with this class is through its implicit
+// conversion operators. However, this class may also be used like a container
+// in that it has .begin() and .end() member functions. It may also be used
+// within a range-for loop.
+//
+// Output containers can be collections of any type that is constructible from
+// an absl::string_view.
+//
+// An Predicate functor may be supplied. This predicate will be used to filter
+// the split strings: only strings for which the predicate returns true will be
+// kept. A Predicate object is any unary functor that takes an absl::string_view
+// and returns bool.
+template <typename Delimiter, typename Predicate>
+class Splitter {
+ public:
+  using DelimiterType = Delimiter;
+  using PredicateType = Predicate;
+  using const_iterator = strings_internal::SplitIterator<Splitter>;
+  using value_type = typename std::iterator_traits<const_iterator>::value_type;
+
+  Splitter(ConvertibleToStringView input_text, Delimiter d, Predicate p)
+      : text_(std::move(input_text)),
+        delimiter_(std::move(d)),
+        predicate_(std::move(p)) {}
+
+  absl::string_view text() const { return text_.value(); }
+  const Delimiter& delimiter() const { return delimiter_; }
+  const Predicate& predicate() const { return predicate_; }
+
+  // Range functions that iterate the split substrings as absl::string_view
+  // objects. These methods enable a Splitter to be used in a range-based for
+  // loop.
+  const_iterator begin() const { return {const_iterator::kInitState, this}; }
+  const_iterator end() const { return {const_iterator::kEndState, this}; }
+
+  // An implicit conversion operator that is restricted to only those containers
+  // that the splitter is convertible to.
+  template <typename Container,
+            typename = typename std::enable_if<
+                SplitterIsConvertibleTo<Container>::value>::type>
+  operator Container() const {  // NOLINT(runtime/explicit)
+    return ConvertToContainer<Container, typename Container::value_type,
+                              HasMappedType<Container>::value>()(*this);
+  }
+
+  // Returns a pair with its .first and .second members set to the first two
+  // strings returned by the begin() iterator. Either/both of .first and .second
+  // will be constructed with empty strings if the iterator doesn't have a
+  // corresponding value.
+  template <typename First, typename Second>
+  operator std::pair<First, Second>() const {  // NOLINT(runtime/explicit)
+    absl::string_view first, second;
+    auto it = begin();
+    if (it != end()) {
+      first = *it;
+      if (++it != end()) {
+        second = *it;
+      }
+    }
+    return {First(first), Second(second)};
+  }
+
+ private:
+  // ConvertToContainer is a functor converting a Splitter to the requested
+  // Container of ValueType. It is specialized below to optimize splitting to
+  // certain combinations of Container and ValueType.
+  //
+  // This base template handles the generic case of storing the split results in
+  // the requested non-map-like container and converting the split substrings to
+  // the requested type.
+  template <typename Container, typename ValueType, bool is_map = false>
+  struct ConvertToContainer {
+    Container operator()(const Splitter& splitter) const {
+      Container c;
+      auto it = std::inserter(c, c.end());
+      for (const auto sp : splitter) {
+        *it++ = ValueType(sp);
+      }
+      return c;
+    }
+  };
+
+  // Partial specialization for a std::vector<absl::string_view>.
+  //
+  // Optimized for the common case of splitting to a
+  // std::vector<absl::string_view>. In this case we first split the results to
+  // a small array of absl::string_view on the stack, to reduce reallocations.
+  template <typename A>
+  struct ConvertToContainer<std::vector<absl::string_view, A>,
+                            absl::string_view, false> {
+    std::vector<absl::string_view, A> operator()(
+        const Splitter& splitter) const {
+      struct raw_view {
+        const char* data;
+        size_t size;
+        operator absl::string_view() const {  // NOLINT(runtime/explicit)
+          return {data, size};
+        }
+      };
+      std::vector<absl::string_view, A> v;
+      std::array<raw_view, 16> ar;
+      for (auto it = splitter.begin(); !it.at_end();) {
+        size_t index = 0;
+        do {
+          ar[index].data = it->data();
+          ar[index].size = it->size();
+          ++it;
+        } while (++index != ar.size() && !it.at_end());
+        v.insert(v.end(), ar.begin(), ar.begin() + index);
+      }
+      return v;
+    }
+  };
+
+  // Partial specialization for a std::vector<std::string>.
+  //
+  // Optimized for the common case of splitting to a std::vector<std::string>.
+  // In this case we first split the results to a std::vector<absl::string_view>
+  // so the returned std::vector<std::string> can have space reserved to avoid
+  // std::string moves.
+  template <typename A>
+  struct ConvertToContainer<std::vector<std::string, A>, std::string, false> {
+    std::vector<std::string, A> operator()(const Splitter& splitter) const {
+      const std::vector<absl::string_view> v = splitter;
+      return std::vector<std::string, A>(v.begin(), v.end());
+    }
+  };
+
+  // Partial specialization for containers of pairs (e.g., maps).
+  //
+  // The algorithm is to insert a new pair into the map for each even-numbered
+  // item, with the even-numbered item as the key with a default-constructed
+  // value. Each odd-numbered item will then be assigned to the last pair's
+  // value.
+  template <typename Container, typename First, typename Second>
+  struct ConvertToContainer<Container, std::pair<const First, Second>, true> {
+    Container operator()(const Splitter& splitter) const {
+      Container m;
+      typename Container::iterator it;
+      bool insert = true;
+      for (const auto sp : splitter) {
+        if (insert) {
+          it = Inserter<Container>::Insert(&m, First(sp), Second());
+        } else {
+          it->second = Second(sp);
+        }
+        insert = !insert;
+      }
+      return m;
+    }
+
+    // Inserts the key and value into the given map, returning an iterator to
+    // the inserted item. Specialized for std::map and std::multimap to use
+    // emplace() and adapt emplace()'s return value.
+    template <typename Map>
+    struct Inserter {
+      using M = Map;
+      template <typename... Args>
+      static typename M::iterator Insert(M* m, Args&&... args) {
+        return m->insert(std::make_pair(std::forward<Args>(args)...)).first;
+      }
+    };
+
+    template <typename... Ts>
+    struct Inserter<std::map<Ts...>> {
+      using M = std::map<Ts...>;
+      template <typename... Args>
+      static typename M::iterator Insert(M* m, Args&&... args) {
+        return m->emplace(std::make_pair(std::forward<Args>(args)...)).first;
+      }
+    };
+
+    template <typename... Ts>
+    struct Inserter<std::multimap<Ts...>> {
+      using M = std::multimap<Ts...>;
+      template <typename... Args>
+      static typename M::iterator Insert(M* m, Args&&... args) {
+        return m->emplace(std::make_pair(std::forward<Args>(args)...));
+      }
+    };
+  };
+
+  ConvertibleToStringView text_;
+  Delimiter delimiter_;
+  Predicate predicate_;
+};
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_STR_SPLIT_INTERNAL_H_
diff --git a/absl/strings/internal/utf8.cc b/absl/strings/internal/utf8.cc
new file mode 100644
index 0000000..82d36c2
--- /dev/null
+++ b/absl/strings/internal/utf8.cc
@@ -0,0 +1,51 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// UTF8 utilities, implemented to reduce dependencies.
+
+#include "absl/strings/internal/utf8.h"
+
+namespace absl {
+namespace strings_internal {
+
+size_t EncodeUTF8Char(char *buffer, char32_t utf8_char) {
+  if (utf8_char <= 0x7F) {
+    *buffer = static_cast<char>(utf8_char);
+    return 1;
+  } else if (utf8_char <= 0x7FF) {
+    buffer[1] = 0x80 | (utf8_char & 0x3F);
+    utf8_char >>= 6;
+    buffer[0] = 0xC0 | utf8_char;
+    return 2;
+  } else if (utf8_char <= 0xFFFF) {
+    buffer[2] = 0x80 | (utf8_char & 0x3F);
+    utf8_char >>= 6;
+    buffer[1] = 0x80 | (utf8_char & 0x3F);
+    utf8_char >>= 6;
+    buffer[0] = 0xE0 | utf8_char;
+    return 3;
+  } else {
+    buffer[3] = 0x80 | (utf8_char & 0x3F);
+    utf8_char >>= 6;
+    buffer[2] = 0x80 | (utf8_char & 0x3F);
+    utf8_char >>= 6;
+    buffer[1] = 0x80 | (utf8_char & 0x3F);
+    utf8_char >>= 6;
+    buffer[0] = 0xF0 | utf8_char;
+    return 4;
+  }
+}
+
+}  // namespace strings_internal
+}  // namespace absl
diff --git a/absl/strings/internal/utf8.h b/absl/strings/internal/utf8.h
new file mode 100644
index 0000000..0423630
--- /dev/null
+++ b/absl/strings/internal/utf8.h
@@ -0,0 +1,46 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// UTF8 utilities, implemented to reduce dependencies.
+
+#ifndef ABSL_STRINGS_INTERNAL_UTF8_H_
+#define ABSL_STRINGS_INTERNAL_UTF8_H_
+
+#include <cstddef>
+#include <cstdint>
+
+namespace absl {
+namespace strings_internal {
+
+// For Unicode code points 0 through 0x10FFFF, EncodeUTF8Char writes
+// out the UTF-8 encoding into buffer, and returns the number of chars
+// it wrote.
+//
+// As described in https://tools.ietf.org/html/rfc3629#section-3 , the encodings
+// are:
+//    00 -     7F : 0xxxxxxx
+//    80 -    7FF : 110xxxxx 10xxxxxx
+//   800 -   FFFF : 1110xxxx 10xxxxxx 10xxxxxx
+// 10000 - 10FFFF : 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
+//
+// Values greater than 0x10FFFF are not supported and may or may not write
+// characters into buffer, however never will more than kMaxEncodedUTF8Size
+// bytes be written, regardless of the value of utf8_char.
+enum { kMaxEncodedUTF8Size = 4 };
+size_t EncodeUTF8Char(char *buffer, char32_t utf8_char);
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_UTF8_H_
diff --git a/absl/strings/internal/utf8_test.cc b/absl/strings/internal/utf8_test.cc
new file mode 100644
index 0000000..88dd503
--- /dev/null
+++ b/absl/strings/internal/utf8_test.cc
@@ -0,0 +1,66 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/utf8.h"
+
+#include <cstdint>
+#include <utility>
+
+#include "gtest/gtest.h"
+#include "absl/base/port.h"
+
+namespace {
+
+#if !defined(__cpp_char8_t)
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++2a-compat"
+#endif
+TEST(EncodeUTF8Char, BasicFunction) {
+  std::pair<char32_t, std::string> tests[] = {{0x0030, u8"\u0030"},
+                                              {0x00A3, u8"\u00A3"},
+                                              {0x00010000, u8"\U00010000"},
+                                              {0x0000FFFF, u8"\U0000FFFF"},
+                                              {0x0010FFFD, u8"\U0010FFFD"}};
+  for (auto &test : tests) {
+    char buf0[7] = {'\x00', '\x00', '\x00', '\x00', '\x00', '\x00', '\x00'};
+    char buf1[7] = {'\xFF', '\xFF', '\xFF', '\xFF', '\xFF', '\xFF', '\xFF'};
+    char *buf0_written =
+        &buf0[absl::strings_internal::EncodeUTF8Char(buf0, test.first)];
+    char *buf1_written =
+        &buf1[absl::strings_internal::EncodeUTF8Char(buf1, test.first)];
+    int apparent_length = 7;
+    while (buf0[apparent_length - 1] == '\x00' &&
+           buf1[apparent_length - 1] == '\xFF') {
+      if (--apparent_length == 0) break;
+    }
+    EXPECT_EQ(apparent_length, buf0_written - buf0);
+    EXPECT_EQ(apparent_length, buf1_written - buf1);
+    EXPECT_EQ(apparent_length, test.second.length());
+    EXPECT_EQ(std::string(buf0, apparent_length), test.second);
+    EXPECT_EQ(std::string(buf1, apparent_length), test.second);
+  }
+  char buf[32] = "Don't Tread On Me";
+  EXPECT_LE(absl::strings_internal::EncodeUTF8Char(buf, 0x00110000),
+            absl::strings_internal::kMaxEncodedUTF8Size);
+  char buf2[32] = "Negative is invalid but sane";
+  EXPECT_LE(absl::strings_internal::EncodeUTF8Char(buf2, -1),
+            absl::strings_internal::kMaxEncodedUTF8Size);
+}
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#endif
+#endif  // !defined(__cpp_char8_t)
+
+}  // namespace
diff --git a/absl/strings/match.cc b/absl/strings/match.cc
new file mode 100644
index 0000000..7b24241
--- /dev/null
+++ b/absl/strings/match.cc
@@ -0,0 +1,38 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/match.h"
+
+#include "absl/strings/internal/memutil.h"
+
+namespace absl {
+
+bool EqualsIgnoreCase(absl::string_view piece1, absl::string_view piece2) {
+  return (piece1.size() == piece2.size() &&
+          0 == absl::strings_internal::memcasecmp(piece1.data(), piece2.data(),
+                                                  piece1.size()));
+  // memcasecmp uses absl::ascii_tolower().
+}
+
+bool StartsWithIgnoreCase(absl::string_view text, absl::string_view prefix) {
+  return (text.size() >= prefix.size()) &&
+         EqualsIgnoreCase(text.substr(0, prefix.size()), prefix);
+}
+
+bool EndsWithIgnoreCase(absl::string_view text, absl::string_view suffix) {
+  return (text.size() >= suffix.size()) &&
+         EqualsIgnoreCase(text.substr(text.size() - suffix.size()), suffix);
+}
+
+}  // namespace absl
diff --git a/absl/strings/match.h b/absl/strings/match.h
new file mode 100644
index 0000000..762f359
--- /dev/null
+++ b/absl/strings/match.h
@@ -0,0 +1,88 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: match.h
+// -----------------------------------------------------------------------------
+//
+// This file contains simple utilities for performing string matching checks.
+// All of these function parameters are specified as `absl::string_view`,
+// meaning that these functions can accept `std::string`, `absl::string_view` or
+// nul-terminated C-style strings.
+//
+// Examples:
+//   std::string s = "foo";
+//   absl::string_view sv = "f";
+//   assert(absl::StrContains(s, sv));
+//
+// Note: The order of parameters in these functions is designed to mimic the
+// order an equivalent member function would exhibit;
+// e.g. `s.Contains(x)` ==> `absl::StrContains(s, x).
+#ifndef ABSL_STRINGS_MATCH_H_
+#define ABSL_STRINGS_MATCH_H_
+
+#include <cstring>
+
+#include "absl/strings/string_view.h"
+
+namespace absl {
+
+// StrContains()
+//
+// Returns whether a given string `haystack` contains the substring `needle`.
+inline bool StrContains(absl::string_view haystack, absl::string_view needle) {
+  return haystack.find(needle, 0) != haystack.npos;
+}
+
+// StartsWith()
+//
+// Returns whether a given string `text` begins with `prefix`.
+inline bool StartsWith(absl::string_view text, absl::string_view prefix) {
+  return prefix.empty() ||
+         (text.size() >= prefix.size() &&
+          memcmp(text.data(), prefix.data(), prefix.size()) == 0);
+}
+
+// EndsWith()
+//
+// Returns whether a given string `text` ends with `suffix`.
+inline bool EndsWith(absl::string_view text, absl::string_view suffix) {
+  return suffix.empty() ||
+         (text.size() >= suffix.size() &&
+          memcmp(text.data() + (text.size() - suffix.size()), suffix.data(),
+                 suffix.size()) == 0);
+}
+
+// EqualsIgnoreCase()
+//
+// Returns whether given ASCII strings `piece1` and `piece2` are equal, ignoring
+// case in the comparison.
+bool EqualsIgnoreCase(absl::string_view piece1, absl::string_view piece2);
+
+// StartsWithIgnoreCase()
+//
+// Returns whether a given ASCII string `text` starts with `prefix`,
+// ignoring case in the comparison.
+bool StartsWithIgnoreCase(absl::string_view text, absl::string_view prefix);
+
+// EndsWithIgnoreCase()
+//
+// Returns whether a given ASCII string `text` ends with `suffix`, ignoring
+// case in the comparison.
+bool EndsWithIgnoreCase(absl::string_view text, absl::string_view suffix);
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_MATCH_H_
diff --git a/absl/strings/match_test.cc b/absl/strings/match_test.cc
new file mode 100644
index 0000000..4c313dd
--- /dev/null
+++ b/absl/strings/match_test.cc
@@ -0,0 +1,110 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/match.h"
+
+#include "gtest/gtest.h"
+
+namespace {
+
+TEST(MatchTest, StartsWith) {
+  const std::string s1("123\0abc", 7);
+  const absl::string_view a("foobar");
+  const absl::string_view b(s1);
+  const absl::string_view e;
+  EXPECT_TRUE(absl::StartsWith(a, a));
+  EXPECT_TRUE(absl::StartsWith(a, "foo"));
+  EXPECT_TRUE(absl::StartsWith(a, e));
+  EXPECT_TRUE(absl::StartsWith(b, s1));
+  EXPECT_TRUE(absl::StartsWith(b, b));
+  EXPECT_TRUE(absl::StartsWith(b, e));
+  EXPECT_TRUE(absl::StartsWith(e, ""));
+  EXPECT_FALSE(absl::StartsWith(a, b));
+  EXPECT_FALSE(absl::StartsWith(b, a));
+  EXPECT_FALSE(absl::StartsWith(e, a));
+}
+
+TEST(MatchTest, EndsWith) {
+  const std::string s1("123\0abc", 7);
+  const absl::string_view a("foobar");
+  const absl::string_view b(s1);
+  const absl::string_view e;
+  EXPECT_TRUE(absl::EndsWith(a, a));
+  EXPECT_TRUE(absl::EndsWith(a, "bar"));
+  EXPECT_TRUE(absl::EndsWith(a, e));
+  EXPECT_TRUE(absl::EndsWith(b, s1));
+  EXPECT_TRUE(absl::EndsWith(b, b));
+  EXPECT_TRUE(absl::EndsWith(b, e));
+  EXPECT_TRUE(absl::EndsWith(e, ""));
+  EXPECT_FALSE(absl::EndsWith(a, b));
+  EXPECT_FALSE(absl::EndsWith(b, a));
+  EXPECT_FALSE(absl::EndsWith(e, a));
+}
+
+TEST(MatchTest, Contains) {
+  absl::string_view a("abcdefg");
+  absl::string_view b("abcd");
+  absl::string_view c("efg");
+  absl::string_view d("gh");
+  EXPECT_TRUE(absl::StrContains(a, a));
+  EXPECT_TRUE(absl::StrContains(a, b));
+  EXPECT_TRUE(absl::StrContains(a, c));
+  EXPECT_FALSE(absl::StrContains(a, d));
+  EXPECT_TRUE(absl::StrContains("", ""));
+  EXPECT_TRUE(absl::StrContains("abc", ""));
+  EXPECT_FALSE(absl::StrContains("", "a"));
+}
+
+TEST(MatchTest, ContainsNull) {
+  const std::string s = "foo";
+  const char* cs = "foo";
+  const absl::string_view sv("foo");
+  const absl::string_view sv2("foo\0bar", 4);
+  EXPECT_EQ(s, "foo");
+  EXPECT_EQ(sv, "foo");
+  EXPECT_NE(sv2, "foo");
+  EXPECT_TRUE(absl::EndsWith(s, sv));
+  EXPECT_TRUE(absl::StartsWith(cs, sv));
+  EXPECT_TRUE(absl::StrContains(cs, sv));
+  EXPECT_FALSE(absl::StrContains(cs, sv2));
+}
+
+TEST(MatchTest, EqualsIgnoreCase) {
+  std::string text = "the";
+  absl::string_view data(text);
+
+  EXPECT_TRUE(absl::EqualsIgnoreCase(data, "The"));
+  EXPECT_TRUE(absl::EqualsIgnoreCase(data, "THE"));
+  EXPECT_TRUE(absl::EqualsIgnoreCase(data, "the"));
+  EXPECT_FALSE(absl::EqualsIgnoreCase(data, "Quick"));
+  EXPECT_FALSE(absl::EqualsIgnoreCase(data, "then"));
+}
+
+TEST(MatchTest, StartsWithIgnoreCase) {
+  EXPECT_TRUE(absl::StartsWithIgnoreCase("foo", "foo"));
+  EXPECT_TRUE(absl::StartsWithIgnoreCase("foo", "Fo"));
+  EXPECT_TRUE(absl::StartsWithIgnoreCase("foo", ""));
+  EXPECT_FALSE(absl::StartsWithIgnoreCase("foo", "fooo"));
+  EXPECT_FALSE(absl::StartsWithIgnoreCase("", "fo"));
+}
+
+TEST(MatchTest, EndsWithIgnoreCase) {
+  EXPECT_TRUE(absl::EndsWithIgnoreCase("foo", "foo"));
+  EXPECT_TRUE(absl::EndsWithIgnoreCase("foo", "Oo"));
+  EXPECT_TRUE(absl::EndsWithIgnoreCase("foo", ""));
+  EXPECT_FALSE(absl::EndsWithIgnoreCase("foo", "fooo"));
+  EXPECT_FALSE(absl::EndsWithIgnoreCase("", "fo"));
+}
+
+}  // namespace
diff --git a/absl/strings/numbers.cc b/absl/strings/numbers.cc
new file mode 100644
index 0000000..38d1486
--- /dev/null
+++ b/absl/strings/numbers.cc
@@ -0,0 +1,905 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file contains string processing functions related to
+// numeric values.
+
+#include "absl/strings/numbers.h"
+
+#include <algorithm>
+#include <cassert>
+#include <cfloat>          // for DBL_DIG and FLT_DIG
+#include <cmath>           // for HUGE_VAL
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <iterator>
+#include <limits>
+#include <memory>
+#include <utility>
+
+#include "absl/base/internal/bits.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/strings/ascii.h"
+#include "absl/strings/charconv.h"
+#include "absl/strings/internal/memutil.h"
+#include "absl/strings/match.h"
+#include "absl/strings/str_cat.h"
+
+namespace absl {
+
+bool SimpleAtof(absl::string_view str, float* out) {
+  *out = 0.0;
+  str = StripAsciiWhitespace(str);
+  if (!str.empty() && str[0] == '+') {
+    str.remove_prefix(1);
+  }
+  auto result = absl::from_chars(str.data(), str.data() + str.size(), *out);
+  if (result.ec == std::errc::invalid_argument) {
+    return false;
+  }
+  if (result.ptr != str.data() + str.size()) {
+    // not all non-whitespace characters consumed
+    return false;
+  }
+  // from_chars() with DR 3081's current wording will return max() on
+  // overflow.  SimpleAtof returns infinity instead.
+  if (result.ec == std::errc::result_out_of_range) {
+    if (*out > 1.0) {
+      *out = std::numeric_limits<float>::infinity();
+    } else if (*out < -1.0) {
+      *out = -std::numeric_limits<float>::infinity();
+    }
+  }
+  return true;
+}
+
+bool SimpleAtod(absl::string_view str, double* out) {
+  *out = 0.0;
+  str = StripAsciiWhitespace(str);
+  if (!str.empty() && str[0] == '+') {
+    str.remove_prefix(1);
+  }
+  auto result = absl::from_chars(str.data(), str.data() + str.size(), *out);
+  if (result.ec == std::errc::invalid_argument) {
+    return false;
+  }
+  if (result.ptr != str.data() + str.size()) {
+    // not all non-whitespace characters consumed
+    return false;
+  }
+  // from_chars() with DR 3081's current wording will return max() on
+  // overflow.  SimpleAtod returns infinity instead.
+  if (result.ec == std::errc::result_out_of_range) {
+    if (*out > 1.0) {
+      *out = std::numeric_limits<double>::infinity();
+    } else if (*out < -1.0) {
+      *out = -std::numeric_limits<double>::infinity();
+    }
+  }
+  return true;
+}
+
+namespace {
+
+// Writes a two-character representation of 'i' to 'buf'. 'i' must be in the
+// range 0 <= i < 100, and buf must have space for two characters. Example:
+//   char buf[2];
+//   PutTwoDigits(42, buf);
+//   // buf[0] == '4'
+//   // buf[1] == '2'
+inline void PutTwoDigits(size_t i, char* buf) {
+  static const char two_ASCII_digits[100][2] = {
+    {'0', '0'}, {'0', '1'}, {'0', '2'}, {'0', '3'}, {'0', '4'},
+    {'0', '5'}, {'0', '6'}, {'0', '7'}, {'0', '8'}, {'0', '9'},
+    {'1', '0'}, {'1', '1'}, {'1', '2'}, {'1', '3'}, {'1', '4'},
+    {'1', '5'}, {'1', '6'}, {'1', '7'}, {'1', '8'}, {'1', '9'},
+    {'2', '0'}, {'2', '1'}, {'2', '2'}, {'2', '3'}, {'2', '4'},
+    {'2', '5'}, {'2', '6'}, {'2', '7'}, {'2', '8'}, {'2', '9'},
+    {'3', '0'}, {'3', '1'}, {'3', '2'}, {'3', '3'}, {'3', '4'},
+    {'3', '5'}, {'3', '6'}, {'3', '7'}, {'3', '8'}, {'3', '9'},
+    {'4', '0'}, {'4', '1'}, {'4', '2'}, {'4', '3'}, {'4', '4'},
+    {'4', '5'}, {'4', '6'}, {'4', '7'}, {'4', '8'}, {'4', '9'},
+    {'5', '0'}, {'5', '1'}, {'5', '2'}, {'5', '3'}, {'5', '4'},
+    {'5', '5'}, {'5', '6'}, {'5', '7'}, {'5', '8'}, {'5', '9'},
+    {'6', '0'}, {'6', '1'}, {'6', '2'}, {'6', '3'}, {'6', '4'},
+    {'6', '5'}, {'6', '6'}, {'6', '7'}, {'6', '8'}, {'6', '9'},
+    {'7', '0'}, {'7', '1'}, {'7', '2'}, {'7', '3'}, {'7', '4'},
+    {'7', '5'}, {'7', '6'}, {'7', '7'}, {'7', '8'}, {'7', '9'},
+    {'8', '0'}, {'8', '1'}, {'8', '2'}, {'8', '3'}, {'8', '4'},
+    {'8', '5'}, {'8', '6'}, {'8', '7'}, {'8', '8'}, {'8', '9'},
+    {'9', '0'}, {'9', '1'}, {'9', '2'}, {'9', '3'}, {'9', '4'},
+    {'9', '5'}, {'9', '6'}, {'9', '7'}, {'9', '8'}, {'9', '9'}
+  };
+  assert(i < 100);
+  memcpy(buf, two_ASCII_digits[i], 2);
+}
+
+}  // namespace
+
+bool SimpleAtob(absl::string_view str, bool* out) {
+  ABSL_RAW_CHECK(out != nullptr, "Output pointer must not be nullptr.");
+  if (EqualsIgnoreCase(str, "true") || EqualsIgnoreCase(str, "t") ||
+      EqualsIgnoreCase(str, "yes") || EqualsIgnoreCase(str, "y") ||
+      EqualsIgnoreCase(str, "1")) {
+    *out = true;
+    return true;
+  }
+  if (EqualsIgnoreCase(str, "false") || EqualsIgnoreCase(str, "f") ||
+      EqualsIgnoreCase(str, "no") || EqualsIgnoreCase(str, "n") ||
+      EqualsIgnoreCase(str, "0")) {
+    *out = false;
+    return true;
+  }
+  return false;
+}
+
+// ----------------------------------------------------------------------
+// FastIntToBuffer() overloads
+//
+// Like the Fast*ToBuffer() functions above, these are intended for speed.
+// Unlike the Fast*ToBuffer() functions, however, these functions write
+// their output to the beginning of the buffer.  The caller is responsible
+// for ensuring that the buffer has enough space to hold the output.
+//
+// Returns a pointer to the end of the string (i.e. the null character
+// terminating the string).
+// ----------------------------------------------------------------------
+
+namespace {
+
+// Used to optimize printing a decimal number's final digit.
+const char one_ASCII_final_digits[10][2] {
+  {'0', 0}, {'1', 0}, {'2', 0}, {'3', 0}, {'4', 0},
+  {'5', 0}, {'6', 0}, {'7', 0}, {'8', 0}, {'9', 0},
+};
+
+}  // namespace
+
+char* numbers_internal::FastIntToBuffer(uint32_t i, char* buffer) {
+  uint32_t digits;
+  // The idea of this implementation is to trim the number of divides to as few
+  // as possible, and also reducing memory stores and branches, by going in
+  // steps of two digits at a time rather than one whenever possible.
+  // The huge-number case is first, in the hopes that the compiler will output
+  // that case in one branch-free block of code, and only output conditional
+  // branches into it from below.
+  if (i >= 1000000000) {     // >= 1,000,000,000
+    digits = i / 100000000;  //      100,000,000
+    i -= digits * 100000000;
+    PutTwoDigits(digits, buffer);
+    buffer += 2;
+  lt100_000_000:
+    digits = i / 1000000;  // 1,000,000
+    i -= digits * 1000000;
+    PutTwoDigits(digits, buffer);
+    buffer += 2;
+  lt1_000_000:
+    digits = i / 10000;  // 10,000
+    i -= digits * 10000;
+    PutTwoDigits(digits, buffer);
+    buffer += 2;
+  lt10_000:
+    digits = i / 100;
+    i -= digits * 100;
+    PutTwoDigits(digits, buffer);
+    buffer += 2;
+ lt100:
+    digits = i;
+    PutTwoDigits(digits, buffer);
+    buffer += 2;
+    *buffer = 0;
+    return buffer;
+  }
+
+  if (i < 100) {
+    digits = i;
+    if (i >= 10) goto lt100;
+    memcpy(buffer, one_ASCII_final_digits[i], 2);
+    return buffer + 1;
+  }
+  if (i < 10000) {  //    10,000
+    if (i >= 1000) goto lt10_000;
+    digits = i / 100;
+    i -= digits * 100;
+    *buffer++ = '0' + digits;
+    goto lt100;
+  }
+  if (i < 1000000) {  //    1,000,000
+    if (i >= 100000) goto lt1_000_000;
+    digits = i / 10000;  //    10,000
+    i -= digits * 10000;
+    *buffer++ = '0' + digits;
+    goto lt10_000;
+  }
+  if (i < 100000000) {  //    100,000,000
+    if (i >= 10000000) goto lt100_000_000;
+    digits = i / 1000000;  //   1,000,000
+    i -= digits * 1000000;
+    *buffer++ = '0' + digits;
+    goto lt1_000_000;
+  }
+  // we already know that i < 1,000,000,000
+  digits = i / 100000000;  //   100,000,000
+  i -= digits * 100000000;
+  *buffer++ = '0' + digits;
+  goto lt100_000_000;
+}
+
+char* numbers_internal::FastIntToBuffer(int32_t i, char* buffer) {
+  uint32_t u = i;
+  if (i < 0) {
+    *buffer++ = '-';
+    // We need to do the negation in modular (i.e., "unsigned")
+    // arithmetic; MSVC++ apprently warns for plain "-u", so
+    // we write the equivalent expression "0 - u" instead.
+    u = 0 - u;
+  }
+  return numbers_internal::FastIntToBuffer(u, buffer);
+}
+
+char* numbers_internal::FastIntToBuffer(uint64_t i, char* buffer) {
+  uint32_t u32 = static_cast<uint32_t>(i);
+  if (u32 == i) return numbers_internal::FastIntToBuffer(u32, buffer);
+
+  // Here we know i has at least 10 decimal digits.
+  uint64_t top_1to11 = i / 1000000000;
+  u32 = static_cast<uint32_t>(i - top_1to11 * 1000000000);
+  uint32_t top_1to11_32 = static_cast<uint32_t>(top_1to11);
+
+  if (top_1to11_32 == top_1to11) {
+    buffer = numbers_internal::FastIntToBuffer(top_1to11_32, buffer);
+  } else {
+    // top_1to11 has more than 32 bits too; print it in two steps.
+    uint32_t top_8to9 = static_cast<uint32_t>(top_1to11 / 100);
+    uint32_t mid_2 = static_cast<uint32_t>(top_1to11 - top_8to9 * 100);
+    buffer = numbers_internal::FastIntToBuffer(top_8to9, buffer);
+    PutTwoDigits(mid_2, buffer);
+    buffer += 2;
+  }
+
+  // We have only 9 digits now, again the maximum uint32_t can handle fully.
+  uint32_t digits = u32 / 10000000;  // 10,000,000
+  u32 -= digits * 10000000;
+  PutTwoDigits(digits, buffer);
+  buffer += 2;
+  digits = u32 / 100000;  // 100,000
+  u32 -= digits * 100000;
+  PutTwoDigits(digits, buffer);
+  buffer += 2;
+  digits = u32 / 1000;  // 1,000
+  u32 -= digits * 1000;
+  PutTwoDigits(digits, buffer);
+  buffer += 2;
+  digits = u32 / 10;
+  u32 -= digits * 10;
+  PutTwoDigits(digits, buffer);
+  buffer += 2;
+  memcpy(buffer, one_ASCII_final_digits[u32], 2);
+  return buffer + 1;
+}
+
+char* numbers_internal::FastIntToBuffer(int64_t i, char* buffer) {
+  uint64_t u = i;
+  if (i < 0) {
+    *buffer++ = '-';
+    u = 0 - u;
+  }
+  return numbers_internal::FastIntToBuffer(u, buffer);
+}
+
+// Given a 128-bit number expressed as a pair of uint64_t, high half first,
+// return that number multiplied by the given 32-bit value.  If the result is
+// too large to fit in a 128-bit number, divide it by 2 until it fits.
+static std::pair<uint64_t, uint64_t> Mul32(std::pair<uint64_t, uint64_t> num,
+                                           uint32_t mul) {
+  uint64_t bits0_31 = num.second & 0xFFFFFFFF;
+  uint64_t bits32_63 = num.second >> 32;
+  uint64_t bits64_95 = num.first & 0xFFFFFFFF;
+  uint64_t bits96_127 = num.first >> 32;
+
+  // The picture so far: each of these 64-bit values has only the lower 32 bits
+  // filled in.
+  // bits96_127:          [ 00000000 xxxxxxxx ]
+  // bits64_95:                    [ 00000000 xxxxxxxx ]
+  // bits32_63:                             [ 00000000 xxxxxxxx ]
+  // bits0_31:                                       [ 00000000 xxxxxxxx ]
+
+  bits0_31 *= mul;
+  bits32_63 *= mul;
+  bits64_95 *= mul;
+  bits96_127 *= mul;
+
+  // Now the top halves may also have value, though all 64 of their bits will
+  // never be set at the same time, since they are a result of a 32x32 bit
+  // multiply.  This makes the carry calculation slightly easier.
+  // bits96_127:          [ mmmmmmmm | mmmmmmmm ]
+  // bits64_95:                    [ | mmmmmmmm mmmmmmmm | ]
+  // bits32_63:                      |        [ mmmmmmmm | mmmmmmmm ]
+  // bits0_31:                       |                 [ | mmmmmmmm mmmmmmmm ]
+  // eventually:        [ bits128_up | ...bits64_127.... | ..bits0_63... ]
+
+  uint64_t bits0_63 = bits0_31 + (bits32_63 << 32);
+  uint64_t bits64_127 = bits64_95 + (bits96_127 << 32) + (bits32_63 >> 32) +
+                        (bits0_63 < bits0_31);
+  uint64_t bits128_up = (bits96_127 >> 32) + (bits64_127 < bits64_95);
+  if (bits128_up == 0) return {bits64_127, bits0_63};
+
+  int shift = 64 - base_internal::CountLeadingZeros64(bits128_up);
+  uint64_t lo = (bits0_63 >> shift) + (bits64_127 << (64 - shift));
+  uint64_t hi = (bits64_127 >> shift) + (bits128_up << (64 - shift));
+  return {hi, lo};
+}
+
+// Compute num * 5 ^ expfive, and return the first 128 bits of the result,
+// where the first bit is always a one.  So PowFive(1, 0) starts 0b100000,
+// PowFive(1, 1) starts 0b101000, PowFive(1, 2) starts 0b110010, etc.
+static std::pair<uint64_t, uint64_t> PowFive(uint64_t num, int expfive) {
+  std::pair<uint64_t, uint64_t> result = {num, 0};
+  while (expfive >= 13) {
+    // 5^13 is the highest power of five that will fit in a 32-bit integer.
+    result = Mul32(result, 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5);
+    expfive -= 13;
+  }
+  constexpr int powers_of_five[13] = {
+      1,
+      5,
+      5 * 5,
+      5 * 5 * 5,
+      5 * 5 * 5 * 5,
+      5 * 5 * 5 * 5 * 5,
+      5 * 5 * 5 * 5 * 5 * 5,
+      5 * 5 * 5 * 5 * 5 * 5 * 5,
+      5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
+      5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
+      5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
+      5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
+      5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5};
+  result = Mul32(result, powers_of_five[expfive & 15]);
+  int shift = base_internal::CountLeadingZeros64(result.first);
+  if (shift != 0) {
+    result.first = (result.first << shift) + (result.second >> (64 - shift));
+    result.second = (result.second << shift);
+  }
+  return result;
+}
+
+struct ExpDigits {
+  int32_t exponent;
+  char digits[6];
+};
+
+// SplitToSix converts value, a positive double-precision floating-point number,
+// into a base-10 exponent and 6 ASCII digits, where the first digit is never
+// zero.  For example, SplitToSix(1) returns an exponent of zero and a digits
+// array of {'1', '0', '0', '0', '0', '0'}.  If value is exactly halfway between
+// two possible representations, e.g. value = 100000.5, then "round to even" is
+// performed.
+static ExpDigits SplitToSix(const double value) {
+  ExpDigits exp_dig;
+  int exp = 5;
+  double d = value;
+  // First step: calculate a close approximation of the output, where the
+  // value d will be between 100,000 and 999,999, representing the digits
+  // in the output ASCII array, and exp is the base-10 exponent.  It would be
+  // faster to use a table here, and to look up the base-2 exponent of value,
+  // however value is an IEEE-754 64-bit number, so the table would have 2,000
+  // entries, which is not cache-friendly.
+  if (d >= 999999.5) {
+    if (d >= 1e+261) exp += 256, d *= 1e-256;
+    if (d >= 1e+133) exp += 128, d *= 1e-128;
+    if (d >= 1e+69) exp += 64, d *= 1e-64;
+    if (d >= 1e+37) exp += 32, d *= 1e-32;
+    if (d >= 1e+21) exp += 16, d *= 1e-16;
+    if (d >= 1e+13) exp += 8, d *= 1e-8;
+    if (d >= 1e+9) exp += 4, d *= 1e-4;
+    if (d >= 1e+7) exp += 2, d *= 1e-2;
+    if (d >= 1e+6) exp += 1, d *= 1e-1;
+  } else {
+    if (d < 1e-250) exp -= 256, d *= 1e256;
+    if (d < 1e-122) exp -= 128, d *= 1e128;
+    if (d < 1e-58) exp -= 64, d *= 1e64;
+    if (d < 1e-26) exp -= 32, d *= 1e32;
+    if (d < 1e-10) exp -= 16, d *= 1e16;
+    if (d < 1e-2) exp -= 8, d *= 1e8;
+    if (d < 1e+2) exp -= 4, d *= 1e4;
+    if (d < 1e+4) exp -= 2, d *= 1e2;
+    if (d < 1e+5) exp -= 1, d *= 1e1;
+  }
+  // At this point, d is in the range [99999.5..999999.5) and exp is in the
+  // range [-324..308]. Since we need to round d up, we want to add a half
+  // and truncate.
+  // However, the technique above may have lost some precision, due to its
+  // repeated multiplication by constants that each may be off by half a bit
+  // of precision.  This only matters if we're close to the edge though.
+  // Since we'd like to know if the fractional part of d is close to a half,
+  // we multiply it by 65536 and see if the fractional part is close to 32768.
+  // (The number doesn't have to be a power of two,but powers of two are faster)
+  uint64_t d64k = d * 65536;
+  int dddddd;  // A 6-digit decimal integer.
+  if ((d64k % 65536) == 32767 || (d64k % 65536) == 32768) {
+    // OK, it's fairly likely that precision was lost above, which is
+    // not a surprise given only 52 mantissa bits are available.  Therefore
+    // redo the calculation using 128-bit numbers.  (64 bits are not enough).
+
+    // Start out with digits rounded down; maybe add one below.
+    dddddd = static_cast<int>(d64k / 65536);
+
+    // mantissa is a 64-bit integer representing M.mmm... * 2^63.  The actual
+    // value we're representing, of course, is M.mmm... * 2^exp2.
+    int exp2;
+    double m = std::frexp(value, &exp2);
+    uint64_t mantissa = m * (32768.0 * 65536.0 * 65536.0 * 65536.0);
+    // std::frexp returns an m value in the range [0.5, 1.0), however we
+    // can't multiply it by 2^64 and convert to an integer because some FPUs
+    // throw an exception when converting an number higher than 2^63 into an
+    // integer - even an unsigned 64-bit integer!  Fortunately it doesn't matter
+    // since m only has 52 significant bits anyway.
+    mantissa <<= 1;
+    exp2 -= 64;  // not needed, but nice for debugging
+
+    // OK, we are here to compare:
+    //     (dddddd + 0.5) * 10^(exp-5)  vs.  mantissa * 2^exp2
+    // so we can round up dddddd if appropriate.  Those values span the full
+    // range of 600 orders of magnitude of IEE 64-bit floating-point.
+    // Fortunately, we already know they are very close, so we don't need to
+    // track the base-2 exponent of both sides.  This greatly simplifies the
+    // the math since the 2^exp2 calculation is unnecessary and the power-of-10
+    // calculation can become a power-of-5 instead.
+
+    std::pair<uint64_t, uint64_t> edge, val;
+    if (exp >= 6) {
+      // Compare (dddddd + 0.5) * 5 ^ (exp - 5) to mantissa
+      // Since we're tossing powers of two, 2 * dddddd + 1 is the
+      // same as dddddd + 0.5
+      edge = PowFive(2 * dddddd + 1, exp - 5);
+
+      val.first = mantissa;
+      val.second = 0;
+    } else {
+      // We can't compare (dddddd + 0.5) * 5 ^ (exp - 5) to mantissa as we did
+      // above because (exp - 5) is negative.  So we compare (dddddd + 0.5) to
+      // mantissa * 5 ^ (5 - exp)
+      edge = PowFive(2 * dddddd + 1, 0);
+
+      val = PowFive(mantissa, 5 - exp);
+    }
+    // printf("exp=%d %016lx %016lx vs %016lx %016lx\n", exp, val.first,
+    //        val.second, edge.first, edge.second);
+    if (val > edge) {
+      dddddd++;
+    } else if (val == edge) {
+      dddddd += (dddddd & 1);
+    }
+  } else {
+    // Here, we are not close to the edge.
+    dddddd = static_cast<int>((d64k + 32768) / 65536);
+  }
+  if (dddddd == 1000000) {
+    dddddd = 100000;
+    exp += 1;
+  }
+  exp_dig.exponent = exp;
+
+  int two_digits = dddddd / 10000;
+  dddddd -= two_digits * 10000;
+  PutTwoDigits(two_digits, &exp_dig.digits[0]);
+
+  two_digits = dddddd / 100;
+  dddddd -= two_digits * 100;
+  PutTwoDigits(two_digits, &exp_dig.digits[2]);
+
+  PutTwoDigits(dddddd, &exp_dig.digits[4]);
+  return exp_dig;
+}
+
+// Helper function for fast formatting of floating-point.
+// The result is the same as "%g", a.k.a. "%.6g".
+size_t numbers_internal::SixDigitsToBuffer(double d, char* const buffer) {
+  static_assert(std::numeric_limits<float>::is_iec559,
+                "IEEE-754/IEC-559 support only");
+
+  char* out = buffer;  // we write data to out, incrementing as we go, but
+                       // FloatToBuffer always returns the address of the buffer
+                       // passed in.
+
+  if (std::isnan(d)) {
+    strcpy(out, "nan");  // NOLINT(runtime/printf)
+    return 3;
+  }
+  if (d == 0) {  // +0 and -0 are handled here
+    if (std::signbit(d)) *out++ = '-';
+    *out++ = '0';
+    *out = 0;
+    return out - buffer;
+  }
+  if (d < 0) {
+    *out++ = '-';
+    d = -d;
+  }
+  if (std::isinf(d)) {
+    strcpy(out, "inf");  // NOLINT(runtime/printf)
+    return out + 3 - buffer;
+  }
+
+  auto exp_dig = SplitToSix(d);
+  int exp = exp_dig.exponent;
+  const char* digits = exp_dig.digits;
+  out[0] = '0';
+  out[1] = '.';
+  switch (exp) {
+    case 5:
+      memcpy(out, &digits[0], 6), out += 6;
+      *out = 0;
+      return out - buffer;
+    case 4:
+      memcpy(out, &digits[0], 5), out += 5;
+      if (digits[5] != '0') {
+        *out++ = '.';
+        *out++ = digits[5];
+      }
+      *out = 0;
+      return out - buffer;
+    case 3:
+      memcpy(out, &digits[0], 4), out += 4;
+      if ((digits[5] | digits[4]) != '0') {
+        *out++ = '.';
+        *out++ = digits[4];
+        if (digits[5] != '0') *out++ = digits[5];
+      }
+      *out = 0;
+      return out - buffer;
+    case 2:
+      memcpy(out, &digits[0], 3), out += 3;
+      *out++ = '.';
+      memcpy(out, &digits[3], 3);
+      out += 3;
+      while (out[-1] == '0') --out;
+      if (out[-1] == '.') --out;
+      *out = 0;
+      return out - buffer;
+    case 1:
+      memcpy(out, &digits[0], 2), out += 2;
+      *out++ = '.';
+      memcpy(out, &digits[2], 4);
+      out += 4;
+      while (out[-1] == '0') --out;
+      if (out[-1] == '.') --out;
+      *out = 0;
+      return out - buffer;
+    case 0:
+      memcpy(out, &digits[0], 1), out += 1;
+      *out++ = '.';
+      memcpy(out, &digits[1], 5);
+      out += 5;
+      while (out[-1] == '0') --out;
+      if (out[-1] == '.') --out;
+      *out = 0;
+      return out - buffer;
+    case -4:
+      out[2] = '0';
+      ++out;
+      ABSL_FALLTHROUGH_INTENDED;
+    case -3:
+      out[2] = '0';
+      ++out;
+      ABSL_FALLTHROUGH_INTENDED;
+    case -2:
+      out[2] = '0';
+      ++out;
+      ABSL_FALLTHROUGH_INTENDED;
+    case -1:
+      out += 2;
+      memcpy(out, &digits[0], 6);
+      out += 6;
+      while (out[-1] == '0') --out;
+      *out = 0;
+      return out - buffer;
+  }
+  assert(exp < -4 || exp >= 6);
+  out[0] = digits[0];
+  assert(out[1] == '.');
+  out += 2;
+  memcpy(out, &digits[1], 5), out += 5;
+  while (out[-1] == '0') --out;
+  if (out[-1] == '.') --out;
+  *out++ = 'e';
+  if (exp > 0) {
+    *out++ = '+';
+  } else {
+    *out++ = '-';
+    exp = -exp;
+  }
+  if (exp > 99) {
+    int dig1 = exp / 100;
+    exp -= dig1 * 100;
+    *out++ = '0' + dig1;
+  }
+  PutTwoDigits(exp, out);
+  out += 2;
+  *out = 0;
+  return out - buffer;
+}
+
+namespace {
+// Represents integer values of digits.
+// Uses 36 to indicate an invalid character since we support
+// bases up to 36.
+static const int8_t kAsciiToInt[256] = {
+    36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,  // 16 36s.
+    36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
+    36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 0,  1,  2,  3,  4,  5,
+    6,  7,  8,  9,  36, 36, 36, 36, 36, 36, 36, 10, 11, 12, 13, 14, 15, 16, 17,
+    18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
+    36, 36, 36, 36, 36, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
+    24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 36, 36, 36, 36, 36, 36,
+    36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
+    36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
+    36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
+    36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
+    36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
+    36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
+    36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36};
+
+// Parse the sign and optional hex or oct prefix in text.
+inline bool safe_parse_sign_and_base(absl::string_view* text /*inout*/,
+                                     int* base_ptr /*inout*/,
+                                     bool* negative_ptr /*output*/) {
+  if (text->data() == nullptr) {
+    return false;
+  }
+
+  const char* start = text->data();
+  const char* end = start + text->size();
+  int base = *base_ptr;
+
+  // Consume whitespace.
+  while (start < end && absl::ascii_isspace(start[0])) {
+    ++start;
+  }
+  while (start < end && absl::ascii_isspace(end[-1])) {
+    --end;
+  }
+  if (start >= end) {
+    return false;
+  }
+
+  // Consume sign.
+  *negative_ptr = (start[0] == '-');
+  if (*negative_ptr || start[0] == '+') {
+    ++start;
+    if (start >= end) {
+      return false;
+    }
+  }
+
+  // Consume base-dependent prefix.
+  //  base 0: "0x" -> base 16, "0" -> base 8, default -> base 10
+  //  base 16: "0x" -> base 16
+  // Also validate the base.
+  if (base == 0) {
+    if (end - start >= 2 && start[0] == '0' &&
+        (start[1] == 'x' || start[1] == 'X')) {
+      base = 16;
+      start += 2;
+      if (start >= end) {
+        // "0x" with no digits after is invalid.
+        return false;
+      }
+    } else if (end - start >= 1 && start[0] == '0') {
+      base = 8;
+      start += 1;
+    } else {
+      base = 10;
+    }
+  } else if (base == 16) {
+    if (end - start >= 2 && start[0] == '0' &&
+        (start[1] == 'x' || start[1] == 'X')) {
+      start += 2;
+      if (start >= end) {
+        // "0x" with no digits after is invalid.
+        return false;
+      }
+    }
+  } else if (base >= 2 && base <= 36) {
+    // okay
+  } else {
+    return false;
+  }
+  *text = absl::string_view(start, end - start);
+  *base_ptr = base;
+  return true;
+}
+
+// Consume digits.
+//
+// The classic loop:
+//
+//   for each digit
+//     value = value * base + digit
+//   value *= sign
+//
+// The classic loop needs overflow checking.  It also fails on the most
+// negative integer, -2147483648 in 32-bit two's complement representation.
+//
+// My improved loop:
+//
+//  if (!negative)
+//    for each digit
+//      value = value * base
+//      value = value + digit
+//  else
+//    for each digit
+//      value = value * base
+//      value = value - digit
+//
+// Overflow checking becomes simple.
+
+// Lookup tables per IntType:
+// vmax/base and vmin/base are precomputed because division costs at least 8ns.
+// TODO(junyer): Doing this per base instead (i.e. an array of structs, not a
+// struct of arrays) would probably be better in terms of d-cache for the most
+// commonly used bases.
+template <typename IntType>
+struct LookupTables {
+  static const IntType kVmaxOverBase[];
+  static const IntType kVminOverBase[];
+};
+
+// An array initializer macro for X/base where base in [0, 36].
+// However, note that lookups for base in [0, 1] should never happen because
+// base has been validated to be in [2, 36] by safe_parse_sign_and_base().
+#define X_OVER_BASE_INITIALIZER(X)                                        \
+  {                                                                       \
+    0, 0, X / 2, X / 3, X / 4, X / 5, X / 6, X / 7, X / 8, X / 9, X / 10, \
+        X / 11, X / 12, X / 13, X / 14, X / 15, X / 16, X / 17, X / 18,   \
+        X / 19, X / 20, X / 21, X / 22, X / 23, X / 24, X / 25, X / 26,   \
+        X / 27, X / 28, X / 29, X / 30, X / 31, X / 32, X / 33, X / 34,   \
+        X / 35, X / 36,                                                   \
+  }
+
+template <typename IntType>
+const IntType LookupTables<IntType>::kVmaxOverBase[] =
+    X_OVER_BASE_INITIALIZER(std::numeric_limits<IntType>::max());
+
+template <typename IntType>
+const IntType LookupTables<IntType>::kVminOverBase[] =
+    X_OVER_BASE_INITIALIZER(std::numeric_limits<IntType>::min());
+
+#undef X_OVER_BASE_INITIALIZER
+
+template <typename IntType>
+inline bool safe_parse_positive_int(absl::string_view text, int base,
+                                    IntType* value_p) {
+  IntType value = 0;
+  const IntType vmax = std::numeric_limits<IntType>::max();
+  assert(vmax > 0);
+  assert(base >= 0);
+  assert(vmax >= static_cast<IntType>(base));
+  const IntType vmax_over_base = LookupTables<IntType>::kVmaxOverBase[base];
+  const char* start = text.data();
+  const char* end = start + text.size();
+  // loop over digits
+  for (; start < end; ++start) {
+    unsigned char c = static_cast<unsigned char>(start[0]);
+    int digit = kAsciiToInt[c];
+    if (digit >= base) {
+      *value_p = value;
+      return false;
+    }
+    if (value > vmax_over_base) {
+      *value_p = vmax;
+      return false;
+    }
+    value *= base;
+    if (value > vmax - digit) {
+      *value_p = vmax;
+      return false;
+    }
+    value += digit;
+  }
+  *value_p = value;
+  return true;
+}
+
+template <typename IntType>
+inline bool safe_parse_negative_int(absl::string_view text, int base,
+                                    IntType* value_p) {
+  IntType value = 0;
+  const IntType vmin = std::numeric_limits<IntType>::min();
+  assert(vmin < 0);
+  assert(vmin <= 0 - base);
+  IntType vmin_over_base = LookupTables<IntType>::kVminOverBase[base];
+  // 2003 c++ standard [expr.mul]
+  // "... the sign of the remainder is implementation-defined."
+  // Although (vmin/base)*base + vmin%base is always vmin.
+  // 2011 c++ standard tightens the spec but we cannot rely on it.
+  // TODO(junyer): Handle this in the lookup table generation.
+  if (vmin % base > 0) {
+    vmin_over_base += 1;
+  }
+  const char* start = text.data();
+  const char* end = start + text.size();
+  // loop over digits
+  for (; start < end; ++start) {
+    unsigned char c = static_cast<unsigned char>(start[0]);
+    int digit = kAsciiToInt[c];
+    if (digit >= base) {
+      *value_p = value;
+      return false;
+    }
+    if (value < vmin_over_base) {
+      *value_p = vmin;
+      return false;
+    }
+    value *= base;
+    if (value < vmin + digit) {
+      *value_p = vmin;
+      return false;
+    }
+    value -= digit;
+  }
+  *value_p = value;
+  return true;
+}
+
+// Input format based on POSIX.1-2008 strtol
+// http://pubs.opengroup.org/onlinepubs/9699919799/functions/strtol.html
+template <typename IntType>
+inline bool safe_int_internal(absl::string_view text, IntType* value_p,
+                              int base) {
+  *value_p = 0;
+  bool negative;
+  if (!safe_parse_sign_and_base(&text, &base, &negative)) {
+    return false;
+  }
+  if (!negative) {
+    return safe_parse_positive_int(text, base, value_p);
+  } else {
+    return safe_parse_negative_int(text, base, value_p);
+  }
+}
+
+template <typename IntType>
+inline bool safe_uint_internal(absl::string_view text, IntType* value_p,
+                               int base) {
+  *value_p = 0;
+  bool negative;
+  if (!safe_parse_sign_and_base(&text, &base, &negative) || negative) {
+    return false;
+  }
+  return safe_parse_positive_int(text, base, value_p);
+}
+}  // anonymous namespace
+
+namespace numbers_internal {
+bool safe_strto32_base(absl::string_view text, int32_t* value, int base) {
+  return safe_int_internal<int32_t>(text, value, base);
+}
+
+bool safe_strto64_base(absl::string_view text, int64_t* value, int base) {
+  return safe_int_internal<int64_t>(text, value, base);
+}
+
+bool safe_strtou32_base(absl::string_view text, uint32_t* value, int base) {
+  return safe_uint_internal<uint32_t>(text, value, base);
+}
+
+bool safe_strtou64_base(absl::string_view text, uint64_t* value, int base) {
+  return safe_uint_internal<uint64_t>(text, value, base);
+}
+}  // namespace numbers_internal
+
+}  // namespace absl
diff --git a/absl/strings/numbers.h b/absl/strings/numbers.h
new file mode 100644
index 0000000..100839b
--- /dev/null
+++ b/absl/strings/numbers.h
@@ -0,0 +1,189 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: numbers.h
+// -----------------------------------------------------------------------------
+//
+// This package contains functions for converting strings to numbers. For
+// converting numbers to strings, use `StrCat()` or `StrAppend()` in str_cat.h,
+// which automatically detect and convert most number values appropriately.
+
+#ifndef ABSL_STRINGS_NUMBERS_H_
+#define ABSL_STRINGS_NUMBERS_H_
+
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
+#include <ctime>
+#include <limits>
+#include <string>
+#include <type_traits>
+
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+#include "absl/numeric/int128.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+
+// SimpleAtoi()
+//
+// Converts the given string into an integer value, returning `true` if
+// successful. The string must reflect a base-10 integer (optionally followed or
+// preceded by ASCII whitespace) whose value falls within the range of the
+// integer type. If any errors are encountered, this function returns `false`,
+// leaving `out` in an unspecified state.
+template <typename int_type>
+ABSL_MUST_USE_RESULT bool SimpleAtoi(absl::string_view str, int_type* out);
+
+// SimpleAtof()
+//
+// Converts the given string (optionally followed or preceded by ASCII
+// whitespace) into a float, which may be rounded on overflow or underflow.
+// See https://en.cppreference.com/w/c/string/byte/strtof for details about the
+// allowed formats for `str`. If any errors are encountered, this function
+// returns `false`, leaving `out` in an unspecified state.
+ABSL_MUST_USE_RESULT bool SimpleAtof(absl::string_view str, float* out);
+
+// SimpleAtod()
+//
+// Converts the given string (optionally followed or preceded by ASCII
+// whitespace) into a double, which may be rounded on overflow or underflow.
+// See https://en.cppreference.com/w/c/string/byte/strtof for details about the
+// allowed formats for `str`. If any errors are encountered, this function
+// returns `false`, leaving `out` in an unspecified state.
+ABSL_MUST_USE_RESULT bool SimpleAtod(absl::string_view str, double* out);
+
+// SimpleAtob()
+//
+// Converts the given string into a boolean, returning `true` if successful.
+// The following case-insensitive strings are interpreted as boolean `true`:
+// "true", "t", "yes", "y", "1". The following case-insensitive strings
+// are interpreted as boolean `false`: "false", "f", "no", "n", "0". If any
+// errors are encountered, this function returns `false`, leaving `out` in an
+// unspecified state.
+ABSL_MUST_USE_RESULT bool SimpleAtob(absl::string_view str, bool* out);
+
+}  // namespace absl
+
+// End of public API.  Implementation details follow.
+
+namespace absl {
+namespace numbers_internal {
+
+// safe_strto?() functions for implementing SimpleAtoi()
+bool safe_strto32_base(absl::string_view text, int32_t* value, int base);
+bool safe_strto64_base(absl::string_view text, int64_t* value, int base);
+bool safe_strtou32_base(absl::string_view text, uint32_t* value, int base);
+bool safe_strtou64_base(absl::string_view text, uint64_t* value, int base);
+
+static const int kFastToBufferSize = 32;
+static const int kSixDigitsToBufferSize = 16;
+
+// Helper function for fast formatting of floating-point values.
+// The result is the same as printf's "%g", a.k.a. "%.6g"; that is, six
+// significant digits are returned, trailing zeros are removed, and numbers
+// outside the range 0.0001-999999 are output using scientific notation
+// (1.23456e+06). This routine is heavily optimized.
+// Required buffer size is `kSixDigitsToBufferSize`.
+size_t SixDigitsToBuffer(double d, char* buffer);
+
+// These functions are intended for speed. All functions take an output buffer
+// as an argument and return a pointer to the last byte they wrote, which is the
+// terminating '\0'. At most `kFastToBufferSize` bytes are written.
+char* FastIntToBuffer(int32_t, char*);
+char* FastIntToBuffer(uint32_t, char*);
+char* FastIntToBuffer(int64_t, char*);
+char* FastIntToBuffer(uint64_t, char*);
+
+// For enums and integer types that are not an exact match for the types above,
+// use templates to call the appropriate one of the four overloads above.
+template <typename int_type>
+char* FastIntToBuffer(int_type i, char* buffer) {
+  static_assert(sizeof(i) <= 64 / 8,
+                "FastIntToBuffer works only with 64-bit-or-less integers.");
+  // TODO(jorg): This signed-ness check is used because it works correctly
+  // with enums, and it also serves to check that int_type is not a pointer.
+  // If one day something like std::is_signed<enum E> works, switch to it.
+  if (static_cast<int_type>(1) - 2 < 0) {  // Signed
+    if (sizeof(i) > 32 / 8) {           // 33-bit to 64-bit
+      return FastIntToBuffer(static_cast<int64_t>(i), buffer);
+    } else {  // 32-bit or less
+      return FastIntToBuffer(static_cast<int32_t>(i), buffer);
+    }
+  } else {                     // Unsigned
+    if (sizeof(i) > 32 / 8) {  // 33-bit to 64-bit
+      return FastIntToBuffer(static_cast<uint64_t>(i), buffer);
+    } else {  // 32-bit or less
+      return FastIntToBuffer(static_cast<uint32_t>(i), buffer);
+    }
+  }
+}
+
+// Implementation of SimpleAtoi, generalized to support arbitrary base (used
+// with base different from 10 elsewhere in Abseil implementation).
+template <typename int_type>
+ABSL_MUST_USE_RESULT bool safe_strtoi_base(absl::string_view s, int_type* out,
+                                           int base) {
+  static_assert(sizeof(*out) == 4 || sizeof(*out) == 8,
+                "SimpleAtoi works only with 32-bit or 64-bit integers.");
+  static_assert(!std::is_floating_point<int_type>::value,
+                "Use SimpleAtof or SimpleAtod instead.");
+  bool parsed;
+  // TODO(jorg): This signed-ness check is used because it works correctly
+  // with enums, and it also serves to check that int_type is not a pointer.
+  // If one day something like std::is_signed<enum E> works, switch to it.
+  if (static_cast<int_type>(1) - 2 < 0) {  // Signed
+    if (sizeof(*out) == 64 / 8) {       // 64-bit
+      int64_t val;
+      parsed = numbers_internal::safe_strto64_base(s, &val, base);
+      *out = static_cast<int_type>(val);
+    } else {  // 32-bit
+      int32_t val;
+      parsed = numbers_internal::safe_strto32_base(s, &val, base);
+      *out = static_cast<int_type>(val);
+    }
+  } else {                         // Unsigned
+    if (sizeof(*out) == 64 / 8) {  // 64-bit
+      uint64_t val;
+      parsed = numbers_internal::safe_strtou64_base(s, &val, base);
+      *out = static_cast<int_type>(val);
+    } else {  // 32-bit
+      uint32_t val;
+      parsed = numbers_internal::safe_strtou32_base(s, &val, base);
+      *out = static_cast<int_type>(val);
+    }
+  }
+  return parsed;
+}
+
+}  // namespace numbers_internal
+
+// SimpleAtoi()
+//
+// Converts a string to an integer, using `safe_strto?()` functions for actual
+// parsing, returning `true` if successful. The `safe_strto?()` functions apply
+// strict checking; the string must be a base-10 integer, optionally followed or
+// preceded by ASCII whitespace, with a value in the range of the corresponding
+// integer type.
+template <typename int_type>
+ABSL_MUST_USE_RESULT bool SimpleAtoi(absl::string_view str, int_type* out) {
+  return numbers_internal::safe_strtoi_base(str, out, 10);
+}
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_NUMBERS_H_
diff --git a/absl/strings/numbers_benchmark.cc b/absl/strings/numbers_benchmark.cc
new file mode 100644
index 0000000..54dbedd
--- /dev/null
+++ b/absl/strings/numbers_benchmark.cc
@@ -0,0 +1,263 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <cstdint>
+#include <random>
+#include <string>
+#include <type_traits>
+#include <vector>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/strings/numbers.h"
+
+namespace {
+
+template <typename T>
+void BM_FastIntToBuffer(benchmark::State& state) {
+  const int inc = state.range(0);
+  char buf[absl::numbers_internal::kFastToBufferSize];
+  // Use the unsigned type to increment to take advantage of well-defined
+  // modular arithmetic.
+  typename std::make_unsigned<T>::type x = 0;
+  for (auto _ : state) {
+    absl::numbers_internal::FastIntToBuffer(static_cast<T>(x), buf);
+    x += inc;
+  }
+}
+BENCHMARK_TEMPLATE(BM_FastIntToBuffer, int32_t)->Range(0, 1 << 15);
+BENCHMARK_TEMPLATE(BM_FastIntToBuffer, int64_t)->Range(0, 1 << 30);
+
+// Creates an integer that would be printed as `num_digits` repeated 7s in the
+// given `base`. `base` must be greater than or equal to 8.
+int64_t RepeatedSevens(int num_digits, int base) {
+  ABSL_RAW_CHECK(base >= 8, "");
+  int64_t num = 7;
+  while (--num_digits) num = base * num + 7;
+  return num;
+}
+
+void BM_safe_strto32_string(benchmark::State& state) {
+  const int digits = state.range(0);
+  const int base = state.range(1);
+  std::string str(digits, '7');  // valid in octal, decimal and hex
+  int32_t value = 0;
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        absl::numbers_internal::safe_strto32_base(str, &value, base));
+  }
+  ABSL_RAW_CHECK(value == RepeatedSevens(digits, base), "");
+}
+BENCHMARK(BM_safe_strto32_string)
+    ->ArgPair(1, 8)
+    ->ArgPair(1, 10)
+    ->ArgPair(1, 16)
+    ->ArgPair(2, 8)
+    ->ArgPair(2, 10)
+    ->ArgPair(2, 16)
+    ->ArgPair(4, 8)
+    ->ArgPair(4, 10)
+    ->ArgPair(4, 16)
+    ->ArgPair(8, 8)
+    ->ArgPair(8, 10)
+    ->ArgPair(8, 16)
+    ->ArgPair(10, 8)
+    ->ArgPair(9, 10);
+
+void BM_safe_strto64_string(benchmark::State& state) {
+  const int digits = state.range(0);
+  const int base = state.range(1);
+  std::string str(digits, '7');  // valid in octal, decimal and hex
+  int64_t value = 0;
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        absl::numbers_internal::safe_strto64_base(str, &value, base));
+  }
+  ABSL_RAW_CHECK(value == RepeatedSevens(digits, base), "");
+}
+BENCHMARK(BM_safe_strto64_string)
+    ->ArgPair(1, 8)
+    ->ArgPair(1, 10)
+    ->ArgPair(1, 16)
+    ->ArgPair(2, 8)
+    ->ArgPair(2, 10)
+    ->ArgPair(2, 16)
+    ->ArgPair(4, 8)
+    ->ArgPair(4, 10)
+    ->ArgPair(4, 16)
+    ->ArgPair(8, 8)
+    ->ArgPair(8, 10)
+    ->ArgPair(8, 16)
+    ->ArgPair(16, 8)
+    ->ArgPair(16, 10)
+    ->ArgPair(16, 16);
+
+void BM_safe_strtou32_string(benchmark::State& state) {
+  const int digits = state.range(0);
+  const int base = state.range(1);
+  std::string str(digits, '7');  // valid in octal, decimal and hex
+  uint32_t value = 0;
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        absl::numbers_internal::safe_strtou32_base(str, &value, base));
+  }
+  ABSL_RAW_CHECK(value == RepeatedSevens(digits, base), "");
+}
+BENCHMARK(BM_safe_strtou32_string)
+    ->ArgPair(1, 8)
+    ->ArgPair(1, 10)
+    ->ArgPair(1, 16)
+    ->ArgPair(2, 8)
+    ->ArgPair(2, 10)
+    ->ArgPair(2, 16)
+    ->ArgPair(4, 8)
+    ->ArgPair(4, 10)
+    ->ArgPair(4, 16)
+    ->ArgPair(8, 8)
+    ->ArgPair(8, 10)
+    ->ArgPair(8, 16)
+    ->ArgPair(10, 8)
+    ->ArgPair(9, 10);
+
+void BM_safe_strtou64_string(benchmark::State& state) {
+  const int digits = state.range(0);
+  const int base = state.range(1);
+  std::string str(digits, '7');  // valid in octal, decimal and hex
+  uint64_t value = 0;
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(
+        absl::numbers_internal::safe_strtou64_base(str, &value, base));
+  }
+  ABSL_RAW_CHECK(value == RepeatedSevens(digits, base), "");
+}
+BENCHMARK(BM_safe_strtou64_string)
+    ->ArgPair(1, 8)
+    ->ArgPair(1, 10)
+    ->ArgPair(1, 16)
+    ->ArgPair(2, 8)
+    ->ArgPair(2, 10)
+    ->ArgPair(2, 16)
+    ->ArgPair(4, 8)
+    ->ArgPair(4, 10)
+    ->ArgPair(4, 16)
+    ->ArgPair(8, 8)
+    ->ArgPair(8, 10)
+    ->ArgPair(8, 16)
+    ->ArgPair(16, 8)
+    ->ArgPair(16, 10)
+    ->ArgPair(16, 16);
+
+// Returns a vector of `num_strings` strings. Each string represents a
+// floating point number with `num_digits` digits before the decimal point and
+// another `num_digits` digits after.
+std::vector<std::string> MakeFloatStrings(int num_strings, int num_digits) {
+  // For convenience, use a random number generator to generate the test data.
+  // We don't actually need random properties, so use a fixed seed.
+  std::minstd_rand0 rng(1);
+  std::uniform_int_distribution<int> random_digit('0', '9');
+
+  std::vector<std::string> float_strings(num_strings);
+  for (std::string& s : float_strings) {
+    s.reserve(2 * num_digits + 1);
+    for (int i = 0; i < num_digits; ++i) {
+      s.push_back(static_cast<char>(random_digit(rng)));
+    }
+    s.push_back('.');
+    for (int i = 0; i < num_digits; ++i) {
+      s.push_back(static_cast<char>(random_digit(rng)));
+    }
+  }
+  return float_strings;
+}
+
+template <typename StringType>
+StringType GetStringAs(const std::string& s) {
+  return static_cast<StringType>(s);
+}
+template <>
+const char* GetStringAs<const char*>(const std::string& s) {
+  return s.c_str();
+}
+
+template <typename StringType>
+std::vector<StringType> GetStringsAs(const std::vector<std::string>& strings) {
+  std::vector<StringType> result;
+  result.reserve(strings.size());
+  for (const std::string& s : strings) {
+    result.push_back(GetStringAs<StringType>(s));
+  }
+  return result;
+}
+
+template <typename T>
+void BM_SimpleAtof(benchmark::State& state) {
+  const int num_strings = state.range(0);
+  const int num_digits = state.range(1);
+  std::vector<std::string> backing_strings =
+      MakeFloatStrings(num_strings, num_digits);
+  std::vector<T> inputs = GetStringsAs<T>(backing_strings);
+  float value;
+  for (auto _ : state) {
+    for (const T& input : inputs) {
+      benchmark::DoNotOptimize(absl::SimpleAtof(input, &value));
+    }
+  }
+}
+BENCHMARK_TEMPLATE(BM_SimpleAtof, absl::string_view)
+    ->ArgPair(10, 1)
+    ->ArgPair(10, 2)
+    ->ArgPair(10, 4)
+    ->ArgPair(10, 8);
+BENCHMARK_TEMPLATE(BM_SimpleAtof, const char*)
+    ->ArgPair(10, 1)
+    ->ArgPair(10, 2)
+    ->ArgPair(10, 4)
+    ->ArgPair(10, 8);
+BENCHMARK_TEMPLATE(BM_SimpleAtof, std::string)
+    ->ArgPair(10, 1)
+    ->ArgPair(10, 2)
+    ->ArgPair(10, 4)
+    ->ArgPair(10, 8);
+
+template <typename T>
+void BM_SimpleAtod(benchmark::State& state) {
+  const int num_strings = state.range(0);
+  const int num_digits = state.range(1);
+  std::vector<std::string> backing_strings =
+      MakeFloatStrings(num_strings, num_digits);
+  std::vector<T> inputs = GetStringsAs<T>(backing_strings);
+  double value;
+  for (auto _ : state) {
+    for (const T& input : inputs) {
+      benchmark::DoNotOptimize(absl::SimpleAtod(input, &value));
+    }
+  }
+}
+BENCHMARK_TEMPLATE(BM_SimpleAtod, absl::string_view)
+    ->ArgPair(10, 1)
+    ->ArgPair(10, 2)
+    ->ArgPair(10, 4)
+    ->ArgPair(10, 8);
+BENCHMARK_TEMPLATE(BM_SimpleAtod, const char*)
+    ->ArgPair(10, 1)
+    ->ArgPair(10, 2)
+    ->ArgPair(10, 4)
+    ->ArgPair(10, 8);
+BENCHMARK_TEMPLATE(BM_SimpleAtod, std::string)
+    ->ArgPair(10, 1)
+    ->ArgPair(10, 2)
+    ->ArgPair(10, 4)
+    ->ArgPair(10, 8);
+
+}  // namespace
diff --git a/absl/strings/numbers_test.cc b/absl/strings/numbers_test.cc
new file mode 100644
index 0000000..77d7e78
--- /dev/null
+++ b/absl/strings/numbers_test.cc
@@ -0,0 +1,1187 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file tests string processing functions related to numeric values.
+
+#include "absl/strings/numbers.h"
+
+#include <sys/types.h>
+#include <cfenv>  // NOLINT(build/c++11)
+#include <cinttypes>
+#include <climits>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <limits>
+#include <numeric>
+#include <random>
+#include <set>
+#include <string>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/strings/str_cat.h"
+
+#include "absl/strings/internal/numbers_test_common.h"
+#include "absl/strings/internal/pow10_helper.h"
+
+namespace {
+
+using absl::numbers_internal::kSixDigitsToBufferSize;
+using absl::numbers_internal::safe_strto32_base;
+using absl::numbers_internal::safe_strto64_base;
+using absl::numbers_internal::safe_strtou32_base;
+using absl::numbers_internal::safe_strtou64_base;
+using absl::numbers_internal::SixDigitsToBuffer;
+using absl::strings_internal::Itoa;
+using absl::strings_internal::strtouint32_test_cases;
+using absl::strings_internal::strtouint64_test_cases;
+using absl::SimpleAtoi;
+using testing::Eq;
+using testing::MatchesRegex;
+
+// Number of floats to test with.
+// 5,000,000 is a reasonable default for a test that only takes a few seconds.
+// 1,000,000,000+ triggers checking for all possible mantissa values for
+// double-precision tests. 2,000,000,000+ triggers checking for every possible
+// single-precision float.
+const int kFloatNumCases = 5000000;
+
+// This is a slow, brute-force routine to compute the exact base-10
+// representation of a double-precision floating-point number.  It
+// is useful for debugging only.
+std::string PerfectDtoa(double d) {
+  if (d == 0) return "0";
+  if (d < 0) return "-" + PerfectDtoa(-d);
+
+  // Basic theory: decompose d into mantissa and exp, where
+  // d = mantissa * 2^exp, and exp is as close to zero as possible.
+  int64_t mantissa, exp = 0;
+  while (d >= 1ULL << 63) ++exp, d *= 0.5;
+  while ((mantissa = d) != d) --exp, d *= 2.0;
+
+  // Then convert mantissa to ASCII, and either double it (if
+  // exp > 0) or halve it (if exp < 0) repeatedly.  "halve it"
+  // in this case means multiplying it by five and dividing by 10.
+  constexpr int maxlen = 1100;  // worst case is actually 1030 or so.
+  char buf[maxlen + 5];
+  for (int64_t num = mantissa, pos = maxlen; --pos >= 0;) {
+    buf[pos] = '0' + (num % 10);
+    num /= 10;
+  }
+  char* begin = &buf[0];
+  char* end = buf + maxlen;
+  for (int i = 0; i != exp; i += (exp > 0) ? 1 : -1) {
+    int carry = 0;
+    for (char* p = end; --p != begin;) {
+      int dig = *p - '0';
+      dig = dig * (exp > 0 ? 2 : 5) + carry;
+      carry = dig / 10;
+      dig %= 10;
+      *p = '0' + dig;
+    }
+  }
+  if (exp < 0) {
+    // "dividing by 10" above means we have to add the decimal point.
+    memmove(end + 1 + exp, end + exp, 1 - exp);
+    end[exp] = '.';
+    ++end;
+  }
+  while (*begin == '0' && begin[1] != '.') ++begin;
+  return {begin, end};
+}
+
+TEST(ToString, PerfectDtoa) {
+  EXPECT_THAT(PerfectDtoa(1), Eq("1"));
+  EXPECT_THAT(PerfectDtoa(0.1),
+              Eq("0.1000000000000000055511151231257827021181583404541015625"));
+  EXPECT_THAT(PerfectDtoa(1e24), Eq("999999999999999983222784"));
+  EXPECT_THAT(PerfectDtoa(5e-324), MatchesRegex("0.0000.*625"));
+  for (int i = 0; i < 100; ++i) {
+    for (double multiplier :
+         {1e-300, 1e-200, 1e-100, 0.1, 1.0, 10.0, 1e100, 1e300}) {
+      double d = multiplier * i;
+      std::string s = PerfectDtoa(d);
+      EXPECT_DOUBLE_EQ(d, strtod(s.c_str(), nullptr));
+    }
+  }
+}
+
+template <typename integer>
+struct MyInteger {
+  integer i;
+  explicit constexpr MyInteger(integer i) : i(i) {}
+  constexpr operator integer() const { return i; }
+
+  constexpr MyInteger operator+(MyInteger other) const { return i + other.i; }
+  constexpr MyInteger operator-(MyInteger other) const { return i - other.i; }
+  constexpr MyInteger operator*(MyInteger other) const { return i * other.i; }
+  constexpr MyInteger operator/(MyInteger other) const { return i / other.i; }
+
+  constexpr bool operator<(MyInteger other) const { return i < other.i; }
+  constexpr bool operator<=(MyInteger other) const { return i <= other.i; }
+  constexpr bool operator==(MyInteger other) const { return i == other.i; }
+  constexpr bool operator>=(MyInteger other) const { return i >= other.i; }
+  constexpr bool operator>(MyInteger other) const { return i > other.i; }
+  constexpr bool operator!=(MyInteger other) const { return i != other.i; }
+
+  integer as_integer() const { return i; }
+};
+
+typedef MyInteger<int64_t> MyInt64;
+typedef MyInteger<uint64_t> MyUInt64;
+
+void CheckInt32(int32_t x) {
+  char buffer[absl::numbers_internal::kFastToBufferSize];
+  char* actual = absl::numbers_internal::FastIntToBuffer(x, buffer);
+  std::string expected = std::to_string(x);
+  EXPECT_EQ(expected, std::string(buffer, actual)) << " Input " << x;
+
+  char* generic_actual = absl::numbers_internal::FastIntToBuffer(x, buffer);
+  EXPECT_EQ(expected, std::string(buffer, generic_actual)) << " Input " << x;
+}
+
+void CheckInt64(int64_t x) {
+  char buffer[absl::numbers_internal::kFastToBufferSize + 3];
+  buffer[0] = '*';
+  buffer[23] = '*';
+  buffer[24] = '*';
+  char* actual = absl::numbers_internal::FastIntToBuffer(x, &buffer[1]);
+  std::string expected = std::to_string(x);
+  EXPECT_EQ(expected, std::string(&buffer[1], actual)) << " Input " << x;
+  EXPECT_EQ(buffer[0], '*');
+  EXPECT_EQ(buffer[23], '*');
+  EXPECT_EQ(buffer[24], '*');
+
+  char* my_actual =
+      absl::numbers_internal::FastIntToBuffer(MyInt64(x), &buffer[1]);
+  EXPECT_EQ(expected, std::string(&buffer[1], my_actual)) << " Input " << x;
+}
+
+void CheckUInt32(uint32_t x) {
+  char buffer[absl::numbers_internal::kFastToBufferSize];
+  char* actual = absl::numbers_internal::FastIntToBuffer(x, buffer);
+  std::string expected = std::to_string(x);
+  EXPECT_EQ(expected, std::string(buffer, actual)) << " Input " << x;
+
+  char* generic_actual = absl::numbers_internal::FastIntToBuffer(x, buffer);
+  EXPECT_EQ(expected, std::string(buffer, generic_actual)) << " Input " << x;
+}
+
+void CheckUInt64(uint64_t x) {
+  char buffer[absl::numbers_internal::kFastToBufferSize + 1];
+  char* actual = absl::numbers_internal::FastIntToBuffer(x, &buffer[1]);
+  std::string expected = std::to_string(x);
+  EXPECT_EQ(expected, std::string(&buffer[1], actual)) << " Input " << x;
+
+  char* generic_actual = absl::numbers_internal::FastIntToBuffer(x, &buffer[1]);
+  EXPECT_EQ(expected, std::string(&buffer[1], generic_actual))
+      << " Input " << x;
+
+  char* my_actual =
+      absl::numbers_internal::FastIntToBuffer(MyUInt64(x), &buffer[1]);
+  EXPECT_EQ(expected, std::string(&buffer[1], my_actual)) << " Input " << x;
+}
+
+void CheckHex64(uint64_t v) {
+  char expected[16 + 1];
+  std::string actual = absl::StrCat(absl::Hex(v, absl::kZeroPad16));
+  snprintf(expected, sizeof(expected), "%016" PRIx64, static_cast<uint64_t>(v));
+  EXPECT_EQ(expected, actual) << " Input " << v;
+}
+
+TEST(Numbers, TestFastPrints) {
+  for (int i = -100; i <= 100; i++) {
+    CheckInt32(i);
+    CheckInt64(i);
+  }
+  for (int i = 0; i <= 100; i++) {
+    CheckUInt32(i);
+    CheckUInt64(i);
+  }
+  // Test min int to make sure that works
+  CheckInt32(INT_MIN);
+  CheckInt32(INT_MAX);
+  CheckInt64(LONG_MIN);
+  CheckInt64(uint64_t{1000000000});
+  CheckInt64(uint64_t{9999999999});
+  CheckInt64(uint64_t{100000000000000});
+  CheckInt64(uint64_t{999999999999999});
+  CheckInt64(uint64_t{1000000000000000000});
+  CheckInt64(uint64_t{1199999999999999999});
+  CheckInt64(int64_t{-700000000000000000});
+  CheckInt64(LONG_MAX);
+  CheckUInt32(std::numeric_limits<uint32_t>::max());
+  CheckUInt64(uint64_t{1000000000});
+  CheckUInt64(uint64_t{9999999999});
+  CheckUInt64(uint64_t{100000000000000});
+  CheckUInt64(uint64_t{999999999999999});
+  CheckUInt64(uint64_t{1000000000000000000});
+  CheckUInt64(uint64_t{1199999999999999999});
+  CheckUInt64(std::numeric_limits<uint64_t>::max());
+
+  for (int i = 0; i < 10000; i++) {
+    CheckHex64(i);
+  }
+  CheckHex64(uint64_t{0x123456789abcdef0});
+}
+
+template <typename int_type, typename in_val_type>
+void VerifySimpleAtoiGood(in_val_type in_value, int_type exp_value) {
+  std::string s = absl::StrCat(in_value);
+  int_type x = static_cast<int_type>(~exp_value);
+  EXPECT_TRUE(SimpleAtoi(s, &x))
+      << "in_value=" << in_value << " s=" << s << " x=" << x;
+  EXPECT_EQ(exp_value, x);
+  x = static_cast<int_type>(~exp_value);
+  EXPECT_TRUE(SimpleAtoi(s.c_str(), &x));
+  EXPECT_EQ(exp_value, x);
+}
+
+template <typename int_type, typename in_val_type>
+void VerifySimpleAtoiBad(in_val_type in_value) {
+  std::string s = absl::StrCat(in_value);
+  int_type x;
+  EXPECT_FALSE(SimpleAtoi(s, &x));
+  EXPECT_FALSE(SimpleAtoi(s.c_str(), &x));
+}
+
+TEST(NumbersTest, Atoi) {
+  // SimpleAtoi(absl::string_view, int32_t)
+  VerifySimpleAtoiGood<int32_t>(0, 0);
+  VerifySimpleAtoiGood<int32_t>(42, 42);
+  VerifySimpleAtoiGood<int32_t>(-42, -42);
+
+  VerifySimpleAtoiGood<int32_t>(std::numeric_limits<int32_t>::min(),
+                                std::numeric_limits<int32_t>::min());
+  VerifySimpleAtoiGood<int32_t>(std::numeric_limits<int32_t>::max(),
+                                std::numeric_limits<int32_t>::max());
+
+  // SimpleAtoi(absl::string_view, uint32_t)
+  VerifySimpleAtoiGood<uint32_t>(0, 0);
+  VerifySimpleAtoiGood<uint32_t>(42, 42);
+  VerifySimpleAtoiBad<uint32_t>(-42);
+
+  VerifySimpleAtoiBad<uint32_t>(std::numeric_limits<int32_t>::min());
+  VerifySimpleAtoiGood<uint32_t>(std::numeric_limits<int32_t>::max(),
+                                 std::numeric_limits<int32_t>::max());
+  VerifySimpleAtoiGood<uint32_t>(std::numeric_limits<uint32_t>::max(),
+                                 std::numeric_limits<uint32_t>::max());
+  VerifySimpleAtoiBad<uint32_t>(std::numeric_limits<int64_t>::min());
+  VerifySimpleAtoiBad<uint32_t>(std::numeric_limits<int64_t>::max());
+  VerifySimpleAtoiBad<uint32_t>(std::numeric_limits<uint64_t>::max());
+
+  // SimpleAtoi(absl::string_view, int64_t)
+  VerifySimpleAtoiGood<int64_t>(0, 0);
+  VerifySimpleAtoiGood<int64_t>(42, 42);
+  VerifySimpleAtoiGood<int64_t>(-42, -42);
+
+  VerifySimpleAtoiGood<int64_t>(std::numeric_limits<int32_t>::min(),
+                                std::numeric_limits<int32_t>::min());
+  VerifySimpleAtoiGood<int64_t>(std::numeric_limits<int32_t>::max(),
+                                std::numeric_limits<int32_t>::max());
+  VerifySimpleAtoiGood<int64_t>(std::numeric_limits<uint32_t>::max(),
+                                std::numeric_limits<uint32_t>::max());
+  VerifySimpleAtoiGood<int64_t>(std::numeric_limits<int64_t>::min(),
+                                std::numeric_limits<int64_t>::min());
+  VerifySimpleAtoiGood<int64_t>(std::numeric_limits<int64_t>::max(),
+                                std::numeric_limits<int64_t>::max());
+  VerifySimpleAtoiBad<int64_t>(std::numeric_limits<uint64_t>::max());
+
+  // SimpleAtoi(absl::string_view, uint64_t)
+  VerifySimpleAtoiGood<uint64_t>(0, 0);
+  VerifySimpleAtoiGood<uint64_t>(42, 42);
+  VerifySimpleAtoiBad<uint64_t>(-42);
+
+  VerifySimpleAtoiBad<uint64_t>(std::numeric_limits<int32_t>::min());
+  VerifySimpleAtoiGood<uint64_t>(std::numeric_limits<int32_t>::max(),
+                                 std::numeric_limits<int32_t>::max());
+  VerifySimpleAtoiGood<uint64_t>(std::numeric_limits<uint32_t>::max(),
+                                 std::numeric_limits<uint32_t>::max());
+  VerifySimpleAtoiBad<uint64_t>(std::numeric_limits<int64_t>::min());
+  VerifySimpleAtoiGood<uint64_t>(std::numeric_limits<int64_t>::max(),
+                                 std::numeric_limits<int64_t>::max());
+  VerifySimpleAtoiGood<uint64_t>(std::numeric_limits<uint64_t>::max(),
+                                 std::numeric_limits<uint64_t>::max());
+
+  // Some other types
+  VerifySimpleAtoiGood<int>(-42, -42);
+  VerifySimpleAtoiGood<int32_t>(-42, -42);
+  VerifySimpleAtoiGood<uint32_t>(42, 42);
+  VerifySimpleAtoiGood<unsigned int>(42, 42);
+  VerifySimpleAtoiGood<int64_t>(-42, -42);
+  VerifySimpleAtoiGood<long>(-42, -42);  // NOLINT(runtime/int)
+  VerifySimpleAtoiGood<uint64_t>(42, 42);
+  VerifySimpleAtoiGood<size_t>(42, 42);
+  VerifySimpleAtoiGood<std::string::size_type>(42, 42);
+}
+
+TEST(NumbersTest, Atoenum) {
+  enum E01 {
+    E01_zero = 0,
+    E01_one = 1,
+  };
+
+  VerifySimpleAtoiGood<E01>(E01_zero, E01_zero);
+  VerifySimpleAtoiGood<E01>(E01_one, E01_one);
+
+  enum E_101 {
+    E_101_minusone = -1,
+    E_101_zero = 0,
+    E_101_one = 1,
+  };
+
+  VerifySimpleAtoiGood<E_101>(E_101_minusone, E_101_minusone);
+  VerifySimpleAtoiGood<E_101>(E_101_zero, E_101_zero);
+  VerifySimpleAtoiGood<E_101>(E_101_one, E_101_one);
+
+  enum E_bigint {
+    E_bigint_zero = 0,
+    E_bigint_one = 1,
+    E_bigint_max31 = static_cast<int32_t>(0x7FFFFFFF),
+  };
+
+  VerifySimpleAtoiGood<E_bigint>(E_bigint_zero, E_bigint_zero);
+  VerifySimpleAtoiGood<E_bigint>(E_bigint_one, E_bigint_one);
+  VerifySimpleAtoiGood<E_bigint>(E_bigint_max31, E_bigint_max31);
+
+  enum E_fullint {
+    E_fullint_zero = 0,
+    E_fullint_one = 1,
+    E_fullint_max31 = static_cast<int32_t>(0x7FFFFFFF),
+    E_fullint_min32 = INT32_MIN,
+  };
+
+  VerifySimpleAtoiGood<E_fullint>(E_fullint_zero, E_fullint_zero);
+  VerifySimpleAtoiGood<E_fullint>(E_fullint_one, E_fullint_one);
+  VerifySimpleAtoiGood<E_fullint>(E_fullint_max31, E_fullint_max31);
+  VerifySimpleAtoiGood<E_fullint>(E_fullint_min32, E_fullint_min32);
+
+  enum E_biguint {
+    E_biguint_zero = 0,
+    E_biguint_one = 1,
+    E_biguint_max31 = static_cast<uint32_t>(0x7FFFFFFF),
+    E_biguint_max32 = static_cast<uint32_t>(0xFFFFFFFF),
+  };
+
+  VerifySimpleAtoiGood<E_biguint>(E_biguint_zero, E_biguint_zero);
+  VerifySimpleAtoiGood<E_biguint>(E_biguint_one, E_biguint_one);
+  VerifySimpleAtoiGood<E_biguint>(E_biguint_max31, E_biguint_max31);
+  VerifySimpleAtoiGood<E_biguint>(E_biguint_max32, E_biguint_max32);
+}
+
+TEST(stringtest, safe_strto32_base) {
+  int32_t value;
+  EXPECT_TRUE(safe_strto32_base("0x34234324", &value, 16));
+  EXPECT_EQ(0x34234324, value);
+
+  EXPECT_TRUE(safe_strto32_base("0X34234324", &value, 16));
+  EXPECT_EQ(0x34234324, value);
+
+  EXPECT_TRUE(safe_strto32_base("34234324", &value, 16));
+  EXPECT_EQ(0x34234324, value);
+
+  EXPECT_TRUE(safe_strto32_base("0", &value, 16));
+  EXPECT_EQ(0, value);
+
+  EXPECT_TRUE(safe_strto32_base(" \t\n -0x34234324", &value, 16));
+  EXPECT_EQ(-0x34234324, value);
+
+  EXPECT_TRUE(safe_strto32_base(" \t\n -34234324", &value, 16));
+  EXPECT_EQ(-0x34234324, value);
+
+  EXPECT_TRUE(safe_strto32_base("7654321", &value, 8));
+  EXPECT_EQ(07654321, value);
+
+  EXPECT_TRUE(safe_strto32_base("-01234", &value, 8));
+  EXPECT_EQ(-01234, value);
+
+  EXPECT_FALSE(safe_strto32_base("1834", &value, 8));
+
+  // Autodetect base.
+  EXPECT_TRUE(safe_strto32_base("0", &value, 0));
+  EXPECT_EQ(0, value);
+
+  EXPECT_TRUE(safe_strto32_base("077", &value, 0));
+  EXPECT_EQ(077, value);  // Octal interpretation
+
+  // Leading zero indicates octal, but then followed by invalid digit.
+  EXPECT_FALSE(safe_strto32_base("088", &value, 0));
+
+  // Leading 0x indicated hex, but then followed by invalid digit.
+  EXPECT_FALSE(safe_strto32_base("0xG", &value, 0));
+
+  // Base-10 version.
+  EXPECT_TRUE(safe_strto32_base("34234324", &value, 10));
+  EXPECT_EQ(34234324, value);
+
+  EXPECT_TRUE(safe_strto32_base("0", &value, 10));
+  EXPECT_EQ(0, value);
+
+  EXPECT_TRUE(safe_strto32_base(" \t\n -34234324", &value, 10));
+  EXPECT_EQ(-34234324, value);
+
+  EXPECT_TRUE(safe_strto32_base("34234324 \n\t ", &value, 10));
+  EXPECT_EQ(34234324, value);
+
+  // Invalid ints.
+  EXPECT_FALSE(safe_strto32_base("", &value, 10));
+  EXPECT_FALSE(safe_strto32_base("  ", &value, 10));
+  EXPECT_FALSE(safe_strto32_base("abc", &value, 10));
+  EXPECT_FALSE(safe_strto32_base("34234324a", &value, 10));
+  EXPECT_FALSE(safe_strto32_base("34234.3", &value, 10));
+
+  // Out of bounds.
+  EXPECT_FALSE(safe_strto32_base("2147483648", &value, 10));
+  EXPECT_FALSE(safe_strto32_base("-2147483649", &value, 10));
+
+  // String version.
+  EXPECT_TRUE(safe_strto32_base(std::string("0x1234"), &value, 16));
+  EXPECT_EQ(0x1234, value);
+
+  // Base-10 std::string version.
+  EXPECT_TRUE(safe_strto32_base("1234", &value, 10));
+  EXPECT_EQ(1234, value);
+}
+
+TEST(stringtest, safe_strto32_range) {
+  // These tests verify underflow/overflow behaviour.
+  int32_t value;
+  EXPECT_FALSE(safe_strto32_base("2147483648", &value, 10));
+  EXPECT_EQ(std::numeric_limits<int32_t>::max(), value);
+
+  EXPECT_TRUE(safe_strto32_base("-2147483648", &value, 10));
+  EXPECT_EQ(std::numeric_limits<int32_t>::min(), value);
+
+  EXPECT_FALSE(safe_strto32_base("-2147483649", &value, 10));
+  EXPECT_EQ(std::numeric_limits<int32_t>::min(), value);
+}
+
+TEST(stringtest, safe_strto64_range) {
+  // These tests verify underflow/overflow behaviour.
+  int64_t value;
+  EXPECT_FALSE(safe_strto64_base("9223372036854775808", &value, 10));
+  EXPECT_EQ(std::numeric_limits<int64_t>::max(), value);
+
+  EXPECT_TRUE(safe_strto64_base("-9223372036854775808", &value, 10));
+  EXPECT_EQ(std::numeric_limits<int64_t>::min(), value);
+
+  EXPECT_FALSE(safe_strto64_base("-9223372036854775809", &value, 10));
+  EXPECT_EQ(std::numeric_limits<int64_t>::min(), value);
+}
+
+TEST(stringtest, safe_strto32_leading_substring) {
+  // These tests verify this comment in numbers.h:
+  // On error, returns false, and sets *value to: [...]
+  //   conversion of leading substring if available ("123@@@" -> 123)
+  //   0 if no leading substring available
+  int32_t value;
+  EXPECT_FALSE(safe_strto32_base("04069@@@", &value, 10));
+  EXPECT_EQ(4069, value);
+
+  EXPECT_FALSE(safe_strto32_base("04069@@@", &value, 8));
+  EXPECT_EQ(0406, value);
+
+  EXPECT_FALSE(safe_strto32_base("04069balloons", &value, 10));
+  EXPECT_EQ(4069, value);
+
+  EXPECT_FALSE(safe_strto32_base("04069balloons", &value, 16));
+  EXPECT_EQ(0x4069ba, value);
+
+  EXPECT_FALSE(safe_strto32_base("@@@", &value, 10));
+  EXPECT_EQ(0, value);  // there was no leading substring
+}
+
+TEST(stringtest, safe_strto64_leading_substring) {
+  // These tests verify this comment in numbers.h:
+  // On error, returns false, and sets *value to: [...]
+  //   conversion of leading substring if available ("123@@@" -> 123)
+  //   0 if no leading substring available
+  int64_t value;
+  EXPECT_FALSE(safe_strto64_base("04069@@@", &value, 10));
+  EXPECT_EQ(4069, value);
+
+  EXPECT_FALSE(safe_strto64_base("04069@@@", &value, 8));
+  EXPECT_EQ(0406, value);
+
+  EXPECT_FALSE(safe_strto64_base("04069balloons", &value, 10));
+  EXPECT_EQ(4069, value);
+
+  EXPECT_FALSE(safe_strto64_base("04069balloons", &value, 16));
+  EXPECT_EQ(0x4069ba, value);
+
+  EXPECT_FALSE(safe_strto64_base("@@@", &value, 10));
+  EXPECT_EQ(0, value);  // there was no leading substring
+}
+
+TEST(stringtest, safe_strto64_base) {
+  int64_t value;
+  EXPECT_TRUE(safe_strto64_base("0x3423432448783446", &value, 16));
+  EXPECT_EQ(int64_t{0x3423432448783446}, value);
+
+  EXPECT_TRUE(safe_strto64_base("3423432448783446", &value, 16));
+  EXPECT_EQ(int64_t{0x3423432448783446}, value);
+
+  EXPECT_TRUE(safe_strto64_base("0", &value, 16));
+  EXPECT_EQ(0, value);
+
+  EXPECT_TRUE(safe_strto64_base(" \t\n -0x3423432448783446", &value, 16));
+  EXPECT_EQ(int64_t{-0x3423432448783446}, value);
+
+  EXPECT_TRUE(safe_strto64_base(" \t\n -3423432448783446", &value, 16));
+  EXPECT_EQ(int64_t{-0x3423432448783446}, value);
+
+  EXPECT_TRUE(safe_strto64_base("123456701234567012", &value, 8));
+  EXPECT_EQ(int64_t{0123456701234567012}, value);
+
+  EXPECT_TRUE(safe_strto64_base("-017777777777777", &value, 8));
+  EXPECT_EQ(int64_t{-017777777777777}, value);
+
+  EXPECT_FALSE(safe_strto64_base("19777777777777", &value, 8));
+
+  // Autodetect base.
+  EXPECT_TRUE(safe_strto64_base("0", &value, 0));
+  EXPECT_EQ(0, value);
+
+  EXPECT_TRUE(safe_strto64_base("077", &value, 0));
+  EXPECT_EQ(077, value);  // Octal interpretation
+
+  // Leading zero indicates octal, but then followed by invalid digit.
+  EXPECT_FALSE(safe_strto64_base("088", &value, 0));
+
+  // Leading 0x indicated hex, but then followed by invalid digit.
+  EXPECT_FALSE(safe_strto64_base("0xG", &value, 0));
+
+  // Base-10 version.
+  EXPECT_TRUE(safe_strto64_base("34234324487834466", &value, 10));
+  EXPECT_EQ(int64_t{34234324487834466}, value);
+
+  EXPECT_TRUE(safe_strto64_base("0", &value, 10));
+  EXPECT_EQ(0, value);
+
+  EXPECT_TRUE(safe_strto64_base(" \t\n -34234324487834466", &value, 10));
+  EXPECT_EQ(int64_t{-34234324487834466}, value);
+
+  EXPECT_TRUE(safe_strto64_base("34234324487834466 \n\t ", &value, 10));
+  EXPECT_EQ(int64_t{34234324487834466}, value);
+
+  // Invalid ints.
+  EXPECT_FALSE(safe_strto64_base("", &value, 10));
+  EXPECT_FALSE(safe_strto64_base("  ", &value, 10));
+  EXPECT_FALSE(safe_strto64_base("abc", &value, 10));
+  EXPECT_FALSE(safe_strto64_base("34234324487834466a", &value, 10));
+  EXPECT_FALSE(safe_strto64_base("34234487834466.3", &value, 10));
+
+  // Out of bounds.
+  EXPECT_FALSE(safe_strto64_base("9223372036854775808", &value, 10));
+  EXPECT_FALSE(safe_strto64_base("-9223372036854775809", &value, 10));
+
+  // String version.
+  EXPECT_TRUE(safe_strto64_base(std::string("0x1234"), &value, 16));
+  EXPECT_EQ(0x1234, value);
+
+  // Base-10 std::string version.
+  EXPECT_TRUE(safe_strto64_base("1234", &value, 10));
+  EXPECT_EQ(1234, value);
+}
+
+const size_t kNumRandomTests = 10000;
+
+template <typename IntType>
+void test_random_integer_parse_base(bool (*parse_func)(absl::string_view,
+                                                       IntType* value,
+                                                       int base)) {
+  using RandomEngine = std::minstd_rand0;
+  std::random_device rd;
+  RandomEngine rng(rd());
+  std::uniform_int_distribution<IntType> random_int(
+      std::numeric_limits<IntType>::min());
+  std::uniform_int_distribution<int> random_base(2, 35);
+  for (size_t i = 0; i < kNumRandomTests; i++) {
+    IntType value = random_int(rng);
+    int base = random_base(rng);
+    std::string str_value;
+    EXPECT_TRUE(Itoa<IntType>(value, base, &str_value));
+    IntType parsed_value;
+
+    // Test successful parse
+    EXPECT_TRUE(parse_func(str_value, &parsed_value, base));
+    EXPECT_EQ(parsed_value, value);
+
+    // Test overflow
+    EXPECT_FALSE(
+        parse_func(absl::StrCat(std::numeric_limits<IntType>::max(), value),
+                   &parsed_value, base));
+
+    // Test underflow
+    if (std::numeric_limits<IntType>::min() < 0) {
+      EXPECT_FALSE(
+          parse_func(absl::StrCat(std::numeric_limits<IntType>::min(), value),
+                     &parsed_value, base));
+    } else {
+      EXPECT_FALSE(parse_func(absl::StrCat("-", value), &parsed_value, base));
+    }
+  }
+}
+
+TEST(stringtest, safe_strto32_random) {
+  test_random_integer_parse_base<int32_t>(&safe_strto32_base);
+}
+TEST(stringtest, safe_strto64_random) {
+  test_random_integer_parse_base<int64_t>(&safe_strto64_base);
+}
+TEST(stringtest, safe_strtou32_random) {
+  test_random_integer_parse_base<uint32_t>(&safe_strtou32_base);
+}
+TEST(stringtest, safe_strtou64_random) {
+  test_random_integer_parse_base<uint64_t>(&safe_strtou64_base);
+}
+
+TEST(stringtest, safe_strtou32_base) {
+  for (int i = 0; strtouint32_test_cases()[i].str != nullptr; ++i) {
+    const auto& e = strtouint32_test_cases()[i];
+    uint32_t value;
+    EXPECT_EQ(e.expect_ok, safe_strtou32_base(e.str, &value, e.base))
+        << "str=\"" << e.str << "\" base=" << e.base;
+    if (e.expect_ok) {
+      EXPECT_EQ(e.expected, value) << "i=" << i << " str=\"" << e.str
+                                   << "\" base=" << e.base;
+    }
+  }
+}
+
+TEST(stringtest, safe_strtou32_base_length_delimited) {
+  for (int i = 0; strtouint32_test_cases()[i].str != nullptr; ++i) {
+    const auto& e = strtouint32_test_cases()[i];
+    std::string tmp(e.str);
+    tmp.append("12");  // Adds garbage at the end.
+
+    uint32_t value;
+    EXPECT_EQ(e.expect_ok,
+              safe_strtou32_base(absl::string_view(tmp.data(), strlen(e.str)),
+                                 &value, e.base))
+        << "str=\"" << e.str << "\" base=" << e.base;
+    if (e.expect_ok) {
+      EXPECT_EQ(e.expected, value) << "i=" << i << " str=" << e.str
+                                   << " base=" << e.base;
+    }
+  }
+}
+
+TEST(stringtest, safe_strtou64_base) {
+  for (int i = 0; strtouint64_test_cases()[i].str != nullptr; ++i) {
+    const auto& e = strtouint64_test_cases()[i];
+    uint64_t value;
+    EXPECT_EQ(e.expect_ok, safe_strtou64_base(e.str, &value, e.base))
+        << "str=\"" << e.str << "\" base=" << e.base;
+    if (e.expect_ok) {
+      EXPECT_EQ(e.expected, value) << "str=" << e.str << " base=" << e.base;
+    }
+  }
+}
+
+TEST(stringtest, safe_strtou64_base_length_delimited) {
+  for (int i = 0; strtouint64_test_cases()[i].str != nullptr; ++i) {
+    const auto& e = strtouint64_test_cases()[i];
+    std::string tmp(e.str);
+    tmp.append("12");  // Adds garbage at the end.
+
+    uint64_t value;
+    EXPECT_EQ(e.expect_ok,
+              safe_strtou64_base(absl::string_view(tmp.data(), strlen(e.str)),
+                                 &value, e.base))
+        << "str=\"" << e.str << "\" base=" << e.base;
+    if (e.expect_ok) {
+      EXPECT_EQ(e.expected, value) << "str=\"" << e.str << "\" base=" << e.base;
+    }
+  }
+}
+
+// feenableexcept() and fedisableexcept() are missing on macOS, MSVC,
+// and WebAssembly.
+#if defined(_MSC_VER) || defined(__APPLE__) || defined(__EMSCRIPTEN__)
+#define ABSL_MISSING_FEENABLEEXCEPT 1
+#define ABSL_MISSING_FEDISABLEEXCEPT 1
+#endif
+
+class SimpleDtoaTest : public testing::Test {
+ protected:
+  void SetUp() override {
+    // Store the current floating point env & clear away any pending exceptions.
+    feholdexcept(&fp_env_);
+#ifndef ABSL_MISSING_FEENABLEEXCEPT
+    // Turn on floating point exceptions.
+    feenableexcept(FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW);
+#endif
+  }
+
+  void TearDown() override {
+    // Restore the floating point environment to the original state.
+    // In theory fedisableexcept is unnecessary; fesetenv will also do it.
+    // In practice, our toolchains have subtle bugs.
+#ifndef ABSL_MISSING_FEDISABLEEXCEPT
+    fedisableexcept(FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW);
+#endif
+    fesetenv(&fp_env_);
+  }
+
+  std::string ToNineDigits(double value) {
+    char buffer[16];  // more than enough for %.9g
+    snprintf(buffer, sizeof(buffer), "%.9g", value);
+    return buffer;
+  }
+
+  fenv_t fp_env_;
+};
+
+// Run the given runnable functor for "cases" test cases, chosen over the
+// available range of float.  pi and e and 1/e are seeded, and then all
+// available integer powers of 2 and 10 are multiplied against them.  In
+// addition to trying all those values, we try the next higher and next lower
+// float, and then we add additional test cases evenly distributed between them.
+// Each test case is passed to runnable as both a positive and negative value.
+template <typename R>
+void ExhaustiveFloat(uint32_t cases, R&& runnable) {
+  runnable(0.0f);
+  runnable(-0.0f);
+  if (cases >= 2e9) {  // more than 2 billion?  Might as well run them all.
+    for (float f = 0; f < std::numeric_limits<float>::max(); ) {
+      f = nextafterf(f, std::numeric_limits<float>::max());
+      runnable(-f);
+      runnable(f);
+    }
+    return;
+  }
+  std::set<float> floats = {3.4028234e38f};
+  for (float f : {1.0, 3.14159265, 2.718281828, 1 / 2.718281828}) {
+    for (float testf = f; testf != 0; testf *= 0.1f) floats.insert(testf);
+    for (float testf = f; testf != 0; testf *= 0.5f) floats.insert(testf);
+    for (float testf = f; testf < 3e38f / 2; testf *= 2.0f)
+      floats.insert(testf);
+    for (float testf = f; testf < 3e38f / 10; testf *= 10) floats.insert(testf);
+  }
+
+  float last = *floats.begin();
+
+  runnable(last);
+  runnable(-last);
+  int iters_per_float = cases / floats.size();
+  if (iters_per_float == 0) iters_per_float = 1;
+  for (float f : floats) {
+    if (f == last) continue;
+    float testf = std::nextafter(last, std::numeric_limits<float>::max());
+    runnable(testf);
+    runnable(-testf);
+    last = testf;
+    if (f == last) continue;
+    double step = (double{f} - last) / iters_per_float;
+    for (double d = last + step; d < f; d += step) {
+      testf = d;
+      if (testf != last) {
+        runnable(testf);
+        runnable(-testf);
+        last = testf;
+      }
+    }
+    testf = std::nextafter(f, 0.0f);
+    if (testf > last) {
+      runnable(testf);
+      runnable(-testf);
+      last = testf;
+    }
+    if (f != last) {
+      runnable(f);
+      runnable(-f);
+      last = f;
+    }
+  }
+}
+
+TEST_F(SimpleDtoaTest, ExhaustiveDoubleToSixDigits) {
+  uint64_t test_count = 0;
+  std::vector<double> mismatches;
+  auto checker = [&](double d) {
+    if (d != d) return;  // rule out NaNs
+    ++test_count;
+    char sixdigitsbuf[kSixDigitsToBufferSize] = {0};
+    SixDigitsToBuffer(d, sixdigitsbuf);
+    char snprintfbuf[kSixDigitsToBufferSize] = {0};
+    snprintf(snprintfbuf, kSixDigitsToBufferSize, "%g", d);
+    if (strcmp(sixdigitsbuf, snprintfbuf) != 0) {
+      mismatches.push_back(d);
+      if (mismatches.size() < 10) {
+        ABSL_RAW_LOG(ERROR, "%s",
+                     absl::StrCat("Six-digit failure with double.  ", "d=", d,
+                                  "=", d, " sixdigits=", sixdigitsbuf,
+                                  " printf(%g)=", snprintfbuf)
+                         .c_str());
+      }
+    }
+  };
+  // Some quick sanity checks...
+  checker(5e-324);
+  checker(1e-308);
+  checker(1.0);
+  checker(1.000005);
+  checker(1.7976931348623157e308);
+  checker(0.00390625);
+#ifndef _MSC_VER
+  // on MSVC, snprintf() rounds it to 0.00195313. SixDigitsToBuffer() rounds it
+  // to 0.00195312 (round half to even).
+  checker(0.001953125);
+#endif
+  checker(0.005859375);
+  // Some cases where the rounding is very very close
+  checker(1.089095e-15);
+  checker(3.274195e-55);
+  checker(6.534355e-146);
+  checker(2.920845e+234);
+
+  if (mismatches.empty()) {
+    test_count = 0;
+    ExhaustiveFloat(kFloatNumCases, checker);
+
+    test_count = 0;
+    std::vector<int> digit_testcases{
+        100000, 100001, 100002, 100005, 100010, 100020, 100050, 100100,  // misc
+        195312, 195313,  // 1.953125 is a case where we round down, just barely.
+        200000, 500000, 800000,  // misc mid-range cases
+        585937, 585938,  // 5.859375 is a case where we round up, just barely.
+        900000, 990000, 999000, 999900, 999990, 999996, 999997, 999998, 999999};
+    if (kFloatNumCases >= 1e9) {
+      // If at least 1 billion test cases were requested, user wants an
+      // exhaustive test. So let's test all mantissas, too.
+      constexpr int min_mantissa = 100000, max_mantissa = 999999;
+      digit_testcases.resize(max_mantissa - min_mantissa + 1);
+      std::iota(digit_testcases.begin(), digit_testcases.end(), min_mantissa);
+    }
+
+    for (int exponent = -324; exponent <= 308; ++exponent) {
+      double powten = absl::strings_internal::Pow10(exponent);
+      if (powten == 0) powten = 5e-324;
+      if (kFloatNumCases >= 1e9) {
+        // The exhaustive test takes a very long time, so log progress.
+        char buf[kSixDigitsToBufferSize];
+        ABSL_RAW_LOG(
+            INFO, "%s",
+            absl::StrCat("Exp ", exponent, " powten=", powten, "(", powten,
+                         ") (",
+                         std::string(buf, SixDigitsToBuffer(powten, buf)), ")")
+                .c_str());
+      }
+      for (int digits : digit_testcases) {
+        if (exponent == 308 && digits >= 179769) break;  // don't overflow!
+        double digiform = (digits + 0.5) * 0.00001;
+        double testval = digiform * powten;
+        double pretestval = nextafter(testval, 0);
+        double posttestval = nextafter(testval, 1.7976931348623157e308);
+        checker(testval);
+        checker(pretestval);
+        checker(posttestval);
+      }
+    }
+  } else {
+    EXPECT_EQ(mismatches.size(), 0);
+    for (size_t i = 0; i < mismatches.size(); ++i) {
+      if (i > 100) i = mismatches.size() - 1;
+      double d = mismatches[i];
+      char sixdigitsbuf[kSixDigitsToBufferSize] = {0};
+      SixDigitsToBuffer(d, sixdigitsbuf);
+      char snprintfbuf[kSixDigitsToBufferSize] = {0};
+      snprintf(snprintfbuf, kSixDigitsToBufferSize, "%g", d);
+      double before = nextafter(d, 0.0);
+      double after = nextafter(d, 1.7976931348623157e308);
+      char b1[32], b2[kSixDigitsToBufferSize];
+      ABSL_RAW_LOG(
+          ERROR, "%s",
+          absl::StrCat(
+              "Mismatch #", i, "  d=", d, " (", ToNineDigits(d), ")",
+              " sixdigits='", sixdigitsbuf, "'", " snprintf='", snprintfbuf,
+              "'", " Before.=", PerfectDtoa(before), " ",
+              (SixDigitsToBuffer(before, b2), b2),
+              " vs snprintf=", (snprintf(b1, sizeof(b1), "%g", before), b1),
+              " Perfect=", PerfectDtoa(d), " ", (SixDigitsToBuffer(d, b2), b2),
+              " vs snprintf=", (snprintf(b1, sizeof(b1), "%g", d), b1),
+              " After.=.", PerfectDtoa(after), " ",
+              (SixDigitsToBuffer(after, b2), b2),
+              " vs snprintf=", (snprintf(b1, sizeof(b1), "%g", after), b1))
+              .c_str());
+    }
+  }
+}
+
+TEST(StrToInt32, Partial) {
+  struct Int32TestLine {
+    std::string input;
+    bool status;
+    int32_t value;
+  };
+  const int32_t int32_min = std::numeric_limits<int32_t>::min();
+  const int32_t int32_max = std::numeric_limits<int32_t>::max();
+  Int32TestLine int32_test_line[] = {
+      {"", false, 0},
+      {" ", false, 0},
+      {"-", false, 0},
+      {"123@@@", false, 123},
+      {absl::StrCat(int32_min, int32_max), false, int32_min},
+      {absl::StrCat(int32_max, int32_max), false, int32_max},
+  };
+
+  for (const Int32TestLine& test_line : int32_test_line) {
+    int32_t value = -2;
+    bool status = safe_strto32_base(test_line.input, &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+    value = -2;
+    status = safe_strto32_base(test_line.input, &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+    value = -2;
+    status = safe_strto32_base(absl::string_view(test_line.input), &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+  }
+}
+
+TEST(StrToUint32, Partial) {
+  struct Uint32TestLine {
+    std::string input;
+    bool status;
+    uint32_t value;
+  };
+  const uint32_t uint32_max = std::numeric_limits<uint32_t>::max();
+  Uint32TestLine uint32_test_line[] = {
+      {"", false, 0},
+      {" ", false, 0},
+      {"-", false, 0},
+      {"123@@@", false, 123},
+      {absl::StrCat(uint32_max, uint32_max), false, uint32_max},
+  };
+
+  for (const Uint32TestLine& test_line : uint32_test_line) {
+    uint32_t value = 2;
+    bool status = safe_strtou32_base(test_line.input, &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+    value = 2;
+    status = safe_strtou32_base(test_line.input, &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+    value = 2;
+    status = safe_strtou32_base(absl::string_view(test_line.input), &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+  }
+}
+
+TEST(StrToInt64, Partial) {
+  struct Int64TestLine {
+    std::string input;
+    bool status;
+    int64_t value;
+  };
+  const int64_t int64_min = std::numeric_limits<int64_t>::min();
+  const int64_t int64_max = std::numeric_limits<int64_t>::max();
+  Int64TestLine int64_test_line[] = {
+      {"", false, 0},
+      {" ", false, 0},
+      {"-", false, 0},
+      {"123@@@", false, 123},
+      {absl::StrCat(int64_min, int64_max), false, int64_min},
+      {absl::StrCat(int64_max, int64_max), false, int64_max},
+  };
+
+  for (const Int64TestLine& test_line : int64_test_line) {
+    int64_t value = -2;
+    bool status = safe_strto64_base(test_line.input, &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+    value = -2;
+    status = safe_strto64_base(test_line.input, &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+    value = -2;
+    status = safe_strto64_base(absl::string_view(test_line.input), &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+  }
+}
+
+TEST(StrToUint64, Partial) {
+  struct Uint64TestLine {
+    std::string input;
+    bool status;
+    uint64_t value;
+  };
+  const uint64_t uint64_max = std::numeric_limits<uint64_t>::max();
+  Uint64TestLine uint64_test_line[] = {
+      {"", false, 0},
+      {" ", false, 0},
+      {"-", false, 0},
+      {"123@@@", false, 123},
+      {absl::StrCat(uint64_max, uint64_max), false, uint64_max},
+  };
+
+  for (const Uint64TestLine& test_line : uint64_test_line) {
+    uint64_t value = 2;
+    bool status = safe_strtou64_base(test_line.input, &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+    value = 2;
+    status = safe_strtou64_base(test_line.input, &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+    value = 2;
+    status = safe_strtou64_base(absl::string_view(test_line.input), &value, 10);
+    EXPECT_EQ(test_line.status, status) << test_line.input;
+    EXPECT_EQ(test_line.value, value) << test_line.input;
+  }
+}
+
+TEST(StrToInt32Base, PrefixOnly) {
+  struct Int32TestLine {
+    std::string input;
+    bool status;
+    int32_t value;
+  };
+  Int32TestLine int32_test_line[] = {
+    { "", false, 0 },
+    { "-", false, 0 },
+    { "-0", true, 0 },
+    { "0", true, 0 },
+    { "0x", false, 0 },
+    { "-0x", false, 0 },
+  };
+  const int base_array[] = { 0, 2, 8, 10, 16 };
+
+  for (const Int32TestLine& line : int32_test_line) {
+    for (const int base : base_array) {
+      int32_t value = 2;
+      bool status = safe_strto32_base(line.input.c_str(), &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+      value = 2;
+      status = safe_strto32_base(line.input, &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+      value = 2;
+      status = safe_strto32_base(absl::string_view(line.input), &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+    }
+  }
+}
+
+TEST(StrToUint32Base, PrefixOnly) {
+  struct Uint32TestLine {
+    std::string input;
+    bool status;
+    uint32_t value;
+  };
+  Uint32TestLine uint32_test_line[] = {
+    { "", false, 0 },
+    { "0", true, 0 },
+    { "0x", false, 0 },
+  };
+  const int base_array[] = { 0, 2, 8, 10, 16 };
+
+  for (const Uint32TestLine& line : uint32_test_line) {
+    for (const int base : base_array) {
+      uint32_t value = 2;
+      bool status = safe_strtou32_base(line.input.c_str(), &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+      value = 2;
+      status = safe_strtou32_base(line.input, &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+      value = 2;
+      status = safe_strtou32_base(absl::string_view(line.input), &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+    }
+  }
+}
+
+TEST(StrToInt64Base, PrefixOnly) {
+  struct Int64TestLine {
+    std::string input;
+    bool status;
+    int64_t value;
+  };
+  Int64TestLine int64_test_line[] = {
+    { "", false, 0 },
+    { "-", false, 0 },
+    { "-0", true, 0 },
+    { "0", true, 0 },
+    { "0x", false, 0 },
+    { "-0x", false, 0 },
+  };
+  const int base_array[] = { 0, 2, 8, 10, 16 };
+
+  for (const Int64TestLine& line : int64_test_line) {
+    for (const int base : base_array) {
+      int64_t value = 2;
+      bool status = safe_strto64_base(line.input.c_str(), &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+      value = 2;
+      status = safe_strto64_base(line.input, &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+      value = 2;
+      status = safe_strto64_base(absl::string_view(line.input), &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+    }
+  }
+}
+
+TEST(StrToUint64Base, PrefixOnly) {
+  struct Uint64TestLine {
+    std::string input;
+    bool status;
+    uint64_t value;
+  };
+  Uint64TestLine uint64_test_line[] = {
+    { "", false, 0 },
+    { "0", true, 0 },
+    { "0x", false, 0 },
+  };
+  const int base_array[] = { 0, 2, 8, 10, 16 };
+
+  for (const Uint64TestLine& line : uint64_test_line) {
+    for (const int base : base_array) {
+      uint64_t value = 2;
+      bool status = safe_strtou64_base(line.input.c_str(), &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+      value = 2;
+      status = safe_strtou64_base(line.input, &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+      value = 2;
+      status = safe_strtou64_base(absl::string_view(line.input), &value, base);
+      EXPECT_EQ(line.status, status) << line.input << " " << base;
+      EXPECT_EQ(line.value, value) << line.input << " " << base;
+    }
+  }
+}
+
+}  // namespace
diff --git a/absl/strings/str_cat.cc b/absl/strings/str_cat.cc
new file mode 100644
index 0000000..9961944
--- /dev/null
+++ b/absl/strings/str_cat.cc
@@ -0,0 +1,245 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/str_cat.h"
+
+#include <assert.h>
+#include <algorithm>
+#include <cstdint>
+#include <cstring>
+
+#include "absl/strings/ascii.h"
+#include "absl/strings/internal/resize_uninitialized.h"
+
+namespace absl {
+
+AlphaNum::AlphaNum(Hex hex) {
+  char* const end = &digits_[numbers_internal::kFastToBufferSize];
+  char* writer = end;
+  uint64_t value = hex.value;
+  static const char hexdigits[] = "0123456789abcdef";
+  do {
+    *--writer = hexdigits[value & 0xF];
+    value >>= 4;
+  } while (value != 0);
+
+  char* beg;
+  if (end - writer < hex.width) {
+    beg = end - hex.width;
+    std::fill_n(beg, writer - beg, hex.fill);
+  } else {
+    beg = writer;
+  }
+
+  piece_ = absl::string_view(beg, end - beg);
+}
+
+AlphaNum::AlphaNum(Dec dec) {
+  assert(dec.width <= numbers_internal::kFastToBufferSize);
+  char* const end = &digits_[numbers_internal::kFastToBufferSize];
+  char* const minfill = end - dec.width;
+  char* writer = end;
+  uint64_t value = dec.value;
+  bool neg = dec.neg;
+  while (value > 9) {
+    *--writer = '0' + (value % 10);
+    value /= 10;
+  }
+  *--writer = '0' + value;
+  if (neg) *--writer = '-';
+
+  ptrdiff_t fillers = writer - minfill;
+  if (fillers > 0) {
+    // Tricky: if the fill character is ' ', then it's <fill><+/-><digits>
+    // But...: if the fill character is '0', then it's <+/-><fill><digits>
+    bool add_sign_again = false;
+    if (neg && dec.fill == '0') {  // If filling with '0',
+      ++writer;                    // ignore the sign we just added
+      add_sign_again = true;       // and re-add the sign later.
+    }
+    writer -= fillers;
+    std::fill_n(writer, fillers, dec.fill);
+    if (add_sign_again) *--writer = '-';
+  }
+
+  piece_ = absl::string_view(writer, end - writer);
+}
+
+// ----------------------------------------------------------------------
+// StrCat()
+//    This merges the given strings or integers, with no delimiter. This
+//    is designed to be the fastest possible way to construct a string out
+//    of a mix of raw C strings, string_views, strings, and integer values.
+// ----------------------------------------------------------------------
+
+// Append is merely a version of memcpy that returns the address of the byte
+// after the area just overwritten.
+static char* Append(char* out, const AlphaNum& x) {
+  // memcpy is allowed to overwrite arbitrary memory, so doing this after the
+  // call would force an extra fetch of x.size().
+  char* after = out + x.size();
+  if (x.size() != 0) {
+    memcpy(out, x.data(), x.size());
+  }
+  return after;
+}
+
+std::string StrCat(const AlphaNum& a, const AlphaNum& b) {
+  std::string result;
+  absl::strings_internal::STLStringResizeUninitialized(&result,
+                                                       a.size() + b.size());
+  char* const begin = &result[0];
+  char* out = begin;
+  out = Append(out, a);
+  out = Append(out, b);
+  assert(out == begin + result.size());
+  return result;
+}
+
+std::string StrCat(const AlphaNum& a, const AlphaNum& b, const AlphaNum& c) {
+  std::string result;
+  strings_internal::STLStringResizeUninitialized(
+      &result, a.size() + b.size() + c.size());
+  char* const begin = &result[0];
+  char* out = begin;
+  out = Append(out, a);
+  out = Append(out, b);
+  out = Append(out, c);
+  assert(out == begin + result.size());
+  return result;
+}
+
+std::string StrCat(const AlphaNum& a, const AlphaNum& b, const AlphaNum& c,
+                   const AlphaNum& d) {
+  std::string result;
+  strings_internal::STLStringResizeUninitialized(
+      &result, a.size() + b.size() + c.size() + d.size());
+  char* const begin = &result[0];
+  char* out = begin;
+  out = Append(out, a);
+  out = Append(out, b);
+  out = Append(out, c);
+  out = Append(out, d);
+  assert(out == begin + result.size());
+  return result;
+}
+
+namespace strings_internal {
+
+// Do not call directly - these are not part of the public API.
+std::string CatPieces(std::initializer_list<absl::string_view> pieces) {
+  std::string result;
+  size_t total_size = 0;
+  for (const absl::string_view piece : pieces) total_size += piece.size();
+  strings_internal::STLStringResizeUninitialized(&result, total_size);
+
+  char* const begin = &result[0];
+  char* out = begin;
+  for (const absl::string_view piece : pieces) {
+    const size_t this_size = piece.size();
+    if (this_size != 0) {
+      memcpy(out, piece.data(), this_size);
+      out += this_size;
+    }
+  }
+  assert(out == begin + result.size());
+  return result;
+}
+
+// It's possible to call StrAppend with an absl::string_view that is itself a
+// fragment of the string we're appending to.  However the results of this are
+// random. Therefore, check for this in debug mode.  Use unsigned math so we
+// only have to do one comparison. Note, there's an exception case: appending an
+// empty string is always allowed.
+#define ASSERT_NO_OVERLAP(dest, src) \
+  assert(((src).size() == 0) ||      \
+         (uintptr_t((src).data() - (dest).data()) > uintptr_t((dest).size())))
+
+void AppendPieces(std::string* dest,
+                  std::initializer_list<absl::string_view> pieces) {
+  size_t old_size = dest->size();
+  size_t total_size = old_size;
+  for (const absl::string_view piece : pieces) {
+    ASSERT_NO_OVERLAP(*dest, piece);
+    total_size += piece.size();
+  }
+  strings_internal::STLStringResizeUninitialized(dest, total_size);
+
+  char* const begin = &(*dest)[0];
+  char* out = begin + old_size;
+  for (const absl::string_view piece : pieces) {
+    const size_t this_size = piece.size();
+    if (this_size != 0) {
+      memcpy(out, piece.data(), this_size);
+      out += this_size;
+    }
+  }
+  assert(out == begin + dest->size());
+}
+
+}  // namespace strings_internal
+
+void StrAppend(std::string* dest, const AlphaNum& a) {
+  ASSERT_NO_OVERLAP(*dest, a);
+  dest->append(a.data(), a.size());
+}
+
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b) {
+  ASSERT_NO_OVERLAP(*dest, a);
+  ASSERT_NO_OVERLAP(*dest, b);
+  std::string::size_type old_size = dest->size();
+  strings_internal::STLStringResizeUninitialized(
+      dest, old_size + a.size() + b.size());
+  char* const begin = &(*dest)[0];
+  char* out = begin + old_size;
+  out = Append(out, a);
+  out = Append(out, b);
+  assert(out == begin + dest->size());
+}
+
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
+               const AlphaNum& c) {
+  ASSERT_NO_OVERLAP(*dest, a);
+  ASSERT_NO_OVERLAP(*dest, b);
+  ASSERT_NO_OVERLAP(*dest, c);
+  std::string::size_type old_size = dest->size();
+  strings_internal::STLStringResizeUninitialized(
+      dest, old_size + a.size() + b.size() + c.size());
+  char* const begin = &(*dest)[0];
+  char* out = begin + old_size;
+  out = Append(out, a);
+  out = Append(out, b);
+  out = Append(out, c);
+  assert(out == begin + dest->size());
+}
+
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
+               const AlphaNum& c, const AlphaNum& d) {
+  ASSERT_NO_OVERLAP(*dest, a);
+  ASSERT_NO_OVERLAP(*dest, b);
+  ASSERT_NO_OVERLAP(*dest, c);
+  ASSERT_NO_OVERLAP(*dest, d);
+  std::string::size_type old_size = dest->size();
+  strings_internal::STLStringResizeUninitialized(
+      dest, old_size + a.size() + b.size() + c.size() + d.size());
+  char* const begin = &(*dest)[0];
+  char* out = begin + old_size;
+  out = Append(out, a);
+  out = Append(out, b);
+  out = Append(out, c);
+  out = Append(out, d);
+  assert(out == begin + dest->size());
+}
+
+}  // namespace absl
diff --git a/absl/strings/str_cat.h b/absl/strings/str_cat.h
new file mode 100644
index 0000000..a99aac0
--- /dev/null
+++ b/absl/strings/str_cat.h
@@ -0,0 +1,405 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: str_cat.h
+// -----------------------------------------------------------------------------
+//
+// This package contains functions for efficiently concatenating and appending
+// strings: `StrCat()` and `StrAppend()`. Most of the work within these routines
+// is actually handled through use of a special AlphaNum type, which was
+// designed to be used as a parameter type that efficiently manages conversion
+// to strings and avoids copies in the above operations.
+//
+// Any routine accepting either a string or a number may accept `AlphaNum`.
+// The basic idea is that by accepting a `const AlphaNum &` as an argument
+// to your function, your callers will automagically convert bools, integers,
+// and floating point values to strings for you.
+//
+// NOTE: Use of `AlphaNum` outside of the //absl/strings package is unsupported
+// except for the specific case of function parameters of type `AlphaNum` or
+// `const AlphaNum &`. In particular, instantiating `AlphaNum` directly as a
+// stack variable is not supported.
+//
+// Conversion from 8-bit values is not accepted because, if it were, then an
+// attempt to pass ':' instead of ":" might result in a 58 ending up in your
+// result.
+//
+// Bools convert to "0" or "1". Pointers to types other than `char *` are not
+// valid inputs. No output is generated for null `char *` pointers.
+//
+// Floating point numbers are formatted with six-digit precision, which is
+// the default for "std::cout <<" or printf "%g" (the same as "%.6g").
+//
+// You can convert to hexadecimal output rather than decimal output using the
+// `Hex` type contained here. To do so, pass `Hex(my_int)` as a parameter to
+// `StrCat()` or `StrAppend()`. You may specify a minimum hex field width using
+// a `PadSpec` enum.
+//
+// -----------------------------------------------------------------------------
+
+#ifndef ABSL_STRINGS_STR_CAT_H_
+#define ABSL_STRINGS_STR_CAT_H_
+
+#include <array>
+#include <cstdint>
+#include <string>
+#include <type_traits>
+#include <vector>
+
+#include "absl/base/port.h"
+#include "absl/strings/numbers.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+
+namespace strings_internal {
+// AlphaNumBuffer allows a way to pass a string to StrCat without having to do
+// memory allocation.  It is simply a pair of a fixed-size character array, and
+// a size.  Please don't use outside of absl, yet.
+template <size_t max_size>
+struct AlphaNumBuffer {
+  std::array<char, max_size> data;
+  size_t size;
+};
+
+}  // namespace strings_internal
+
+// Enum that specifies the number of significant digits to return in a `Hex` or
+// `Dec` conversion and fill character to use. A `kZeroPad2` value, for example,
+// would produce hexadecimal strings such as "0a","0f" and a 'kSpacePad5' value
+// would produce hexadecimal strings such as "    a","    f".
+enum PadSpec : uint8_t {
+  kNoPad = 1,
+  kZeroPad2,
+  kZeroPad3,
+  kZeroPad4,
+  kZeroPad5,
+  kZeroPad6,
+  kZeroPad7,
+  kZeroPad8,
+  kZeroPad9,
+  kZeroPad10,
+  kZeroPad11,
+  kZeroPad12,
+  kZeroPad13,
+  kZeroPad14,
+  kZeroPad15,
+  kZeroPad16,
+  kZeroPad17,
+  kZeroPad18,
+  kZeroPad19,
+  kZeroPad20,
+
+  kSpacePad2 = kZeroPad2 + 64,
+  kSpacePad3,
+  kSpacePad4,
+  kSpacePad5,
+  kSpacePad6,
+  kSpacePad7,
+  kSpacePad8,
+  kSpacePad9,
+  kSpacePad10,
+  kSpacePad11,
+  kSpacePad12,
+  kSpacePad13,
+  kSpacePad14,
+  kSpacePad15,
+  kSpacePad16,
+  kSpacePad17,
+  kSpacePad18,
+  kSpacePad19,
+  kSpacePad20,
+};
+
+// -----------------------------------------------------------------------------
+// Hex
+// -----------------------------------------------------------------------------
+//
+// `Hex` stores a set of hexadecimal string conversion parameters for use
+// within `AlphaNum` string conversions.
+struct Hex {
+  uint64_t value;
+  uint8_t width;
+  char fill;
+
+  template <typename Int>
+  explicit Hex(
+      Int v, PadSpec spec = absl::kNoPad,
+      typename std::enable_if<sizeof(Int) == 1 &&
+                              !std::is_pointer<Int>::value>::type* = nullptr)
+      : Hex(spec, static_cast<uint8_t>(v)) {}
+  template <typename Int>
+  explicit Hex(
+      Int v, PadSpec spec = absl::kNoPad,
+      typename std::enable_if<sizeof(Int) == 2 &&
+                              !std::is_pointer<Int>::value>::type* = nullptr)
+      : Hex(spec, static_cast<uint16_t>(v)) {}
+  template <typename Int>
+  explicit Hex(
+      Int v, PadSpec spec = absl::kNoPad,
+      typename std::enable_if<sizeof(Int) == 4 &&
+                              !std::is_pointer<Int>::value>::type* = nullptr)
+      : Hex(spec, static_cast<uint32_t>(v)) {}
+  template <typename Int>
+  explicit Hex(
+      Int v, PadSpec spec = absl::kNoPad,
+      typename std::enable_if<sizeof(Int) == 8 &&
+                              !std::is_pointer<Int>::value>::type* = nullptr)
+      : Hex(spec, static_cast<uint64_t>(v)) {}
+  template <typename Pointee>
+  explicit Hex(Pointee* v, PadSpec spec = absl::kNoPad)
+      : Hex(spec, reinterpret_cast<uintptr_t>(v)) {}
+
+ private:
+  Hex(PadSpec spec, uint64_t v)
+      : value(v),
+        width(spec == absl::kNoPad
+                  ? 1
+                  : spec >= absl::kSpacePad2 ? spec - absl::kSpacePad2 + 2
+                                             : spec - absl::kZeroPad2 + 2),
+        fill(spec >= absl::kSpacePad2 ? ' ' : '0') {}
+};
+
+// -----------------------------------------------------------------------------
+// Dec
+// -----------------------------------------------------------------------------
+//
+// `Dec` stores a set of decimal string conversion parameters for use
+// within `AlphaNum` string conversions.  Dec is slower than the default
+// integer conversion, so use it only if you need padding.
+struct Dec {
+  uint64_t value;
+  uint8_t width;
+  char fill;
+  bool neg;
+
+  template <typename Int>
+  explicit Dec(Int v, PadSpec spec = absl::kNoPad,
+               typename std::enable_if<(sizeof(Int) <= 8)>::type* = nullptr)
+      : value(v >= 0 ? static_cast<uint64_t>(v)
+                     : uint64_t{0} - static_cast<uint64_t>(v)),
+        width(spec == absl::kNoPad
+                  ? 1
+                  : spec >= absl::kSpacePad2 ? spec - absl::kSpacePad2 + 2
+                                             : spec - absl::kZeroPad2 + 2),
+        fill(spec >= absl::kSpacePad2 ? ' ' : '0'),
+        neg(v < 0) {}
+};
+
+// -----------------------------------------------------------------------------
+// AlphaNum
+// -----------------------------------------------------------------------------
+//
+// The `AlphaNum` class acts as the main parameter type for `StrCat()` and
+// `StrAppend()`, providing efficient conversion of numeric, boolean, and
+// hexadecimal values (through the `Hex` type) into strings.
+
+class AlphaNum {
+ public:
+  // No bool ctor -- bools convert to an integral type.
+  // A bool ctor would also convert incoming pointers (bletch).
+
+  AlphaNum(int x)  // NOLINT(runtime/explicit)
+      : piece_(digits_,
+               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+  AlphaNum(unsigned int x)  // NOLINT(runtime/explicit)
+      : piece_(digits_,
+               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+  AlphaNum(long x)  // NOLINT(*)
+      : piece_(digits_,
+               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+  AlphaNum(unsigned long x)  // NOLINT(*)
+      : piece_(digits_,
+               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+  AlphaNum(long long x)  // NOLINT(*)
+      : piece_(digits_,
+               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+  AlphaNum(unsigned long long x)  // NOLINT(*)
+      : piece_(digits_,
+               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+
+  AlphaNum(float f)  // NOLINT(runtime/explicit)
+      : piece_(digits_, numbers_internal::SixDigitsToBuffer(f, digits_)) {}
+  AlphaNum(double f)  // NOLINT(runtime/explicit)
+      : piece_(digits_, numbers_internal::SixDigitsToBuffer(f, digits_)) {}
+
+  AlphaNum(Hex hex);  // NOLINT(runtime/explicit)
+  AlphaNum(Dec dec);  // NOLINT(runtime/explicit)
+
+  template <size_t size>
+  AlphaNum(  // NOLINT(runtime/explicit)
+      const strings_internal::AlphaNumBuffer<size>& buf)
+      : piece_(&buf.data[0], buf.size) {}
+
+  AlphaNum(const char* c_str) : piece_(c_str) {}  // NOLINT(runtime/explicit)
+  AlphaNum(absl::string_view pc) : piece_(pc) {}  // NOLINT(runtime/explicit)
+
+  template <typename Allocator>
+  AlphaNum(  // NOLINT(runtime/explicit)
+      const std::basic_string<char, std::char_traits<char>, Allocator>& str)
+      : piece_(str) {}
+
+  // Use std::string literals ":" instead of character literals ':'.
+  AlphaNum(char c) = delete;  // NOLINT(runtime/explicit)
+
+  AlphaNum(const AlphaNum&) = delete;
+  AlphaNum& operator=(const AlphaNum&) = delete;
+
+  absl::string_view::size_type size() const { return piece_.size(); }
+  const char* data() const { return piece_.data(); }
+  absl::string_view Piece() const { return piece_; }
+
+  // Normal enums are already handled by the integer formatters.
+  // This overload matches only scoped enums.
+  template <typename T,
+            typename = typename std::enable_if<
+                std::is_enum<T>{} && !std::is_convertible<T, int>{}>::type>
+  AlphaNum(T e)  // NOLINT(runtime/explicit)
+      : AlphaNum(static_cast<typename std::underlying_type<T>::type>(e)) {}
+
+  // vector<bool>::reference and const_reference require special help to
+  // convert to `AlphaNum` because it requires two user defined conversions.
+  template <
+      typename T,
+      typename std::enable_if<
+          std::is_class<T>::value &&
+          (std::is_same<T, std::vector<bool>::reference>::value ||
+           std::is_same<T, std::vector<bool>::const_reference>::value)>::type* =
+          nullptr>
+  AlphaNum(T e) : AlphaNum(static_cast<bool>(e)) {}  // NOLINT(runtime/explicit)
+
+ private:
+  absl::string_view piece_;
+  char digits_[numbers_internal::kFastToBufferSize];
+};
+
+// -----------------------------------------------------------------------------
+// StrCat()
+// -----------------------------------------------------------------------------
+//
+// Merges given strings or numbers, using no delimiter(s).
+//
+// `StrCat()` is designed to be the fastest possible way to construct a string
+// out of a mix of raw C strings, string_views, strings, bool values,
+// and numeric values.
+//
+// Don't use `StrCat()` for user-visible strings. The localization process
+// works poorly on strings built up out of fragments.
+//
+// For clarity and performance, don't use `StrCat()` when appending to a
+// string. Use `StrAppend()` instead. In particular, avoid using any of these
+// (anti-)patterns:
+//
+//   str.append(StrCat(...))
+//   str += StrCat(...)
+//   str = StrCat(str, ...)
+//
+// The last case is the worst, with a potential to change a loop
+// from a linear time operation with O(1) dynamic allocations into a
+// quadratic time operation with O(n) dynamic allocations.
+//
+// See `StrAppend()` below for more information.
+
+namespace strings_internal {
+
+// Do not call directly - this is not part of the public API.
+std::string CatPieces(std::initializer_list<absl::string_view> pieces);
+void AppendPieces(std::string* dest,
+                  std::initializer_list<absl::string_view> pieces);
+
+}  // namespace strings_internal
+
+ABSL_MUST_USE_RESULT inline std::string StrCat() { return std::string(); }
+
+ABSL_MUST_USE_RESULT inline std::string StrCat(const AlphaNum& a) {
+  return std::string(a.data(), a.size());
+}
+
+ABSL_MUST_USE_RESULT std::string StrCat(const AlphaNum& a, const AlphaNum& b);
+ABSL_MUST_USE_RESULT std::string StrCat(const AlphaNum& a, const AlphaNum& b,
+                                        const AlphaNum& c);
+ABSL_MUST_USE_RESULT std::string StrCat(const AlphaNum& a, const AlphaNum& b,
+                                        const AlphaNum& c, const AlphaNum& d);
+
+// Support 5 or more arguments
+template <typename... AV>
+ABSL_MUST_USE_RESULT inline std::string StrCat(
+    const AlphaNum& a, const AlphaNum& b, const AlphaNum& c, const AlphaNum& d,
+    const AlphaNum& e, const AV&... args) {
+  return strings_internal::CatPieces(
+      {a.Piece(), b.Piece(), c.Piece(), d.Piece(), e.Piece(),
+       static_cast<const AlphaNum&>(args).Piece()...});
+}
+
+// -----------------------------------------------------------------------------
+// StrAppend()
+// -----------------------------------------------------------------------------
+//
+// Appends a string or set of strings to an existing string, in a similar
+// fashion to `StrCat()`.
+//
+// WARNING: `StrAppend(&str, a, b, c, ...)` requires that none of the
+// a, b, c, parameters be a reference into str. For speed, `StrAppend()` does
+// not try to check each of its input arguments to be sure that they are not
+// a subset of the string being appended to. That is, while this will work:
+//
+//   std::string s = "foo";
+//   s += s;
+//
+// This output is undefined:
+//
+//   std::string s = "foo";
+//   StrAppend(&s, s);
+//
+// This output is undefined as well, since `absl::string_view` does not own its
+// data:
+//
+//   std::string s = "foobar";
+//   absl::string_view p = s;
+//   StrAppend(&s, p);
+
+inline void StrAppend(std::string*) {}
+void StrAppend(std::string* dest, const AlphaNum& a);
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b);
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
+               const AlphaNum& c);
+void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
+               const AlphaNum& c, const AlphaNum& d);
+
+// Support 5 or more arguments
+template <typename... AV>
+inline void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
+                      const AlphaNum& c, const AlphaNum& d, const AlphaNum& e,
+                      const AV&... args) {
+  strings_internal::AppendPieces(
+      dest, {a.Piece(), b.Piece(), c.Piece(), d.Piece(), e.Piece(),
+             static_cast<const AlphaNum&>(args).Piece()...});
+}
+
+// Helper function for the future StrCat default floating-point format, %.6g
+// This is fast.
+inline strings_internal::AlphaNumBuffer<
+    numbers_internal::kSixDigitsToBufferSize>
+SixDigits(double d) {
+  strings_internal::AlphaNumBuffer<numbers_internal::kSixDigitsToBufferSize>
+      result;
+  result.size = numbers_internal::SixDigitsToBuffer(d, &result.data[0]);
+  return result;
+}
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_STR_CAT_H_
diff --git a/absl/strings/str_cat_benchmark.cc b/absl/strings/str_cat_benchmark.cc
new file mode 100644
index 0000000..14c63b3
--- /dev/null
+++ b/absl/strings/str_cat_benchmark.cc
@@ -0,0 +1,140 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/str_cat.h"
+
+#include <cstdint>
+#include <string>
+
+#include "benchmark/benchmark.h"
+#include "absl/strings/substitute.h"
+
+namespace {
+
+const char kStringOne[] = "Once Upon A Time, ";
+const char kStringTwo[] = "There was a std::string benchmark";
+
+// We want to include negative numbers in the benchmark, so this function
+// is used to count 0, 1, -1, 2, -2, 3, -3, ...
+inline int IncrementAlternatingSign(int i) {
+  return i > 0 ? -i : 1 - i;
+}
+
+void BM_Sum_By_StrCat(benchmark::State& state) {
+  int i = 0;
+  char foo[100];
+  for (auto _ : state) {
+    // NOLINTNEXTLINE(runtime/printf)
+    strcpy(foo, absl::StrCat(kStringOne, i, kStringTwo, i * 65536ULL).c_str());
+    int sum = 0;
+    for (char* f = &foo[0]; *f != 0; ++f) {
+      sum += *f;
+    }
+    benchmark::DoNotOptimize(sum);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_Sum_By_StrCat);
+
+void BM_StrCat_By_snprintf(benchmark::State& state) {
+  int i = 0;
+  char on_stack[1000];
+  for (auto _ : state) {
+    snprintf(on_stack, sizeof(on_stack), "%s %s:%d", kStringOne, kStringTwo, i);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_StrCat_By_snprintf);
+
+void BM_StrCat_By_Strings(benchmark::State& state) {
+  int i = 0;
+  for (auto _ : state) {
+    std::string result =
+        std::string(kStringOne) + " " + kStringTwo + ":" + absl::StrCat(i);
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_StrCat_By_Strings);
+
+void BM_StrCat_By_StringOpPlus(benchmark::State& state) {
+  int i = 0;
+  for (auto _ : state) {
+    std::string result = kStringOne;
+    result += " ";
+    result += kStringTwo;
+    result += ":";
+    result += absl::StrCat(i);
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_StrCat_By_StringOpPlus);
+
+void BM_StrCat_By_StrCat(benchmark::State& state) {
+  int i = 0;
+  for (auto _ : state) {
+    std::string result = absl::StrCat(kStringOne, " ", kStringTwo, ":", i);
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_StrCat_By_StrCat);
+
+void BM_HexCat_By_StrCat(benchmark::State& state) {
+  int i = 0;
+  for (auto _ : state) {
+    std::string result =
+        absl::StrCat(kStringOne, " ", absl::Hex(int64_t{i} + 0x10000000));
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_HexCat_By_StrCat);
+
+void BM_HexCat_By_Substitute(benchmark::State& state) {
+  int i = 0;
+  for (auto _ : state) {
+    std::string result = absl::Substitute(
+        "$0 $1", kStringOne, reinterpret_cast<void*>(int64_t{i} + 0x10000000));
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_HexCat_By_Substitute);
+
+void BM_FloatToString_By_StrCat(benchmark::State& state) {
+  int i = 0;
+  float foo = 0.0f;
+  for (auto _ : state) {
+    std::string result = absl::StrCat(foo += 1.001f, " != ", int64_t{i});
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_FloatToString_By_StrCat);
+
+void BM_DoubleToString_By_SixDigits(benchmark::State& state) {
+  int i = 0;
+  double foo = 0.0;
+  for (auto _ : state) {
+    std::string result =
+        absl::StrCat(absl::SixDigits(foo += 1.001), " != ", int64_t{i});
+    benchmark::DoNotOptimize(result);
+    i = IncrementAlternatingSign(i);
+  }
+}
+BENCHMARK(BM_DoubleToString_By_SixDigits);
+
+}  // namespace
diff --git a/absl/strings/str_cat_test.cc b/absl/strings/str_cat_test.cc
new file mode 100644
index 0000000..be39880
--- /dev/null
+++ b/absl/strings/str_cat_test.cc
@@ -0,0 +1,610 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Unit tests for all str_cat.h functions
+
+#include "absl/strings/str_cat.h"
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "absl/strings/substitute.h"
+
+#ifdef __ANDROID__
+// Android assert messages only go to system log, so death tests cannot inspect
+// the message for matching.
+#define ABSL_EXPECT_DEBUG_DEATH(statement, regex) \
+  EXPECT_DEBUG_DEATH(statement, ".*")
+#else
+#define ABSL_EXPECT_DEBUG_DEATH(statement, regex) \
+  EXPECT_DEBUG_DEATH(statement, regex)
+#endif
+
+namespace {
+
+// Test absl::StrCat of ints and longs of various sizes and signdedness.
+TEST(StrCat, Ints) {
+  const short s = -1;  // NOLINT(runtime/int)
+  const uint16_t us = 2;
+  const int i = -3;
+  const unsigned int ui = 4;
+  const long l = -5;                 // NOLINT(runtime/int)
+  const unsigned long ul = 6;        // NOLINT(runtime/int)
+  const long long ll = -7;           // NOLINT(runtime/int)
+  const unsigned long long ull = 8;  // NOLINT(runtime/int)
+  const ptrdiff_t ptrdiff = -9;
+  const size_t size = 10;
+  const intptr_t intptr = -12;
+  const uintptr_t uintptr = 13;
+  std::string answer;
+  answer = absl::StrCat(s, us);
+  EXPECT_EQ(answer, "-12");
+  answer = absl::StrCat(i, ui);
+  EXPECT_EQ(answer, "-34");
+  answer = absl::StrCat(l, ul);
+  EXPECT_EQ(answer, "-56");
+  answer = absl::StrCat(ll, ull);
+  EXPECT_EQ(answer, "-78");
+  answer = absl::StrCat(ptrdiff, size);
+  EXPECT_EQ(answer, "-910");
+  answer = absl::StrCat(ptrdiff, intptr);
+  EXPECT_EQ(answer, "-9-12");
+  answer = absl::StrCat(uintptr, 0);
+  EXPECT_EQ(answer, "130");
+}
+
+TEST(StrCat, Enums) {
+  enum SmallNumbers { One = 1, Ten = 10 } e = Ten;
+  EXPECT_EQ("10", absl::StrCat(e));
+  EXPECT_EQ("-5", absl::StrCat(SmallNumbers(-5)));
+
+  enum class Option { Boxers = 1, Briefs = -1 };
+
+  EXPECT_EQ("-1", absl::StrCat(Option::Briefs));
+
+  enum class Airplane : uint64_t {
+    Airbus = 1,
+    Boeing = 1000,
+    Canary = 10000000000  // too big for "int"
+  };
+
+  EXPECT_EQ("10000000000", absl::StrCat(Airplane::Canary));
+
+  enum class TwoGig : int32_t {
+    TwoToTheZero = 1,
+    TwoToTheSixteenth = 1 << 16,
+    TwoToTheThirtyFirst = INT32_MIN
+  };
+  EXPECT_EQ("65536", absl::StrCat(TwoGig::TwoToTheSixteenth));
+  EXPECT_EQ("-2147483648", absl::StrCat(TwoGig::TwoToTheThirtyFirst));
+  EXPECT_EQ("-1", absl::StrCat(static_cast<TwoGig>(-1)));
+
+  enum class FourGig : uint32_t {
+    TwoToTheZero = 1,
+    TwoToTheSixteenth = 1 << 16,
+    TwoToTheThirtyFirst = 1U << 31  // too big for "int"
+  };
+  EXPECT_EQ("65536", absl::StrCat(FourGig::TwoToTheSixteenth));
+  EXPECT_EQ("2147483648", absl::StrCat(FourGig::TwoToTheThirtyFirst));
+  EXPECT_EQ("4294967295", absl::StrCat(static_cast<FourGig>(-1)));
+
+  EXPECT_EQ("10000000000", absl::StrCat(Airplane::Canary));
+}
+
+TEST(StrCat, Basics) {
+  std::string result;
+
+  std::string strs[] = {"Hello", "Cruel", "World"};
+
+  std::string stdstrs[] = {
+    "std::Hello",
+    "std::Cruel",
+    "std::World"
+  };
+
+  absl::string_view pieces[] = {"Hello", "Cruel", "World"};
+
+  const char* c_strs[] = {
+    "Hello",
+    "Cruel",
+    "World"
+  };
+
+  int32_t i32s[] = {'H', 'C', 'W'};
+  uint64_t ui64s[] = {12345678910LL, 10987654321LL};
+
+  EXPECT_EQ(absl::StrCat(), "");
+
+  result = absl::StrCat(false, true, 2, 3);
+  EXPECT_EQ(result, "0123");
+
+  result = absl::StrCat(-1);
+  EXPECT_EQ(result, "-1");
+
+  result = absl::StrCat(absl::SixDigits(0.5));
+  EXPECT_EQ(result, "0.5");
+
+  result = absl::StrCat(strs[1], pieces[2]);
+  EXPECT_EQ(result, "CruelWorld");
+
+  result = absl::StrCat(stdstrs[1], " ", stdstrs[2]);
+  EXPECT_EQ(result, "std::Cruel std::World");
+
+  result = absl::StrCat(strs[0], ", ", pieces[2]);
+  EXPECT_EQ(result, "Hello, World");
+
+  result = absl::StrCat(strs[0], ", ", strs[1], " ", strs[2], "!");
+  EXPECT_EQ(result, "Hello, Cruel World!");
+
+  result = absl::StrCat(pieces[0], ", ", pieces[1], " ", pieces[2]);
+  EXPECT_EQ(result, "Hello, Cruel World");
+
+  result = absl::StrCat(c_strs[0], ", ", c_strs[1], " ", c_strs[2]);
+  EXPECT_EQ(result, "Hello, Cruel World");
+
+  result = absl::StrCat("ASCII ", i32s[0], ", ", i32s[1], " ", i32s[2], "!");
+  EXPECT_EQ(result, "ASCII 72, 67 87!");
+
+  result = absl::StrCat(ui64s[0], ", ", ui64s[1], "!");
+  EXPECT_EQ(result, "12345678910, 10987654321!");
+
+  std::string one =
+      "1";  // Actually, it's the size of this std::string that we want; a
+            // 64-bit build distinguishes between size_t and uint64_t,
+            // even though they're both unsigned 64-bit values.
+  result = absl::StrCat("And a ", one.size(), " and a ",
+                        &result[2] - &result[0], " and a ", one, " 2 3 4", "!");
+  EXPECT_EQ(result, "And a 1 and a 2 and a 1 2 3 4!");
+
+  // result = absl::StrCat("Single chars won't compile", '!');
+  // result = absl::StrCat("Neither will nullptrs", nullptr);
+  result =
+      absl::StrCat("To output a char by ASCII/numeric value, use +: ", '!' + 0);
+  EXPECT_EQ(result, "To output a char by ASCII/numeric value, use +: 33");
+
+  float f = 100000.5;
+  result = absl::StrCat("A hundred K and a half is ", absl::SixDigits(f));
+  EXPECT_EQ(result, "A hundred K and a half is 100000");
+
+  f = 100001.5;
+  result =
+      absl::StrCat("A hundred K and one and a half is ", absl::SixDigits(f));
+  EXPECT_EQ(result, "A hundred K and one and a half is 100002");
+
+  double d = 100000.5;
+  d *= d;
+  result =
+      absl::StrCat("A hundred K and a half squared is ", absl::SixDigits(d));
+  EXPECT_EQ(result, "A hundred K and a half squared is 1.00001e+10");
+
+  result = absl::StrCat(1, 2, 333, 4444, 55555, 666666, 7777777, 88888888,
+                        999999999);
+  EXPECT_EQ(result, "12333444455555666666777777788888888999999999");
+}
+
+TEST(StrCat, CornerCases) {
+  std::string result;
+
+  result = absl::StrCat("");  // NOLINT
+  EXPECT_EQ(result, "");
+  result = absl::StrCat("", "");
+  EXPECT_EQ(result, "");
+  result = absl::StrCat("", "", "");
+  EXPECT_EQ(result, "");
+  result = absl::StrCat("", "", "", "");
+  EXPECT_EQ(result, "");
+  result = absl::StrCat("", "", "", "", "");
+  EXPECT_EQ(result, "");
+}
+
+// A minimal allocator that uses malloc().
+template <typename T>
+struct Mallocator {
+  typedef T value_type;
+  typedef size_t size_type;
+  typedef ptrdiff_t difference_type;
+  typedef T* pointer;
+  typedef const T* const_pointer;
+  typedef T& reference;
+  typedef const T& const_reference;
+
+  size_type max_size() const {
+    return size_t(std::numeric_limits<size_type>::max()) / sizeof(value_type);
+  }
+  template <typename U>
+  struct rebind {
+    typedef Mallocator<U> other;
+  };
+  Mallocator() = default;
+  template <class U>
+  Mallocator(const Mallocator<U>&) {}  // NOLINT(runtime/explicit)
+
+  T* allocate(size_t n) { return static_cast<T*>(std::malloc(n * sizeof(T))); }
+  void deallocate(T* p, size_t) { std::free(p); }
+};
+template <typename T, typename U>
+bool operator==(const Mallocator<T>&, const Mallocator<U>&) {
+  return true;
+}
+template <typename T, typename U>
+bool operator!=(const Mallocator<T>&, const Mallocator<U>&) {
+  return false;
+}
+
+TEST(StrCat, CustomAllocator) {
+  using mstring =
+      std::basic_string<char, std::char_traits<char>, Mallocator<char>>;
+  const mstring str1("PARACHUTE OFF A BLIMP INTO MOSCONE!!");
+
+  const mstring str2("Read this book about coffee tables");
+
+  std::string result = absl::StrCat(str1, str2);
+  EXPECT_EQ(result,
+            "PARACHUTE OFF A BLIMP INTO MOSCONE!!"
+            "Read this book about coffee tables");
+}
+
+TEST(StrCat, MaxArgs) {
+  std::string result;
+  // Test 10 up to 26 arguments, the old maximum
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a");
+  EXPECT_EQ(result, "123456789a");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b");
+  EXPECT_EQ(result, "123456789ab");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c");
+  EXPECT_EQ(result, "123456789abc");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d");
+  EXPECT_EQ(result, "123456789abcd");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e");
+  EXPECT_EQ(result, "123456789abcde");
+  result =
+      absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f");
+  EXPECT_EQ(result, "123456789abcdef");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g");
+  EXPECT_EQ(result, "123456789abcdefg");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g", "h");
+  EXPECT_EQ(result, "123456789abcdefgh");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g", "h", "i");
+  EXPECT_EQ(result, "123456789abcdefghi");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g", "h", "i", "j");
+  EXPECT_EQ(result, "123456789abcdefghij");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g", "h", "i", "j", "k");
+  EXPECT_EQ(result, "123456789abcdefghijk");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g", "h", "i", "j", "k", "l");
+  EXPECT_EQ(result, "123456789abcdefghijkl");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g", "h", "i", "j", "k", "l", "m");
+  EXPECT_EQ(result, "123456789abcdefghijklm");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g", "h", "i", "j", "k", "l", "m", "n");
+  EXPECT_EQ(result, "123456789abcdefghijklmn");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g", "h", "i", "j", "k", "l", "m", "n", "o");
+  EXPECT_EQ(result, "123456789abcdefghijklmno");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g", "h", "i", "j", "k", "l", "m", "n", "o", "p");
+  EXPECT_EQ(result, "123456789abcdefghijklmnop");
+  result = absl::StrCat(1, 2, 3, 4, 5, 6, 7, 8, 9, "a", "b", "c", "d", "e", "f",
+                        "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q");
+  EXPECT_EQ(result, "123456789abcdefghijklmnopq");
+  // No limit thanks to C++11's variadic templates
+  result = absl::StrCat(
+      1, 2, 3, 4, 5, 6, 7, 8, 9, 10, "a", "b", "c", "d", "e", "f", "g", "h",
+      "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w",
+      "x", "y", "z", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L",
+      "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z");
+  EXPECT_EQ(result,
+            "12345678910abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ");
+}
+
+TEST(StrAppend, Basics) {
+  std::string result = "existing text";
+
+  std::string strs[] = {"Hello", "Cruel", "World"};
+
+  std::string stdstrs[] = {
+    "std::Hello",
+    "std::Cruel",
+    "std::World"
+  };
+
+  absl::string_view pieces[] = {"Hello", "Cruel", "World"};
+
+  const char* c_strs[] = {
+    "Hello",
+    "Cruel",
+    "World"
+  };
+
+  int32_t i32s[] = {'H', 'C', 'W'};
+  uint64_t ui64s[] = {12345678910LL, 10987654321LL};
+
+  std::string::size_type old_size = result.size();
+  absl::StrAppend(&result);
+  EXPECT_EQ(result.size(), old_size);
+
+  old_size = result.size();
+  absl::StrAppend(&result, strs[0]);
+  EXPECT_EQ(result.substr(old_size), "Hello");
+
+  old_size = result.size();
+  absl::StrAppend(&result, strs[1], pieces[2]);
+  EXPECT_EQ(result.substr(old_size), "CruelWorld");
+
+  old_size = result.size();
+  absl::StrAppend(&result, stdstrs[0], ", ", pieces[2]);
+  EXPECT_EQ(result.substr(old_size), "std::Hello, World");
+
+  old_size = result.size();
+  absl::StrAppend(&result, strs[0], ", ", stdstrs[1], " ", strs[2], "!");
+  EXPECT_EQ(result.substr(old_size), "Hello, std::Cruel World!");
+
+  old_size = result.size();
+  absl::StrAppend(&result, pieces[0], ", ", pieces[1], " ", pieces[2]);
+  EXPECT_EQ(result.substr(old_size), "Hello, Cruel World");
+
+  old_size = result.size();
+  absl::StrAppend(&result, c_strs[0], ", ", c_strs[1], " ", c_strs[2]);
+  EXPECT_EQ(result.substr(old_size), "Hello, Cruel World");
+
+  old_size = result.size();
+  absl::StrAppend(&result, "ASCII ", i32s[0], ", ", i32s[1], " ", i32s[2], "!");
+  EXPECT_EQ(result.substr(old_size), "ASCII 72, 67 87!");
+
+  old_size = result.size();
+  absl::StrAppend(&result, ui64s[0], ", ", ui64s[1], "!");
+  EXPECT_EQ(result.substr(old_size), "12345678910, 10987654321!");
+
+  std::string one =
+      "1";  // Actually, it's the size of this std::string that we want; a
+            // 64-bit build distinguishes between size_t and uint64_t,
+            // even though they're both unsigned 64-bit values.
+  old_size = result.size();
+  absl::StrAppend(&result, "And a ", one.size(), " and a ",
+                  &result[2] - &result[0], " and a ", one, " 2 3 4", "!");
+  EXPECT_EQ(result.substr(old_size), "And a 1 and a 2 and a 1 2 3 4!");
+
+  // result = absl::StrCat("Single chars won't compile", '!');
+  // result = absl::StrCat("Neither will nullptrs", nullptr);
+  old_size = result.size();
+  absl::StrAppend(&result,
+                  "To output a char by ASCII/numeric value, use +: ", '!' + 0);
+  EXPECT_EQ(result.substr(old_size),
+            "To output a char by ASCII/numeric value, use +: 33");
+
+  // Test 9 arguments, the old maximum
+  old_size = result.size();
+  absl::StrAppend(&result, 1, 22, 333, 4444, 55555, 666666, 7777777, 88888888,
+                  9);
+  EXPECT_EQ(result.substr(old_size), "1223334444555556666667777777888888889");
+
+  // No limit thanks to C++11's variadic templates
+  old_size = result.size();
+  absl::StrAppend(
+      &result, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,                           //
+      "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m",  //
+      "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z",  //
+      "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",  //
+      "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z",  //
+      "No limit thanks to C++11's variadic templates");
+  EXPECT_EQ(result.substr(old_size),
+            "12345678910abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+            "No limit thanks to C++11's variadic templates");
+}
+
+TEST(StrCat, VectorBoolReferenceTypes) {
+  std::vector<bool> v;
+  v.push_back(true);
+  v.push_back(false);
+  std::vector<bool> const& cv = v;
+  // Test that vector<bool>::reference and vector<bool>::const_reference
+  // are handled as if the were really bool types and not the proxy types
+  // they really are.
+  std::string result = absl::StrCat(v[0], v[1], cv[0], cv[1]); // NOLINT
+  EXPECT_EQ(result, "1010");
+}
+
+// Passing nullptr to memcpy is undefined behavior and this test
+// provides coverage of codepaths that handle empty strings with nullptrs.
+TEST(StrCat, AvoidsMemcpyWithNullptr) {
+  EXPECT_EQ(absl::StrCat(42, absl::string_view{}), "42");
+
+  // Cover CatPieces code.
+  EXPECT_EQ(absl::StrCat(1, 2, 3, 4, 5, absl::string_view{}), "12345");
+
+  // Cover AppendPieces.
+  std::string result;
+  absl::StrAppend(&result, 1, 2, 3, 4, 5, absl::string_view{});
+  EXPECT_EQ(result, "12345");
+}
+
+#ifdef GTEST_HAS_DEATH_TEST
+TEST(StrAppend, Death) {
+  std::string s = "self";
+  // on linux it's "assertion", on mac it's "Assertion",
+  // on chromiumos it's "Assertion ... failed".
+  ABSL_EXPECT_DEBUG_DEATH(absl::StrAppend(&s, s.c_str() + 1),
+                          "ssertion.*failed");
+  ABSL_EXPECT_DEBUG_DEATH(absl::StrAppend(&s, s), "ssertion.*failed");
+}
+#endif  // GTEST_HAS_DEATH_TEST
+
+TEST(StrAppend, CornerCases) {
+  std::string result;
+  absl::StrAppend(&result, "");
+  EXPECT_EQ(result, "");
+  absl::StrAppend(&result, "", "");
+  EXPECT_EQ(result, "");
+  absl::StrAppend(&result, "", "", "");
+  EXPECT_EQ(result, "");
+  absl::StrAppend(&result, "", "", "", "");
+  EXPECT_EQ(result, "");
+  absl::StrAppend(&result, "", "", "", "", "");
+  EXPECT_EQ(result, "");
+}
+
+TEST(StrAppend, CornerCasesNonEmptyAppend) {
+  for (std::string result : {"hello", "a std::string too long to fit in the SSO"}) {
+    const std::string expected = result;
+    absl::StrAppend(&result, "");
+    EXPECT_EQ(result, expected);
+    absl::StrAppend(&result, "", "");
+    EXPECT_EQ(result, expected);
+    absl::StrAppend(&result, "", "", "");
+    EXPECT_EQ(result, expected);
+    absl::StrAppend(&result, "", "", "", "");
+    EXPECT_EQ(result, expected);
+    absl::StrAppend(&result, "", "", "", "", "");
+    EXPECT_EQ(result, expected);
+  }
+}
+
+template <typename IntType>
+void CheckHex(IntType v, const char* nopad_format, const char* zeropad_format,
+              const char* spacepad_format) {
+  char expected[256];
+
+  std::string actual = absl::StrCat(absl::Hex(v, absl::kNoPad));
+  snprintf(expected, sizeof(expected), nopad_format, v);
+  EXPECT_EQ(expected, actual) << " decimal value " << v;
+
+  for (int spec = absl::kZeroPad2; spec <= absl::kZeroPad20; ++spec) {
+    std::string actual =
+        absl::StrCat(absl::Hex(v, static_cast<absl::PadSpec>(spec)));
+    snprintf(expected, sizeof(expected), zeropad_format,
+             spec - absl::kZeroPad2 + 2, v);
+    EXPECT_EQ(expected, actual) << " decimal value " << v;
+  }
+
+  for (int spec = absl::kSpacePad2; spec <= absl::kSpacePad20; ++spec) {
+    std::string actual =
+        absl::StrCat(absl::Hex(v, static_cast<absl::PadSpec>(spec)));
+    snprintf(expected, sizeof(expected), spacepad_format,
+             spec - absl::kSpacePad2 + 2, v);
+    EXPECT_EQ(expected, actual) << " decimal value " << v;
+  }
+}
+
+template <typename IntType>
+void CheckDec(IntType v, const char* nopad_format, const char* zeropad_format,
+              const char* spacepad_format) {
+  char expected[256];
+
+  std::string actual = absl::StrCat(absl::Dec(v, absl::kNoPad));
+  snprintf(expected, sizeof(expected), nopad_format, v);
+  EXPECT_EQ(expected, actual) << " decimal value " << v;
+
+  for (int spec = absl::kZeroPad2; spec <= absl::kZeroPad20; ++spec) {
+    std::string actual =
+        absl::StrCat(absl::Dec(v, static_cast<absl::PadSpec>(spec)));
+    snprintf(expected, sizeof(expected), zeropad_format,
+             spec - absl::kZeroPad2 + 2, v);
+    EXPECT_EQ(expected, actual)
+        << " decimal value " << v << " format '" << zeropad_format
+        << "' digits " << (spec - absl::kZeroPad2 + 2);
+  }
+
+  for (int spec = absl::kSpacePad2; spec <= absl::kSpacePad20; ++spec) {
+    std::string actual =
+        absl::StrCat(absl::Dec(v, static_cast<absl::PadSpec>(spec)));
+    snprintf(expected, sizeof(expected), spacepad_format,
+             spec - absl::kSpacePad2 + 2, v);
+    EXPECT_EQ(expected, actual)
+        << " decimal value " << v << " format '" << spacepad_format
+        << "' digits " << (spec - absl::kSpacePad2 + 2);
+  }
+}
+
+void CheckHexDec64(uint64_t v) {
+  unsigned long long ullv = v;  // NOLINT(runtime/int)
+
+  CheckHex(ullv, "%llx", "%0*llx", "%*llx");
+  CheckDec(ullv, "%llu", "%0*llu", "%*llu");
+
+  long long llv = static_cast<long long>(ullv);  // NOLINT(runtime/int)
+  CheckDec(llv, "%lld", "%0*lld", "%*lld");
+
+  if (sizeof(v) == sizeof(&v)) {
+    auto uintptr = static_cast<uintptr_t>(v);
+    void* ptr = reinterpret_cast<void*>(uintptr);
+    CheckHex(ptr, "%llx", "%0*llx", "%*llx");
+  }
+}
+
+void CheckHexDec32(uint32_t uv) {
+  CheckHex(uv, "%x", "%0*x", "%*x");
+  CheckDec(uv, "%u", "%0*u", "%*u");
+  int32_t v = static_cast<int32_t>(uv);
+  CheckDec(v, "%d", "%0*d", "%*d");
+
+  if (sizeof(v) == sizeof(&v)) {
+    auto uintptr = static_cast<uintptr_t>(v);
+    void* ptr = reinterpret_cast<void*>(uintptr);
+    CheckHex(ptr, "%x", "%0*x", "%*x");
+  }
+}
+
+void CheckAll(uint64_t v) {
+  CheckHexDec64(v);
+  CheckHexDec32(static_cast<uint32_t>(v));
+}
+
+void TestFastPrints() {
+  // Test all small ints; there aren't many and they're common.
+  for (int i = 0; i < 10000; i++) {
+    CheckAll(i);
+  }
+
+  CheckAll(std::numeric_limits<uint64_t>::max());
+  CheckAll(std::numeric_limits<uint64_t>::max() - 1);
+  CheckAll(std::numeric_limits<int64_t>::min());
+  CheckAll(std::numeric_limits<int64_t>::min() + 1);
+  CheckAll(std::numeric_limits<uint32_t>::max());
+  CheckAll(std::numeric_limits<uint32_t>::max() - 1);
+  CheckAll(std::numeric_limits<int32_t>::min());
+  CheckAll(std::numeric_limits<int32_t>::min() + 1);
+  CheckAll(999999999);              // fits in 32 bits
+  CheckAll(1000000000);             // fits in 32 bits
+  CheckAll(9999999999);             // doesn't fit in 32 bits
+  CheckAll(10000000000);            // doesn't fit in 32 bits
+  CheckAll(999999999999999999);     // fits in signed 64-bit
+  CheckAll(9999999999999999999u);   // fits in unsigned 64-bit, but not signed.
+  CheckAll(1000000000000000000);    // fits in signed 64-bit
+  CheckAll(10000000000000000000u);  // fits in unsigned 64-bit, but not signed.
+
+  CheckAll(999999999876543210);    // check all decimal digits, signed
+  CheckAll(9999999999876543210u);  // check all decimal digits, unsigned.
+  CheckAll(0x123456789abcdef0);    // check all hex digits
+  CheckAll(0x12345678);
+
+  int8_t minus_one_8bit = -1;
+  EXPECT_EQ("ff", absl::StrCat(absl::Hex(minus_one_8bit)));
+
+  int16_t minus_one_16bit = -1;
+  EXPECT_EQ("ffff", absl::StrCat(absl::Hex(minus_one_16bit)));
+}
+
+TEST(Numbers, TestFunctionsMovedOverFromNumbersMain) {
+  TestFastPrints();
+}
+
+}  // namespace
diff --git a/absl/strings/str_format.h b/absl/strings/str_format.h
new file mode 100644
index 0000000..607e2bc
--- /dev/null
+++ b/absl/strings/str_format.h
@@ -0,0 +1,529 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: str_format.h
+// -----------------------------------------------------------------------------
+//
+// The `str_format` library is a typesafe replacement for the family of
+// `printf()` string formatting routines within the `<cstdio>` standard library
+// header. Like the `printf` family, the `str_format` uses a "format string" to
+// perform argument substitutions based on types. See the `FormatSpec` section
+// below for format string documentation.
+//
+// Example:
+//
+//   std::string s = absl::StrFormat(
+//                      "%s %s You have $%d!", "Hello", name, dollars);
+//
+// The library consists of the following basic utilities:
+//
+//   * `absl::StrFormat()`, a type-safe replacement for `std::sprintf()`, to
+//     write a format string to a `string` value.
+//   * `absl::StrAppendFormat()` to append a format string to a `string`
+//   * `absl::StreamFormat()` to more efficiently write a format string to a
+//     stream, such as`std::cout`.
+//   * `absl::PrintF()`, `absl::FPrintF()` and `absl::SNPrintF()` as
+//     replacements for `std::printf()`, `std::fprintf()` and `std::snprintf()`.
+//
+//     Note: a version of `std::sprintf()` is not supported as it is
+//     generally unsafe due to buffer overflows.
+//
+// Additionally, you can provide a format string (and its associated arguments)
+// using one of the following abstractions:
+//
+//   * A `FormatSpec` class template fully encapsulates a format string and its
+//     type arguments and is usually provided to `str_format` functions as a
+//     variadic argument of type `FormatSpec<Arg...>`. The `FormatSpec<Args...>`
+//     template is evaluated at compile-time, providing type safety.
+//   * A `ParsedFormat` instance, which encapsulates a specific, pre-compiled
+//     format string for a specific set of type(s), and which can be passed
+//     between API boundaries. (The `FormatSpec` type should not be used
+//     directly except as an argument type for wrapper functions.)
+//
+// The `str_format` library provides the ability to output its format strings to
+// arbitrary sink types:
+//
+//   * A generic `Format()` function to write outputs to arbitrary sink types,
+//     which must implement a `RawSinkFormat` interface. (See
+//     `str_format_sink.h` for more information.)
+//
+//   * A `FormatUntyped()` function that is similar to `Format()` except it is
+//     loosely typed. `FormatUntyped()` is not a template and does not perform
+//     any compile-time checking of the format string; instead, it returns a
+//     boolean from a runtime check.
+//
+// In addition, the `str_format` library provides extension points for
+// augmenting formatting to new types. These extensions are fully documented
+// within the `str_format_extension.h` header file.
+
+#ifndef ABSL_STRINGS_STR_FORMAT_H_
+#define ABSL_STRINGS_STR_FORMAT_H_
+
+#include <cstdio>
+#include <string>
+
+#include "absl/strings/internal/str_format/arg.h"  // IWYU pragma: export
+#include "absl/strings/internal/str_format/bind.h"  // IWYU pragma: export
+#include "absl/strings/internal/str_format/checker.h"  // IWYU pragma: export
+#include "absl/strings/internal/str_format/extension.h"  // IWYU pragma: export
+#include "absl/strings/internal/str_format/parser.h"  // IWYU pragma: export
+
+namespace absl {
+
+// UntypedFormatSpec
+//
+// A type-erased class that can be used directly within untyped API entry
+// points. An `UntypedFormatSpec` is specifically used as an argument to
+// `FormatUntyped()`.
+//
+// Example:
+//
+//   absl::UntypedFormatSpec format("%d");
+//   std::string out;
+//   CHECK(absl::FormatUntyped(&out, format, {absl::FormatArg(1)}));
+class UntypedFormatSpec {
+ public:
+  UntypedFormatSpec() = delete;
+  UntypedFormatSpec(const UntypedFormatSpec&) = delete;
+  UntypedFormatSpec& operator=(const UntypedFormatSpec&) = delete;
+
+  explicit UntypedFormatSpec(string_view s) : spec_(s) {}
+
+ protected:
+  explicit UntypedFormatSpec(const str_format_internal::ParsedFormatBase* pc)
+      : spec_(pc) {}
+
+ private:
+  friend str_format_internal::UntypedFormatSpecImpl;
+  str_format_internal::UntypedFormatSpecImpl spec_;
+};
+
+// FormatStreamed()
+//
+// Takes a streamable argument and returns an object that can print it
+// with '%s'. Allows printing of types that have an `operator<<` but no
+// intrinsic type support within `StrFormat()` itself.
+//
+// Example:
+//
+//   absl::StrFormat("%s", absl::FormatStreamed(obj));
+template <typename T>
+str_format_internal::StreamedWrapper<T> FormatStreamed(const T& v) {
+  return str_format_internal::StreamedWrapper<T>(v);
+}
+
+// FormatCountCapture
+//
+// This class provides a way to safely wrap `StrFormat()` captures of `%n`
+// conversions, which denote the number of characters written by a formatting
+// operation to this point, into an integer value.
+//
+// This wrapper is designed to allow safe usage of `%n` within `StrFormat(); in
+// the `printf()` family of functions, `%n` is not safe to use, as the `int *`
+// buffer can be used to capture arbitrary data.
+//
+// Example:
+//
+//   int n = 0;
+//   std::string s = absl::StrFormat("%s%d%n", "hello", 123,
+//                       absl::FormatCountCapture(&n));
+//   EXPECT_EQ(8, n);
+class FormatCountCapture {
+ public:
+  explicit FormatCountCapture(int* p) : p_(p) {}
+
+ private:
+  // FormatCountCaptureHelper is used to define FormatConvertImpl() for this
+  // class.
+  friend struct str_format_internal::FormatCountCaptureHelper;
+  // Unused() is here because of the false positive from -Wunused-private-field
+  // p_ is used in the templated function of the friend FormatCountCaptureHelper
+  // class.
+  int* Unused() { return p_; }
+  int* p_;
+};
+
+// FormatSpec
+//
+// The `FormatSpec` type defines the makeup of a format string within the
+// `str_format` library. It is a variadic class template that is evaluated at
+// compile-time, according to the format string and arguments that are passed to
+// it.
+//
+// You should not need to manipulate this type directly. You should only name it
+// if you are writing wrapper functions which accept format arguments that will
+// be provided unmodified to functions in this library. Such a wrapper function
+// might be a class method that provides format arguments and/or internally uses
+// the result of formatting.
+//
+// For a `FormatSpec` to be valid at compile-time, it must be provided as
+// either:
+//
+// * A `constexpr` literal or `absl::string_view`, which is how it most often
+//   used.
+// * A `ParsedFormat` instantiation, which ensures the format string is
+//   valid before use. (See below.)
+//
+// Example:
+//
+//   // Provided as a string literal.
+//   absl::StrFormat("Welcome to %s, Number %d!", "The Village", 6);
+//
+//   // Provided as a constexpr absl::string_view.
+//   constexpr absl::string_view formatString = "Welcome to %s, Number %d!";
+//   absl::StrFormat(formatString, "The Village", 6);
+//
+//   // Provided as a pre-compiled ParsedFormat object.
+//   // Note that this example is useful only for illustration purposes.
+//   absl::ParsedFormat<'s', 'd'> formatString("Welcome to %s, Number %d!");
+//   absl::StrFormat(formatString, "TheVillage", 6);
+//
+// A format string generally follows the POSIX syntax as used within the POSIX
+// `printf` specification.
+//
+// (See http://pubs.opengroup.org/onlinepubs/9699919799/functions/fprintf.html.)
+//
+// In specific, the `FormatSpec` supports the following type specifiers:
+//   * `c` for characters
+//   * `s` for strings
+//   * `d` or `i` for integers
+//   * `o` for unsigned integer conversions into octal
+//   * `x` or `X` for unsigned integer conversions into hex
+//   * `u` for unsigned integers
+//   * `f` or `F` for floating point values into decimal notation
+//   * `e` or `E` for floating point values into exponential notation
+//   * `a` or `A` for floating point values into hex exponential notation
+//   * `g` or `G` for floating point values into decimal or exponential
+//     notation based on their precision
+//   * `p` for pointer address values
+//   * `n` for the special case of writing out the number of characters
+//     written to this point. The resulting value must be captured within an
+//     `absl::FormatCountCapture` type.
+//
+// Implementation-defined behavior:
+//   * A null pointer provided to "%s" or "%p" is output as "(nil)".
+//   * A non-null pointer provided to "%p" is output in hex as if by %#x or
+//     %#lx.
+//
+// NOTE: `o`, `x\X` and `u` will convert signed values to their unsigned
+// counterpart before formatting.
+//
+// Examples:
+//     "%c", 'a'                -> "a"
+//     "%c", 32                 -> " "
+//     "%s", "C"                -> "C"
+//     "%s", std::string("C++") -> "C++"
+//     "%d", -10                -> "-10"
+//     "%o", 10                 -> "12"
+//     "%x", 16                 -> "10"
+//     "%f", 123456789          -> "123456789.000000"
+//     "%e", .01                -> "1.00000e-2"
+//     "%a", -3.0               -> "-0x1.8p+1"
+//     "%g", .01                -> "1e-2"
+//     "%p", (void*)&value      -> "0x7ffdeb6ad2a4"
+//
+//     int n = 0;
+//     std::string s = absl::StrFormat(
+//         "%s%d%n", "hello", 123, absl::FormatCountCapture(&n));
+//     EXPECT_EQ(8, n);
+//
+// The `FormatSpec` intrinsically supports all of these fundamental C++ types:
+//
+// *   Characters: `char`, `signed char`, `unsigned char`
+// *   Integers: `int`, `short`, `unsigned short`, `unsigned`, `long`,
+//         `unsigned long`, `long long`, `unsigned long long`
+// *   Floating-point: `float`, `double`, `long double`
+//
+// However, in the `str_format` library, a format conversion specifies a broader
+// C++ conceptual category instead of an exact type. For example, `%s` binds to
+// any string-like argument, so `std::string`, `absl::string_view`, and
+// `const char*` are all accepted. Likewise, `%d` accepts any integer-like
+// argument, etc.
+
+template <typename... Args>
+using FormatSpec =
+    typename str_format_internal::FormatSpecDeductionBarrier<Args...>::type;
+
+// ParsedFormat
+//
+// A `ParsedFormat` is a class template representing a preparsed `FormatSpec`,
+// with template arguments specifying the conversion characters used within the
+// format string. Such characters must be valid format type specifiers, and
+// these type specifiers are checked at compile-time.
+//
+// Instances of `ParsedFormat` can be created, copied, and reused to speed up
+// formatting loops. A `ParsedFormat` may either be constructed statically, or
+// dynamically through its `New()` factory function, which only constructs a
+// runtime object if the format is valid at that time.
+//
+// Example:
+//
+//   // Verified at compile time.
+//   absl::ParsedFormat<'s', 'd'> formatString("Welcome to %s, Number %d!");
+//   absl::StrFormat(formatString, "TheVillage", 6);
+//
+//   // Verified at runtime.
+//   auto format_runtime = absl::ParsedFormat<'d'>::New(format_string);
+//   if (format_runtime) {
+//     value = absl::StrFormat(*format_runtime, i);
+//   } else {
+//     ... error case ...
+//   }
+template <char... Conv>
+using ParsedFormat = str_format_internal::ExtendedParsedFormat<
+    str_format_internal::ConversionCharToConv(Conv)...>;
+
+// StrFormat()
+//
+// Returns a `string` given a `printf()`-style format string and zero or more
+// additional arguments. Use it as you would `sprintf()`. `StrFormat()` is the
+// primary formatting function within the `str_format` library, and should be
+// used in most cases where you need type-safe conversion of types into
+// formatted strings.
+//
+// The format string generally consists of ordinary character data along with
+// one or more format conversion specifiers (denoted by the `%` character).
+// Ordinary character data is returned unchanged into the result string, while
+// each conversion specification performs a type substitution from
+// `StrFormat()`'s other arguments. See the comments for `FormatSpec` for full
+// information on the makeup of this format string.
+//
+// Example:
+//
+//   std::string s = absl::StrFormat(
+//       "Welcome to %s, Number %d!", "The Village", 6);
+//   EXPECT_EQ("Welcome to The Village, Number 6!", s);
+//
+// Returns an empty string in case of error.
+template <typename... Args>
+ABSL_MUST_USE_RESULT std::string StrFormat(const FormatSpec<Args...>& format,
+                                           const Args&... args) {
+  return str_format_internal::FormatPack(
+      str_format_internal::UntypedFormatSpecImpl::Extract(format),
+      {str_format_internal::FormatArgImpl(args)...});
+}
+
+// StrAppendFormat()
+//
+// Appends to a `dst` string given a format string, and zero or more additional
+// arguments, returning `*dst` as a convenience for chaining purposes. Appends
+// nothing in case of error (but possibly alters its capacity).
+//
+// Example:
+//
+//   std::string orig("For example PI is approximately ");
+//   std::cout << StrAppendFormat(&orig, "%12.6f", 3.14);
+template <typename... Args>
+std::string& StrAppendFormat(std::string* dst,
+                             const FormatSpec<Args...>& format,
+                             const Args&... args) {
+  return str_format_internal::AppendPack(
+      dst, str_format_internal::UntypedFormatSpecImpl::Extract(format),
+      {str_format_internal::FormatArgImpl(args)...});
+}
+
+// StreamFormat()
+//
+// Writes to an output stream given a format string and zero or more arguments,
+// generally in a manner that is more efficient than streaming the result of
+// `absl:: StrFormat()`. The returned object must be streamed before the full
+// expression ends.
+//
+// Example:
+//
+//   std::cout << StreamFormat("%12.6f", 3.14);
+template <typename... Args>
+ABSL_MUST_USE_RESULT str_format_internal::Streamable StreamFormat(
+    const FormatSpec<Args...>& format, const Args&... args) {
+  return str_format_internal::Streamable(
+      str_format_internal::UntypedFormatSpecImpl::Extract(format),
+      {str_format_internal::FormatArgImpl(args)...});
+}
+
+// PrintF()
+//
+// Writes to stdout given a format string and zero or more arguments. This
+// function is functionally equivalent to `std::printf()` (and type-safe);
+// prefer `absl::PrintF()` over `std::printf()`.
+//
+// Example:
+//
+//   std::string_view s = "Ulaanbaatar";
+//   absl::PrintF("The capital of Mongolia is %s", s);
+//
+//   Outputs: "The capital of Mongolia is Ulaanbaatar"
+//
+template <typename... Args>
+int PrintF(const FormatSpec<Args...>& format, const Args&... args) {
+  return str_format_internal::FprintF(
+      stdout, str_format_internal::UntypedFormatSpecImpl::Extract(format),
+      {str_format_internal::FormatArgImpl(args)...});
+}
+
+// FPrintF()
+//
+// Writes to a file given a format string and zero or more arguments. This
+// function is functionally equivalent to `std::fprintf()` (and type-safe);
+// prefer `absl::FPrintF()` over `std::fprintf()`.
+//
+// Example:
+//
+//   std::string_view s = "Ulaanbaatar";
+//   absl::FPrintF(stdout, "The capital of Mongolia is %s", s);
+//
+//   Outputs: "The capital of Mongolia is Ulaanbaatar"
+//
+template <typename... Args>
+int FPrintF(std::FILE* output, const FormatSpec<Args...>& format,
+            const Args&... args) {
+  return str_format_internal::FprintF(
+      output, str_format_internal::UntypedFormatSpecImpl::Extract(format),
+      {str_format_internal::FormatArgImpl(args)...});
+}
+
+// SNPrintF()
+//
+// Writes to a sized buffer given a format string and zero or more arguments.
+// This function is functionally equivalent to `std::snprintf()` (and
+// type-safe); prefer `absl::SNPrintF()` over `std::snprintf()`.
+//
+// Example:
+//
+//   std::string_view s = "Ulaanbaatar";
+//   char output[128];
+//   absl::SNPrintF(output, sizeof(output),
+//                  "The capital of Mongolia is %s", s);
+//
+//   Post-condition: output == "The capital of Mongolia is Ulaanbaatar"
+//
+template <typename... Args>
+int SNPrintF(char* output, std::size_t size, const FormatSpec<Args...>& format,
+             const Args&... args) {
+  return str_format_internal::SnprintF(
+      output, size, str_format_internal::UntypedFormatSpecImpl::Extract(format),
+      {str_format_internal::FormatArgImpl(args)...});
+}
+
+// -----------------------------------------------------------------------------
+// Custom Output Formatting Functions
+// -----------------------------------------------------------------------------
+
+// FormatRawSink
+//
+// FormatRawSink is a type erased wrapper around arbitrary sink objects
+// specifically used as an argument to `Format()`.
+// FormatRawSink does not own the passed sink object. The passed object must
+// outlive the FormatRawSink.
+class FormatRawSink {
+ public:
+  // Implicitly convert from any type that provides the hook function as
+  // described above.
+  template <typename T,
+            typename = typename std::enable_if<std::is_constructible<
+                str_format_internal::FormatRawSinkImpl, T*>::value>::type>
+  FormatRawSink(T* raw)  // NOLINT
+      : sink_(raw) {}
+
+ private:
+  friend str_format_internal::FormatRawSinkImpl;
+  str_format_internal::FormatRawSinkImpl sink_;
+};
+
+// Format()
+//
+// Writes a formatted string to an arbitrary sink object (implementing the
+// `absl::FormatRawSink` interface), using a format string and zero or more
+// additional arguments.
+//
+// By default, `std::string` and `std::ostream` are supported as destination
+// objects. If a `std::string` is used the formatted string is appended to it.
+//
+// `absl::Format()` is a generic version of `absl::StrFormat(), for custom
+// sinks. The format string, like format strings for `StrFormat()`, is checked
+// at compile-time.
+//
+// On failure, this function returns `false` and the state of the sink is
+// unspecified.
+template <typename... Args>
+bool Format(FormatRawSink raw_sink, const FormatSpec<Args...>& format,
+            const Args&... args) {
+  return str_format_internal::FormatUntyped(
+      str_format_internal::FormatRawSinkImpl::Extract(raw_sink),
+      str_format_internal::UntypedFormatSpecImpl::Extract(format),
+      {str_format_internal::FormatArgImpl(args)...});
+}
+
+// FormatArg
+//
+// A type-erased handle to a format argument specifically used as an argument to
+// `FormatUntyped()`. You may construct `FormatArg` by passing
+// reference-to-const of any printable type. `FormatArg` is both copyable and
+// assignable. The source data must outlive the `FormatArg` instance. See
+// example below.
+//
+using FormatArg = str_format_internal::FormatArgImpl;
+
+// FormatUntyped()
+//
+// Writes a formatted string to an arbitrary sink object (implementing the
+// `absl::FormatRawSink` interface), using an `UntypedFormatSpec` and zero or
+// more additional arguments.
+//
+// This function acts as the most generic formatting function in the
+// `str_format` library. The caller provides a raw sink, an unchecked format
+// string, and (usually) a runtime specified list of arguments; no compile-time
+// checking of formatting is performed within this function. As a result, a
+// caller should check the return value to verify that no error occurred.
+// On failure, this function returns `false` and the state of the sink is
+// unspecified.
+//
+// The arguments are provided in an `absl::Span<const absl::FormatArg>`.
+// Each `absl::FormatArg` object binds to a single argument and keeps a
+// reference to it. The values used to create the `FormatArg` objects must
+// outlive this function call. (See `str_format_arg.h` for information on
+// the `FormatArg` class.)_
+//
+// Example:
+//
+//   std::optional<std::string> FormatDynamic(
+//       const std::string& in_format,
+//       const vector<std::string>& in_args) {
+//     std::string out;
+//     std::vector<absl::FormatArg> args;
+//     for (const auto& v : in_args) {
+//       // It is important that 'v' is a reference to the objects in in_args.
+//       // The values we pass to FormatArg must outlive the call to
+//       // FormatUntyped.
+//       args.emplace_back(v);
+//     }
+//     absl::UntypedFormatSpec format(in_format);
+//     if (!absl::FormatUntyped(&out, format, args)) {
+//       return std::nullopt;
+//     }
+//     return std::move(out);
+//   }
+//
+ABSL_MUST_USE_RESULT inline bool FormatUntyped(
+    FormatRawSink raw_sink, const UntypedFormatSpec& format,
+    absl::Span<const FormatArg> args) {
+  return str_format_internal::FormatUntyped(
+      str_format_internal::FormatRawSinkImpl::Extract(raw_sink),
+      str_format_internal::UntypedFormatSpecImpl::Extract(format), args);
+}
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_STR_FORMAT_H_
diff --git a/absl/strings/str_format_test.cc b/absl/strings/str_format_test.cc
new file mode 100644
index 0000000..cfd81bb
--- /dev/null
+++ b/absl/strings/str_format_test.cc
@@ -0,0 +1,647 @@
+
+#include <cstdarg>
+#include <cstdint>
+#include <cstdio>
+#include <string>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/strings/str_format.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+namespace {
+using str_format_internal::FormatArgImpl;
+
+using FormatEntryPointTest = ::testing::Test;
+
+TEST_F(FormatEntryPointTest, Format) {
+  std::string sink;
+  EXPECT_TRUE(Format(&sink, "A format %d", 123));
+  EXPECT_EQ("A format 123", sink);
+  sink.clear();
+
+  ParsedFormat<'d'> pc("A format %d");
+  EXPECT_TRUE(Format(&sink, pc, 123));
+  EXPECT_EQ("A format 123", sink);
+}
+TEST_F(FormatEntryPointTest, UntypedFormat) {
+  constexpr const char* formats[] = {
+    "",
+    "a",
+    "%80d",
+#if !defined(_MSC_VER) && !defined(__ANDROID__) && !defined(__native_client__)
+    // MSVC, NaCL and Android don't support positional syntax.
+    "complicated multipart %% %1$d format %1$0999d",
+#endif  // _MSC_VER
+  };
+  for (const char* fmt : formats) {
+    std::string actual;
+    int i = 123;
+    FormatArgImpl arg_123(i);
+    absl::Span<const FormatArgImpl> args(&arg_123, 1);
+    UntypedFormatSpec format(fmt);
+
+    EXPECT_TRUE(FormatUntyped(&actual, format, args));
+    char buf[4096]{};
+    snprintf(buf, sizeof(buf), fmt, 123);
+    EXPECT_EQ(
+        str_format_internal::FormatPack(
+            str_format_internal::UntypedFormatSpecImpl::Extract(format), args),
+        buf);
+    EXPECT_EQ(actual, buf);
+  }
+  // The internal version works with a preparsed format.
+  ParsedFormat<'d'> pc("A format %d");
+  int i = 345;
+  FormatArg arg(i);
+  std::string out;
+  EXPECT_TRUE(str_format_internal::FormatUntyped(
+      &out, str_format_internal::UntypedFormatSpecImpl(&pc), {&arg, 1}));
+  EXPECT_EQ("A format 345", out);
+}
+
+TEST_F(FormatEntryPointTest, StringFormat) {
+  EXPECT_EQ("123", StrFormat("%d", 123));
+  constexpr absl::string_view view("=%d=", 4);
+  EXPECT_EQ("=123=", StrFormat(view, 123));
+}
+
+TEST_F(FormatEntryPointTest, AppendFormat) {
+  std::string s;
+  std::string& r = StrAppendFormat(&s, "%d", 123);
+  EXPECT_EQ(&s, &r);  // should be same object
+  EXPECT_EQ("123", r);
+}
+
+TEST_F(FormatEntryPointTest, AppendFormatFail) {
+  std::string s = "orig";
+
+  UntypedFormatSpec format(" more %d");
+  FormatArgImpl arg("not an int");
+
+  EXPECT_EQ("orig",
+            str_format_internal::AppendPack(
+                &s, str_format_internal::UntypedFormatSpecImpl::Extract(format),
+                {&arg, 1}));
+}
+
+
+TEST_F(FormatEntryPointTest, ManyArgs) {
+  EXPECT_EQ("24", StrFormat("%24$d", 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
+                            14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24));
+  EXPECT_EQ("60", StrFormat("%60$d", 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
+                            14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26,
+                            27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
+                            40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52,
+                            53, 54, 55, 56, 57, 58, 59, 60));
+}
+
+TEST_F(FormatEntryPointTest, Preparsed) {
+  ParsedFormat<'d'> pc("%d");
+  EXPECT_EQ("123", StrFormat(pc, 123));
+  // rvalue ok?
+  EXPECT_EQ("123", StrFormat(ParsedFormat<'d'>("%d"), 123));
+  constexpr absl::string_view view("=%d=", 4);
+  EXPECT_EQ("=123=", StrFormat(ParsedFormat<'d'>(view), 123));
+}
+
+TEST_F(FormatEntryPointTest, FormatCountCapture) {
+  int n = 0;
+  EXPECT_EQ("", StrFormat("%n", FormatCountCapture(&n)));
+  EXPECT_EQ(0, n);
+  EXPECT_EQ("123", StrFormat("%d%n", 123, FormatCountCapture(&n)));
+  EXPECT_EQ(3, n);
+}
+
+TEST_F(FormatEntryPointTest, FormatCountCaptureWrongType) {
+  // Should reject int*.
+  int n = 0;
+  UntypedFormatSpec format("%d%n");
+  int i = 123, *ip = &n;
+  FormatArgImpl args[2] = {FormatArgImpl(i), FormatArgImpl(ip)};
+
+  EXPECT_EQ("", str_format_internal::FormatPack(
+                    str_format_internal::UntypedFormatSpecImpl::Extract(format),
+                    absl::MakeSpan(args)));
+}
+
+TEST_F(FormatEntryPointTest, FormatCountCaptureMultiple) {
+  int n1 = 0;
+  int n2 = 0;
+  EXPECT_EQ("    1         2",
+            StrFormat("%5d%n%10d%n", 1, FormatCountCapture(&n1), 2,
+                      FormatCountCapture(&n2)));
+  EXPECT_EQ(5, n1);
+  EXPECT_EQ(15, n2);
+}
+
+TEST_F(FormatEntryPointTest, FormatCountCaptureExample) {
+  int n;
+  std::string s;
+  StrAppendFormat(&s, "%s: %n%s\n", "(1,1)", FormatCountCapture(&n), "(1,2)");
+  StrAppendFormat(&s, "%*s%s\n", n, "", "(2,2)");
+  EXPECT_EQ(7, n);
+  EXPECT_EQ(
+      "(1,1): (1,2)\n"
+      "       (2,2)\n",
+      s);
+}
+
+TEST_F(FormatEntryPointTest, Stream) {
+  const std::string formats[] = {
+    "",
+    "a",
+    "%80d",
+    "%d %u %c %s %f %g",
+#if !defined(_MSC_VER) && !defined(__ANDROID__) && !defined(__native_client__)
+    // MSVC, NaCL and Android don't support positional syntax.
+    "complicated multipart %% %1$d format %1$080d",
+#endif  // _MSC_VER
+  };
+  std::string buf(4096, '\0');
+  for (const auto& fmt : formats) {
+    const auto parsed =
+        ParsedFormat<'d', 'u', 'c', 's', 'f', 'g'>::NewAllowIgnored(fmt);
+    std::ostringstream oss;
+    oss << StreamFormat(*parsed, 123, 3, 49, "multistreaming!!!", 1.01, 1.01);
+    int fmt_result = snprintf(&*buf.begin(), buf.size(), fmt.c_str(),  //
+                                 123, 3, 49, "multistreaming!!!", 1.01, 1.01);
+    ASSERT_TRUE(oss) << fmt;
+    ASSERT_TRUE(fmt_result >= 0 && static_cast<size_t>(fmt_result) < buf.size())
+        << fmt_result;
+    EXPECT_EQ(buf.c_str(), oss.str());
+  }
+}
+
+TEST_F(FormatEntryPointTest, StreamOk) {
+  std::ostringstream oss;
+  oss << StreamFormat("hello %d", 123);
+  EXPECT_EQ("hello 123", oss.str());
+  EXPECT_TRUE(oss.good());
+}
+
+TEST_F(FormatEntryPointTest, StreamFail) {
+  std::ostringstream oss;
+  UntypedFormatSpec format("hello %d");
+  FormatArgImpl arg("non-numeric");
+  oss << str_format_internal::Streamable(
+      str_format_internal::UntypedFormatSpecImpl::Extract(format), {&arg, 1});
+  EXPECT_EQ("hello ", oss.str());  // partial write
+  EXPECT_TRUE(oss.fail());
+}
+
+std::string WithSnprintf(const char* fmt, ...) {
+  std::string buf;
+  buf.resize(128);
+  va_list va;
+  va_start(va, fmt);
+  int r = vsnprintf(&*buf.begin(), buf.size(), fmt, va);
+  va_end(va);
+  EXPECT_GE(r, 0);
+  EXPECT_LT(r, buf.size());
+  buf.resize(r);
+  return buf;
+}
+
+TEST_F(FormatEntryPointTest, FloatPrecisionArg) {
+  // Test that positional parameters for width and precision
+  // are indexed to precede the value.
+  // Also sanity check the same formats against snprintf.
+  EXPECT_EQ("0.1", StrFormat("%.1f", 0.1));
+  EXPECT_EQ("0.1", WithSnprintf("%.1f", 0.1));
+  EXPECT_EQ("  0.1", StrFormat("%*.1f", 5, 0.1));
+  EXPECT_EQ("  0.1", WithSnprintf("%*.1f", 5, 0.1));
+  EXPECT_EQ("0.1", StrFormat("%.*f", 1, 0.1));
+  EXPECT_EQ("0.1", WithSnprintf("%.*f", 1, 0.1));
+  EXPECT_EQ("  0.1", StrFormat("%*.*f", 5, 1, 0.1));
+  EXPECT_EQ("  0.1", WithSnprintf("%*.*f", 5, 1, 0.1));
+}
+namespace streamed_test {
+struct X {};
+std::ostream& operator<<(std::ostream& os, const X&) {
+  return os << "X";
+}
+}  // streamed_test
+
+TEST_F(FormatEntryPointTest, FormatStreamed) {
+  EXPECT_EQ("123", StrFormat("%s", FormatStreamed(123)));
+  EXPECT_EQ("  123", StrFormat("%5s", FormatStreamed(123)));
+  EXPECT_EQ("123  ", StrFormat("%-5s", FormatStreamed(123)));
+  EXPECT_EQ("X", StrFormat("%s", FormatStreamed(streamed_test::X())));
+  EXPECT_EQ("123", StrFormat("%s", FormatStreamed(StreamFormat("%d", 123))));
+}
+
+// Helper class that creates a temporary file and exposes a FILE* to it.
+// It will close the file on destruction.
+class TempFile {
+ public:
+  TempFile() : file_(std::tmpfile()) {}
+  ~TempFile() { std::fclose(file_); }
+
+  std::FILE* file() const { return file_; }
+
+  // Read the file into a std::string.
+  std::string ReadFile() {
+    std::fseek(file_, 0, SEEK_END);
+    int size = std::ftell(file_);
+    EXPECT_GT(size, 0);
+    std::rewind(file_);
+    std::string str(2 * size, ' ');
+    int read_bytes = std::fread(&str[0], 1, str.size(), file_);
+    EXPECT_EQ(read_bytes, size);
+    str.resize(read_bytes);
+    EXPECT_TRUE(std::feof(file_));
+    return str;
+  }
+
+ private:
+  std::FILE* file_;
+};
+
+TEST_F(FormatEntryPointTest, FPrintF) {
+  TempFile tmp;
+  int result =
+      FPrintF(tmp.file(), "STRING: %s NUMBER: %010d", std::string("ABC"), -19);
+  EXPECT_EQ(result, 30);
+  EXPECT_EQ(tmp.ReadFile(), "STRING: ABC NUMBER: -000000019");
+}
+
+TEST_F(FormatEntryPointTest, FPrintFError) {
+  errno = 0;
+  int result = FPrintF(stdin, "ABC");
+  EXPECT_LT(result, 0);
+  EXPECT_EQ(errno, EBADF);
+}
+
+#ifdef __GLIBC__
+TEST_F(FormatEntryPointTest, FprintfTooLarge) {
+  std::FILE* f = std::fopen("/dev/null", "w");
+  int width = 2000000000;
+  errno = 0;
+  int result = FPrintF(f, "%*d %*d", width, 0, width, 0);
+  EXPECT_LT(result, 0);
+  EXPECT_EQ(errno, EFBIG);
+  std::fclose(f);
+}
+
+TEST_F(FormatEntryPointTest, PrintF) {
+  int stdout_tmp = dup(STDOUT_FILENO);
+
+  TempFile tmp;
+  std::fflush(stdout);
+  dup2(fileno(tmp.file()), STDOUT_FILENO);
+
+  int result = PrintF("STRING: %s NUMBER: %010d", std::string("ABC"), -19);
+
+  std::fflush(stdout);
+  dup2(stdout_tmp, STDOUT_FILENO);
+  close(stdout_tmp);
+
+  EXPECT_EQ(result, 30);
+  EXPECT_EQ(tmp.ReadFile(), "STRING: ABC NUMBER: -000000019");
+}
+#endif  // __GLIBC__
+
+TEST_F(FormatEntryPointTest, SNPrintF) {
+  char buffer[16];
+  int result =
+      SNPrintF(buffer, sizeof(buffer), "STRING: %s", std::string("ABC"));
+  EXPECT_EQ(result, 11);
+  EXPECT_EQ(std::string(buffer), "STRING: ABC");
+
+  result = SNPrintF(buffer, sizeof(buffer), "NUMBER: %d", 123456);
+  EXPECT_EQ(result, 14);
+  EXPECT_EQ(std::string(buffer), "NUMBER: 123456");
+
+  result = SNPrintF(buffer, sizeof(buffer), "NUMBER: %d", 1234567);
+  EXPECT_EQ(result, 15);
+  EXPECT_EQ(std::string(buffer), "NUMBER: 1234567");
+
+  result = SNPrintF(buffer, sizeof(buffer), "NUMBER: %d", 12345678);
+  EXPECT_EQ(result, 16);
+  EXPECT_EQ(std::string(buffer), "NUMBER: 1234567");
+
+  result = SNPrintF(buffer, sizeof(buffer), "NUMBER: %d", 123456789);
+  EXPECT_EQ(result, 17);
+  EXPECT_EQ(std::string(buffer), "NUMBER: 1234567");
+
+  result = SNPrintF(nullptr, 0, "Just checking the %s of the output.", "size");
+  EXPECT_EQ(result, 37);
+}
+
+TEST(StrFormat, BehavesAsDocumented) {
+  std::string s = absl::StrFormat("%s, %d!", "Hello", 123);
+  EXPECT_EQ("Hello, 123!", s);
+  // The format of a replacement is
+  // '%'[position][flags][width['.'precision]][length_modifier][format]
+  EXPECT_EQ(absl::StrFormat("%1$+3.2Lf", 1.1), "+1.10");
+  // Text conversion:
+  //     "c" - Character.              Eg: 'a' -> "A", 20 -> " "
+  EXPECT_EQ(StrFormat("%c", 'a'), "a");
+  EXPECT_EQ(StrFormat("%c", 0x20), " ");
+  //           Formats char and integral types: int, long, uint64_t, etc.
+  EXPECT_EQ(StrFormat("%c", int{'a'}), "a");
+  EXPECT_EQ(StrFormat("%c", long{'a'}), "a");  // NOLINT
+  EXPECT_EQ(StrFormat("%c", uint64_t{'a'}), "a");
+  //     "s" - std::string       Eg: "C" -> "C", std::string("C++") -> "C++"
+  //           Formats std::string, char*, string_view, and Cord.
+  EXPECT_EQ(StrFormat("%s", "C"), "C");
+  EXPECT_EQ(StrFormat("%s", std::string("C++")), "C++");
+  EXPECT_EQ(StrFormat("%s", string_view("view")), "view");
+  // Integral Conversion
+  //     These format integral types: char, int, long, uint64_t, etc.
+  EXPECT_EQ(StrFormat("%d", char{10}), "10");
+  EXPECT_EQ(StrFormat("%d", int{10}), "10");
+  EXPECT_EQ(StrFormat("%d", long{10}), "10");  // NOLINT
+  EXPECT_EQ(StrFormat("%d", uint64_t{10}), "10");
+  //     d,i - signed decimal          Eg: -10 -> "-10"
+  EXPECT_EQ(StrFormat("%d", -10), "-10");
+  EXPECT_EQ(StrFormat("%i", -10), "-10");
+  //      o  - octal                   Eg:  10 -> "12"
+  EXPECT_EQ(StrFormat("%o", 10), "12");
+  //      u  - unsigned decimal        Eg:  10 -> "10"
+  EXPECT_EQ(StrFormat("%u", 10), "10");
+  //     x/X - lower,upper case hex    Eg:  10 -> "a"/"A"
+  EXPECT_EQ(StrFormat("%x", 10), "a");
+  EXPECT_EQ(StrFormat("%X", 10), "A");
+  // Floating-point, with upper/lower-case output.
+  //     These format floating points types: float, double, long double, etc.
+  EXPECT_EQ(StrFormat("%.1f", float{1}), "1.0");
+  EXPECT_EQ(StrFormat("%.1f", double{1}), "1.0");
+  const long double long_double = 1.0;
+  EXPECT_EQ(StrFormat("%.1f", long_double), "1.0");
+  //     These also format integral types: char, int, long, uint64_t, etc.:
+  EXPECT_EQ(StrFormat("%.1f", char{1}), "1.0");
+  EXPECT_EQ(StrFormat("%.1f", int{1}), "1.0");
+  EXPECT_EQ(StrFormat("%.1f", long{1}), "1.0");  // NOLINT
+  EXPECT_EQ(StrFormat("%.1f", uint64_t{1}), "1.0");
+  //     f/F - decimal.                Eg: 123456789 -> "123456789.000000"
+  EXPECT_EQ(StrFormat("%f", 123456789), "123456789.000000");
+  EXPECT_EQ(StrFormat("%F", 123456789), "123456789.000000");
+  //     e/E - exponentiated           Eg: .01 -> "1.00000e-2"/"1.00000E-2"
+  EXPECT_EQ(StrFormat("%e", .01), "1.000000e-02");
+  EXPECT_EQ(StrFormat("%E", .01), "1.000000E-02");
+  //     g/G - exponentiate to fit     Eg: .01 -> "0.01", 1e10 ->"1e+10"/"1E+10"
+  EXPECT_EQ(StrFormat("%g", .01), "0.01");
+  EXPECT_EQ(StrFormat("%g", 1e10), "1e+10");
+  EXPECT_EQ(StrFormat("%G", 1e10), "1E+10");
+  //     a/A - lower,upper case hex    Eg: -3.0 -> "-0x1.8p+1"/"-0X1.8P+1"
+
+// On Android platform <=21, there is a regression in hexfloat formatting.
+#if !defined(__ANDROID_API__) || __ANDROID_API__ > 21
+  EXPECT_EQ(StrFormat("%.1a", -3.0), "-0x1.8p+1");  // .1 to fix MSVC output
+  EXPECT_EQ(StrFormat("%.1A", -3.0), "-0X1.8P+1");  // .1 to fix MSVC output
+#endif
+
+  // Other conversion
+  int64_t value = 0x7ffdeb4;
+  auto ptr_value = static_cast<uintptr_t>(value);
+  const int& something = *reinterpret_cast<const int*>(ptr_value);
+  EXPECT_EQ(StrFormat("%p", &something), StrFormat("0x%x", ptr_value));
+
+  // Output widths are supported, with optional flags.
+  EXPECT_EQ(StrFormat("%3d", 1), "  1");
+  EXPECT_EQ(StrFormat("%3d", 123456), "123456");
+  EXPECT_EQ(StrFormat("%06.2f", 1.234), "001.23");
+  EXPECT_EQ(StrFormat("%+d", 1), "+1");
+  EXPECT_EQ(StrFormat("% d", 1), " 1");
+  EXPECT_EQ(StrFormat("%-4d", -1), "-1  ");
+  EXPECT_EQ(StrFormat("%#o", 10), "012");
+  EXPECT_EQ(StrFormat("%#x", 15), "0xf");
+  EXPECT_EQ(StrFormat("%04d", 8), "0008");
+  // Posix positional substitution.
+  EXPECT_EQ(absl::StrFormat("%2$s, %3$s, %1$s!", "vici", "veni", "vidi"),
+            "veni, vidi, vici!");
+  // Length modifiers are ignored.
+  EXPECT_EQ(StrFormat("%hhd", int{1}), "1");
+  EXPECT_EQ(StrFormat("%hd", int{1}), "1");
+  EXPECT_EQ(StrFormat("%ld", int{1}), "1");
+  EXPECT_EQ(StrFormat("%lld", int{1}), "1");
+  EXPECT_EQ(StrFormat("%Ld", int{1}), "1");
+  EXPECT_EQ(StrFormat("%jd", int{1}), "1");
+  EXPECT_EQ(StrFormat("%zd", int{1}), "1");
+  EXPECT_EQ(StrFormat("%td", int{1}), "1");
+  EXPECT_EQ(StrFormat("%qd", int{1}), "1");
+}
+
+using str_format_internal::ExtendedParsedFormat;
+using str_format_internal::ParsedFormatBase;
+
+struct SummarizeConsumer {
+  std::string* out;
+  explicit SummarizeConsumer(std::string* out) : out(out) {}
+
+  bool Append(string_view s) {
+    *out += "[" + std::string(s) + "]";
+    return true;
+  }
+
+  bool ConvertOne(const str_format_internal::UnboundConversion& conv,
+                  string_view s) {
+    *out += "{";
+    *out += std::string(s);
+    *out += ":";
+    *out += std::to_string(conv.arg_position) + "$";
+    if (conv.width.is_from_arg()) {
+      *out += std::to_string(conv.width.get_from_arg()) + "$*";
+    }
+    if (conv.precision.is_from_arg()) {
+      *out += "." + std::to_string(conv.precision.get_from_arg()) + "$*";
+    }
+    *out += conv.conv.Char();
+    *out += "}";
+    return true;
+  }
+};
+
+std::string SummarizeParsedFormat(const ParsedFormatBase& pc) {
+  std::string out;
+  if (!pc.ProcessFormat(SummarizeConsumer(&out))) out += "!";
+  return out;
+}
+
+using ParsedFormatTest = ::testing::Test;
+
+TEST_F(ParsedFormatTest, SimpleChecked) {
+  EXPECT_EQ("[ABC]{d:1$d}[DEF]",
+            SummarizeParsedFormat(ParsedFormat<'d'>("ABC%dDEF")));
+  EXPECT_EQ("{s:1$s}[FFF]{d:2$d}[ZZZ]{f:3$f}",
+            SummarizeParsedFormat(ParsedFormat<'s', 'd', 'f'>("%sFFF%dZZZ%f")));
+  EXPECT_EQ("{s:1$s}[ ]{.*d:3$.2$*d}",
+            SummarizeParsedFormat(ParsedFormat<'s', '*', 'd'>("%s %.*d")));
+}
+
+TEST_F(ParsedFormatTest, SimpleUncheckedCorrect) {
+  auto f = ParsedFormat<'d'>::New("ABC%dDEF");
+  ASSERT_TRUE(f);
+  EXPECT_EQ("[ABC]{d:1$d}[DEF]", SummarizeParsedFormat(*f));
+
+  std::string format = "%sFFF%dZZZ%f";
+  auto f2 = ParsedFormat<'s', 'd', 'f'>::New(format);
+
+  ASSERT_TRUE(f2);
+  EXPECT_EQ("{s:1$s}[FFF]{d:2$d}[ZZZ]{f:3$f}", SummarizeParsedFormat(*f2));
+
+  f2 = ParsedFormat<'s', 'd', 'f'>::New("%s %d %f");
+
+  ASSERT_TRUE(f2);
+  EXPECT_EQ("{s:1$s}[ ]{d:2$d}[ ]{f:3$f}", SummarizeParsedFormat(*f2));
+
+  auto star = ParsedFormat<'*', 'd'>::New("%*d");
+  ASSERT_TRUE(star);
+  EXPECT_EQ("{*d:2$1$*d}", SummarizeParsedFormat(*star));
+
+  auto dollar = ParsedFormat<'d', 's'>::New("%2$s %1$d");
+  ASSERT_TRUE(dollar);
+  EXPECT_EQ("{2$s:2$s}[ ]{1$d:1$d}", SummarizeParsedFormat(*dollar));
+  // with reuse
+  dollar = ParsedFormat<'d', 's'>::New("%2$s %1$d %1$d");
+  ASSERT_TRUE(dollar);
+  EXPECT_EQ("{2$s:2$s}[ ]{1$d:1$d}[ ]{1$d:1$d}",
+            SummarizeParsedFormat(*dollar));
+}
+
+TEST_F(ParsedFormatTest, SimpleUncheckedIgnoredArgs) {
+  EXPECT_FALSE((ParsedFormat<'d', 's'>::New("ABC")));
+  EXPECT_FALSE((ParsedFormat<'d', 's'>::New("%dABC")));
+  EXPECT_FALSE((ParsedFormat<'d', 's'>::New("ABC%2$s")));
+  auto f = ParsedFormat<'d', 's'>::NewAllowIgnored("ABC");
+  ASSERT_TRUE(f);
+  EXPECT_EQ("[ABC]", SummarizeParsedFormat(*f));
+  f = ParsedFormat<'d', 's'>::NewAllowIgnored("%dABC");
+  ASSERT_TRUE(f);
+  EXPECT_EQ("{d:1$d}[ABC]", SummarizeParsedFormat(*f));
+  f = ParsedFormat<'d', 's'>::NewAllowIgnored("ABC%2$s");
+  ASSERT_TRUE(f);
+  EXPECT_EQ("[ABC]{2$s:2$s}", SummarizeParsedFormat(*f));
+}
+
+TEST_F(ParsedFormatTest, SimpleUncheckedUnsupported) {
+  EXPECT_FALSE(ParsedFormat<'d'>::New("%1$d %1$x"));
+  EXPECT_FALSE(ParsedFormat<'x'>::New("%1$d %1$x"));
+}
+
+TEST_F(ParsedFormatTest, SimpleUncheckedIncorrect) {
+  EXPECT_FALSE(ParsedFormat<'d'>::New(""));
+
+  EXPECT_FALSE(ParsedFormat<'d'>::New("ABC%dDEF%d"));
+
+  std::string format = "%sFFF%dZZZ%f";
+  EXPECT_FALSE((ParsedFormat<'s', 'd', 'g'>::New(format)));
+}
+
+using str_format_internal::Conv;
+
+TEST_F(ParsedFormatTest, UncheckedCorrect) {
+  auto f = ExtendedParsedFormat<Conv::d>::New("ABC%dDEF");
+  ASSERT_TRUE(f);
+  EXPECT_EQ("[ABC]{d:1$d}[DEF]", SummarizeParsedFormat(*f));
+
+  std::string format = "%sFFF%dZZZ%f";
+  auto f2 =
+      ExtendedParsedFormat<Conv::string, Conv::d, Conv::floating>::New(format);
+
+  ASSERT_TRUE(f2);
+  EXPECT_EQ("{s:1$s}[FFF]{d:2$d}[ZZZ]{f:3$f}", SummarizeParsedFormat(*f2));
+
+  f2 = ExtendedParsedFormat<Conv::string, Conv::d, Conv::floating>::New(
+      "%s %d %f");
+
+  ASSERT_TRUE(f2);
+  EXPECT_EQ("{s:1$s}[ ]{d:2$d}[ ]{f:3$f}", SummarizeParsedFormat(*f2));
+
+  auto star = ExtendedParsedFormat<Conv::star, Conv::d>::New("%*d");
+  ASSERT_TRUE(star);
+  EXPECT_EQ("{*d:2$1$*d}", SummarizeParsedFormat(*star));
+
+  auto dollar = ExtendedParsedFormat<Conv::d, Conv::s>::New("%2$s %1$d");
+  ASSERT_TRUE(dollar);
+  EXPECT_EQ("{2$s:2$s}[ ]{1$d:1$d}", SummarizeParsedFormat(*dollar));
+  // with reuse
+  dollar = ExtendedParsedFormat<Conv::d, Conv::s>::New("%2$s %1$d %1$d");
+  ASSERT_TRUE(dollar);
+  EXPECT_EQ("{2$s:2$s}[ ]{1$d:1$d}[ ]{1$d:1$d}",
+            SummarizeParsedFormat(*dollar));
+}
+
+TEST_F(ParsedFormatTest, UncheckedIgnoredArgs) {
+  EXPECT_FALSE((ExtendedParsedFormat<Conv::d, Conv::s>::New("ABC")));
+  EXPECT_FALSE((ExtendedParsedFormat<Conv::d, Conv::s>::New("%dABC")));
+  EXPECT_FALSE((ExtendedParsedFormat<Conv::d, Conv::s>::New("ABC%2$s")));
+  auto f = ExtendedParsedFormat<Conv::d, Conv::s>::NewAllowIgnored("ABC");
+  ASSERT_TRUE(f);
+  EXPECT_EQ("[ABC]", SummarizeParsedFormat(*f));
+  f = ExtendedParsedFormat<Conv::d, Conv::s>::NewAllowIgnored("%dABC");
+  ASSERT_TRUE(f);
+  EXPECT_EQ("{d:1$d}[ABC]", SummarizeParsedFormat(*f));
+  f = ExtendedParsedFormat<Conv::d, Conv::s>::NewAllowIgnored("ABC%2$s");
+  ASSERT_TRUE(f);
+  EXPECT_EQ("[ABC]{2$s:2$s}", SummarizeParsedFormat(*f));
+}
+
+TEST_F(ParsedFormatTest, UncheckedMultipleTypes) {
+  auto dx = ExtendedParsedFormat<Conv::d | Conv::x>::New("%1$d %1$x");
+  EXPECT_TRUE(dx);
+  EXPECT_EQ("{1$d:1$d}[ ]{1$x:1$x}", SummarizeParsedFormat(*dx));
+
+  dx = ExtendedParsedFormat<Conv::d | Conv::x>::New("%1$d");
+  EXPECT_TRUE(dx);
+  EXPECT_EQ("{1$d:1$d}", SummarizeParsedFormat(*dx));
+}
+
+TEST_F(ParsedFormatTest, UncheckedIncorrect) {
+  EXPECT_FALSE(ExtendedParsedFormat<Conv::d>::New(""));
+
+  EXPECT_FALSE(ExtendedParsedFormat<Conv::d>::New("ABC%dDEF%d"));
+
+  std::string format = "%sFFF%dZZZ%f";
+  EXPECT_FALSE((ExtendedParsedFormat<Conv::s, Conv::d, Conv::g>::New(format)));
+}
+
+TEST_F(ParsedFormatTest, RegressionMixPositional) {
+  EXPECT_FALSE((ExtendedParsedFormat<Conv::d, Conv::o>::New("%1$d %o")));
+}
+
+using FormatWrapperTest = ::testing::Test;
+
+// Plain wrapper for StrFormat.
+template <typename... Args>
+std::string WrappedFormat(const absl::FormatSpec<Args...>& format,
+                          const Args&... args) {
+  return StrFormat(format, args...);
+}
+
+TEST_F(FormatWrapperTest, ConstexprStringFormat) {
+  EXPECT_EQ(WrappedFormat("%s there", "hello"), "hello there");
+}
+
+TEST_F(FormatWrapperTest, ParsedFormat) {
+  ParsedFormat<'s'> format("%s there");
+  EXPECT_EQ(WrappedFormat(format, "hello"), "hello there");
+}
+
+}  // namespace
+}  // namespace absl
+
+// Some codegen thunks that we can use to easily dump the generated assembly for
+// different StrFormat calls.
+
+std::string CodegenAbslStrFormatInt(int i) {  // NOLINT
+  return absl::StrFormat("%d", i);
+}
+
+std::string CodegenAbslStrFormatIntStringInt64(int i, const std::string& s,
+                                               int64_t i64) {  // NOLINT
+  return absl::StrFormat("%d %s %d", i, s, i64);
+}
+
+void CodegenAbslStrAppendFormatInt(std::string* out, int i) {  // NOLINT
+  absl::StrAppendFormat(out, "%d", i);
+}
+
+void CodegenAbslStrAppendFormatIntStringInt64(std::string* out, int i,
+                                              const std::string& s,
+                                              int64_t i64) {  // NOLINT
+  absl::StrAppendFormat(out, "%d %s %d", i, s, i64);
+}
diff --git a/absl/strings/str_join.h b/absl/strings/str_join.h
new file mode 100644
index 0000000..4772f5d
--- /dev/null
+++ b/absl/strings/str_join.h
@@ -0,0 +1,291 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: str_join.h
+// -----------------------------------------------------------------------------
+//
+// This header file contains functions for joining a range of elements and
+// returning the result as a std::string. StrJoin operations are specified by
+// passing a range, a separator string to use between the elements joined, and
+// an optional Formatter responsible for converting each argument in the range
+// to a string. If omitted, a default `AlphaNumFormatter()` is called on the
+// elements to be joined, using the same formatting that `absl::StrCat()` uses.
+// This package defines a number of default formatters, and you can define your
+// own implementations.
+//
+// Ranges are specified by passing a container with `std::begin()` and
+// `std::end()` iterators, container-specific `begin()` and `end()` iterators, a
+// brace-initialized `std::initializer_list`, or a `std::tuple` of heterogeneous
+// objects. The separator string is specified as an `absl::string_view`.
+//
+// Because the default formatter uses the `absl::AlphaNum` class,
+// `absl::StrJoin()`, like `absl::StrCat()`, will work out-of-the-box on
+// collections of strings, ints, floats, doubles, etc.
+//
+// Example:
+//
+//   std::vector<std::string> v = {"foo", "bar", "baz"};
+//   std::string s = absl::StrJoin(v, "-");
+//   EXPECT_EQ("foo-bar-baz", s);
+//
+// See comments on the `absl::StrJoin()` function for more examples.
+
+#ifndef ABSL_STRINGS_STR_JOIN_H_
+#define ABSL_STRINGS_STR_JOIN_H_
+
+#include <cstdio>
+#include <cstring>
+#include <initializer_list>
+#include <iterator>
+#include <string>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/macros.h"
+#include "absl/strings/internal/str_join_internal.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+
+// -----------------------------------------------------------------------------
+// Concept: Formatter
+// -----------------------------------------------------------------------------
+//
+// A Formatter is a function object that is responsible for formatting its
+// argument as a string and appending it to a given output std::string.
+// Formatters may be implemented as function objects, lambdas, or normal
+// functions. You may provide your own Formatter to enable `absl::StrJoin()` to
+// work with arbitrary types.
+//
+// The following is an example of a custom Formatter that simply uses
+// `std::to_string()` to format an integer as a std::string.
+//
+//   struct MyFormatter {
+//     void operator()(std::string* out, int i) const {
+//       out->append(std::to_string(i));
+//     }
+//   };
+//
+// You would use the above formatter by passing an instance of it as the final
+// argument to `absl::StrJoin()`:
+//
+//   std::vector<int> v = {1, 2, 3, 4};
+//   std::string s = absl::StrJoin(v, "-", MyFormatter());
+//   EXPECT_EQ("1-2-3-4", s);
+//
+// The following standard formatters are provided within this file:
+//
+// - `AlphaNumFormatter()` (the default)
+// - `StreamFormatter()`
+// - `PairFormatter()`
+// - `DereferenceFormatter()`
+
+// AlphaNumFormatter()
+//
+// Default formatter used if none is specified. Uses `absl::AlphaNum` to convert
+// numeric arguments to strings.
+inline strings_internal::AlphaNumFormatterImpl AlphaNumFormatter() {
+  return strings_internal::AlphaNumFormatterImpl();
+}
+
+// StreamFormatter()
+//
+// Formats its argument using the << operator.
+inline strings_internal::StreamFormatterImpl StreamFormatter() {
+  return strings_internal::StreamFormatterImpl();
+}
+
+// Function Template: PairFormatter(Formatter, absl::string_view, Formatter)
+//
+// Formats a `std::pair` by putting a given separator between the pair's
+// `.first` and `.second` members. This formatter allows you to specify
+// custom Formatters for both the first and second member of each pair.
+template <typename FirstFormatter, typename SecondFormatter>
+inline strings_internal::PairFormatterImpl<FirstFormatter, SecondFormatter>
+PairFormatter(FirstFormatter f1, absl::string_view sep, SecondFormatter f2) {
+  return strings_internal::PairFormatterImpl<FirstFormatter, SecondFormatter>(
+      std::move(f1), sep, std::move(f2));
+}
+
+// Function overload of PairFormatter() for using a default
+// `AlphaNumFormatter()` for each Formatter in the pair.
+inline strings_internal::PairFormatterImpl<
+    strings_internal::AlphaNumFormatterImpl,
+    strings_internal::AlphaNumFormatterImpl>
+PairFormatter(absl::string_view sep) {
+  return PairFormatter(AlphaNumFormatter(), sep, AlphaNumFormatter());
+}
+
+// Function Template: DereferenceFormatter(Formatter)
+//
+// Formats its argument by dereferencing it and then applying the given
+// formatter. This formatter is useful for formatting a container of
+// pointer-to-T. This pattern often shows up when joining repeated fields in
+// protocol buffers.
+template <typename Formatter>
+strings_internal::DereferenceFormatterImpl<Formatter> DereferenceFormatter(
+    Formatter&& f) {
+  return strings_internal::DereferenceFormatterImpl<Formatter>(
+      std::forward<Formatter>(f));
+}
+
+// Function overload of `DererefenceFormatter()` for using a default
+// `AlphaNumFormatter()`.
+inline strings_internal::DereferenceFormatterImpl<
+    strings_internal::AlphaNumFormatterImpl>
+DereferenceFormatter() {
+  return strings_internal::DereferenceFormatterImpl<
+      strings_internal::AlphaNumFormatterImpl>(AlphaNumFormatter());
+}
+
+// -----------------------------------------------------------------------------
+// StrJoin()
+// -----------------------------------------------------------------------------
+//
+// Joins a range of elements and returns the result as a std::string.
+// `absl::StrJoin()` takes a range, a separator string to use between the
+// elements joined, and an optional Formatter responsible for converting each
+// argument in the range to a string.
+//
+// If omitted, the default `AlphaNumFormatter()` is called on the elements to be
+// joined.
+//
+// Example 1:
+//   // Joins a collection of strings. This pattern also works with a collection
+//   // of `absl::string_view` or even `const char*`.
+//   std::vector<std::string> v = {"foo", "bar", "baz"};
+//   std::string s = absl::StrJoin(v, "-");
+//   EXPECT_EQ("foo-bar-baz", s);
+//
+// Example 2:
+//   // Joins the values in the given `std::initializer_list<>` specified using
+//   // brace initialization. This pattern also works with an initializer_list
+//   // of ints or `absl::string_view` -- any `AlphaNum`-compatible type.
+//   std::string s = absl::StrJoin({"foo", "bar", "baz"}, "-");
+//   EXPECT_EQ("foo-bar-baz", s);
+//
+// Example 3:
+//   // Joins a collection of ints. This pattern also works with floats,
+//   // doubles, int64s -- any `StrCat()`-compatible type.
+//   std::vector<int> v = {1, 2, 3, -4};
+//   std::string s = absl::StrJoin(v, "-");
+//   EXPECT_EQ("1-2-3--4", s);
+//
+// Example 4:
+//   // Joins a collection of pointer-to-int. By default, pointers are
+//   // dereferenced and the pointee is formatted using the default format for
+//   // that type; such dereferencing occurs for all levels of indirection, so
+//   // this pattern works just as well for `std::vector<int**>` as for
+//   // `std::vector<int*>`.
+//   int x = 1, y = 2, z = 3;
+//   std::vector<int*> v = {&x, &y, &z};
+//   std::string s = absl::StrJoin(v, "-");
+//   EXPECT_EQ("1-2-3", s);
+//
+// Example 5:
+//   // Dereferencing of `std::unique_ptr<>` is also supported:
+//   std::vector<std::unique_ptr<int>> v
+//   v.emplace_back(new int(1));
+//   v.emplace_back(new int(2));
+//   v.emplace_back(new int(3));
+//   std::string s = absl::StrJoin(v, "-");
+//   EXPECT_EQ("1-2-3", s);
+//
+// Example 6:
+//   // Joins a `std::map`, with each key-value pair separated by an equals
+//   // sign. This pattern would also work with, say, a
+//   // `std::vector<std::pair<>>`.
+//   std::map<std::string, int> m = {
+//       std::make_pair("a", 1),
+//       std::make_pair("b", 2),
+//       std::make_pair("c", 3)};
+//   std::string s = absl::StrJoin(m, ",", absl::PairFormatter("="));
+//   EXPECT_EQ("a=1,b=2,c=3", s);
+//
+// Example 7:
+//   // These examples show how `absl::StrJoin()` handles a few common edge
+//   // cases:
+//   std::vector<std::string> v_empty;
+//   EXPECT_EQ("", absl::StrJoin(v_empty, "-"));
+//
+//   std::vector<std::string> v_one_item = {"foo"};
+//   EXPECT_EQ("foo", absl::StrJoin(v_one_item, "-"));
+//
+//   std::vector<std::string> v_empty_string = {""};
+//   EXPECT_EQ("", absl::StrJoin(v_empty_string, "-"));
+//
+//   std::vector<std::string> v_one_item_empty_string = {"a", ""};
+//   EXPECT_EQ("a-", absl::StrJoin(v_one_item_empty_string, "-"));
+//
+//   std::vector<std::string> v_two_empty_string = {"", ""};
+//   EXPECT_EQ("-", absl::StrJoin(v_two_empty_string, "-"));
+//
+// Example 8:
+//   // Joins a `std::tuple<T...>` of heterogeneous types, converting each to
+//   // a std::string using the `absl::AlphaNum` class.
+//   std::string s = absl::StrJoin(std::make_tuple(123, "abc", 0.456), "-");
+//   EXPECT_EQ("123-abc-0.456", s);
+
+template <typename Iterator, typename Formatter>
+std::string StrJoin(Iterator start, Iterator end, absl::string_view sep,
+                    Formatter&& fmt) {
+  return strings_internal::JoinAlgorithm(start, end, sep, fmt);
+}
+
+template <typename Range, typename Formatter>
+std::string StrJoin(const Range& range, absl::string_view separator,
+                    Formatter&& fmt) {
+  return strings_internal::JoinRange(range, separator, fmt);
+}
+
+template <typename T, typename Formatter>
+std::string StrJoin(std::initializer_list<T> il, absl::string_view separator,
+                    Formatter&& fmt) {
+  return strings_internal::JoinRange(il, separator, fmt);
+}
+
+template <typename... T, typename Formatter>
+std::string StrJoin(const std::tuple<T...>& value, absl::string_view separator,
+                    Formatter&& fmt) {
+  return strings_internal::JoinAlgorithm(value, separator, fmt);
+}
+
+template <typename Iterator>
+std::string StrJoin(Iterator start, Iterator end, absl::string_view separator) {
+  return strings_internal::JoinRange(start, end, separator);
+}
+
+template <typename Range>
+std::string StrJoin(const Range& range, absl::string_view separator) {
+  return strings_internal::JoinRange(range, separator);
+}
+
+template <typename T>
+std::string StrJoin(std::initializer_list<T> il,
+                    absl::string_view separator) {
+  return strings_internal::JoinRange(il, separator);
+}
+
+template <typename... T>
+std::string StrJoin(const std::tuple<T...>& value,
+                    absl::string_view separator) {
+  return strings_internal::JoinAlgorithm(value, separator, AlphaNumFormatter());
+}
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_STR_JOIN_H_
diff --git a/absl/strings/str_join_benchmark.cc b/absl/strings/str_join_benchmark.cc
new file mode 100644
index 0000000..d6f689f
--- /dev/null
+++ b/absl/strings/str_join_benchmark.cc
@@ -0,0 +1,97 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/str_join.h"
+
+#include <string>
+#include <vector>
+#include <utility>
+
+#include "benchmark/benchmark.h"
+
+namespace {
+
+void BM_Join2_Strings(benchmark::State& state) {
+  const int string_len = state.range(0);
+  const int num_strings = state.range(1);
+  const std::string s(string_len, 'x');
+  const std::vector<std::string> v(num_strings, s);
+  for (auto _ : state) {
+    std::string s = absl::StrJoin(v, "-");
+    benchmark::DoNotOptimize(s);
+  }
+}
+BENCHMARK(BM_Join2_Strings)
+    ->ArgPair(1 << 0, 1 << 3)
+    ->ArgPair(1 << 10, 1 << 3)
+    ->ArgPair(1 << 13, 1 << 3)
+    ->ArgPair(1 << 0, 1 << 10)
+    ->ArgPair(1 << 10, 1 << 10)
+    ->ArgPair(1 << 13, 1 << 10)
+    ->ArgPair(1 << 0, 1 << 13)
+    ->ArgPair(1 << 10, 1 << 13)
+    ->ArgPair(1 << 13, 1 << 13);
+
+void BM_Join2_Ints(benchmark::State& state) {
+  const int num_ints = state.range(0);
+  const std::vector<int> v(num_ints, 42);
+  for (auto _ : state) {
+    std::string s = absl::StrJoin(v, "-");
+    benchmark::DoNotOptimize(s);
+  }
+}
+BENCHMARK(BM_Join2_Ints)->Range(0, 1 << 13);
+
+void BM_Join2_KeysAndValues(benchmark::State& state) {
+  const int string_len = state.range(0);
+  const int num_pairs = state.range(1);
+  const std::string s(string_len, 'x');
+  const std::vector<std::pair<std::string, int>> v(num_pairs,
+                                                   std::make_pair(s, 42));
+  for (auto _ : state) {
+    std::string s = absl::StrJoin(v, ",", absl::PairFormatter("="));
+    benchmark::DoNotOptimize(s);
+  }
+}
+BENCHMARK(BM_Join2_KeysAndValues)
+    ->ArgPair(1 << 0, 1 << 3)
+    ->ArgPair(1 << 10, 1 << 3)
+    ->ArgPair(1 << 13, 1 << 3)
+    ->ArgPair(1 << 0, 1 << 10)
+    ->ArgPair(1 << 10, 1 << 10)
+    ->ArgPair(1 << 13, 1 << 10)
+    ->ArgPair(1 << 0, 1 << 13)
+    ->ArgPair(1 << 10, 1 << 13)
+    ->ArgPair(1 << 13, 1 << 13);
+
+void BM_JoinStreamable(benchmark::State& state) {
+  const int string_len = state.range(0);
+  const int num_strings = state.range(1);
+  const std::vector<std::string> v(num_strings, std::string(string_len, 'x'));
+  for (auto _ : state) {
+    std::string s = absl::StrJoin(v, "", absl::StreamFormatter());
+    benchmark::DoNotOptimize(s);
+  }
+}
+BENCHMARK(BM_JoinStreamable)
+    ->ArgPair(0, 0)
+    ->ArgPair(16, 1)
+    ->ArgPair(256, 1)
+    ->ArgPair(16, 16)
+    ->ArgPair(256, 16)
+    ->ArgPair(16, 256)
+    ->ArgPair(256, 256);
+
+}  // namespace
diff --git a/absl/strings/str_join_test.cc b/absl/strings/str_join_test.cc
new file mode 100644
index 0000000..921d9c2
--- /dev/null
+++ b/absl/strings/str_join_test.cc
@@ -0,0 +1,474 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Unit tests for all join.h functions
+
+#include "absl/strings/str_join.h"
+
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <functional>
+#include <initializer_list>
+#include <map>
+#include <memory>
+#include <ostream>
+#include <tuple>
+#include <type_traits>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "absl/base/macros.h"
+#include "absl/memory/memory.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_split.h"
+
+namespace {
+
+TEST(StrJoin, APIExamples) {
+  {
+    // Collection of strings
+    std::vector<std::string> v = {"foo", "bar", "baz"};
+    EXPECT_EQ("foo-bar-baz", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // Collection of absl::string_view
+    std::vector<absl::string_view> v = {"foo", "bar", "baz"};
+    EXPECT_EQ("foo-bar-baz", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // Collection of const char*
+    std::vector<const char*> v = {"foo", "bar", "baz"};
+    EXPECT_EQ("foo-bar-baz", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // Collection of non-const char*
+    std::string a = "foo", b = "bar", c = "baz";
+    std::vector<char*> v = {&a[0], &b[0], &c[0]};
+    EXPECT_EQ("foo-bar-baz", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // Collection of ints
+    std::vector<int> v = {1, 2, 3, -4};
+    EXPECT_EQ("1-2-3--4", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // Literals passed as a std::initializer_list
+    std::string s = absl::StrJoin({"a", "b", "c"}, "-");
+    EXPECT_EQ("a-b-c", s);
+  }
+  {
+    // Join a std::tuple<T...>.
+    std::string s = absl::StrJoin(std::make_tuple(123, "abc", 0.456), "-");
+    EXPECT_EQ("123-abc-0.456", s);
+  }
+
+  {
+    // Collection of unique_ptrs
+    std::vector<std::unique_ptr<int>> v;
+    v.emplace_back(new int(1));
+    v.emplace_back(new int(2));
+    v.emplace_back(new int(3));
+    EXPECT_EQ("1-2-3", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // Array of ints
+    const int a[] = {1, 2, 3, -4};
+    EXPECT_EQ("1-2-3--4", absl::StrJoin(a, a + ABSL_ARRAYSIZE(a), "-"));
+  }
+
+  {
+    // Collection of pointers
+    int x = 1, y = 2, z = 3;
+    std::vector<int*> v = {&x, &y, &z};
+    EXPECT_EQ("1-2-3", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // Collection of pointers to pointers
+    int x = 1, y = 2, z = 3;
+    int *px = &x, *py = &y, *pz = &z;
+    std::vector<int**> v = {&px, &py, &pz};
+    EXPECT_EQ("1-2-3", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // Collection of pointers to std::string
+    std::string a("a"), b("b");
+    std::vector<std::string*> v = {&a, &b};
+    EXPECT_EQ("a-b", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // A std::map, which is a collection of std::pair<>s.
+    std::map<std::string, int> m = {{"a", 1}, {"b", 2}, {"c", 3}};
+    EXPECT_EQ("a=1,b=2,c=3", absl::StrJoin(m, ",", absl::PairFormatter("=")));
+  }
+
+  {
+    // Shows absl::StrSplit and absl::StrJoin working together. This example is
+    // equivalent to s/=/-/g.
+    const std::string s = "a=b=c=d";
+    EXPECT_EQ("a-b-c-d", absl::StrJoin(absl::StrSplit(s, "="), "-"));
+  }
+
+  //
+  // A few examples of edge cases
+  //
+
+  {
+    // Empty range yields an empty std::string.
+    std::vector<std::string> v;
+    EXPECT_EQ("", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // A range of 1 element gives a std::string with that element but no
+    // separator.
+    std::vector<std::string> v = {"foo"};
+    EXPECT_EQ("foo", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // A range with a single empty std::string element
+    std::vector<std::string> v = {""};
+    EXPECT_EQ("", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // A range with 2 elements, one of which is an empty std::string
+    std::vector<std::string> v = {"a", ""};
+    EXPECT_EQ("a-", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // A range with 2 empty elements.
+    std::vector<std::string> v = {"", ""};
+    EXPECT_EQ("-", absl::StrJoin(v, "-"));
+  }
+
+  {
+    // A std::vector of bool.
+    std::vector<bool> v = {true, false, true};
+    EXPECT_EQ("1-0-1", absl::StrJoin(v, "-"));
+  }
+}
+
+TEST(StrJoin, CustomFormatter) {
+  std::vector<std::string> v{"One", "Two", "Three"};
+  {
+    std::string joined =
+        absl::StrJoin(v, "", [](std::string* out, const std::string& in) {
+          absl::StrAppend(out, "(", in, ")");
+        });
+    EXPECT_EQ("(One)(Two)(Three)", joined);
+  }
+  {
+    class ImmovableFormatter {
+     public:
+      void operator()(std::string* out, const std::string& in) {
+        absl::StrAppend(out, "(", in, ")");
+      }
+      ImmovableFormatter() {}
+      ImmovableFormatter(const ImmovableFormatter&) = delete;
+    };
+    EXPECT_EQ("(One)(Two)(Three)", absl::StrJoin(v, "", ImmovableFormatter()));
+  }
+  {
+    class OverloadedFormatter {
+     public:
+      void operator()(std::string* out, const std::string& in) {
+        absl::StrAppend(out, "(", in, ")");
+      }
+      void operator()(std::string* out, const std::string& in) const {
+        absl::StrAppend(out, "[", in, "]");
+      }
+    };
+    EXPECT_EQ("(One)(Two)(Three)", absl::StrJoin(v, "", OverloadedFormatter()));
+    const OverloadedFormatter fmt = {};
+    EXPECT_EQ("[One][Two][Three]", absl::StrJoin(v, "", fmt));
+  }
+}
+
+//
+// Tests the Formatters
+//
+
+TEST(AlphaNumFormatter, FormatterAPI) {
+  // Not an exhaustive test. See strings/strcat_test.h for the exhaustive test
+  // of what AlphaNum can convert.
+  auto f = absl::AlphaNumFormatter();
+  std::string s;
+  f(&s, "Testing: ");
+  f(&s, static_cast<int>(1));
+  f(&s, static_cast<int16_t>(2));
+  f(&s, static_cast<int64_t>(3));
+  f(&s, static_cast<float>(4));
+  f(&s, static_cast<double>(5));
+  f(&s, static_cast<unsigned>(6));
+  f(&s, static_cast<size_t>(7));
+  f(&s, absl::string_view(" OK"));
+  EXPECT_EQ("Testing: 1234567 OK", s);
+}
+
+// Make sure people who are mistakenly using std::vector<bool> even though
+// they're not memory-constrained can use absl::AlphaNumFormatter().
+TEST(AlphaNumFormatter, VectorOfBool) {
+  auto f = absl::AlphaNumFormatter();
+  std::string s;
+  std::vector<bool> v = {true, false, true};
+  f(&s, *v.cbegin());
+  f(&s, *v.begin());
+  f(&s, v[1]);
+  EXPECT_EQ("110", s);
+}
+
+TEST(AlphaNumFormatter, AlphaNum) {
+  auto f = absl::AlphaNumFormatter();
+  std::string s;
+  f(&s, absl::AlphaNum("hello"));
+  EXPECT_EQ("hello", s);
+}
+
+struct StreamableType {
+  std::string contents;
+};
+inline std::ostream& operator<<(std::ostream& os, const StreamableType& t) {
+  os << "Streamable:" << t.contents;
+  return os;
+}
+
+TEST(StreamFormatter, FormatterAPI) {
+  auto f = absl::StreamFormatter();
+  std::string s;
+  f(&s, "Testing: ");
+  f(&s, static_cast<int>(1));
+  f(&s, static_cast<int16_t>(2));
+  f(&s, static_cast<int64_t>(3));
+  f(&s, static_cast<float>(4));
+  f(&s, static_cast<double>(5));
+  f(&s, static_cast<unsigned>(6));
+  f(&s, static_cast<size_t>(7));
+  f(&s, absl::string_view(" OK "));
+  StreamableType streamable = {"object"};
+  f(&s, streamable);
+  EXPECT_EQ("Testing: 1234567 OK Streamable:object", s);
+}
+
+// A dummy formatter that wraps each element in parens. Used in some tests
+// below.
+struct TestingParenFormatter {
+  template <typename T>
+  void operator()(std::string* s, const T& t) {
+    absl::StrAppend(s, "(", t, ")");
+  }
+};
+
+TEST(PairFormatter, FormatterAPI) {
+  {
+    // Tests default PairFormatter(sep) that uses AlphaNumFormatter for the
+    // 'first' and 'second' members.
+    const auto f = absl::PairFormatter("=");
+    std::string s;
+    f(&s, std::make_pair("a", "b"));
+    f(&s, std::make_pair(1, 2));
+    EXPECT_EQ("a=b1=2", s);
+  }
+
+  {
+    // Tests using a custom formatter for the 'first' and 'second' members.
+    auto f = absl::PairFormatter(TestingParenFormatter(), "=",
+                                 TestingParenFormatter());
+    std::string s;
+    f(&s, std::make_pair("a", "b"));
+    f(&s, std::make_pair(1, 2));
+    EXPECT_EQ("(a)=(b)(1)=(2)", s);
+  }
+}
+
+TEST(DereferenceFormatter, FormatterAPI) {
+  {
+    // Tests wrapping the default AlphaNumFormatter.
+    const absl::strings_internal::DereferenceFormatterImpl<
+        absl::strings_internal::AlphaNumFormatterImpl>
+        f;
+    int x = 1, y = 2, z = 3;
+    std::string s;
+    f(&s, &x);
+    f(&s, &y);
+    f(&s, &z);
+    EXPECT_EQ("123", s);
+  }
+
+  {
+    // Tests wrapping std::string's default formatter.
+    absl::strings_internal::DereferenceFormatterImpl<
+        absl::strings_internal::DefaultFormatter<std::string>::Type>
+        f;
+
+    std::string x = "x";
+    std::string y = "y";
+    std::string z = "z";
+    std::string s;
+    f(&s, &x);
+    f(&s, &y);
+    f(&s, &z);
+    EXPECT_EQ(s, "xyz");
+  }
+
+  {
+    // Tests wrapping a custom formatter.
+    auto f = absl::DereferenceFormatter(TestingParenFormatter());
+    int x = 1, y = 2, z = 3;
+    std::string s;
+    f(&s, &x);
+    f(&s, &y);
+    f(&s, &z);
+    EXPECT_EQ("(1)(2)(3)", s);
+  }
+
+  {
+    absl::strings_internal::DereferenceFormatterImpl<
+        absl::strings_internal::AlphaNumFormatterImpl>
+        f;
+    auto x = std::unique_ptr<int>(new int(1));
+    auto y = std::unique_ptr<int>(new int(2));
+    auto z = std::unique_ptr<int>(new int(3));
+    std::string s;
+    f(&s, x);
+    f(&s, y);
+    f(&s, z);
+    EXPECT_EQ("123", s);
+  }
+}
+
+//
+// Tests the interfaces for the 4 public Join function overloads. The semantics
+// of the algorithm is covered in the above APIExamples test.
+//
+TEST(StrJoin, PublicAPIOverloads) {
+  std::vector<std::string> v = {"a", "b", "c"};
+
+  // Iterators + formatter
+  EXPECT_EQ("a-b-c",
+            absl::StrJoin(v.begin(), v.end(), "-", absl::AlphaNumFormatter()));
+  // Range + formatter
+  EXPECT_EQ("a-b-c", absl::StrJoin(v, "-", absl::AlphaNumFormatter()));
+  // Iterators, no formatter
+  EXPECT_EQ("a-b-c", absl::StrJoin(v.begin(), v.end(), "-"));
+  // Range, no formatter
+  EXPECT_EQ("a-b-c", absl::StrJoin(v, "-"));
+}
+
+TEST(StrJoin, Array) {
+  const absl::string_view a[] = {"a", "b", "c"};
+  EXPECT_EQ("a-b-c", absl::StrJoin(a, "-"));
+}
+
+TEST(StrJoin, InitializerList) {
+  { EXPECT_EQ("a-b-c", absl::StrJoin({"a", "b", "c"}, "-")); }
+
+  {
+    auto a = {"a", "b", "c"};
+    EXPECT_EQ("a-b-c", absl::StrJoin(a, "-"));
+  }
+
+  {
+    std::initializer_list<const char*> a = {"a", "b", "c"};
+    EXPECT_EQ("a-b-c", absl::StrJoin(a, "-"));
+  }
+
+  {
+    std::initializer_list<std::string> a = {"a", "b", "c"};
+    EXPECT_EQ("a-b-c", absl::StrJoin(a, "-"));
+  }
+
+  {
+    std::initializer_list<absl::string_view> a = {"a", "b", "c"};
+    EXPECT_EQ("a-b-c", absl::StrJoin(a, "-"));
+  }
+
+  {
+    // Tests initializer_list with a non-default formatter
+    auto a = {"a", "b", "c"};
+    TestingParenFormatter f;
+    EXPECT_EQ("(a)-(b)-(c)", absl::StrJoin(a, "-", f));
+  }
+
+  {
+    // initializer_list of ints
+    EXPECT_EQ("1-2-3", absl::StrJoin({1, 2, 3}, "-"));
+  }
+
+  {
+    // Tests initializer_list of ints with a non-default formatter
+    auto a = {1, 2, 3};
+    TestingParenFormatter f;
+    EXPECT_EQ("(1)-(2)-(3)", absl::StrJoin(a, "-", f));
+  }
+}
+
+TEST(StrJoin, Tuple) {
+  EXPECT_EQ("", absl::StrJoin(std::make_tuple(), "-"));
+  EXPECT_EQ("hello", absl::StrJoin(std::make_tuple("hello"), "-"));
+
+  int x(10);
+  std::string y("hello");
+  double z(3.14);
+  EXPECT_EQ("10-hello-3.14", absl::StrJoin(std::make_tuple(x, y, z), "-"));
+
+  // Faster! Faster!!
+  EXPECT_EQ("10-hello-3.14",
+            absl::StrJoin(std::make_tuple(x, std::cref(y), z), "-"));
+
+  struct TestFormatter {
+    char buffer[128];
+    void operator()(std::string* out, int v) {
+      snprintf(buffer, sizeof(buffer), "%#.8x", v);
+      out->append(buffer);
+    }
+    void operator()(std::string* out, double v) {
+      snprintf(buffer, sizeof(buffer), "%#.0f", v);
+      out->append(buffer);
+    }
+    void operator()(std::string* out, const std::string& v) {
+      snprintf(buffer, sizeof(buffer), "%.4s", v.c_str());
+      out->append(buffer);
+    }
+  };
+  EXPECT_EQ("0x0000000a-hell-3.",
+            absl::StrJoin(std::make_tuple(x, y, z), "-", TestFormatter()));
+  EXPECT_EQ(
+      "0x0000000a-hell-3.",
+      absl::StrJoin(std::make_tuple(x, std::cref(y), z), "-", TestFormatter()));
+  EXPECT_EQ("0x0000000a-hell-3.",
+            absl::StrJoin(std::make_tuple(&x, &y, &z), "-",
+                          absl::DereferenceFormatter(TestFormatter())));
+  EXPECT_EQ("0x0000000a-hell-3.",
+            absl::StrJoin(std::make_tuple(absl::make_unique<int>(x),
+                                          absl::make_unique<std::string>(y),
+                                          absl::make_unique<double>(z)),
+                          "-", absl::DereferenceFormatter(TestFormatter())));
+  EXPECT_EQ("0x0000000a-hell-3.",
+            absl::StrJoin(std::make_tuple(absl::make_unique<int>(x), &y, &z),
+                          "-", absl::DereferenceFormatter(TestFormatter())));
+}
+
+}  // namespace
diff --git a/absl/strings/str_replace.cc b/absl/strings/str_replace.cc
new file mode 100644
index 0000000..280f63d
--- /dev/null
+++ b/absl/strings/str_replace.cc
@@ -0,0 +1,80 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/str_replace.h"
+
+#include "absl/strings/str_cat.h"
+
+namespace absl {
+namespace strings_internal {
+
+using FixedMapping =
+    std::initializer_list<std::pair<absl::string_view, absl::string_view>>;
+
+// Applies the ViableSubstitutions in subs_ptr to the absl::string_view s, and
+// stores the result in *result_ptr. Returns the number of substitutions that
+// occurred.
+int ApplySubstitutions(
+    absl::string_view s,
+    std::vector<strings_internal::ViableSubstitution>* subs_ptr,
+    std::string* result_ptr) {
+  auto& subs = *subs_ptr;
+  int substitutions = 0;
+  size_t pos = 0;
+  while (!subs.empty()) {
+    auto& sub = subs.back();
+    if (sub.offset >= pos) {
+      if (pos <= s.size()) {
+        StrAppend(result_ptr, s.substr(pos, sub.offset - pos), sub.replacement);
+      }
+      pos = sub.offset + sub.old.size();
+      substitutions += 1;
+    }
+    sub.offset = s.find(sub.old, pos);
+    if (sub.offset == s.npos) {
+      subs.pop_back();
+    } else {
+      // Insertion sort to ensure the last ViableSubstitution continues to be
+      // before all the others.
+      size_t index = subs.size();
+      while (--index && subs[index - 1].OccursBefore(subs[index])) {
+        std::swap(subs[index], subs[index - 1]);
+      }
+    }
+  }
+  result_ptr->append(s.data() + pos, s.size() - pos);
+  return substitutions;
+}
+
+}  // namespace strings_internal
+
+// We can implement this in terms of the generic StrReplaceAll, but
+// we must specify the template overload because C++ cannot deduce the type
+// of an initializer_list parameter to a function, and also if we don't specify
+// the type, we just call ourselves.
+//
+// Note that we implement them here, rather than in the header, so that they
+// aren't inlined.
+
+std::string StrReplaceAll(absl::string_view s,
+                          strings_internal::FixedMapping replacements) {
+  return StrReplaceAll<strings_internal::FixedMapping>(s, replacements);
+}
+
+int StrReplaceAll(strings_internal::FixedMapping replacements,
+                  std::string* target) {
+  return StrReplaceAll<strings_internal::FixedMapping>(replacements, target);
+}
+
+}  // namespace absl
diff --git a/absl/strings/str_replace.h b/absl/strings/str_replace.h
new file mode 100644
index 0000000..30540d0
--- /dev/null
+++ b/absl/strings/str_replace.h
@@ -0,0 +1,217 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: str_replace.h
+// -----------------------------------------------------------------------------
+//
+// This file defines `absl::StrReplaceAll()`, a general-purpose string
+// replacement function designed for large, arbitrary text substitutions,
+// especially on strings which you are receiving from some other system for
+// further processing (e.g. processing regular expressions, escaping HTML
+// entities, etc.). `StrReplaceAll` is designed to be efficient even when only
+// one substitution is being performed, or when substitution is rare.
+//
+// If the string being modified is known at compile-time, and the substitutions
+// vary, `absl::Substitute()` may be a better choice.
+//
+// Example:
+//
+// std::string html_escaped = absl::StrReplaceAll(user_input, {
+//                                                {"&", "&amp;"},
+//                                                {"<", "&lt;"},
+//                                                {">", "&gt;"},
+//                                                {"\"", "&quot;"},
+//                                                {"'", "&#39;"}});
+#ifndef ABSL_STRINGS_STR_REPLACE_H_
+#define ABSL_STRINGS_STR_REPLACE_H_
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "absl/base/attributes.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+
+// StrReplaceAll()
+//
+// Replaces character sequences within a given string with replacements provided
+// within an initializer list of key/value pairs. Candidate replacements are
+// considered in order as they occur within the string, with earlier matches
+// taking precedence, and longer matches taking precedence for candidates
+// starting at the same position in the string. Once a substitution is made, the
+// replaced text is not considered for any further substitutions.
+//
+// Example:
+//
+//   std::string s = absl::StrReplaceAll(
+//       "$who bought $count #Noun. Thanks $who!",
+//       {{"$count", absl::StrCat(5)},
+//        {"$who", "Bob"},
+//        {"#Noun", "Apples"}});
+//   EXPECT_EQ("Bob bought 5 Apples. Thanks Bob!", s);
+ABSL_MUST_USE_RESULT std::string StrReplaceAll(
+    absl::string_view s,
+    std::initializer_list<std::pair<absl::string_view, absl::string_view>>
+        replacements);
+
+// Overload of `StrReplaceAll()` to accept a container of key/value replacement
+// pairs (typically either an associative map or a `std::vector` of `std::pair`
+// elements). A vector of pairs is generally more efficient.
+//
+// Examples:
+//
+//   std::map<const absl::string_view, const absl::string_view> replacements;
+//   replacements["$who"] = "Bob";
+//   replacements["$count"] = "5";
+//   replacements["#Noun"] = "Apples";
+//   std::string s = absl::StrReplaceAll(
+//       "$who bought $count #Noun. Thanks $who!",
+//       replacements);
+//   EXPECT_EQ("Bob bought 5 Apples. Thanks Bob!", s);
+//
+//   // A std::vector of std::pair elements can be more efficient.
+//   std::vector<std::pair<const absl::string_view, std::string>> replacements;
+//   replacements.push_back({"&", "&amp;"});
+//   replacements.push_back({"<", "&lt;"});
+//   replacements.push_back({">", "&gt;"});
+//   std::string s = absl::StrReplaceAll("if (ptr < &foo)",
+//                                  replacements);
+//   EXPECT_EQ("if (ptr &lt; &amp;foo)", s);
+template <typename StrToStrMapping>
+std::string StrReplaceAll(absl::string_view s,
+                          const StrToStrMapping& replacements);
+
+// Overload of `StrReplaceAll()` to replace character sequences within a given
+// output string *in place* with replacements provided within an initializer
+// list of key/value pairs, returning the number of substitutions that occurred.
+//
+// Example:
+//
+//   std::string s = std::string("$who bought $count #Noun. Thanks $who!");
+//   int count;
+//   count = absl::StrReplaceAll({{"$count", absl::StrCat(5)},
+//                               {"$who", "Bob"},
+//                               {"#Noun", "Apples"}}, &s);
+//  EXPECT_EQ(count, 4);
+//  EXPECT_EQ("Bob bought 5 Apples. Thanks Bob!", s);
+int StrReplaceAll(
+    std::initializer_list<std::pair<absl::string_view, absl::string_view>>
+        replacements,
+    std::string* target);
+
+// Overload of `StrReplaceAll()` to replace patterns within a given output
+// string *in place* with replacements provided within a container of key/value
+// pairs.
+//
+// Example:
+//
+//   std::string s = std::string("if (ptr < &foo)");
+//   int count = absl::StrReplaceAll({{"&", "&amp;"},
+//                                    {"<", "&lt;"},
+//                                    {">", "&gt;"}}, &s);
+//  EXPECT_EQ(count, 2);
+//  EXPECT_EQ("if (ptr &lt; &amp;foo)", s);
+template <typename StrToStrMapping>
+int StrReplaceAll(const StrToStrMapping& replacements, std::string* target);
+
+// Implementation details only, past this point.
+namespace strings_internal {
+
+struct ViableSubstitution {
+  absl::string_view old;
+  absl::string_view replacement;
+  size_t offset;
+
+  ViableSubstitution(absl::string_view old_str,
+                     absl::string_view replacement_str, size_t offset_val)
+      : old(old_str), replacement(replacement_str), offset(offset_val) {}
+
+  // One substitution occurs "before" another (takes priority) if either
+  // it has the lowest offset, or it has the same offset but a larger size.
+  bool OccursBefore(const ViableSubstitution& y) const {
+    if (offset != y.offset) return offset < y.offset;
+    return old.size() > y.old.size();
+  }
+};
+
+// Build a vector of ViableSubstitutions based on the given list of
+// replacements. subs can be implemented as a priority_queue. However, it turns
+// out that most callers have small enough a list of substitutions that the
+// overhead of such a queue isn't worth it.
+template <typename StrToStrMapping>
+std::vector<ViableSubstitution> FindSubstitutions(
+    absl::string_view s, const StrToStrMapping& replacements) {
+  std::vector<ViableSubstitution> subs;
+  subs.reserve(replacements.size());
+
+  for (const auto& rep : replacements) {
+    using std::get;
+    absl::string_view old(get<0>(rep));
+
+    size_t pos = s.find(old);
+    if (pos == s.npos) continue;
+
+    // Ignore attempts to replace "". This condition is almost never true,
+    // but above condition is frequently true. That's why we test for this
+    // now and not before.
+    if (old.empty()) continue;
+
+    subs.emplace_back(old, get<1>(rep), pos);
+
+    // Insertion sort to ensure the last ViableSubstitution comes before
+    // all the others.
+    size_t index = subs.size();
+    while (--index && subs[index - 1].OccursBefore(subs[index])) {
+      std::swap(subs[index], subs[index - 1]);
+    }
+  }
+  return subs;
+}
+
+int ApplySubstitutions(absl::string_view s,
+                       std::vector<ViableSubstitution>* subs_ptr,
+                       std::string* result_ptr);
+
+}  // namespace strings_internal
+
+template <typename StrToStrMapping>
+std::string StrReplaceAll(absl::string_view s,
+                          const StrToStrMapping& replacements) {
+  auto subs = strings_internal::FindSubstitutions(s, replacements);
+  std::string result;
+  result.reserve(s.size());
+  strings_internal::ApplySubstitutions(s, &subs, &result);
+  return result;
+}
+
+template <typename StrToStrMapping>
+int StrReplaceAll(const StrToStrMapping& replacements, std::string* target) {
+  auto subs = strings_internal::FindSubstitutions(*target, replacements);
+  if (subs.empty()) return 0;
+
+  std::string result;
+  result.reserve(target->size());
+  int substitutions =
+      strings_internal::ApplySubstitutions(*target, &subs, &result);
+  target->swap(result);
+  return substitutions;
+}
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_STR_REPLACE_H_
diff --git a/absl/strings/str_replace_benchmark.cc b/absl/strings/str_replace_benchmark.cc
new file mode 100644
index 0000000..95b2dc1
--- /dev/null
+++ b/absl/strings/str_replace_benchmark.cc
@@ -0,0 +1,122 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/str_replace.h"
+
+#include <cstring>
+#include <string>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/internal/raw_logging.h"
+
+namespace {
+
+std::string* big_string;
+std::string* after_replacing_the;
+std::string* after_replacing_many;
+
+struct Replacement {
+  const char* needle;
+  const char* replacement;
+} replacements[] = {
+    {"the", "box"},          //
+    {"brown", "quick"},      //
+    {"jumped", "liquored"},  //
+    {"dozen", "brown"},      //
+    {"lazy", "pack"},        //
+    {"liquor", "shakes"},    //
+};
+
+// Here, we set up a string for use in global-replace benchmarks.
+// We started with a million blanks, and then deterministically insert
+// 10,000 copies each of two pangrams.  The result is a string that is
+// 40% blank space and 60% these words.  'the' occurs 18,247 times and
+// all the substitutions together occur 49,004 times.
+//
+// We then create "after_replacing_the" to be a string that is a result of
+// replacing "the" with "box" in big_string.
+//
+// And then we create "after_replacing_many" to be a string that is result
+// of preferring several substitutions.
+void SetUpStrings() {
+  if (big_string == nullptr) {
+    size_t r = 0;
+    big_string = new std::string(1000 * 1000, ' ');
+    for (std::string phrase : {"the quick brown fox jumped over the lazy dogs",
+                               "pack my box with the five dozen liquor jugs"}) {
+      for (int i = 0; i < 10 * 1000; ++i) {
+        r = r * 237 + 41;  // not very random.
+        memcpy(&(*big_string)[r % (big_string->size() - phrase.size())],
+               phrase.data(), phrase.size());
+      }
+    }
+    // big_string->resize(50);
+    // OK, we've set up the std::string, now let's set up expectations - first by
+    // just replacing "the" with "box"
+    after_replacing_the = new std::string(*big_string);
+    for (size_t pos = 0;
+         (pos = after_replacing_the->find("the", pos)) != std::string::npos;) {
+      memcpy(&(*after_replacing_the)[pos], "box", 3);
+    }
+    // And then with all the replacements.
+    after_replacing_many = new std::string(*big_string);
+    for (size_t pos = 0;;) {
+      size_t next_pos = static_cast<size_t>(-1);
+      const char* needle_string = nullptr;
+      const char* replacement_string = nullptr;
+      for (const auto& r : replacements) {
+        auto needlepos = after_replacing_many->find(r.needle, pos);
+        if (needlepos != std::string::npos && needlepos < next_pos) {
+          next_pos = needlepos;
+          needle_string = r.needle;
+          replacement_string = r.replacement;
+        }
+      }
+      if (next_pos > after_replacing_many->size()) break;
+      after_replacing_many->replace(next_pos, strlen(needle_string),
+                                    replacement_string);
+      next_pos += strlen(replacement_string);
+      pos = next_pos;
+    }
+  }
+}
+
+void BM_StrReplaceAllOneReplacement(benchmark::State& state) {
+  SetUpStrings();
+  std::string src = *big_string;
+  for (auto _ : state) {
+    std::string dest = absl::StrReplaceAll(src, {{"the", "box"}});
+    ABSL_RAW_CHECK(dest == *after_replacing_the,
+                   "not benchmarking intended behavior");
+  }
+}
+BENCHMARK(BM_StrReplaceAllOneReplacement);
+
+void BM_StrReplaceAll(benchmark::State& state) {
+  SetUpStrings();
+  std::string src = *big_string;
+  for (auto _ : state) {
+    std::string dest = absl::StrReplaceAll(src, {{"the", "box"},
+                                                 {"brown", "quick"},
+                                                 {"jumped", "liquored"},
+                                                 {"dozen", "brown"},
+                                                 {"lazy", "pack"},
+                                                 {"liquor", "shakes"}});
+    ABSL_RAW_CHECK(dest == *after_replacing_many,
+                   "not benchmarking intended behavior");
+  }
+}
+BENCHMARK(BM_StrReplaceAll);
+
+}  // namespace
diff --git a/absl/strings/str_replace_test.cc b/absl/strings/str_replace_test.cc
new file mode 100644
index 0000000..1ca23af
--- /dev/null
+++ b/absl/strings/str_replace_test.cc
@@ -0,0 +1,341 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/str_replace.h"
+
+#include <list>
+#include <map>
+#include <tuple>
+
+#include "gtest/gtest.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_split.h"
+
+TEST(StrReplaceAll, OneReplacement) {
+  std::string s;
+
+  // Empty std::string.
+  s = absl::StrReplaceAll(s, {{"", ""}});
+  EXPECT_EQ(s, "");
+  s = absl::StrReplaceAll(s, {{"x", ""}});
+  EXPECT_EQ(s, "");
+  s = absl::StrReplaceAll(s, {{"", "y"}});
+  EXPECT_EQ(s, "");
+  s = absl::StrReplaceAll(s, {{"x", "y"}});
+  EXPECT_EQ(s, "");
+
+  // Empty substring.
+  s = absl::StrReplaceAll("abc", {{"", ""}});
+  EXPECT_EQ(s, "abc");
+  s = absl::StrReplaceAll("abc", {{"", "y"}});
+  EXPECT_EQ(s, "abc");
+  s = absl::StrReplaceAll("abc", {{"x", ""}});
+  EXPECT_EQ(s, "abc");
+
+  // Substring not found.
+  s = absl::StrReplaceAll("abc", {{"xyz", "123"}});
+  EXPECT_EQ(s, "abc");
+
+  // Replace entire std::string.
+  s = absl::StrReplaceAll("abc", {{"abc", "xyz"}});
+  EXPECT_EQ(s, "xyz");
+
+  // Replace once at the start.
+  s = absl::StrReplaceAll("abc", {{"a", "x"}});
+  EXPECT_EQ(s, "xbc");
+
+  // Replace once in the middle.
+  s = absl::StrReplaceAll("abc", {{"b", "x"}});
+  EXPECT_EQ(s, "axc");
+
+  // Replace once at the end.
+  s = absl::StrReplaceAll("abc", {{"c", "x"}});
+  EXPECT_EQ(s, "abx");
+
+  // Replace multiple times with varying lengths of original/replacement.
+  s = absl::StrReplaceAll("ababa", {{"a", "xxx"}});
+  EXPECT_EQ(s, "xxxbxxxbxxx");
+
+  s = absl::StrReplaceAll("ababa", {{"b", "xxx"}});
+  EXPECT_EQ(s, "axxxaxxxa");
+
+  s = absl::StrReplaceAll("aaabaaabaaa", {{"aaa", "x"}});
+  EXPECT_EQ(s, "xbxbx");
+
+  s = absl::StrReplaceAll("abbbabbba", {{"bbb", "x"}});
+  EXPECT_EQ(s, "axaxa");
+
+  // Overlapping matches are replaced greedily.
+  s = absl::StrReplaceAll("aaa", {{"aa", "x"}});
+  EXPECT_EQ(s, "xa");
+
+  // The replacements are not recursive.
+  s = absl::StrReplaceAll("aaa", {{"aa", "a"}});
+  EXPECT_EQ(s, "aa");
+}
+
+TEST(StrReplaceAll, ManyReplacements) {
+  std::string s;
+
+  // Empty std::string.
+  s = absl::StrReplaceAll("", {{"", ""}, {"x", ""}, {"", "y"}, {"x", "y"}});
+  EXPECT_EQ(s, "");
+
+  // Empty substring.
+  s = absl::StrReplaceAll("abc", {{"", ""}, {"", "y"}, {"x", ""}});
+  EXPECT_EQ(s, "abc");
+
+  // Replace entire std::string, one char at a time
+  s = absl::StrReplaceAll("abc", {{"a", "x"}, {"b", "y"}, {"c", "z"}});
+  EXPECT_EQ(s, "xyz");
+  s = absl::StrReplaceAll("zxy", {{"z", "x"}, {"x", "y"}, {"y", "z"}});
+  EXPECT_EQ(s, "xyz");
+
+  // Replace once at the start (longer matches take precedence)
+  s = absl::StrReplaceAll("abc", {{"a", "x"}, {"ab", "xy"}, {"abc", "xyz"}});
+  EXPECT_EQ(s, "xyz");
+
+  // Replace once in the middle.
+  s = absl::StrReplaceAll(
+      "Abc!", {{"a", "x"}, {"ab", "xy"}, {"b", "y"}, {"bc", "yz"}, {"c", "z"}});
+  EXPECT_EQ(s, "Ayz!");
+
+  // Replace once at the end.
+  s = absl::StrReplaceAll(
+      "Abc!",
+      {{"a", "x"}, {"ab", "xy"}, {"b", "y"}, {"bc!", "yz?"}, {"c!", "z;"}});
+  EXPECT_EQ(s, "Ayz?");
+
+  // Replace multiple times with varying lengths of original/replacement.
+  s = absl::StrReplaceAll("ababa", {{"a", "xxx"}, {"b", "XXXX"}});
+  EXPECT_EQ(s, "xxxXXXXxxxXXXXxxx");
+
+  // Overlapping matches are replaced greedily.
+  s = absl::StrReplaceAll("aaa", {{"aa", "x"}, {"a", "X"}});
+  EXPECT_EQ(s, "xX");
+  s = absl::StrReplaceAll("aaa", {{"a", "X"}, {"aa", "x"}});
+  EXPECT_EQ(s, "xX");
+
+  // Two well-known sentences
+  s = absl::StrReplaceAll("the quick brown fox jumped over the lazy dogs",
+                          {
+                              {"brown", "box"},
+                              {"dogs", "jugs"},
+                              {"fox", "with"},
+                              {"jumped", "five"},
+                              {"over", "dozen"},
+                              {"quick", "my"},
+                              {"the", "pack"},
+                              {"the lazy", "liquor"},
+                          });
+  EXPECT_EQ(s, "pack my box with five dozen liquor jugs");
+}
+
+TEST(StrReplaceAll, ManyReplacementsInMap) {
+  std::map<const char *, const char *> replacements;
+  replacements["$who"] = "Bob";
+  replacements["$count"] = "5";
+  replacements["#Noun"] = "Apples";
+  std::string s = absl::StrReplaceAll("$who bought $count #Noun. Thanks $who!",
+                                      replacements);
+  EXPECT_EQ("Bob bought 5 Apples. Thanks Bob!", s);
+}
+
+TEST(StrReplaceAll, ReplacementsInPlace) {
+  std::string s = std::string("$who bought $count #Noun. Thanks $who!");
+  int count;
+  count = absl::StrReplaceAll({{"$count", absl::StrCat(5)},
+                              {"$who", "Bob"},
+                              {"#Noun", "Apples"}}, &s);
+  EXPECT_EQ(count, 4);
+  EXPECT_EQ("Bob bought 5 Apples. Thanks Bob!", s);
+}
+
+TEST(StrReplaceAll, ReplacementsInPlaceInMap) {
+  std::string s = std::string("$who bought $count #Noun. Thanks $who!");
+  std::map<absl::string_view, absl::string_view> replacements;
+  replacements["$who"] = "Bob";
+  replacements["$count"] = "5";
+  replacements["#Noun"] = "Apples";
+  int count;
+  count = absl::StrReplaceAll(replacements, &s);
+  EXPECT_EQ(count, 4);
+  EXPECT_EQ("Bob bought 5 Apples. Thanks Bob!", s);
+}
+
+struct Cont {
+  Cont() {}
+  explicit Cont(absl::string_view src) : data(src) {}
+
+  absl::string_view data;
+};
+
+template <int index>
+absl::string_view get(const Cont& c) {
+  auto splitter = absl::StrSplit(c.data, ':');
+  auto it = splitter.begin();
+  for (int i = 0; i < index; ++i) ++it;
+
+  return *it;
+}
+
+TEST(StrReplaceAll, VariableNumber) {
+  std::string s;
+  {
+    std::vector<std::pair<std::string, std::string>> replacements;
+
+    s = "abc";
+    EXPECT_EQ(0, absl::StrReplaceAll(replacements, &s));
+    EXPECT_EQ("abc", s);
+
+    s = "abc";
+    replacements.push_back({"a", "A"});
+    EXPECT_EQ(1, absl::StrReplaceAll(replacements, &s));
+    EXPECT_EQ("Abc", s);
+
+    s = "abc";
+    replacements.push_back({"b", "B"});
+    EXPECT_EQ(2, absl::StrReplaceAll(replacements, &s));
+    EXPECT_EQ("ABc", s);
+
+    s = "abc";
+    replacements.push_back({"d", "D"});
+    EXPECT_EQ(2, absl::StrReplaceAll(replacements, &s));
+    EXPECT_EQ("ABc", s);
+
+    EXPECT_EQ("ABcABc", absl::StrReplaceAll("abcabc", replacements));
+  }
+
+  {
+    std::map<const char*, const char*> replacements;
+    replacements["aa"] = "x";
+    replacements["a"] = "X";
+    s = "aaa";
+    EXPECT_EQ(2, absl::StrReplaceAll(replacements, &s));
+    EXPECT_EQ("xX", s);
+
+    EXPECT_EQ("xxX", absl::StrReplaceAll("aaaaa", replacements));
+  }
+
+  {
+    std::list<std::pair<absl::string_view, absl::string_view>> replacements = {
+        {"a", "x"}, {"b", "y"}, {"c", "z"}};
+
+    std::string s = absl::StrReplaceAll("abc", replacements);
+    EXPECT_EQ(s, "xyz");
+  }
+
+  {
+    using X = std::tuple<absl::string_view, std::string, int>;
+    std::vector<X> replacements(3);
+    replacements[0] = X{"a", "x", 1};
+    replacements[1] = X{"b", "y", 0};
+    replacements[2] = X{"c", "z", -1};
+
+    std::string s = absl::StrReplaceAll("abc", replacements);
+    EXPECT_EQ(s, "xyz");
+  }
+
+  {
+    std::vector<Cont> replacements(3);
+    replacements[0] = Cont{"a:x"};
+    replacements[1] = Cont{"b:y"};
+    replacements[2] = Cont{"c:z"};
+
+    std::string s = absl::StrReplaceAll("abc", replacements);
+    EXPECT_EQ(s, "xyz");
+  }
+}
+
+// Same as above, but using the in-place variant of absl::StrReplaceAll,
+// that returns the # of replacements performed.
+TEST(StrReplaceAll, Inplace) {
+  std::string s;
+  int reps;
+
+  // Empty std::string.
+  s = "";
+  reps = absl::StrReplaceAll({{"", ""}, {"x", ""}, {"", "y"}, {"x", "y"}}, &s);
+  EXPECT_EQ(reps, 0);
+  EXPECT_EQ(s, "");
+
+  // Empty substring.
+  s = "abc";
+  reps = absl::StrReplaceAll({{"", ""}, {"", "y"}, {"x", ""}}, &s);
+  EXPECT_EQ(reps, 0);
+  EXPECT_EQ(s, "abc");
+
+  // Replace entire std::string, one char at a time
+  s = "abc";
+  reps = absl::StrReplaceAll({{"a", "x"}, {"b", "y"}, {"c", "z"}}, &s);
+  EXPECT_EQ(reps, 3);
+  EXPECT_EQ(s, "xyz");
+  s = "zxy";
+  reps = absl::StrReplaceAll({{"z", "x"}, {"x", "y"}, {"y", "z"}}, &s);
+  EXPECT_EQ(reps, 3);
+  EXPECT_EQ(s, "xyz");
+
+  // Replace once at the start (longer matches take precedence)
+  s = "abc";
+  reps = absl::StrReplaceAll({{"a", "x"}, {"ab", "xy"}, {"abc", "xyz"}}, &s);
+  EXPECT_EQ(reps, 1);
+  EXPECT_EQ(s, "xyz");
+
+  // Replace once in the middle.
+  s = "Abc!";
+  reps = absl::StrReplaceAll(
+      {{"a", "x"}, {"ab", "xy"}, {"b", "y"}, {"bc", "yz"}, {"c", "z"}}, &s);
+  EXPECT_EQ(reps, 1);
+  EXPECT_EQ(s, "Ayz!");
+
+  // Replace once at the end.
+  s = "Abc!";
+  reps = absl::StrReplaceAll(
+      {{"a", "x"}, {"ab", "xy"}, {"b", "y"}, {"bc!", "yz?"}, {"c!", "z;"}}, &s);
+  EXPECT_EQ(reps, 1);
+  EXPECT_EQ(s, "Ayz?");
+
+  // Replace multiple times with varying lengths of original/replacement.
+  s = "ababa";
+  reps = absl::StrReplaceAll({{"a", "xxx"}, {"b", "XXXX"}}, &s);
+  EXPECT_EQ(reps, 5);
+  EXPECT_EQ(s, "xxxXXXXxxxXXXXxxx");
+
+  // Overlapping matches are replaced greedily.
+  s = "aaa";
+  reps = absl::StrReplaceAll({{"aa", "x"}, {"a", "X"}}, &s);
+  EXPECT_EQ(reps, 2);
+  EXPECT_EQ(s, "xX");
+  s = "aaa";
+  reps = absl::StrReplaceAll({{"a", "X"}, {"aa", "x"}}, &s);
+  EXPECT_EQ(reps, 2);
+  EXPECT_EQ(s, "xX");
+
+  // Two well-known sentences
+  s = "the quick brown fox jumped over the lazy dogs";
+  reps = absl::StrReplaceAll(
+      {
+          {"brown", "box"},
+          {"dogs", "jugs"},
+          {"fox", "with"},
+          {"jumped", "five"},
+          {"over", "dozen"},
+          {"quick", "my"},
+          {"the", "pack"},
+          {"the lazy", "liquor"},
+      },
+      &s);
+  EXPECT_EQ(reps, 8);
+  EXPECT_EQ(s, "pack my box with five dozen liquor jugs");
+}
diff --git a/absl/strings/str_split.cc b/absl/strings/str_split.cc
new file mode 100644
index 0000000..2593130
--- /dev/null
+++ b/absl/strings/str_split.cc
@@ -0,0 +1,137 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/str_split.h"
+
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <cstdlib>
+#include <cstring>
+#include <iterator>
+#include <limits>
+#include <memory>
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/strings/ascii.h"
+
+namespace absl {
+
+namespace {
+
+// This GenericFind() template function encapsulates the finding algorithm
+// shared between the ByString and ByAnyChar delimiters. The FindPolicy
+// template parameter allows each delimiter to customize the actual find
+// function to use and the length of the found delimiter. For example, the
+// Literal delimiter will ultimately use absl::string_view::find(), and the
+// AnyOf delimiter will use absl::string_view::find_first_of().
+template <typename FindPolicy>
+absl::string_view GenericFind(absl::string_view text,
+                              absl::string_view delimiter, size_t pos,
+                              FindPolicy find_policy) {
+  if (delimiter.empty() && text.length() > 0) {
+    // Special case for empty std::string delimiters: always return a zero-length
+    // absl::string_view referring to the item at position 1 past pos.
+    return absl::string_view(text.data() + pos + 1, 0);
+  }
+  size_t found_pos = absl::string_view::npos;
+  absl::string_view found(text.data() + text.size(),
+                          0);  // By default, not found
+  found_pos = find_policy.Find(text, delimiter, pos);
+  if (found_pos != absl::string_view::npos) {
+    found = absl::string_view(text.data() + found_pos,
+                              find_policy.Length(delimiter));
+  }
+  return found;
+}
+
+// Finds using absl::string_view::find(), therefore the length of the found
+// delimiter is delimiter.length().
+struct LiteralPolicy {
+  size_t Find(absl::string_view text, absl::string_view delimiter, size_t pos) {
+    return text.find(delimiter, pos);
+  }
+  size_t Length(absl::string_view delimiter) { return delimiter.length(); }
+};
+
+// Finds using absl::string_view::find_first_of(), therefore the length of the
+// found delimiter is 1.
+struct AnyOfPolicy {
+  size_t Find(absl::string_view text, absl::string_view delimiter, size_t pos) {
+    return text.find_first_of(delimiter, pos);
+  }
+  size_t Length(absl::string_view /* delimiter */) { return 1; }
+};
+
+}  // namespace
+
+//
+// ByString
+//
+
+ByString::ByString(absl::string_view sp) : delimiter_(sp) {}
+
+absl::string_view ByString::Find(absl::string_view text, size_t pos) const {
+  if (delimiter_.length() == 1) {
+    // Much faster to call find on a single character than on an
+    // absl::string_view.
+    size_t found_pos = text.find(delimiter_[0], pos);
+    if (found_pos == absl::string_view::npos)
+      return absl::string_view(text.data() + text.size(), 0);
+    return text.substr(found_pos, 1);
+  }
+  return GenericFind(text, delimiter_, pos, LiteralPolicy());
+}
+
+//
+// ByChar
+//
+
+absl::string_view ByChar::Find(absl::string_view text, size_t pos) const {
+  size_t found_pos = text.find(c_, pos);
+  if (found_pos == absl::string_view::npos)
+    return absl::string_view(text.data() + text.size(), 0);
+  return text.substr(found_pos, 1);
+}
+
+//
+// ByAnyChar
+//
+
+ByAnyChar::ByAnyChar(absl::string_view sp) : delimiters_(sp) {}
+
+absl::string_view ByAnyChar::Find(absl::string_view text, size_t pos) const {
+  return GenericFind(text, delimiters_, pos, AnyOfPolicy());
+}
+
+//
+// ByLength
+//
+ByLength::ByLength(ptrdiff_t length) : length_(length) {
+  ABSL_RAW_CHECK(length > 0, "");
+}
+
+absl::string_view ByLength::Find(absl::string_view text,
+                                      size_t pos) const {
+  pos = std::min(pos, text.size());  // truncate `pos`
+  absl::string_view substr = text.substr(pos);
+  // If the std::string is shorter than the chunk size we say we
+  // "can't find the delimiter" so this will be the last chunk.
+  if (substr.length() <= static_cast<size_t>(length_))
+    return absl::string_view(text.data() + text.size(), 0);
+
+  return absl::string_view(substr.data() + length_, 0);
+}
+
+}  // namespace absl
diff --git a/absl/strings/str_split.h b/absl/strings/str_split.h
new file mode 100644
index 0000000..7333078
--- /dev/null
+++ b/absl/strings/str_split.h
@@ -0,0 +1,511 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: str_split.h
+// -----------------------------------------------------------------------------
+//
+// This file contains functions for splitting strings. It defines the main
+// `StrSplit()` function, several delimiters for determining the boundaries on
+// which to split the string, and predicates for filtering delimited results.
+// `StrSplit()` adapts the returned collection to the type specified by the
+// caller.
+//
+// Example:
+//
+//   // Splits the given string on commas. Returns the results in a
+//   // vector of strings.
+//   std::vector<std::string> v = absl::StrSplit("a,b,c", ',');
+//   // Can also use ","
+//   // v[0] == "a", v[1] == "b", v[2] == "c"
+//
+// See StrSplit() below for more information.
+#ifndef ABSL_STRINGS_STR_SPLIT_H_
+#define ABSL_STRINGS_STR_SPLIT_H_
+
+#include <algorithm>
+#include <cstddef>
+#include <map>
+#include <set>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/strings/internal/str_split_internal.h"
+#include "absl/strings/string_view.h"
+#include "absl/strings/strip.h"
+
+namespace absl {
+
+//------------------------------------------------------------------------------
+// Delimiters
+//------------------------------------------------------------------------------
+//
+// `StrSplit()` uses delimiters to define the boundaries between elements in the
+// provided input. Several `Delimiter` types are defined below. If a string
+// (`const char*`, `std::string`, or `absl::string_view`) is passed in place of
+// an explicit `Delimiter` object, `StrSplit()` treats it the same way as if it
+// were passed a `ByString` delimiter.
+//
+// A `Delimiter` is an object with a `Find()` function that knows how to find
+// the first occurrence of itself in a given `absl::string_view`.
+//
+// The following `Delimiter` types are available for use within `StrSplit()`:
+//
+//   - `ByString` (default for string arguments)
+//   - `ByChar` (default for a char argument)
+//   - `ByAnyChar`
+//   - `ByLength`
+//   - `MaxSplits`
+//
+// A Delimiter's `Find()` member function will be passed an input `text` that is
+// to be split and a position (`pos`) to begin searching for the next delimiter
+// in `text`. The returned absl::string_view should refer to the next occurrence
+// (after `pos`) of the represented delimiter; this returned absl::string_view
+// represents the next location where the input `text` should be broken.
+//
+// The returned absl::string_view may be zero-length if the Delimiter does not
+// represent a part of the string (e.g., a fixed-length delimiter). If no
+// delimiter is found in the input `text`, a zero-length absl::string_view
+// referring to `text.end()` should be returned (e.g.,
+// `text.substr(text.size())`). It is important that the returned
+// absl::string_view always be within the bounds of the input `text` given as an
+// argument--it must not refer to a string that is physically located outside of
+// the given string.
+//
+// The following example is a simple Delimiter object that is created with a
+// single char and will look for that char in the text passed to the `Find()`
+// function:
+//
+//   struct SimpleDelimiter {
+//     const char c_;
+//     explicit SimpleDelimiter(char c) : c_(c) {}
+//     absl::string_view Find(absl::string_view text, size_t pos) {
+//       auto found = text.find(c_, pos);
+//       if (found == absl::string_view::npos)
+//         return text.substr(text.size());
+//
+//       return text.substr(found, 1);
+//     }
+//   };
+
+// ByString
+//
+// A sub-string delimiter. If `StrSplit()` is passed a string in place of a
+// `Delimiter` object, the string will be implicitly converted into a
+// `ByString` delimiter.
+//
+// Example:
+//
+//   // Because a string literal is converted to an `absl::ByString`,
+//   // the following two splits are equivalent.
+//
+//   std::vector<std::string> v1 = absl::StrSplit("a, b, c", ", ");
+//
+//   using absl::ByString;
+//   std::vector<std::string> v2 = absl::StrSplit("a, b, c",
+//                                                ByString(", "));
+//   // v[0] == "a", v[1] == "b", v[2] == "c"
+class ByString {
+ public:
+  explicit ByString(absl::string_view sp);
+  absl::string_view Find(absl::string_view text, size_t pos) const;
+
+ private:
+  const std::string delimiter_;
+};
+
+// ByChar
+//
+// A single character delimiter. `ByChar` is functionally equivalent to a
+// 1-char string within a `ByString` delimiter, but slightly more efficient.
+//
+// Example:
+//
+//   // Because a char literal is converted to a absl::ByChar,
+//   // the following two splits are equivalent.
+//   std::vector<std::string> v1 = absl::StrSplit("a,b,c", ',');
+//   using absl::ByChar;
+//   std::vector<std::string> v2 = absl::StrSplit("a,b,c", ByChar(','));
+//   // v[0] == "a", v[1] == "b", v[2] == "c"
+//
+// `ByChar` is also the default delimiter if a single character is given
+// as the delimiter to `StrSplit()`. For example, the following calls are
+// equivalent:
+//
+//   std::vector<std::string> v = absl::StrSplit("a-b", '-');
+//
+//   using absl::ByChar;
+//   std::vector<std::string> v = absl::StrSplit("a-b", ByChar('-'));
+//
+class ByChar {
+ public:
+  explicit ByChar(char c) : c_(c) {}
+  absl::string_view Find(absl::string_view text, size_t pos) const;
+
+ private:
+  char c_;
+};
+
+// ByAnyChar
+//
+// A delimiter that will match any of the given byte-sized characters within
+// its provided string.
+//
+// Note: this delimiter works with single-byte string data, but does not work
+// with variable-width encodings, such as UTF-8.
+//
+// Example:
+//
+//   using absl::ByAnyChar;
+//   std::vector<std::string> v = absl::StrSplit("a,b=c", ByAnyChar(",="));
+//   // v[0] == "a", v[1] == "b", v[2] == "c"
+//
+// If `ByAnyChar` is given the empty string, it behaves exactly like
+// `ByString` and matches each individual character in the input string.
+//
+class ByAnyChar {
+ public:
+  explicit ByAnyChar(absl::string_view sp);
+  absl::string_view Find(absl::string_view text, size_t pos) const;
+
+ private:
+  const std::string delimiters_;
+};
+
+// ByLength
+//
+// A delimiter for splitting into equal-length strings. The length argument to
+// the constructor must be greater than 0.
+//
+// Note: this delimiter works with single-byte string data, but does not work
+// with variable-width encodings, such as UTF-8.
+//
+// Example:
+//
+//   using absl::ByLength;
+//   std::vector<std::string> v = absl::StrSplit("123456789", ByLength(3));
+
+//   // v[0] == "123", v[1] == "456", v[2] == "789"
+//
+// Note that the string does not have to be a multiple of the fixed split
+// length. In such a case, the last substring will be shorter.
+//
+//   using absl::ByLength;
+//   std::vector<std::string> v = absl::StrSplit("12345", ByLength(2));
+//
+//   // v[0] == "12", v[1] == "34", v[2] == "5"
+class ByLength {
+ public:
+  explicit ByLength(ptrdiff_t length);
+  absl::string_view Find(absl::string_view text, size_t pos) const;
+
+ private:
+  const ptrdiff_t length_;
+};
+
+namespace strings_internal {
+
+// A traits-like metafunction for selecting the default Delimiter object type
+// for a particular Delimiter type. The base case simply exposes type Delimiter
+// itself as the delimiter's Type. However, there are specializations for
+// string-like objects that map them to the ByString delimiter object.
+// This allows functions like absl::StrSplit() and absl::MaxSplits() to accept
+// string-like objects (e.g., ',') as delimiter arguments but they will be
+// treated as if a ByString delimiter was given.
+template <typename Delimiter>
+struct SelectDelimiter {
+  using type = Delimiter;
+};
+
+template <>
+struct SelectDelimiter<char> {
+  using type = ByChar;
+};
+template <>
+struct SelectDelimiter<char*> {
+  using type = ByString;
+};
+template <>
+struct SelectDelimiter<const char*> {
+  using type = ByString;
+};
+template <>
+struct SelectDelimiter<absl::string_view> {
+  using type = ByString;
+};
+template <>
+struct SelectDelimiter<std::string> {
+  using type = ByString;
+};
+
+// Wraps another delimiter and sets a max number of matches for that delimiter.
+template <typename Delimiter>
+class MaxSplitsImpl {
+ public:
+  MaxSplitsImpl(Delimiter delimiter, int limit)
+      : delimiter_(delimiter), limit_(limit), count_(0) {}
+  absl::string_view Find(absl::string_view text, size_t pos) {
+    if (count_++ == limit_) {
+      return absl::string_view(text.data() + text.size(),
+                               0);  // No more matches.
+    }
+    return delimiter_.Find(text, pos);
+  }
+
+ private:
+  Delimiter delimiter_;
+  const int limit_;
+  int count_;
+};
+
+}  // namespace strings_internal
+
+// MaxSplits()
+//
+// A delimiter that limits the number of matches which can occur to the passed
+// `limit`. The last element in the returned collection will contain all
+// remaining unsplit pieces, which may contain instances of the delimiter.
+// The collection will contain at most `limit` + 1 elements.
+// Example:
+//
+//   using absl::MaxSplits;
+//   std::vector<std::string> v = absl::StrSplit("a,b,c", MaxSplits(',', 1));
+//
+//   // v[0] == "a", v[1] == "b,c"
+template <typename Delimiter>
+inline strings_internal::MaxSplitsImpl<
+    typename strings_internal::SelectDelimiter<Delimiter>::type>
+MaxSplits(Delimiter delimiter, int limit) {
+  typedef
+      typename strings_internal::SelectDelimiter<Delimiter>::type DelimiterType;
+  return strings_internal::MaxSplitsImpl<DelimiterType>(
+      DelimiterType(delimiter), limit);
+}
+
+//------------------------------------------------------------------------------
+// Predicates
+//------------------------------------------------------------------------------
+//
+// Predicates filter the results of a `StrSplit()` by determining whether or not
+// a resultant element is included in the result set. A predicate may be passed
+// as an optional third argument to the `StrSplit()` function.
+//
+// Predicates are unary functions (or functors) that take a single
+// `absl::string_view` argument and return a bool indicating whether the
+// argument should be included (`true`) or excluded (`false`).
+//
+// Predicates are useful when filtering out empty substrings. By default, empty
+// substrings may be returned by `StrSplit()`, which is similar to the way split
+// functions work in other programming languages.
+
+// AllowEmpty()
+//
+// Always returns `true`, indicating that all strings--including empty
+// strings--should be included in the split output. This predicate is not
+// strictly needed because this is the default behavior of `StrSplit()`;
+// however, it might be useful at some call sites to make the intent explicit.
+//
+// Example:
+//
+//  std::vector<std::string> v = absl::StrSplit(" a , ,,b,", ',', AllowEmpty());
+//
+//  // v[0] == " a ", v[1] == " ", v[2] == "", v[3] = "b", v[4] == ""
+struct AllowEmpty {
+  bool operator()(absl::string_view) const { return true; }
+};
+
+// SkipEmpty()
+//
+// Returns `false` if the given `absl::string_view` is empty, indicating that
+// `StrSplit()` should omit the empty string.
+//
+// Example:
+//
+//   std::vector<std::string> v = absl::StrSplit(",a,,b,", ',', SkipEmpty());
+//
+//   // v[0] == "a", v[1] == "b"
+//
+// Note: `SkipEmpty()` does not consider a string containing only whitespace
+// to be empty. To skip such whitespace as well, use the `SkipWhitespace()`
+// predicate.
+struct SkipEmpty {
+  bool operator()(absl::string_view sp) const { return !sp.empty(); }
+};
+
+// SkipWhitespace()
+//
+// Returns `false` if the given `absl::string_view` is empty *or* contains only
+// whitespace, indicating that `StrSplit()` should omit the string.
+//
+// Example:
+//
+//   std::vector<std::string> v = absl::StrSplit(" a , ,,b,",
+//                                               ',', SkipWhitespace());
+//   // v[0] == " a ", v[1] == "b"
+//
+//   // SkipEmpty() would return whitespace elements
+//   std::vector<std::string> v = absl::StrSplit(" a , ,,b,", ',', SkipEmpty());
+//   // v[0] == " a ", v[1] == " ", v[2] == "b"
+struct SkipWhitespace {
+  bool operator()(absl::string_view sp) const {
+    sp = absl::StripAsciiWhitespace(sp);
+    return !sp.empty();
+  }
+};
+
+//------------------------------------------------------------------------------
+//                                  StrSplit()
+//------------------------------------------------------------------------------
+
+// StrSplit()
+//
+// Splits a given string based on the provided `Delimiter` object, returning the
+// elements within the type specified by the caller. Optionally, you may pass a
+// `Predicate` to `StrSplit()` indicating whether to include or exclude the
+// resulting element within the final result set. (See the overviews for
+// Delimiters and Predicates above.)
+//
+// Example:
+//
+//   std::vector<std::string> v = absl::StrSplit("a,b,c,d", ',');
+//   // v[0] == "a", v[1] == "b", v[2] == "c", v[3] == "d"
+//
+// You can also provide an explicit `Delimiter` object:
+//
+// Example:
+//
+//   using absl::ByAnyChar;
+//   std::vector<std::string> v = absl::StrSplit("a,b=c", ByAnyChar(",="));
+//   // v[0] == "a", v[1] == "b", v[2] == "c"
+//
+// See above for more information on delimiters.
+//
+// By default, empty strings are included in the result set. You can optionally
+// include a third `Predicate` argument to apply a test for whether the
+// resultant element should be included in the result set:
+//
+// Example:
+//
+//   std::vector<std::string> v = absl::StrSplit(" a , ,,b,",
+//                                               ',', SkipWhitespace());
+//   // v[0] == " a ", v[1] == "b"
+//
+// See above for more information on predicates.
+//
+//------------------------------------------------------------------------------
+// StrSplit() Return Types
+//------------------------------------------------------------------------------
+//
+// The `StrSplit()` function adapts the returned collection to the collection
+// specified by the caller (e.g. `std::vector` above). The returned collections
+// may contain `std::string`, `absl::string_view` (in which case the original
+// string being split must ensure that it outlives the collection), or any
+// object that can be explicitly created from an `absl::string_view`. This
+// behavior works for:
+//
+// 1) All standard STL containers including `std::vector`, `std::list`,
+//    `std::deque`, `std::set`,`std::multiset`, 'std::map`, and `std::multimap`
+// 2) `std::pair` (which is not actually a container). See below.
+//
+// Example:
+//
+//   // The results are returned as `absl::string_view` objects. Note that we
+//   // have to ensure that the input string outlives any results.
+//   std::vector<absl::string_view> v = absl::StrSplit("a,b,c", ',');
+//
+//   // Stores results in a std::set<std::string>, which also performs
+//   // de-duplication and orders the elements in ascending order.
+//   std::set<std::string> a = absl::StrSplit("b,a,c,a,b", ',');
+//   // v[0] == "a", v[1] == "b", v[2] = "c"
+//
+//   // `StrSplit()` can be used within a range-based for loop, in which case
+//   // each element will be of type `absl::string_view`.
+//   std::vector<std::string> v;
+//   for (const auto sv : absl::StrSplit("a,b,c", ',')) {
+//     if (sv != "b") v.emplace_back(sv);
+//   }
+//   // v[0] == "a", v[1] == "c"
+//
+//   // Stores results in a map. The map implementation assumes that the input
+//   // is provided as a series of key/value pairs. For example, the 0th element
+//   // resulting from the split will be stored as a key to the 1st element. If
+//   // an odd number of elements are resolved, the last element is paired with
+//   // a default-constructed value (e.g., empty string).
+//   std::map<std::string, std::string> m = absl::StrSplit("a,b,c", ',');
+//   // m["a"] == "b", m["c"] == ""     // last component value equals ""
+//
+// Splitting to `std::pair` is an interesting case because it can hold only two
+// elements and is not a collection type. When splitting to a `std::pair` the
+// first two split strings become the `std::pair` `.first` and `.second`
+// members, respectively. The remaining split substrings are discarded. If there
+// are less than two split substrings, the empty string is used for the
+// corresponding
+// `std::pair` member.
+//
+// Example:
+//
+//   // Stores first two split strings as the members in a std::pair.
+//   std::pair<std::string, std::string> p = absl::StrSplit("a,b,c", ',');
+//   // p.first == "a", p.second == "b"       // "c" is omitted.
+//
+// The `StrSplit()` function can be used multiple times to perform more
+// complicated splitting logic, such as intelligently parsing key-value pairs.
+//
+// Example:
+//
+//   // The input string "a=b=c,d=e,f=,g" becomes
+//   // { "a" => "b=c", "d" => "e", "f" => "", "g" => "" }
+//   std::map<std::string, std::string> m;
+//   for (absl::string_view sp : absl::StrSplit("a=b=c,d=e,f=,g", ',')) {
+//     m.insert(absl::StrSplit(sp, absl::MaxSplits('=', 1)));
+//   }
+//   EXPECT_EQ("b=c", m.find("a")->second);
+//   EXPECT_EQ("e", m.find("d")->second);
+//   EXPECT_EQ("", m.find("f")->second);
+//   EXPECT_EQ("", m.find("g")->second);
+//
+// WARNING: Due to a legacy bug that is maintained for backward compatibility,
+// splitting the following empty string_views produces different results:
+//
+//   absl::StrSplit(absl::string_view(""), '-');  // {""}
+//   absl::StrSplit(absl::string_view(), '-');    // {}, but should be {""}
+//
+// Try not to depend on this distinction because the bug may one day be fixed.
+template <typename Delimiter>
+strings_internal::Splitter<
+    typename strings_internal::SelectDelimiter<Delimiter>::type, AllowEmpty>
+StrSplit(strings_internal::ConvertibleToStringView text, Delimiter d) {
+  using DelimiterType =
+      typename strings_internal::SelectDelimiter<Delimiter>::type;
+  return strings_internal::Splitter<DelimiterType, AllowEmpty>(
+      std::move(text), DelimiterType(d), AllowEmpty());
+}
+
+template <typename Delimiter, typename Predicate>
+strings_internal::Splitter<
+    typename strings_internal::SelectDelimiter<Delimiter>::type, Predicate>
+StrSplit(strings_internal::ConvertibleToStringView text, Delimiter d,
+         Predicate p) {
+  using DelimiterType =
+      typename strings_internal::SelectDelimiter<Delimiter>::type;
+  return strings_internal::Splitter<DelimiterType, Predicate>(
+      std::move(text), DelimiterType(d), std::move(p));
+}
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_STR_SPLIT_H_
diff --git a/absl/strings/str_split_benchmark.cc b/absl/strings/str_split_benchmark.cc
new file mode 100644
index 0000000..f38dfcf
--- /dev/null
+++ b/absl/strings/str_split_benchmark.cc
@@ -0,0 +1,180 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/str_split.h"
+
+#include <iterator>
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/strings/string_view.h"
+
+namespace {
+
+std::string MakeTestString(int desired_length) {
+  static const int kAverageValueLen = 25;
+  std::string test(desired_length * kAverageValueLen, 'x');
+  for (int i = 1; i < test.size(); i += kAverageValueLen) {
+    test[i] = ';';
+  }
+  return test;
+}
+
+void BM_Split2StringView(benchmark::State& state) {
+  std::string test = MakeTestString(state.range(0));
+  for (auto _ : state) {
+    std::vector<absl::string_view> result = absl::StrSplit(test, ';');
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_Split2StringView, 0, 1 << 20);
+
+static const absl::string_view kDelimiters = ";:,.";
+
+std::string MakeMultiDelimiterTestString(int desired_length) {
+  static const int kAverageValueLen = 25;
+  std::string test(desired_length * kAverageValueLen, 'x');
+  for (int i = 0; i * kAverageValueLen < test.size(); ++i) {
+    // Cycle through a variety of delimiters.
+    test[i * kAverageValueLen] = kDelimiters[i % kDelimiters.size()];
+  }
+  return test;
+}
+
+// Measure StrSplit with ByAnyChar with four delimiters to choose from.
+void BM_Split2StringViewByAnyChar(benchmark::State& state) {
+  std::string test = MakeMultiDelimiterTestString(state.range(0));
+  for (auto _ : state) {
+    std::vector<absl::string_view> result =
+        absl::StrSplit(test, absl::ByAnyChar(kDelimiters));
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_Split2StringViewByAnyChar, 0, 1 << 20);
+
+void BM_Split2StringViewLifted(benchmark::State& state) {
+  std::string test = MakeTestString(state.range(0));
+  std::vector<absl::string_view> result;
+  for (auto _ : state) {
+    result = absl::StrSplit(test, ';');
+  }
+  benchmark::DoNotOptimize(result);
+}
+BENCHMARK_RANGE(BM_Split2StringViewLifted, 0, 1 << 20);
+
+void BM_Split2String(benchmark::State& state) {
+  std::string test = MakeTestString(state.range(0));
+  for (auto _ : state) {
+    std::vector<std::string> result = absl::StrSplit(test, ';');
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_Split2String, 0, 1 << 20);
+
+// This benchmark is for comparing Split2 to Split1 (SplitStringUsing). In
+// particular, this benchmark uses SkipEmpty() to match SplitStringUsing's
+// behavior.
+void BM_Split2SplitStringUsing(benchmark::State& state) {
+  std::string test = MakeTestString(state.range(0));
+  for (auto _ : state) {
+    std::vector<std::string> result =
+        absl::StrSplit(test, ';', absl::SkipEmpty());
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_Split2SplitStringUsing, 0, 1 << 20);
+
+void BM_SplitStringToUnorderedSet(benchmark::State& state) {
+  const int len = state.range(0);
+  std::string test(len, 'x');
+  for (int i = 1; i < len; i += 2) {
+    test[i] = ';';
+  }
+  for (auto _ : state) {
+    std::unordered_set<std::string> result =
+        absl::StrSplit(test, ':', absl::SkipEmpty());
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_SplitStringToUnorderedSet, 0, 1 << 20);
+
+void BM_SplitStringToUnorderedMap(benchmark::State& state) {
+  const int len = state.range(0);
+  std::string test(len, 'x');
+  for (int i = 1; i < len; i += 2) {
+    test[i] = ';';
+  }
+  for (auto _ : state) {
+    std::unordered_map<std::string, std::string> result =
+        absl::StrSplit(test, ':', absl::SkipEmpty());
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_SplitStringToUnorderedMap, 0, 1 << 20);
+
+void BM_SplitStringAllowEmpty(benchmark::State& state) {
+  const int len = state.range(0);
+  std::string test(len, 'x');
+  for (int i = 1; i < len; i += 2) {
+    test[i] = ';';
+  }
+  for (auto _ : state) {
+    std::vector<std::string> result = absl::StrSplit(test, ';');
+    benchmark::DoNotOptimize(result);
+  }
+}
+BENCHMARK_RANGE(BM_SplitStringAllowEmpty, 0, 1 << 20);
+
+struct OneCharLiteral {
+  char operator()() const { return 'X'; }
+};
+
+struct OneCharStringLiteral {
+  const char* operator()() const { return "X"; }
+};
+
+template <typename DelimiterFactory>
+void BM_SplitStringWithOneChar(benchmark::State& state) {
+  const auto delimiter = DelimiterFactory()();
+  std::vector<absl::string_view> pieces;
+  size_t v = 0;
+  for (auto _ : state) {
+    pieces = absl::StrSplit("The quick brown fox jumps over the lazy dog",
+                            delimiter);
+    v += pieces.size();
+  }
+  ABSL_RAW_CHECK(v == state.iterations(), "");
+}
+BENCHMARK_TEMPLATE(BM_SplitStringWithOneChar, OneCharLiteral);
+BENCHMARK_TEMPLATE(BM_SplitStringWithOneChar, OneCharStringLiteral);
+
+template <typename DelimiterFactory>
+void BM_SplitStringWithOneCharNoVector(benchmark::State& state) {
+  const auto delimiter = DelimiterFactory()();
+  size_t v = 0;
+  for (auto _ : state) {
+    auto splitter = absl::StrSplit(
+        "The quick brown fox jumps over the lazy dog", delimiter);
+    v += std::distance(splitter.begin(), splitter.end());
+  }
+  ABSL_RAW_CHECK(v == state.iterations(), "");
+}
+BENCHMARK_TEMPLATE(BM_SplitStringWithOneCharNoVector, OneCharLiteral);
+BENCHMARK_TEMPLATE(BM_SplitStringWithOneCharNoVector, OneCharStringLiteral);
+
+}  // namespace
diff --git a/absl/strings/str_split_test.cc b/absl/strings/str_split_test.cc
new file mode 100644
index 0000000..02f27bc
--- /dev/null
+++ b/absl/strings/str_split_test.cc
@@ -0,0 +1,939 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/str_split.h"
+
+#include <deque>
+#include <initializer_list>
+#include <list>
+#include <map>
+#include <memory>
+#include <string>
+#include <type_traits>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/dynamic_annotations.h"  // for RunningOnValgrind
+#include "absl/base/macros.h"
+#include "absl/strings/numbers.h"
+
+namespace {
+
+using ::testing::ElementsAre;
+using ::testing::Pair;
+using ::testing::UnorderedElementsAre;
+
+TEST(Split, TraitsTest) {
+  static_assert(!absl::strings_internal::SplitterIsConvertibleTo<int>::value,
+                "");
+  static_assert(
+      !absl::strings_internal::SplitterIsConvertibleTo<std::string>::value, "");
+  static_assert(absl::strings_internal::SplitterIsConvertibleTo<
+                    std::vector<std::string>>::value,
+                "");
+  static_assert(
+      !absl::strings_internal::SplitterIsConvertibleTo<std::vector<int>>::value,
+      "");
+  static_assert(absl::strings_internal::SplitterIsConvertibleTo<
+                    std::vector<absl::string_view>>::value,
+                "");
+  static_assert(absl::strings_internal::SplitterIsConvertibleTo<
+                    std::map<std::string, std::string>>::value,
+                "");
+  static_assert(absl::strings_internal::SplitterIsConvertibleTo<
+                    std::map<absl::string_view, absl::string_view>>::value,
+                "");
+  static_assert(!absl::strings_internal::SplitterIsConvertibleTo<
+                    std::map<int, std::string>>::value,
+                "");
+  static_assert(!absl::strings_internal::SplitterIsConvertibleTo<
+                    std::map<std::string, int>>::value,
+                "");
+}
+
+// This tests the overall split API, which is made up of the absl::StrSplit()
+// function and the Delimiter objects in the absl:: namespace.
+// This TEST macro is outside of any namespace to require full specification of
+// namespaces just like callers will need to use.
+TEST(Split, APIExamples) {
+  {
+    // Passes std::string delimiter. Assumes the default of ByString.
+    std::vector<std::string> v = absl::StrSplit("a,b,c", ",");  // NOLINT
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+
+    // Equivalent to...
+    using absl::ByString;
+    v = absl::StrSplit("a,b,c", ByString(","));
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+
+    // Equivalent to...
+    EXPECT_THAT(absl::StrSplit("a,b,c", ByString(",")),
+                ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // Same as above, but using a single character as the delimiter.
+    std::vector<std::string> v = absl::StrSplit("a,b,c", ',');
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+
+    // Equivalent to...
+    using absl::ByChar;
+    v = absl::StrSplit("a,b,c", ByChar(','));
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // Uses the Literal std::string "=>" as the delimiter.
+    const std::vector<std::string> v = absl::StrSplit("a=>b=>c", "=>");
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // The substrings are returned as string_views, eliminating copying.
+    std::vector<absl::string_view> v = absl::StrSplit("a,b,c", ',');
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // Leading and trailing empty substrings.
+    std::vector<std::string> v = absl::StrSplit(",a,b,c,", ',');
+    EXPECT_THAT(v, ElementsAre("", "a", "b", "c", ""));
+  }
+
+  {
+    // Splits on a delimiter that is not found.
+    std::vector<std::string> v = absl::StrSplit("abc", ',');
+    EXPECT_THAT(v, ElementsAre("abc"));
+  }
+
+  {
+    // Splits the input std::string into individual characters by using an empty
+    // std::string as the delimiter.
+    std::vector<std::string> v = absl::StrSplit("abc", "");
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // Splits std::string data with embedded NUL characters, using NUL as the
+    // delimiter. A simple delimiter of "\0" doesn't work because strlen() will
+    // say that's the empty std::string when constructing the absl::string_view
+    // delimiter. Instead, a non-empty std::string containing NUL can be used as the
+    // delimiter.
+    std::string embedded_nulls("a\0b\0c", 5);
+    std::string null_delim("\0", 1);
+    std::vector<std::string> v = absl::StrSplit(embedded_nulls, null_delim);
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // Stores first two split strings as the members in a std::pair.
+    std::pair<std::string, std::string> p = absl::StrSplit("a,b,c", ',');
+    EXPECT_EQ("a", p.first);
+    EXPECT_EQ("b", p.second);
+    // "c" is omitted because std::pair can hold only two elements.
+  }
+
+  {
+    // Results stored in std::set<std::string>
+    std::set<std::string> v = absl::StrSplit("a,b,c,a,b,c,a,b,c", ',');
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // Uses a non-const char* delimiter.
+    char a[] = ",";
+    char* d = a + 0;
+    std::vector<std::string> v = absl::StrSplit("a,b,c", d);
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // Results split using either of , or ;
+    using absl::ByAnyChar;
+    std::vector<std::string> v = absl::StrSplit("a,b;c", ByAnyChar(",;"));
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // Uses the SkipWhitespace predicate.
+    using absl::SkipWhitespace;
+    std::vector<std::string> v =
+        absl::StrSplit(" a , ,,b,", ',', SkipWhitespace());
+    EXPECT_THAT(v, ElementsAre(" a ", "b"));
+  }
+
+  {
+    // Uses the ByLength delimiter.
+    using absl::ByLength;
+    std::vector<std::string> v = absl::StrSplit("abcdefg", ByLength(3));
+    EXPECT_THAT(v, ElementsAre("abc", "def", "g"));
+  }
+
+  {
+    // Different forms of initialization / conversion.
+    std::vector<std::string> v1 = absl::StrSplit("a,b,c", ',');
+    EXPECT_THAT(v1, ElementsAre("a", "b", "c"));
+    std::vector<std::string> v2(absl::StrSplit("a,b,c", ','));
+    EXPECT_THAT(v2, ElementsAre("a", "b", "c"));
+    auto v3 = std::vector<std::string>(absl::StrSplit("a,b,c", ','));
+    EXPECT_THAT(v3, ElementsAre("a", "b", "c"));
+    v3 = absl::StrSplit("a,b,c", ',');
+    EXPECT_THAT(v3, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // Results stored in a std::map.
+    std::map<std::string, std::string> m = absl::StrSplit("a,1,b,2,a,3", ',');
+    EXPECT_EQ(2, m.size());
+    EXPECT_EQ("3", m["a"]);
+    EXPECT_EQ("2", m["b"]);
+  }
+
+  {
+    // Results stored in a std::multimap.
+    std::multimap<std::string, std::string> m =
+        absl::StrSplit("a,1,b,2,a,3", ',');
+    EXPECT_EQ(3, m.size());
+    auto it = m.find("a");
+    EXPECT_EQ("1", it->second);
+    ++it;
+    EXPECT_EQ("3", it->second);
+    it = m.find("b");
+    EXPECT_EQ("2", it->second);
+  }
+
+  {
+    // Demonstrates use in a range-based for loop in C++11.
+    std::string s = "x,x,x,x,x,x,x";
+    for (absl::string_view sp : absl::StrSplit(s, ',')) {
+      EXPECT_EQ("x", sp);
+    }
+  }
+
+  {
+    // Demonstrates use with a Predicate in a range-based for loop.
+    using absl::SkipWhitespace;
+    std::string s = " ,x,,x,,x,x,x,,";
+    for (absl::string_view sp : absl::StrSplit(s, ',', SkipWhitespace())) {
+      EXPECT_EQ("x", sp);
+    }
+  }
+
+  {
+    // Demonstrates a "smart" split to std::map using two separate calls to
+    // absl::StrSplit. One call to split the records, and another call to split
+    // the keys and values. This also uses the Limit delimiter so that the
+    // std::string "a=b=c" will split to "a" -> "b=c".
+    std::map<std::string, std::string> m;
+    for (absl::string_view sp : absl::StrSplit("a=b=c,d=e,f=,g", ',')) {
+      m.insert(absl::StrSplit(sp, absl::MaxSplits('=', 1)));
+    }
+    EXPECT_EQ("b=c", m.find("a")->second);
+    EXPECT_EQ("e", m.find("d")->second);
+    EXPECT_EQ("", m.find("f")->second);
+    EXPECT_EQ("", m.find("g")->second);
+  }
+}
+
+//
+// Tests for SplitIterator
+//
+
+TEST(SplitIterator, Basics) {
+  auto splitter = absl::StrSplit("a,b", ',');
+  auto it = splitter.begin();
+  auto end = splitter.end();
+
+  EXPECT_NE(it, end);
+  EXPECT_EQ("a", *it);  // tests dereference
+  ++it;                 // tests preincrement
+  EXPECT_NE(it, end);
+  EXPECT_EQ("b",
+            std::string(it->data(), it->size()));  // tests dereference as ptr
+  it++;                                            // tests postincrement
+  EXPECT_EQ(it, end);
+}
+
+// Simple Predicate to skip a particular string.
+class Skip {
+ public:
+  explicit Skip(const std::string& s) : s_(s) {}
+  bool operator()(absl::string_view sp) { return sp != s_; }
+
+ private:
+  std::string s_;
+};
+
+TEST(SplitIterator, Predicate) {
+  auto splitter = absl::StrSplit("a,b,c", ',', Skip("b"));
+  auto it = splitter.begin();
+  auto end = splitter.end();
+
+  EXPECT_NE(it, end);
+  EXPECT_EQ("a", *it);  // tests dereference
+  ++it;                 // tests preincrement -- "b" should be skipped here.
+  EXPECT_NE(it, end);
+  EXPECT_EQ("c",
+            std::string(it->data(), it->size()));  // tests dereference as ptr
+  it++;                                            // tests postincrement
+  EXPECT_EQ(it, end);
+}
+
+TEST(SplitIterator, EdgeCases) {
+  // Expected input and output, assuming a delimiter of ','
+  struct {
+    std::string in;
+    std::vector<std::string> expect;
+  } specs[] = {
+      {"", {""}},
+      {"foo", {"foo"}},
+      {",", {"", ""}},
+      {",foo", {"", "foo"}},
+      {"foo,", {"foo", ""}},
+      {",foo,", {"", "foo", ""}},
+      {"foo,bar", {"foo", "bar"}},
+  };
+
+  for (const auto& spec : specs) {
+    SCOPED_TRACE(spec.in);
+    auto splitter = absl::StrSplit(spec.in, ',');
+    auto it = splitter.begin();
+    auto end = splitter.end();
+    for (const auto& expected : spec.expect) {
+      EXPECT_NE(it, end);
+      EXPECT_EQ(expected, *it++);
+    }
+    EXPECT_EQ(it, end);
+  }
+}
+
+TEST(Splitter, Const) {
+  const auto splitter = absl::StrSplit("a,b,c", ',');
+  EXPECT_THAT(splitter, ElementsAre("a", "b", "c"));
+}
+
+TEST(Split, EmptyAndNull) {
+  // Attention: Splitting a null absl::string_view is different than splitting
+  // an empty absl::string_view even though both string_views are considered
+  // equal. This behavior is likely surprising and undesirable. However, to
+  // maintain backward compatibility, there is a small "hack" in
+  // str_split_internal.h that preserves this behavior. If that behavior is ever
+  // changed/fixed, this test will need to be updated.
+  EXPECT_THAT(absl::StrSplit(absl::string_view(""), '-'), ElementsAre(""));
+  EXPECT_THAT(absl::StrSplit(absl::string_view(), '-'), ElementsAre());
+}
+
+TEST(SplitIterator, EqualityAsEndCondition) {
+  auto splitter = absl::StrSplit("a,b,c", ',');
+  auto it = splitter.begin();
+  auto it2 = it;
+
+  // Increments it2 twice to point to "c" in the input text.
+  ++it2;
+  ++it2;
+  EXPECT_EQ("c", *it2);
+
+  // This test uses a non-end SplitIterator as the terminating condition in a
+  // for loop. This relies on SplitIterator equality for non-end SplitIterators
+  // working correctly. At this point it2 points to "c", and we use that as the
+  // "end" condition in this test.
+  std::vector<absl::string_view> v;
+  for (; it != it2; ++it) {
+    v.push_back(*it);
+  }
+  EXPECT_THAT(v, ElementsAre("a", "b"));
+}
+
+//
+// Tests for Splitter
+//
+
+TEST(Splitter, RangeIterators) {
+  auto splitter = absl::StrSplit("a,b,c", ',');
+  std::vector<absl::string_view> output;
+  for (const absl::string_view p : splitter) {
+    output.push_back(p);
+  }
+  EXPECT_THAT(output, ElementsAre("a", "b", "c"));
+}
+
+// Some template functions for use in testing conversion operators
+template <typename ContainerType, typename Splitter>
+void TestConversionOperator(const Splitter& splitter) {
+  ContainerType output = splitter;
+  EXPECT_THAT(output, UnorderedElementsAre("a", "b", "c", "d"));
+}
+
+template <typename MapType, typename Splitter>
+void TestMapConversionOperator(const Splitter& splitter) {
+  MapType m = splitter;
+  EXPECT_THAT(m, UnorderedElementsAre(Pair("a", "b"), Pair("c", "d")));
+}
+
+template <typename FirstType, typename SecondType, typename Splitter>
+void TestPairConversionOperator(const Splitter& splitter) {
+  std::pair<FirstType, SecondType> p = splitter;
+  EXPECT_EQ(p, (std::pair<FirstType, SecondType>("a", "b")));
+}
+
+TEST(Splitter, ConversionOperator) {
+  auto splitter = absl::StrSplit("a,b,c,d", ',');
+
+  TestConversionOperator<std::vector<absl::string_view>>(splitter);
+  TestConversionOperator<std::vector<std::string>>(splitter);
+  TestConversionOperator<std::list<absl::string_view>>(splitter);
+  TestConversionOperator<std::list<std::string>>(splitter);
+  TestConversionOperator<std::deque<absl::string_view>>(splitter);
+  TestConversionOperator<std::deque<std::string>>(splitter);
+  TestConversionOperator<std::set<absl::string_view>>(splitter);
+  TestConversionOperator<std::set<std::string>>(splitter);
+  TestConversionOperator<std::multiset<absl::string_view>>(splitter);
+  TestConversionOperator<std::multiset<std::string>>(splitter);
+  TestConversionOperator<std::unordered_set<std::string>>(splitter);
+
+  // Tests conversion to map-like objects.
+
+  TestMapConversionOperator<std::map<absl::string_view, absl::string_view>>(
+      splitter);
+  TestMapConversionOperator<std::map<absl::string_view, std::string>>(splitter);
+  TestMapConversionOperator<std::map<std::string, absl::string_view>>(splitter);
+  TestMapConversionOperator<std::map<std::string, std::string>>(splitter);
+  TestMapConversionOperator<
+      std::multimap<absl::string_view, absl::string_view>>(splitter);
+  TestMapConversionOperator<std::multimap<absl::string_view, std::string>>(
+      splitter);
+  TestMapConversionOperator<std::multimap<std::string, absl::string_view>>(
+      splitter);
+  TestMapConversionOperator<std::multimap<std::string, std::string>>(splitter);
+  TestMapConversionOperator<std::unordered_map<std::string, std::string>>(
+      splitter);
+
+  // Tests conversion to std::pair
+
+  TestPairConversionOperator<absl::string_view, absl::string_view>(splitter);
+  TestPairConversionOperator<absl::string_view, std::string>(splitter);
+  TestPairConversionOperator<std::string, absl::string_view>(splitter);
+  TestPairConversionOperator<std::string, std::string>(splitter);
+}
+
+// A few additional tests for conversion to std::pair. This conversion is
+// different from others because a std::pair always has exactly two elements:
+// .first and .second. The split has to work even when the split has
+// less-than, equal-to, and more-than 2 strings.
+TEST(Splitter, ToPair) {
+  {
+    // Empty std::string
+    std::pair<std::string, std::string> p = absl::StrSplit("", ',');
+    EXPECT_EQ("", p.first);
+    EXPECT_EQ("", p.second);
+  }
+
+  {
+    // Only first
+    std::pair<std::string, std::string> p = absl::StrSplit("a", ',');
+    EXPECT_EQ("a", p.first);
+    EXPECT_EQ("", p.second);
+  }
+
+  {
+    // Only second
+    std::pair<std::string, std::string> p = absl::StrSplit(",b", ',');
+    EXPECT_EQ("", p.first);
+    EXPECT_EQ("b", p.second);
+  }
+
+  {
+    // First and second.
+    std::pair<std::string, std::string> p = absl::StrSplit("a,b", ',');
+    EXPECT_EQ("a", p.first);
+    EXPECT_EQ("b", p.second);
+  }
+
+  {
+    // First and second and then more stuff that will be ignored.
+    std::pair<std::string, std::string> p = absl::StrSplit("a,b,c", ',');
+    EXPECT_EQ("a", p.first);
+    EXPECT_EQ("b", p.second);
+    // "c" is omitted.
+  }
+}
+
+TEST(Splitter, Predicates) {
+  static const char kTestChars[] = ",a, ,b,";
+  using absl::AllowEmpty;
+  using absl::SkipEmpty;
+  using absl::SkipWhitespace;
+
+  {
+    // No predicate. Does not skip empties.
+    auto splitter = absl::StrSplit(kTestChars, ',');
+    std::vector<std::string> v = splitter;
+    EXPECT_THAT(v, ElementsAre("", "a", " ", "b", ""));
+  }
+
+  {
+    // Allows empty strings. Same behavior as no predicate at all.
+    auto splitter = absl::StrSplit(kTestChars, ',', AllowEmpty());
+    std::vector<std::string> v_allowempty = splitter;
+    EXPECT_THAT(v_allowempty, ElementsAre("", "a", " ", "b", ""));
+
+    // Ensures AllowEmpty equals the behavior with no predicate.
+    auto splitter_nopredicate = absl::StrSplit(kTestChars, ',');
+    std::vector<std::string> v_nopredicate = splitter_nopredicate;
+    EXPECT_EQ(v_allowempty, v_nopredicate);
+  }
+
+  {
+    // Skips empty strings.
+    auto splitter = absl::StrSplit(kTestChars, ',', SkipEmpty());
+    std::vector<std::string> v = splitter;
+    EXPECT_THAT(v, ElementsAre("a", " ", "b"));
+  }
+
+  {
+    // Skips empty and all-whitespace strings.
+    auto splitter = absl::StrSplit(kTestChars, ',', SkipWhitespace());
+    std::vector<std::string> v = splitter;
+    EXPECT_THAT(v, ElementsAre("a", "b"));
+  }
+}
+
+//
+// Tests for StrSplit()
+//
+
+TEST(Split, Basics) {
+  {
+    // Doesn't really do anything useful because the return value is ignored,
+    // but it should work.
+    absl::StrSplit("a,b,c", ',');
+  }
+
+  {
+    std::vector<absl::string_view> v = absl::StrSplit("a,b,c", ',');
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    std::vector<std::string> v = absl::StrSplit("a,b,c", ',');
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+  }
+
+  {
+    // Ensures that assignment works. This requires a little extra work with
+    // C++11 because of overloads with initializer_list.
+    std::vector<std::string> v;
+    v = absl::StrSplit("a,b,c", ',');
+
+    EXPECT_THAT(v, ElementsAre("a", "b", "c"));
+    std::map<std::string, std::string> m;
+    m = absl::StrSplit("a,b,c", ',');
+    EXPECT_EQ(2, m.size());
+    std::unordered_map<std::string, std::string> hm;
+    hm = absl::StrSplit("a,b,c", ',');
+    EXPECT_EQ(2, hm.size());
+  }
+}
+
+absl::string_view ReturnStringView() { return "Hello World"; }
+const char* ReturnConstCharP() { return "Hello World"; }
+char* ReturnCharP() { return const_cast<char*>("Hello World"); }
+
+TEST(Split, AcceptsCertainTemporaries) {
+  std::vector<std::string> v;
+  v = absl::StrSplit(ReturnStringView(), ' ');
+  EXPECT_THAT(v, ElementsAre("Hello", "World"));
+  v = absl::StrSplit(ReturnConstCharP(), ' ');
+  EXPECT_THAT(v, ElementsAre("Hello", "World"));
+  v = absl::StrSplit(ReturnCharP(), ' ');
+  EXPECT_THAT(v, ElementsAre("Hello", "World"));
+}
+
+TEST(Split, Temporary) {
+  // Use a std::string longer than the SSO length, so that when the temporary is
+  // destroyed, if the splitter keeps a reference to the std::string's contents,
+  // it'll reference freed memory instead of just dead on-stack memory.
+  const char input[] = "a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u";
+  EXPECT_LT(sizeof(std::string), ABSL_ARRAYSIZE(input))
+      << "Input should be larger than fits on the stack.";
+
+  // This happens more often in C++11 as part of a range-based for loop.
+  auto splitter = absl::StrSplit(std::string(input), ',');
+  std::string expected = "a";
+  for (absl::string_view letter : splitter) {
+    EXPECT_EQ(expected, letter);
+    ++expected[0];
+  }
+  EXPECT_EQ("v", expected);
+
+  // This happens more often in C++11 as part of a range-based for loop.
+  auto std_splitter = absl::StrSplit(std::string(input), ',');
+  expected = "a";
+  for (absl::string_view letter : std_splitter) {
+    EXPECT_EQ(expected, letter);
+    ++expected[0];
+  }
+  EXPECT_EQ("v", expected);
+}
+
+template <typename T>
+static std::unique_ptr<T> CopyToHeap(const T& value) {
+  return std::unique_ptr<T>(new T(value));
+}
+
+TEST(Split, LvalueCaptureIsCopyable) {
+  std::string input = "a,b";
+  auto heap_splitter = CopyToHeap(absl::StrSplit(input, ','));
+  auto stack_splitter = *heap_splitter;
+  heap_splitter.reset();
+  std::vector<std::string> result = stack_splitter;
+  EXPECT_THAT(result, testing::ElementsAre("a", "b"));
+}
+
+TEST(Split, TemporaryCaptureIsCopyable) {
+  auto heap_splitter = CopyToHeap(absl::StrSplit(std::string("a,b"), ','));
+  auto stack_splitter = *heap_splitter;
+  heap_splitter.reset();
+  std::vector<std::string> result = stack_splitter;
+  EXPECT_THAT(result, testing::ElementsAre("a", "b"));
+}
+
+TEST(Split, SplitterIsCopyableAndMoveable) {
+  auto a = absl::StrSplit("foo", '-');
+
+  // Ensures that the following expressions compile.
+  auto b = a;             // Copy construct
+  auto c = std::move(a);  // Move construct
+  b = c;                  // Copy assign
+  c = std::move(b);       // Move assign
+
+  EXPECT_THAT(c, ElementsAre("foo"));
+}
+
+TEST(Split, StringDelimiter) {
+  {
+    std::vector<absl::string_view> v = absl::StrSplit("a,b", ',');
+    EXPECT_THAT(v, ElementsAre("a", "b"));
+  }
+
+  {
+    std::vector<absl::string_view> v = absl::StrSplit("a,b", std::string(","));
+    EXPECT_THAT(v, ElementsAre("a", "b"));
+  }
+
+  {
+    std::vector<absl::string_view> v =
+        absl::StrSplit("a,b", absl::string_view(","));
+    EXPECT_THAT(v, ElementsAre("a", "b"));
+  }
+}
+
+#if !defined(__cpp_char8_t)
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++2a-compat"
+#endif
+TEST(Split, UTF8) {
+  // Tests splitting utf8 strings and utf8 delimiters.
+  std::string utf8_string = u8"\u03BA\u1F79\u03C3\u03BC\u03B5";
+  {
+    // A utf8 input std::string with an ascii delimiter.
+    std::string to_split = "a," + utf8_string;
+    std::vector<absl::string_view> v = absl::StrSplit(to_split, ',');
+    EXPECT_THAT(v, ElementsAre("a", utf8_string));
+  }
+
+  {
+    // A utf8 input std::string and a utf8 delimiter.
+    std::string to_split = "a," + utf8_string + ",b";
+    std::string unicode_delimiter = "," + utf8_string + ",";
+    std::vector<absl::string_view> v =
+        absl::StrSplit(to_split, unicode_delimiter);
+    EXPECT_THAT(v, ElementsAre("a", "b"));
+  }
+
+  {
+    // A utf8 input std::string and ByAnyChar with ascii chars.
+    std::vector<absl::string_view> v =
+        absl::StrSplit(u8"Foo h\u00E4llo th\u4E1Ere", absl::ByAnyChar(" \t"));
+    EXPECT_THAT(v, ElementsAre("Foo", u8"h\u00E4llo", u8"th\u4E1Ere"));
+  }
+}
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#endif
+#endif  // !defined(__cpp_char8_t)
+
+TEST(Split, EmptyStringDelimiter) {
+  {
+    std::vector<std::string> v = absl::StrSplit("", "");
+    EXPECT_THAT(v, ElementsAre(""));
+  }
+
+  {
+    std::vector<std::string> v = absl::StrSplit("a", "");
+    EXPECT_THAT(v, ElementsAre("a"));
+  }
+
+  {
+    std::vector<std::string> v = absl::StrSplit("ab", "");
+    EXPECT_THAT(v, ElementsAre("a", "b"));
+  }
+
+  {
+    std::vector<std::string> v = absl::StrSplit("a b", "");
+    EXPECT_THAT(v, ElementsAre("a", " ", "b"));
+  }
+}
+
+TEST(Split, SubstrDelimiter) {
+  std::vector<absl::string_view> results;
+  absl::string_view delim("//");
+
+  results = absl::StrSplit("", delim);
+  EXPECT_THAT(results, ElementsAre(""));
+
+  results = absl::StrSplit("//", delim);
+  EXPECT_THAT(results, ElementsAre("", ""));
+
+  results = absl::StrSplit("ab", delim);
+  EXPECT_THAT(results, ElementsAre("ab"));
+
+  results = absl::StrSplit("ab//", delim);
+  EXPECT_THAT(results, ElementsAre("ab", ""));
+
+  results = absl::StrSplit("ab/", delim);
+  EXPECT_THAT(results, ElementsAre("ab/"));
+
+  results = absl::StrSplit("a/b", delim);
+  EXPECT_THAT(results, ElementsAre("a/b"));
+
+  results = absl::StrSplit("a//b", delim);
+  EXPECT_THAT(results, ElementsAre("a", "b"));
+
+  results = absl::StrSplit("a///b", delim);
+  EXPECT_THAT(results, ElementsAre("a", "/b"));
+
+  results = absl::StrSplit("a////b", delim);
+  EXPECT_THAT(results, ElementsAre("a", "", "b"));
+}
+
+TEST(Split, EmptyResults) {
+  std::vector<absl::string_view> results;
+
+  results = absl::StrSplit("", '#');
+  EXPECT_THAT(results, ElementsAre(""));
+
+  results = absl::StrSplit("#", '#');
+  EXPECT_THAT(results, ElementsAre("", ""));
+
+  results = absl::StrSplit("#cd", '#');
+  EXPECT_THAT(results, ElementsAre("", "cd"));
+
+  results = absl::StrSplit("ab#cd#", '#');
+  EXPECT_THAT(results, ElementsAre("ab", "cd", ""));
+
+  results = absl::StrSplit("ab##cd", '#');
+  EXPECT_THAT(results, ElementsAre("ab", "", "cd"));
+
+  results = absl::StrSplit("ab##", '#');
+  EXPECT_THAT(results, ElementsAre("ab", "", ""));
+
+  results = absl::StrSplit("ab#ab#", '#');
+  EXPECT_THAT(results, ElementsAre("ab", "ab", ""));
+
+  results = absl::StrSplit("aaaa", 'a');
+  EXPECT_THAT(results, ElementsAre("", "", "", "", ""));
+
+  results = absl::StrSplit("", '#', absl::SkipEmpty());
+  EXPECT_THAT(results, ElementsAre());
+}
+
+template <typename Delimiter>
+static bool IsFoundAtStartingPos(absl::string_view text, Delimiter d,
+                                 size_t starting_pos, int expected_pos) {
+  absl::string_view found = d.Find(text, starting_pos);
+  return found.data() != text.data() + text.size() &&
+         expected_pos == found.data() - text.data();
+}
+
+// Helper function for testing Delimiter objects. Returns true if the given
+// Delimiter is found in the given string at the given position. This function
+// tests two cases:
+//   1. The actual text given, staring at position 0
+//   2. The text given with leading padding that should be ignored
+template <typename Delimiter>
+static bool IsFoundAt(absl::string_view text, Delimiter d, int expected_pos) {
+  const std::string leading_text = ",x,y,z,";
+  return IsFoundAtStartingPos(text, d, 0, expected_pos) &&
+         IsFoundAtStartingPos(leading_text + std::string(text), d,
+                              leading_text.length(),
+                              expected_pos + leading_text.length());
+}
+
+//
+// Tests for ByString
+//
+
+// Tests using any delimiter that represents a single comma.
+template <typename Delimiter>
+void TestComma(Delimiter d) {
+  EXPECT_TRUE(IsFoundAt(",", d, 0));
+  EXPECT_TRUE(IsFoundAt("a,", d, 1));
+  EXPECT_TRUE(IsFoundAt(",b", d, 0));
+  EXPECT_TRUE(IsFoundAt("a,b", d, 1));
+  EXPECT_TRUE(IsFoundAt("a,b,", d, 1));
+  EXPECT_TRUE(IsFoundAt("a,b,c", d, 1));
+  EXPECT_FALSE(IsFoundAt("", d, -1));
+  EXPECT_FALSE(IsFoundAt(" ", d, -1));
+  EXPECT_FALSE(IsFoundAt("a", d, -1));
+  EXPECT_FALSE(IsFoundAt("a b c", d, -1));
+  EXPECT_FALSE(IsFoundAt("a;b;c", d, -1));
+  EXPECT_FALSE(IsFoundAt(";", d, -1));
+}
+
+TEST(Delimiter, ByString) {
+  using absl::ByString;
+  TestComma(ByString(","));
+
+  // Works as named variable.
+  ByString comma_string(",");
+  TestComma(comma_string);
+
+  // The first occurrence of empty std::string ("") in a std::string is at position 0.
+  // There is a test below that demonstrates this for absl::string_view::find().
+  // If the ByString delimiter returned position 0 for this, there would
+  // be an infinite loop in the SplitIterator code. To avoid this, empty std::string
+  // is a special case in that it always returns the item at position 1.
+  absl::string_view abc("abc");
+  EXPECT_EQ(0, abc.find(""));  // "" is found at position 0
+  ByString empty("");
+  EXPECT_FALSE(IsFoundAt("", empty, 0));
+  EXPECT_FALSE(IsFoundAt("a", empty, 0));
+  EXPECT_TRUE(IsFoundAt("ab", empty, 1));
+  EXPECT_TRUE(IsFoundAt("abc", empty, 1));
+}
+
+TEST(Split, ByChar) {
+  using absl::ByChar;
+  TestComma(ByChar(','));
+
+  // Works as named variable.
+  ByChar comma_char(',');
+  TestComma(comma_char);
+}
+
+//
+// Tests for ByAnyChar
+//
+
+TEST(Delimiter, ByAnyChar) {
+  using absl::ByAnyChar;
+  ByAnyChar one_delim(",");
+  // Found
+  EXPECT_TRUE(IsFoundAt(",", one_delim, 0));
+  EXPECT_TRUE(IsFoundAt("a,", one_delim, 1));
+  EXPECT_TRUE(IsFoundAt("a,b", one_delim, 1));
+  EXPECT_TRUE(IsFoundAt(",b", one_delim, 0));
+  // Not found
+  EXPECT_FALSE(IsFoundAt("", one_delim, -1));
+  EXPECT_FALSE(IsFoundAt(" ", one_delim, -1));
+  EXPECT_FALSE(IsFoundAt("a", one_delim, -1));
+  EXPECT_FALSE(IsFoundAt("a;b;c", one_delim, -1));
+  EXPECT_FALSE(IsFoundAt(";", one_delim, -1));
+
+  ByAnyChar two_delims(",;");
+  // Found
+  EXPECT_TRUE(IsFoundAt(",", two_delims, 0));
+  EXPECT_TRUE(IsFoundAt(";", two_delims, 0));
+  EXPECT_TRUE(IsFoundAt(",;", two_delims, 0));
+  EXPECT_TRUE(IsFoundAt(";,", two_delims, 0));
+  EXPECT_TRUE(IsFoundAt(",;b", two_delims, 0));
+  EXPECT_TRUE(IsFoundAt(";,b", two_delims, 0));
+  EXPECT_TRUE(IsFoundAt("a;,", two_delims, 1));
+  EXPECT_TRUE(IsFoundAt("a,;", two_delims, 1));
+  EXPECT_TRUE(IsFoundAt("a;,b", two_delims, 1));
+  EXPECT_TRUE(IsFoundAt("a,;b", two_delims, 1));
+  // Not found
+  EXPECT_FALSE(IsFoundAt("", two_delims, -1));
+  EXPECT_FALSE(IsFoundAt(" ", two_delims, -1));
+  EXPECT_FALSE(IsFoundAt("a", two_delims, -1));
+  EXPECT_FALSE(IsFoundAt("a=b=c", two_delims, -1));
+  EXPECT_FALSE(IsFoundAt("=", two_delims, -1));
+
+  // ByAnyChar behaves just like ByString when given a delimiter of empty
+  // std::string. That is, it always returns a zero-length absl::string_view
+  // referring to the item at position 1, not position 0.
+  ByAnyChar empty("");
+  EXPECT_FALSE(IsFoundAt("", empty, 0));
+  EXPECT_FALSE(IsFoundAt("a", empty, 0));
+  EXPECT_TRUE(IsFoundAt("ab", empty, 1));
+  EXPECT_TRUE(IsFoundAt("abc", empty, 1));
+}
+
+//
+// Tests for ByLength
+//
+
+TEST(Delimiter, ByLength) {
+  using absl::ByLength;
+
+  ByLength four_char_delim(4);
+
+  // Found
+  EXPECT_TRUE(IsFoundAt("abcde", four_char_delim, 4));
+  EXPECT_TRUE(IsFoundAt("abcdefghijklmnopqrstuvwxyz", four_char_delim, 4));
+  EXPECT_TRUE(IsFoundAt("a b,c\nd", four_char_delim, 4));
+  // Not found
+  EXPECT_FALSE(IsFoundAt("", four_char_delim, 0));
+  EXPECT_FALSE(IsFoundAt("a", four_char_delim, 0));
+  EXPECT_FALSE(IsFoundAt("ab", four_char_delim, 0));
+  EXPECT_FALSE(IsFoundAt("abc", four_char_delim, 0));
+  EXPECT_FALSE(IsFoundAt("abcd", four_char_delim, 0));
+}
+
+TEST(Split, WorksWithLargeStrings) {
+  if (sizeof(size_t) > 4) {
+    std::string s((uint32_t{1} << 31) + 1, 'x');  // 2G + 1 byte
+    s.back() = '-';
+    std::vector<absl::string_view> v = absl::StrSplit(s, '-');
+    EXPECT_EQ(2, v.size());
+    // The first element will contain 2G of 'x's.
+    // testing::StartsWith is too slow with a 2G std::string.
+    EXPECT_EQ('x', v[0][0]);
+    EXPECT_EQ('x', v[0][1]);
+    EXPECT_EQ('x', v[0][3]);
+    EXPECT_EQ("", v[1]);
+  }
+}
+
+TEST(SplitInternalTest, TypeTraits) {
+  EXPECT_FALSE(absl::strings_internal::HasMappedType<int>::value);
+  EXPECT_TRUE(
+      (absl::strings_internal::HasMappedType<std::map<int, int>>::value));
+  EXPECT_FALSE(absl::strings_internal::HasValueType<int>::value);
+  EXPECT_TRUE(
+      (absl::strings_internal::HasValueType<std::map<int, int>>::value));
+  EXPECT_FALSE(absl::strings_internal::HasConstIterator<int>::value);
+  EXPECT_TRUE(
+      (absl::strings_internal::HasConstIterator<std::map<int, int>>::value));
+  EXPECT_FALSE(absl::strings_internal::IsInitializerList<int>::value);
+  EXPECT_TRUE((absl::strings_internal::IsInitializerList<
+               std::initializer_list<int>>::value));
+}
+
+}  // namespace
diff --git a/absl/strings/string_view.cc b/absl/strings/string_view.cc
new file mode 100644
index 0000000..dc034a8
--- /dev/null
+++ b/absl/strings/string_view.cc
@@ -0,0 +1,233 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/string_view.h"
+
+#ifndef ABSL_HAVE_STD_STRING_VIEW
+
+#include <algorithm>
+#include <climits>
+#include <cstring>
+#include <ostream>
+
+#include "absl/strings/internal/memutil.h"
+
+namespace absl {
+
+namespace {
+void WritePadding(std::ostream& o, size_t pad) {
+  char fill_buf[32];
+  memset(fill_buf, o.fill(), sizeof(fill_buf));
+  while (pad) {
+    size_t n = std::min(pad, sizeof(fill_buf));
+    o.write(fill_buf, n);
+    pad -= n;
+  }
+}
+
+class LookupTable {
+ public:
+  // For each character in wanted, sets the index corresponding
+  // to the ASCII code of that character. This is used by
+  // the find_.*_of methods below to tell whether or not a character is in
+  // the lookup table in constant time.
+  explicit LookupTable(string_view wanted) {
+    for (char c : wanted) {
+      table_[Index(c)] = true;
+    }
+  }
+  bool operator[](char c) const { return table_[Index(c)]; }
+
+ private:
+  static unsigned char Index(char c) { return static_cast<unsigned char>(c); }
+  bool table_[UCHAR_MAX + 1] = {};
+};
+
+}  // namespace
+
+std::ostream& operator<<(std::ostream& o, string_view piece) {
+  std::ostream::sentry sentry(o);
+  if (sentry) {
+    size_t lpad = 0;
+    size_t rpad = 0;
+    if (static_cast<size_t>(o.width()) > piece.size()) {
+      size_t pad = o.width() - piece.size();
+      if ((o.flags() & o.adjustfield) == o.left) {
+        rpad = pad;
+      } else {
+        lpad = pad;
+      }
+    }
+    if (lpad) WritePadding(o, lpad);
+    o.write(piece.data(), piece.size());
+    if (rpad) WritePadding(o, rpad);
+    o.width(0);
+  }
+  return o;
+}
+
+string_view::size_type string_view::find(string_view s, size_type pos) const
+    noexcept {
+  if (empty() || pos > length_) {
+    if (empty() && pos == 0 && s.empty()) return 0;
+    return npos;
+  }
+  const char* result =
+      strings_internal::memmatch(ptr_ + pos, length_ - pos, s.ptr_, s.length_);
+  return result ? result - ptr_ : npos;
+}
+
+string_view::size_type string_view::find(char c, size_type pos) const noexcept {
+  if (empty() || pos >= length_) {
+    return npos;
+  }
+  const char* result =
+      static_cast<const char*>(memchr(ptr_ + pos, c, length_ - pos));
+  return result != nullptr ? result - ptr_ : npos;
+}
+
+string_view::size_type string_view::rfind(string_view s, size_type pos) const
+    noexcept {
+  if (length_ < s.length_) return npos;
+  if (s.empty()) return std::min(length_, pos);
+  const char* last = ptr_ + std::min(length_ - s.length_, pos) + s.length_;
+  const char* result = std::find_end(ptr_, last, s.ptr_, s.ptr_ + s.length_);
+  return result != last ? result - ptr_ : npos;
+}
+
+// Search range is [0..pos] inclusive.  If pos == npos, search everything.
+string_view::size_type string_view::rfind(char c, size_type pos) const
+    noexcept {
+  // Note: memrchr() is not available on Windows.
+  if (empty()) return npos;
+  for (size_type i = std::min(pos, length_ - 1);; --i) {
+    if (ptr_[i] == c) {
+      return i;
+    }
+    if (i == 0) break;
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find_first_of(string_view s,
+                                                  size_type pos) const
+    noexcept {
+  if (empty() || s.empty()) {
+    return npos;
+  }
+  // Avoid the cost of LookupTable() for a single-character search.
+  if (s.length_ == 1) return find_first_of(s.ptr_[0], pos);
+  LookupTable tbl(s);
+  for (size_type i = pos; i < length_; ++i) {
+    if (tbl[ptr_[i]]) {
+      return i;
+    }
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find_first_not_of(string_view s,
+                                                      size_type pos) const
+    noexcept {
+  if (empty()) return npos;
+  // Avoid the cost of LookupTable() for a single-character search.
+  if (s.length_ == 1) return find_first_not_of(s.ptr_[0], pos);
+  LookupTable tbl(s);
+  for (size_type i = pos; i < length_; ++i) {
+    if (!tbl[ptr_[i]]) {
+      return i;
+    }
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find_first_not_of(char c,
+                                                      size_type pos) const
+    noexcept {
+  if (empty()) return npos;
+  for (; pos < length_; ++pos) {
+    if (ptr_[pos] != c) {
+      return pos;
+    }
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find_last_of(string_view s,
+                                                 size_type pos) const noexcept {
+  if (empty() || s.empty()) return npos;
+  // Avoid the cost of LookupTable() for a single-character search.
+  if (s.length_ == 1) return find_last_of(s.ptr_[0], pos);
+  LookupTable tbl(s);
+  for (size_type i = std::min(pos, length_ - 1);; --i) {
+    if (tbl[ptr_[i]]) {
+      return i;
+    }
+    if (i == 0) break;
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find_last_not_of(string_view s,
+                                                     size_type pos) const
+    noexcept {
+  if (empty()) return npos;
+  size_type i = std::min(pos, length_ - 1);
+  if (s.empty()) return i;
+  // Avoid the cost of LookupTable() for a single-character search.
+  if (s.length_ == 1) return find_last_not_of(s.ptr_[0], pos);
+  LookupTable tbl(s);
+  for (;; --i) {
+    if (!tbl[ptr_[i]]) {
+      return i;
+    }
+    if (i == 0) break;
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find_last_not_of(char c,
+                                                     size_type pos) const
+    noexcept {
+  if (empty()) return npos;
+  size_type i = std::min(pos, length_ - 1);
+  for (;; --i) {
+    if (ptr_[i] != c) {
+      return i;
+    }
+    if (i == 0) break;
+  }
+  return npos;
+}
+
+// MSVC has non-standard behavior that implicitly creates definitions for static
+// const members. These implicit definitions conflict with explicit out-of-class
+// member definitions that are required by the C++ standard, resulting in
+// LNK1169 "multiply defined" errors at link time. __declspec(selectany) asks
+// MSVC to choose only one definition for the symbol it decorates. See details
+// at https://msdn.microsoft.com/en-us/library/34h23df8(v=vs.100).aspx
+#ifdef _MSC_VER
+#define ABSL_STRING_VIEW_SELECTANY __declspec(selectany)
+#else
+#define ABSL_STRING_VIEW_SELECTANY
+#endif
+
+ABSL_STRING_VIEW_SELECTANY
+constexpr string_view::size_type string_view::npos;
+ABSL_STRING_VIEW_SELECTANY
+constexpr string_view::size_type string_view::kMaxSize;
+
+}  // namespace absl
+
+#endif  // ABSL_HAVE_STD_STRING_VIEW
diff --git a/absl/strings/string_view.h b/absl/strings/string_view.h
new file mode 100644
index 0000000..68b90aa
--- /dev/null
+++ b/absl/strings/string_view.h
@@ -0,0 +1,596 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: string_view.h
+// -----------------------------------------------------------------------------
+//
+// This file contains the definition of the `absl::string_view` class. A
+// `string_view` points to a contiguous span of characters, often part or all of
+// another `std::string`, double-quoted string literal, character array, or even
+// another `string_view`.
+//
+// This `absl::string_view` abstraction is designed to be a drop-in
+// replacement for the C++17 `std::string_view` abstraction.
+#ifndef ABSL_STRINGS_STRING_VIEW_H_
+#define ABSL_STRINGS_STRING_VIEW_H_
+
+#include <algorithm>
+#include "absl/base/config.h"
+
+#ifdef ABSL_HAVE_STD_STRING_VIEW
+
+#include <string_view>  // IWYU pragma: export
+
+namespace absl {
+using std::string_view;
+}  // namespace absl
+
+#else  // ABSL_HAVE_STD_STRING_VIEW
+
+#include <cassert>
+#include <cstddef>
+#include <cstring>
+#include <iosfwd>
+#include <iterator>
+#include <limits>
+#include <string>
+
+#include "absl/base/internal/throw_delegate.h"
+#include "absl/base/macros.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"
+
+namespace absl {
+
+// absl::string_view
+//
+// A `string_view` provides a lightweight view into the string data provided by
+// a `std::string`, double-quoted string literal, character array, or even
+// another `string_view`. A `string_view` does *not* own the string to which it
+// points, and that data cannot be modified through the view.
+//
+// You can use `string_view` as a function or method parameter anywhere a
+// parameter can receive a double-quoted string literal, `const char*`,
+// `std::string`, or another `absl::string_view` argument with no need to copy
+// the string data. Systematic use of `string_view` within function arguments
+// reduces data copies and `strlen()` calls.
+//
+// Because of its small size, prefer passing `string_view` by value:
+//
+//   void MyFunction(absl::string_view arg);
+//
+// If circumstances require, you may also pass one by const reference:
+//
+//   void MyFunction(const absl::string_view& arg);  // not preferred
+//
+// Passing by value generates slightly smaller code for many architectures.
+//
+// In either case, the source data of the `string_view` must outlive the
+// `string_view` itself.
+//
+// A `string_view` is also suitable for local variables if you know that the
+// lifetime of the underlying object is longer than the lifetime of your
+// `string_view` variable. However, beware of binding a `string_view` to a
+// temporary value:
+//
+//   // BAD use of string_view: lifetime problem
+//   absl::string_view sv = obj.ReturnAString();
+//
+//   // GOOD use of string_view: str outlives sv
+//   std::string str = obj.ReturnAString();
+//   absl::string_view sv = str;
+//
+// Due to lifetime issues, a `string_view` is sometimes a poor choice for a
+// return value and usually a poor choice for a data member. If you do use a
+// `string_view` this way, it is your responsibility to ensure that the object
+// pointed to by the `string_view` outlives the `string_view`.
+//
+// A `string_view` may represent a whole string or just part of a string. For
+// example, when splitting a string, `std::vector<absl::string_view>` is a
+// natural data type for the output.
+//
+// When constructed from a source which is nul-terminated, the `string_view`
+// itself will not include the nul-terminator unless a specific size (including
+// the nul) is passed to the constructor. As a result, common idioms that work
+// on nul-terminated strings do not work on `string_view` objects. If you write
+// code that scans a `string_view`, you must check its length rather than test
+// for nul, for example. Note, however, that nuls may still be embedded within
+// a `string_view` explicitly.
+//
+// You may create a null `string_view` in two ways:
+//
+//   absl::string_view sv();
+//   absl::string_view sv(nullptr, 0);
+//
+// For the above, `sv.data() == nullptr`, `sv.length() == 0`, and
+// `sv.empty() == true`. Also, if you create a `string_view` with a non-null
+// pointer then `sv.data() != nullptr`. Thus, you can use `string_view()` to
+// signal an undefined value that is different from other `string_view` values
+// in a similar fashion to how `const char* p1 = nullptr;` is different from
+// `const char* p2 = "";`. However, in practice, it is not recommended to rely
+// on this behavior.
+//
+// Be careful not to confuse a null `string_view` with an empty one. A null
+// `string_view` is an empty `string_view`, but some empty `string_view`s are
+// not null. Prefer checking for emptiness over checking for null.
+//
+// There are many ways to create an empty string_view:
+//
+//   const char* nullcp = nullptr;
+//   // string_view.size() will return 0 in all cases.
+//   absl::string_view();
+//   absl::string_view(nullcp, 0);
+//   absl::string_view("");
+//   absl::string_view("", 0);
+//   absl::string_view("abcdef", 0);
+//   absl::string_view("abcdef" + 6, 0);
+//
+// All empty `string_view` objects whether null or not, are equal:
+//
+//   absl::string_view() == absl::string_view("", 0)
+//   absl::string_view(nullptr, 0) == absl::string_view("abcdef"+6, 0)
+class string_view {
+ public:
+  using traits_type = std::char_traits<char>;
+  using value_type = char;
+  using pointer = char*;
+  using const_pointer = const char*;
+  using reference = char&;
+  using const_reference = const char&;
+  using const_iterator = const char*;
+  using iterator = const_iterator;
+  using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+  using reverse_iterator = const_reverse_iterator;
+  using size_type = size_t;
+  using difference_type = std::ptrdiff_t;
+
+  static constexpr size_type npos = static_cast<size_type>(-1);
+
+  // Null `string_view` constructor
+  constexpr string_view() noexcept : ptr_(nullptr), length_(0) {}
+
+  // Implicit constructors
+
+  template <typename Allocator>
+  string_view(  // NOLINT(runtime/explicit)
+      const std::basic_string<char, std::char_traits<char>, Allocator>&
+          str) noexcept
+      : ptr_(str.data()), length_(CheckLengthInternal(str.size())) {}
+
+  // Implicit constructor of a `string_view` from nul-terminated `str`. When
+  // accepting possibly null strings, use `absl::NullSafeStringView(str)`
+  // instead (see below).
+  constexpr string_view(const char* str)  // NOLINT(runtime/explicit)
+      : ptr_(str),
+        length_(str ? CheckLengthInternal(StrlenInternal(str)) : 0) {}
+
+  // Implicit constructor of a `string_view` from a `const char*` and length.
+  constexpr string_view(const char* data, size_type len)
+      : ptr_(data), length_(CheckLengthInternal(len)) {}
+
+  // NOTE: Harmlessly omitted to work around gdb bug.
+  //   constexpr string_view(const string_view&) noexcept = default;
+  //   string_view& operator=(const string_view&) noexcept = default;
+
+  // Iterators
+
+  // string_view::begin()
+  //
+  // Returns an iterator pointing to the first character at the beginning of the
+  // `string_view`, or `end()` if the `string_view` is empty.
+  constexpr const_iterator begin() const noexcept { return ptr_; }
+
+  // string_view::end()
+  //
+  // Returns an iterator pointing just beyond the last character at the end of
+  // the `string_view`. This iterator acts as a placeholder; attempting to
+  // access it results in undefined behavior.
+  constexpr const_iterator end() const noexcept { return ptr_ + length_; }
+
+  // string_view::cbegin()
+  //
+  // Returns a const iterator pointing to the first character at the beginning
+  // of the `string_view`, or `end()` if the `string_view` is empty.
+  constexpr const_iterator cbegin() const noexcept { return begin(); }
+
+  // string_view::cend()
+  //
+  // Returns a const iterator pointing just beyond the last character at the end
+  // of the `string_view`. This pointer acts as a placeholder; attempting to
+  // access its element results in undefined behavior.
+  constexpr const_iterator cend() const noexcept { return end(); }
+
+  // string_view::rbegin()
+  //
+  // Returns a reverse iterator pointing to the last character at the end of the
+  // `string_view`, or `rend()` if the `string_view` is empty.
+  const_reverse_iterator rbegin() const noexcept {
+    return const_reverse_iterator(end());
+  }
+
+  // string_view::rend()
+  //
+  // Returns a reverse iterator pointing just before the first character at the
+  // beginning of the `string_view`. This pointer acts as a placeholder;
+  // attempting to access its element results in undefined behavior.
+  const_reverse_iterator rend() const noexcept {
+    return const_reverse_iterator(begin());
+  }
+
+  // string_view::crbegin()
+  //
+  // Returns a const reverse iterator pointing to the last character at the end
+  // of the `string_view`, or `crend()` if the `string_view` is empty.
+  const_reverse_iterator crbegin() const noexcept { return rbegin(); }
+
+  // string_view::crend()
+  //
+  // Returns a const reverse iterator pointing just before the first character
+  // at the beginning of the `string_view`. This pointer acts as a placeholder;
+  // attempting to access its element results in undefined behavior.
+  const_reverse_iterator crend() const noexcept { return rend(); }
+
+  // Capacity Utilities
+
+  // string_view::size()
+  //
+  // Returns the number of characters in the `string_view`.
+  constexpr size_type size() const noexcept {
+    return length_;
+  }
+
+  // string_view::length()
+  //
+  // Returns the number of characters in the `string_view`. Alias for `size()`.
+  constexpr size_type length() const noexcept { return size(); }
+
+  // string_view::max_size()
+  //
+  // Returns the maximum number of characters the `string_view` can hold.
+  constexpr size_type max_size() const noexcept { return kMaxSize; }
+
+  // string_view::empty()
+  //
+  // Checks if the `string_view` is empty (refers to no characters).
+  constexpr bool empty() const noexcept { return length_ == 0; }
+
+  // string_view::operator[]
+  //
+  // Returns the ith element of the `string_view` using the array operator.
+  // Note that this operator does not perform any bounds checking.
+  constexpr const_reference operator[](size_type i) const { return ptr_[i]; }
+
+  // string_view::at()
+  //
+  // Returns the ith element of the `string_view`. Bounds checking is performed,
+  // and an exception of type `std::out_of_range` will be thrown on invalid
+  // access.
+  constexpr const_reference at(size_type i) const {
+    return ABSL_PREDICT_TRUE(i < size())
+               ? ptr_[i]
+               : (base_internal::ThrowStdOutOfRange("absl::string_view::at"),
+                  ptr_[i]);
+  }
+
+  // string_view::front()
+  //
+  // Returns the first element of a `string_view`.
+  constexpr const_reference front() const { return ptr_[0]; }
+
+  // string_view::back()
+  //
+  // Returns the last element of a `string_view`.
+  constexpr const_reference back() const { return ptr_[size() - 1]; }
+
+  // string_view::data()
+  //
+  // Returns a pointer to the underlying character array (which is of course
+  // stored elsewhere). Note that `string_view::data()` may contain embedded nul
+  // characters, but the returned buffer may or may not be nul-terminated;
+  // therefore, do not pass `data()` to a routine that expects a nul-terminated
+  // std::string.
+  constexpr const_pointer data() const noexcept { return ptr_; }
+
+  // Modifiers
+
+  // string_view::remove_prefix()
+  //
+  // Removes the first `n` characters from the `string_view`. Note that the
+  // underlying std::string is not changed, only the view.
+  void remove_prefix(size_type n) {
+    assert(n <= length_);
+    ptr_ += n;
+    length_ -= n;
+  }
+
+  // string_view::remove_suffix()
+  //
+  // Removes the last `n` characters from the `string_view`. Note that the
+  // underlying std::string is not changed, only the view.
+  void remove_suffix(size_type n) {
+    assert(n <= length_);
+    length_ -= n;
+  }
+
+  // string_view::swap()
+  //
+  // Swaps this `string_view` with another `string_view`.
+  void swap(string_view& s) noexcept {
+    auto t = *this;
+    *this = s;
+    s = t;
+  }
+
+  // Explicit conversion operators
+
+  // Converts to `std::basic_string`.
+  template <typename A>
+  explicit operator std::basic_string<char, traits_type, A>() const {
+    if (!data()) return {};
+    return std::basic_string<char, traits_type, A>(data(), size());
+  }
+
+  // string_view::copy()
+  //
+  // Copies the contents of the `string_view` at offset `pos` and length `n`
+  // into `buf`.
+  size_type copy(char* buf, size_type n, size_type pos = 0) const {
+    if (ABSL_PREDICT_FALSE(pos > length_)) {
+      base_internal::ThrowStdOutOfRange("absl::string_view::copy");
+    }
+    size_type rlen = (std::min)(length_ - pos, n);
+    if (rlen > 0) {
+      const char* start = ptr_ + pos;
+      traits_type::copy(buf, start, rlen);
+    }
+    return rlen;
+  }
+
+  // string_view::substr()
+  //
+  // Returns a "substring" of the `string_view` (at offset `pos` and length
+  // `n`) as another string_view. This function throws `std::out_of_bounds` if
+  // `pos > size`.
+  string_view substr(size_type pos, size_type n = npos) const {
+    if (ABSL_PREDICT_FALSE(pos > length_))
+      base_internal::ThrowStdOutOfRange("absl::string_view::substr");
+    n = (std::min)(n, length_ - pos);
+    return string_view(ptr_ + pos, n);
+  }
+
+  // string_view::compare()
+  //
+  // Performs a lexicographical comparison between the `string_view` and
+  // another `absl::string_view`, returning -1 if `this` is less than, 0 if
+  // `this` is equal to, and 1 if `this` is greater than the passed std::string
+  // view. Note that in the case of data equality, a further comparison is made
+  // on the respective sizes of the two `string_view`s to determine which is
+  // smaller, equal, or greater.
+  int compare(string_view x) const noexcept {
+    auto min_length = (std::min)(length_, x.length_);
+    if (min_length > 0) {
+      int r = memcmp(ptr_, x.ptr_, min_length);
+      if (r < 0) return -1;
+      if (r > 0) return 1;
+    }
+    if (length_ < x.length_) return -1;
+    if (length_ > x.length_) return 1;
+    return 0;
+  }
+
+  // Overload of `string_view::compare()` for comparing a substring of the
+  // 'string_view` and another `absl::string_view`.
+  int compare(size_type pos1, size_type count1, string_view v) const {
+    return substr(pos1, count1).compare(v);
+  }
+
+  // Overload of `string_view::compare()` for comparing a substring of the
+  // `string_view` and a substring of another `absl::string_view`.
+  int compare(size_type pos1, size_type count1, string_view v, size_type pos2,
+              size_type count2) const {
+    return substr(pos1, count1).compare(v.substr(pos2, count2));
+  }
+
+  // Overload of `string_view::compare()` for comparing a `string_view` and a
+  // a different  C-style std::string `s`.
+  int compare(const char* s) const { return compare(string_view(s)); }
+
+  // Overload of `string_view::compare()` for comparing a substring of the
+  // `string_view` and a different std::string C-style std::string `s`.
+  int compare(size_type pos1, size_type count1, const char* s) const {
+    return substr(pos1, count1).compare(string_view(s));
+  }
+
+  // Overload of `string_view::compare()` for comparing a substring of the
+  // `string_view` and a substring of a different C-style std::string `s`.
+  int compare(size_type pos1, size_type count1, const char* s,
+              size_type count2) const {
+    return substr(pos1, count1).compare(string_view(s, count2));
+  }
+
+  // Find Utilities
+
+  // string_view::find()
+  //
+  // Finds the first occurrence of the substring `s` within the `string_view`,
+  // returning the position of the first character's match, or `npos` if no
+  // match was found.
+  size_type find(string_view s, size_type pos = 0) const noexcept;
+
+  // Overload of `string_view::find()` for finding the given character `c`
+  // within the `string_view`.
+  size_type find(char c, size_type pos = 0) const noexcept;
+
+  // string_view::rfind()
+  //
+  // Finds the last occurrence of a substring `s` within the `string_view`,
+  // returning the position of the first character's match, or `npos` if no
+  // match was found.
+  size_type rfind(string_view s, size_type pos = npos) const
+      noexcept;
+
+  // Overload of `string_view::rfind()` for finding the last given character `c`
+  // within the `string_view`.
+  size_type rfind(char c, size_type pos = npos) const noexcept;
+
+  // string_view::find_first_of()
+  //
+  // Finds the first occurrence of any of the characters in `s` within the
+  // `string_view`, returning the start position of the match, or `npos` if no
+  // match was found.
+  size_type find_first_of(string_view s, size_type pos = 0) const
+      noexcept;
+
+  // Overload of `string_view::find_first_of()` for finding a character `c`
+  // within the `string_view`.
+  size_type find_first_of(char c, size_type pos = 0) const
+      noexcept {
+    return find(c, pos);
+  }
+
+  // string_view::find_last_of()
+  //
+  // Finds the last occurrence of any of the characters in `s` within the
+  // `string_view`, returning the start position of the match, or `npos` if no
+  // match was found.
+  size_type find_last_of(string_view s, size_type pos = npos) const
+      noexcept;
+
+  // Overload of `string_view::find_last_of()` for finding a character `c`
+  // within the `string_view`.
+  size_type find_last_of(char c, size_type pos = npos) const
+      noexcept {
+    return rfind(c, pos);
+  }
+
+  // string_view::find_first_not_of()
+  //
+  // Finds the first occurrence of any of the characters not in `s` within the
+  // `string_view`, returning the start position of the first non-match, or
+  // `npos` if no non-match was found.
+  size_type find_first_not_of(string_view s, size_type pos = 0) const noexcept;
+
+  // Overload of `string_view::find_first_not_of()` for finding a character
+  // that is not `c` within the `string_view`.
+  size_type find_first_not_of(char c, size_type pos = 0) const noexcept;
+
+  // string_view::find_last_not_of()
+  //
+  // Finds the last occurrence of any of the characters not in `s` within the
+  // `string_view`, returning the start position of the last non-match, or
+  // `npos` if no non-match was found.
+  size_type find_last_not_of(string_view s,
+                                          size_type pos = npos) const noexcept;
+
+  // Overload of `string_view::find_last_not_of()` for finding a character
+  // that is not `c` within the `string_view`.
+  size_type find_last_not_of(char c, size_type pos = npos) const
+      noexcept;
+
+ private:
+  static constexpr size_type kMaxSize =
+      (std::numeric_limits<difference_type>::max)();
+
+  static constexpr size_type CheckLengthInternal(size_type len) {
+    return ABSL_ASSERT(len <= kMaxSize), len;
+  }
+
+  static constexpr size_type StrlenInternal(const char* str) {
+#if defined(_MSC_VER) && _MSC_VER >= 1910 && !defined(__clang__)
+    // MSVC 2017+ can evaluate this at compile-time.
+    const char* begin = str;
+    while (*str != '\0') ++str;
+    return str - begin;
+#elif ABSL_HAVE_BUILTIN(__builtin_strlen) || \
+    (defined(__GNUC__) && !defined(__clang__))
+    // GCC has __builtin_strlen according to
+    // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Other-Builtins.html, but
+    // ABSL_HAVE_BUILTIN doesn't detect that, so we use the extra checks above.
+    // __builtin_strlen is constexpr.
+    return __builtin_strlen(str);
+#else
+    return str ? strlen(str) : 0;
+#endif
+  }
+
+  const char* ptr_;
+  size_type length_;
+};
+
+// This large function is defined inline so that in a fairly common case where
+// one of the arguments is a literal, the compiler can elide a lot of the
+// following comparisons.
+inline bool operator==(string_view x, string_view y) noexcept {
+  auto len = x.size();
+  if (len != y.size()) {
+    return false;
+  }
+
+  return x.data() == y.data() || len <= 0 ||
+         memcmp(x.data(), y.data(), len) == 0;
+}
+
+inline bool operator!=(string_view x, string_view y) noexcept {
+  return !(x == y);
+}
+
+inline bool operator<(string_view x, string_view y) noexcept {
+  auto min_size = (std::min)(x.size(), y.size());
+  const int r = min_size == 0 ? 0 : memcmp(x.data(), y.data(), min_size);
+  return (r < 0) || (r == 0 && x.size() < y.size());
+}
+
+inline bool operator>(string_view x, string_view y) noexcept { return y < x; }
+
+inline bool operator<=(string_view x, string_view y) noexcept {
+  return !(y < x);
+}
+
+inline bool operator>=(string_view x, string_view y) noexcept {
+  return !(x < y);
+}
+
+// IO Insertion Operator
+std::ostream& operator<<(std::ostream& o, string_view piece);
+
+}  // namespace absl
+
+#endif  // ABSL_HAVE_STD_STRING_VIEW
+
+namespace absl {
+
+// ClippedSubstr()
+//
+// Like `s.substr(pos, n)`, but clips `pos` to an upper bound of `s.size()`.
+// Provided because std::string_view::substr throws if `pos > size()`
+inline string_view ClippedSubstr(string_view s, size_t pos,
+                                 size_t n = string_view::npos) {
+  pos = (std::min)(pos, static_cast<size_t>(s.size()));
+  return s.substr(pos, n);
+}
+
+// NullSafeStringView()
+//
+// Creates an `absl::string_view` from a pointer `p` even if it's null-valued.
+// This function should be used where an `absl::string_view` can be created from
+// a possibly-null pointer.
+inline string_view NullSafeStringView(const char* p) {
+  return p ? string_view(p) : string_view();
+}
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_STRING_VIEW_H_
diff --git a/absl/strings/string_view_benchmark.cc b/absl/strings/string_view_benchmark.cc
new file mode 100644
index 0000000..46909cb
--- /dev/null
+++ b/absl/strings/string_view_benchmark.cc
@@ -0,0 +1,329 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/string_view.h"
+
+#include <algorithm>
+#include <cstdint>
+#include <map>
+#include <random>
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/attributes.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/macros.h"
+#include "absl/strings/str_cat.h"
+
+namespace {
+
+// Provide a forcibly out-of-line wrapper for operator== that can be used in
+// benchmarks to measure the impact of inlining.
+ABSL_ATTRIBUTE_NOINLINE
+bool NonInlinedEq(absl::string_view a, absl::string_view b) { return a == b; }
+
+// We use functions that cannot be inlined to perform the comparison loops so
+// that inlining of the operator== can't optimize away *everything*.
+ABSL_ATTRIBUTE_NOINLINE
+void DoEqualityComparisons(benchmark::State& state, absl::string_view a,
+                           absl::string_view b) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(a == b);
+  }
+}
+
+void BM_EqualIdentical(benchmark::State& state) {
+  std::string x(state.range(0), 'a');
+  DoEqualityComparisons(state, x, x);
+}
+BENCHMARK(BM_EqualIdentical)->DenseRange(0, 3)->Range(4, 1 << 10);
+
+void BM_EqualSame(benchmark::State& state) {
+  std::string x(state.range(0), 'a');
+  std::string y = x;
+  DoEqualityComparisons(state, x, y);
+}
+BENCHMARK(BM_EqualSame)
+    ->DenseRange(0, 10)
+    ->Arg(20)
+    ->Arg(40)
+    ->Arg(70)
+    ->Arg(110)
+    ->Range(160, 4096);
+
+void BM_EqualDifferent(benchmark::State& state) {
+  const int len = state.range(0);
+  std::string x(len, 'a');
+  std::string y = x;
+  if (len > 0) {
+    y[len - 1] = 'b';
+  }
+  DoEqualityComparisons(state, x, y);
+}
+BENCHMARK(BM_EqualDifferent)->DenseRange(0, 3)->Range(4, 1 << 10);
+
+// This benchmark is intended to check that important simplifications can be
+// made with absl::string_view comparisons against constant strings. The idea is
+// that if constant strings cause redundant components of the comparison, the
+// compiler should detect and eliminate them. Here we use 8 different strings,
+// each with the same size. Provided our comparison makes the implementation
+// inline-able by the compiler, it should fold all of these away into a single
+// size check once per loop iteration.
+ABSL_ATTRIBUTE_NOINLINE
+void DoConstantSizeInlinedEqualityComparisons(benchmark::State& state,
+                                              absl::string_view a) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(a == "aaa");
+    benchmark::DoNotOptimize(a == "bbb");
+    benchmark::DoNotOptimize(a == "ccc");
+    benchmark::DoNotOptimize(a == "ddd");
+    benchmark::DoNotOptimize(a == "eee");
+    benchmark::DoNotOptimize(a == "fff");
+    benchmark::DoNotOptimize(a == "ggg");
+    benchmark::DoNotOptimize(a == "hhh");
+  }
+}
+void BM_EqualConstantSizeInlined(benchmark::State& state) {
+  std::string x(state.range(0), 'a');
+  DoConstantSizeInlinedEqualityComparisons(state, x);
+}
+// We only need to check for size of 3, and <> 3 as this benchmark only has to
+// do with size differences.
+BENCHMARK(BM_EqualConstantSizeInlined)->DenseRange(2, 4);
+
+// This benchmark exists purely to give context to the above timings: this is
+// what they would look like if the compiler is completely unable to simplify
+// between two comparisons when they are comparing against constant strings.
+ABSL_ATTRIBUTE_NOINLINE
+void DoConstantSizeNonInlinedEqualityComparisons(benchmark::State& state,
+                                                 absl::string_view a) {
+  for (auto _ : state) {
+    // Force these out-of-line to compare with the above function.
+    benchmark::DoNotOptimize(NonInlinedEq(a, "aaa"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "bbb"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "ccc"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "ddd"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "eee"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "fff"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "ggg"));
+    benchmark::DoNotOptimize(NonInlinedEq(a, "hhh"));
+  }
+}
+
+void BM_EqualConstantSizeNonInlined(benchmark::State& state) {
+  std::string x(state.range(0), 'a');
+  DoConstantSizeNonInlinedEqualityComparisons(state, x);
+}
+// We only need to check for size of 3, and <> 3 as this benchmark only has to
+// do with size differences.
+BENCHMARK(BM_EqualConstantSizeNonInlined)->DenseRange(2, 4);
+
+void BM_CompareSame(benchmark::State& state) {
+  const int len = state.range(0);
+  std::string x;
+  for (int i = 0; i < len; i++) {
+    x += 'a';
+  }
+  std::string y = x;
+  absl::string_view a = x;
+  absl::string_view b = y;
+
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(a.compare(b));
+  }
+}
+BENCHMARK(BM_CompareSame)->DenseRange(0, 3)->Range(4, 1 << 10);
+
+void BM_find_string_view_len_one(benchmark::State& state) {
+  std::string haystack(state.range(0), '0');
+  absl::string_view s(haystack);
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(s.find("x"));  // not present; length 1
+  }
+}
+BENCHMARK(BM_find_string_view_len_one)->Range(1, 1 << 20);
+
+void BM_find_string_view_len_two(benchmark::State& state) {
+  std::string haystack(state.range(0), '0');
+  absl::string_view s(haystack);
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(s.find("xx"));  // not present; length 2
+  }
+}
+BENCHMARK(BM_find_string_view_len_two)->Range(1, 1 << 20);
+
+void BM_find_one_char(benchmark::State& state) {
+  std::string haystack(state.range(0), '0');
+  absl::string_view s(haystack);
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(s.find('x'));  // not present
+  }
+}
+BENCHMARK(BM_find_one_char)->Range(1, 1 << 20);
+
+void BM_rfind_one_char(benchmark::State& state) {
+  std::string haystack(state.range(0), '0');
+  absl::string_view s(haystack);
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(s.rfind('x'));  // not present
+  }
+}
+BENCHMARK(BM_rfind_one_char)->Range(1, 1 << 20);
+
+void BM_worst_case_find_first_of(benchmark::State& state, int haystack_len) {
+  const int needle_len = state.range(0);
+  std::string needle;
+  for (int i = 0; i < needle_len; ++i) {
+    needle += 'a' + i;
+  }
+  std::string haystack(haystack_len, '0');  // 1000 zeros.
+
+  absl::string_view s(haystack);
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(s.find_first_of(needle));
+  }
+}
+
+void BM_find_first_of_short(benchmark::State& state) {
+  BM_worst_case_find_first_of(state, 10);
+}
+
+void BM_find_first_of_medium(benchmark::State& state) {
+  BM_worst_case_find_first_of(state, 100);
+}
+
+void BM_find_first_of_long(benchmark::State& state) {
+  BM_worst_case_find_first_of(state, 1000);
+}
+
+BENCHMARK(BM_find_first_of_short)->DenseRange(0, 4)->Arg(8)->Arg(16)->Arg(32);
+BENCHMARK(BM_find_first_of_medium)->DenseRange(0, 4)->Arg(8)->Arg(16)->Arg(32);
+BENCHMARK(BM_find_first_of_long)->DenseRange(0, 4)->Arg(8)->Arg(16)->Arg(32);
+
+struct EasyMap : public std::map<absl::string_view, uint64_t> {
+  explicit EasyMap(size_t) {}
+};
+
+// This templated benchmark helper function is intended to stress operator== or
+// operator< in a realistic test.  It surely isn't entirely realistic, but it's
+// a start.  The test creates a map of type Map, a template arg, and populates
+// it with table_size key/value pairs. Each key has WordsPerKey words.  After
+// creating the map, a number of lookups are done in random order.  Some keys
+// are used much more frequently than others in this phase of the test.
+template <typename Map, int WordsPerKey>
+void StringViewMapBenchmark(benchmark::State& state) {
+  const int table_size = state.range(0);
+  const double kFractionOfKeysThatAreHot = 0.2;
+  const int kNumLookupsOfHotKeys = 20;
+  const int kNumLookupsOfColdKeys = 1;
+  const char* words[] = {"the",   "quick",  "brown",    "fox",      "jumped",
+                         "over",  "the",    "lazy",     "dog",      "and",
+                         "found", "a",      "large",    "mushroom", "and",
+                         "a",     "couple", "crickets", "eating",   "pie"};
+  // Create some keys that consist of words in random order.
+  std::random_device r;
+  std::seed_seq seed({r(), r(), r(), r(), r(), r(), r(), r()});
+  std::mt19937 rng(seed);
+  std::vector<std::string> keys(table_size);
+  std::vector<int> all_indices;
+  const int kBlockSize = 1 << 12;
+  std::unordered_set<std::string> t(kBlockSize);
+  std::uniform_int_distribution<int> uniform(0, ABSL_ARRAYSIZE(words) - 1);
+  for (int i = 0; i < table_size; i++) {
+    all_indices.push_back(i);
+    do {
+      keys[i].clear();
+      for (int j = 0; j < WordsPerKey; j++) {
+        absl::StrAppend(&keys[i], j > 0 ? " " : "", words[uniform(rng)]);
+      }
+    } while (!t.insert(keys[i]).second);
+  }
+
+  // Create a list of strings to lookup: a permutation of the array of
+  // keys we just created, with repeats.  "Hot" keys get repeated more.
+  std::shuffle(all_indices.begin(), all_indices.end(), rng);
+  const int num_hot = table_size * kFractionOfKeysThatAreHot;
+  const int num_cold = table_size - num_hot;
+  std::vector<int> hot_indices(all_indices.begin(),
+                               all_indices.begin() + num_hot);
+  std::vector<int> indices;
+  for (int i = 0; i < kNumLookupsOfColdKeys; i++) {
+    indices.insert(indices.end(), all_indices.begin(), all_indices.end());
+  }
+  for (int i = 0; i < kNumLookupsOfHotKeys - kNumLookupsOfColdKeys; i++) {
+    indices.insert(indices.end(), hot_indices.begin(), hot_indices.end());
+  }
+  std::shuffle(indices.begin(), indices.end(), rng);
+  ABSL_RAW_CHECK(
+      num_cold * kNumLookupsOfColdKeys + num_hot * kNumLookupsOfHotKeys ==
+          indices.size(),
+      "");
+  // After constructing the array we probe it with absl::string_views built from
+  // test_strings.  This means operator== won't see equal pointers, so
+  // it'll have to check for equal lengths and equal characters.
+  std::vector<std::string> test_strings(indices.size());
+  for (int i = 0; i < indices.size(); i++) {
+    test_strings[i] = keys[indices[i]];
+  }
+
+  // Run the benchmark. It includes map construction but is mostly
+  // map lookups.
+  for (auto _ : state) {
+    Map h(table_size);
+    for (int i = 0; i < table_size; i++) {
+      h[keys[i]] = i * 2;
+    }
+    ABSL_RAW_CHECK(h.size() == table_size, "");
+    uint64_t sum = 0;
+    for (int i = 0; i < indices.size(); i++) {
+      sum += h[test_strings[i]];
+    }
+    benchmark::DoNotOptimize(sum);
+  }
+}
+
+void BM_StdMap_4(benchmark::State& state) {
+  StringViewMapBenchmark<EasyMap, 4>(state);
+}
+BENCHMARK(BM_StdMap_4)->Range(1 << 10, 1 << 16);
+
+void BM_StdMap_8(benchmark::State& state) {
+  StringViewMapBenchmark<EasyMap, 8>(state);
+}
+BENCHMARK(BM_StdMap_8)->Range(1 << 10, 1 << 16);
+
+void BM_CopyToStringNative(benchmark::State& state) {
+  std::string src(state.range(0), 'x');
+  absl::string_view sv(src);
+  std::string dst;
+  for (auto _ : state) {
+    dst.assign(sv.begin(), sv.end());
+  }
+}
+BENCHMARK(BM_CopyToStringNative)->Range(1 << 3, 1 << 12);
+
+void BM_AppendToStringNative(benchmark::State& state) {
+  std::string src(state.range(0), 'x');
+  absl::string_view sv(src);
+  std::string dst;
+  for (auto _ : state) {
+    dst.clear();
+    dst.insert(dst.end(), sv.begin(), sv.end());
+  }
+}
+BENCHMARK(BM_AppendToStringNative)->Range(1 << 3, 1 << 12);
+
+}  // namespace
diff --git a/absl/strings/string_view_test.cc b/absl/strings/string_view_test.cc
new file mode 100644
index 0000000..eb8b170
--- /dev/null
+++ b/absl/strings/string_view_test.cc
@@ -0,0 +1,1184 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/string_view.h"
+
+#include <stdlib.h>
+#include <iomanip>
+#include <iterator>
+#include <limits>
+#include <map>
+#include <sstream>
+#include <stdexcept>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+#include "gtest/gtest.h"
+#include "absl/base/config.h"
+#include "absl/base/dynamic_annotations.h"
+
+#if defined(ABSL_HAVE_STD_STRING_VIEW) || defined(__ANDROID__)
+// We don't control the death messaging when using std::string_view.
+// Android assert messages only go to system log, so death tests cannot inspect
+// the message for matching.
+#define ABSL_EXPECT_DEATH_IF_SUPPORTED(statement, regex) \
+  EXPECT_DEATH_IF_SUPPORTED(statement, ".*")
+#else
+#define ABSL_EXPECT_DEATH_IF_SUPPORTED(statement, regex) \
+  EXPECT_DEATH_IF_SUPPORTED(statement, regex)
+#endif
+
+namespace {
+
+// A minimal allocator that uses malloc().
+template <typename T>
+struct Mallocator {
+  typedef T value_type;
+  typedef size_t size_type;
+  typedef ptrdiff_t difference_type;
+  typedef T* pointer;
+  typedef const T* const_pointer;
+  typedef T& reference;
+  typedef const T& const_reference;
+
+  size_type max_size() const {
+    return size_t(std::numeric_limits<size_type>::max()) / sizeof(value_type);
+  }
+  template <typename U>
+  struct rebind {
+    typedef Mallocator<U> other;
+  };
+  Mallocator() = default;
+  template <class U>
+  Mallocator(const Mallocator<U>&) {}  // NOLINT(runtime/explicit)
+
+  T* allocate(size_t n) { return static_cast<T*>(std::malloc(n * sizeof(T))); }
+  void deallocate(T* p, size_t) { std::free(p); }
+};
+template <typename T, typename U>
+bool operator==(const Mallocator<T>&, const Mallocator<U>&) {
+  return true;
+}
+template <typename T, typename U>
+bool operator!=(const Mallocator<T>&, const Mallocator<U>&) {
+  return false;
+}
+
+TEST(StringViewTest, Ctor) {
+  {
+    // Null.
+    absl::string_view s10;
+    EXPECT_TRUE(s10.data() == nullptr);
+    EXPECT_EQ(0, s10.length());
+  }
+
+  {
+    // const char* without length.
+    const char* hello = "hello";
+    absl::string_view s20(hello);
+    EXPECT_TRUE(s20.data() == hello);
+    EXPECT_EQ(5, s20.length());
+
+    // const char* with length.
+    absl::string_view s21(hello, 4);
+    EXPECT_TRUE(s21.data() == hello);
+    EXPECT_EQ(4, s21.length());
+
+    // Not recommended, but valid C++
+    absl::string_view s22(hello, 6);
+    EXPECT_TRUE(s22.data() == hello);
+    EXPECT_EQ(6, s22.length());
+  }
+
+  {
+    // std::string.
+    std::string hola = "hola";
+    absl::string_view s30(hola);
+    EXPECT_TRUE(s30.data() == hola.data());
+    EXPECT_EQ(4, s30.length());
+
+    // std::string with embedded '\0'.
+    hola.push_back('\0');
+    hola.append("h2");
+    hola.push_back('\0');
+    absl::string_view s31(hola);
+    EXPECT_TRUE(s31.data() == hola.data());
+    EXPECT_EQ(8, s31.length());
+  }
+
+  {
+    using mstring =
+        std::basic_string<char, std::char_traits<char>, Mallocator<char>>;
+    mstring str1("BUNGIE-JUMPING!");
+    const mstring str2("SLEEPING!");
+
+    absl::string_view s1(str1);
+    s1.remove_prefix(strlen("BUNGIE-JUM"));
+
+    absl::string_view s2(str2);
+    s2.remove_prefix(strlen("SLEE"));
+
+    EXPECT_EQ(s1, s2);
+    EXPECT_EQ(s1, "PING!");
+  }
+
+  // TODO(mec): absl::string_view(const absl::string_view&);
+}
+
+TEST(StringViewTest, Swap) {
+  absl::string_view a("a");
+  absl::string_view b("bbb");
+  EXPECT_TRUE(noexcept(a.swap(b)));
+  a.swap(b);
+  EXPECT_EQ(a, "bbb");
+  EXPECT_EQ(b, "a");
+  a.swap(b);
+  EXPECT_EQ(a, "a");
+  EXPECT_EQ(b, "bbb");
+}
+
+TEST(StringViewTest, STLComparator) {
+  std::string s1("foo");
+  std::string s2("bar");
+  std::string s3("baz");
+
+  absl::string_view p1(s1);
+  absl::string_view p2(s2);
+  absl::string_view p3(s3);
+
+  typedef std::map<absl::string_view, int> TestMap;
+  TestMap map;
+
+  map.insert(std::make_pair(p1, 0));
+  map.insert(std::make_pair(p2, 1));
+  map.insert(std::make_pair(p3, 2));
+  EXPECT_EQ(map.size(), 3);
+
+  TestMap::const_iterator iter = map.begin();
+  EXPECT_EQ(iter->second, 1);
+  ++iter;
+  EXPECT_EQ(iter->second, 2);
+  ++iter;
+  EXPECT_EQ(iter->second, 0);
+  ++iter;
+  EXPECT_TRUE(iter == map.end());
+
+  TestMap::iterator new_iter = map.find("zot");
+  EXPECT_TRUE(new_iter == map.end());
+
+  new_iter = map.find("bar");
+  EXPECT_TRUE(new_iter != map.end());
+
+  map.erase(new_iter);
+  EXPECT_EQ(map.size(), 2);
+
+  iter = map.begin();
+  EXPECT_EQ(iter->second, 2);
+  ++iter;
+  EXPECT_EQ(iter->second, 0);
+  ++iter;
+  EXPECT_TRUE(iter == map.end());
+}
+
+#define COMPARE(result, op, x, y)                                      \
+  EXPECT_EQ(result, absl::string_view((x)) op absl::string_view((y))); \
+  EXPECT_EQ(result, absl::string_view((x)).compare(absl::string_view((y))) op 0)
+
+TEST(StringViewTest, ComparisonOperators) {
+  COMPARE(true, ==, "",   "");
+  COMPARE(true, ==, "", absl::string_view());
+  COMPARE(true, ==, absl::string_view(), "");
+  COMPARE(true, ==, "a",  "a");
+  COMPARE(true, ==, "aa", "aa");
+  COMPARE(false, ==, "a",  "");
+  COMPARE(false, ==, "",   "a");
+  COMPARE(false, ==, "a",  "b");
+  COMPARE(false, ==, "a",  "aa");
+  COMPARE(false, ==, "aa", "a");
+
+  COMPARE(false, !=, "",   "");
+  COMPARE(false, !=, "a",  "a");
+  COMPARE(false, !=, "aa", "aa");
+  COMPARE(true, !=, "a",  "");
+  COMPARE(true, !=, "",   "a");
+  COMPARE(true, !=, "a",  "b");
+  COMPARE(true, !=, "a",  "aa");
+  COMPARE(true, !=, "aa", "a");
+
+  COMPARE(true, <, "a",  "b");
+  COMPARE(true, <, "a",  "aa");
+  COMPARE(true, <, "aa", "b");
+  COMPARE(true, <, "aa", "bb");
+  COMPARE(false, <, "a",  "a");
+  COMPARE(false, <, "b",  "a");
+  COMPARE(false, <, "aa", "a");
+  COMPARE(false, <, "b",  "aa");
+  COMPARE(false, <, "bb", "aa");
+
+  COMPARE(true, <=, "a",  "a");
+  COMPARE(true, <=, "a",  "b");
+  COMPARE(true, <=, "a",  "aa");
+  COMPARE(true, <=, "aa", "b");
+  COMPARE(true, <=, "aa", "bb");
+  COMPARE(false, <=, "b",  "a");
+  COMPARE(false, <=, "aa", "a");
+  COMPARE(false, <=, "b",  "aa");
+  COMPARE(false, <=, "bb", "aa");
+
+  COMPARE(false, >=, "a",  "b");
+  COMPARE(false, >=, "a",  "aa");
+  COMPARE(false, >=, "aa", "b");
+  COMPARE(false, >=, "aa", "bb");
+  COMPARE(true, >=, "a",  "a");
+  COMPARE(true, >=, "b",  "a");
+  COMPARE(true, >=, "aa", "a");
+  COMPARE(true, >=, "b",  "aa");
+  COMPARE(true, >=, "bb", "aa");
+
+  COMPARE(false, >, "a",  "a");
+  COMPARE(false, >, "a",  "b");
+  COMPARE(false, >, "a",  "aa");
+  COMPARE(false, >, "aa", "b");
+  COMPARE(false, >, "aa", "bb");
+  COMPARE(true, >, "b",  "a");
+  COMPARE(true, >, "aa", "a");
+  COMPARE(true, >, "b",  "aa");
+  COMPARE(true, >, "bb", "aa");
+}
+
+TEST(StringViewTest, ComparisonOperatorsByCharacterPosition) {
+  std::string x;
+  for (int i = 0; i < 256; i++) {
+    x += 'a';
+    std::string y = x;
+    COMPARE(true, ==, x, y);
+    for (int j = 0; j < i; j++) {
+      std::string z = x;
+      z[j] = 'b';       // Differs in position 'j'
+      COMPARE(false, ==, x, z);
+      COMPARE(true, <, x, z);
+      COMPARE(true, >, z, x);
+      if (j + 1 < i) {
+        z[j + 1] = 'A';  // Differs in position 'j+1' as well
+        COMPARE(false, ==, x, z);
+        COMPARE(true, <, x, z);
+        COMPARE(true, >, z, x);
+        z[j + 1] = 'z';  // Differs in position 'j+1' as well
+        COMPARE(false, ==, x, z);
+        COMPARE(true, <, x, z);
+        COMPARE(true, >, z, x);
+      }
+    }
+  }
+}
+#undef COMPARE
+
+// Sadly, our users often confuse std::string::npos with
+// absl::string_view::npos; So much so that we test here that they are the same.
+// They need to both be unsigned, and both be the maximum-valued integer of
+// their type.
+
+template <typename T>
+struct is_type {
+  template <typename U>
+  static bool same(U) {
+    return false;
+  }
+  static bool same(T) { return true; }
+};
+
+TEST(StringViewTest, NposMatchesStdStringView) {
+  EXPECT_EQ(absl::string_view::npos, std::string::npos);
+
+  EXPECT_TRUE(is_type<size_t>::same(absl::string_view::npos));
+  EXPECT_FALSE(is_type<size_t>::same(""));
+
+  // Make sure absl::string_view::npos continues to be a header constant.
+  char test[absl::string_view::npos & 1] = {0};
+  EXPECT_EQ(0, test[0]);
+}
+
+TEST(StringViewTest, STL1) {
+  const absl::string_view a("abcdefghijklmnopqrstuvwxyz");
+  const absl::string_view b("abc");
+  const absl::string_view c("xyz");
+  const absl::string_view d("foobar");
+  const absl::string_view e;
+  std::string temp("123");
+  temp += '\0';
+  temp += "456";
+  const absl::string_view f(temp);
+
+  EXPECT_EQ(a[6], 'g');
+  EXPECT_EQ(b[0], 'a');
+  EXPECT_EQ(c[2], 'z');
+  EXPECT_EQ(f[3], '\0');
+  EXPECT_EQ(f[5], '5');
+
+  EXPECT_EQ(*d.data(), 'f');
+  EXPECT_EQ(d.data()[5], 'r');
+  EXPECT_TRUE(e.data() == nullptr);
+
+  EXPECT_EQ(*a.begin(), 'a');
+  EXPECT_EQ(*(b.begin() + 2), 'c');
+  EXPECT_EQ(*(c.end() - 1), 'z');
+
+  EXPECT_EQ(*a.rbegin(), 'z');
+  EXPECT_EQ(*(b.rbegin() + 2), 'a');
+  EXPECT_EQ(*(c.rend() - 1), 'x');
+  EXPECT_TRUE(a.rbegin() + 26 == a.rend());
+
+  EXPECT_EQ(a.size(), 26);
+  EXPECT_EQ(b.size(), 3);
+  EXPECT_EQ(c.size(), 3);
+  EXPECT_EQ(d.size(), 6);
+  EXPECT_EQ(e.size(), 0);
+  EXPECT_EQ(f.size(), 7);
+
+  EXPECT_TRUE(!d.empty());
+  EXPECT_TRUE(d.begin() != d.end());
+  EXPECT_TRUE(d.begin() + 6 == d.end());
+
+  EXPECT_TRUE(e.empty());
+  EXPECT_TRUE(e.begin() == e.end());
+
+  char buf[4] = { '%', '%', '%', '%' };
+  EXPECT_EQ(a.copy(buf, 4), 4);
+  EXPECT_EQ(buf[0], a[0]);
+  EXPECT_EQ(buf[1], a[1]);
+  EXPECT_EQ(buf[2], a[2]);
+  EXPECT_EQ(buf[3], a[3]);
+  EXPECT_EQ(a.copy(buf, 3, 7), 3);
+  EXPECT_EQ(buf[0], a[7]);
+  EXPECT_EQ(buf[1], a[8]);
+  EXPECT_EQ(buf[2], a[9]);
+  EXPECT_EQ(buf[3], a[3]);
+  EXPECT_EQ(c.copy(buf, 99), 3);
+  EXPECT_EQ(buf[0], c[0]);
+  EXPECT_EQ(buf[1], c[1]);
+  EXPECT_EQ(buf[2], c[2]);
+  EXPECT_EQ(buf[3], a[3]);
+#ifdef ABSL_HAVE_EXCEPTIONS
+  EXPECT_THROW(a.copy(buf, 1, 27), std::out_of_range);
+#else
+  ABSL_EXPECT_DEATH_IF_SUPPORTED(a.copy(buf, 1, 27), "absl::string_view::copy");
+#endif
+}
+
+// Separated from STL1() because some compilers produce an overly
+// large stack frame for the combined function.
+TEST(StringViewTest, STL2) {
+  const absl::string_view a("abcdefghijklmnopqrstuvwxyz");
+  const absl::string_view b("abc");
+  const absl::string_view c("xyz");
+  absl::string_view d("foobar");
+  const absl::string_view e;
+  const absl::string_view f(
+      "123"
+      "\0"
+      "456",
+      7);
+
+  d = absl::string_view();
+  EXPECT_EQ(d.size(), 0);
+  EXPECT_TRUE(d.empty());
+  EXPECT_TRUE(d.data() == nullptr);
+  EXPECT_TRUE(d.begin() == d.end());
+
+  EXPECT_EQ(a.find(b), 0);
+  EXPECT_EQ(a.find(b, 1), absl::string_view::npos);
+  EXPECT_EQ(a.find(c), 23);
+  EXPECT_EQ(a.find(c, 9), 23);
+  EXPECT_EQ(a.find(c, absl::string_view::npos), absl::string_view::npos);
+  EXPECT_EQ(b.find(c), absl::string_view::npos);
+  EXPECT_EQ(b.find(c, absl::string_view::npos), absl::string_view::npos);
+  EXPECT_EQ(a.find(d), 0);
+  EXPECT_EQ(a.find(e), 0);
+  EXPECT_EQ(a.find(d, 12), 12);
+  EXPECT_EQ(a.find(e, 17), 17);
+  absl::string_view g("xx not found bb");
+  EXPECT_EQ(a.find(g), absl::string_view::npos);
+  // empty std::string nonsense
+  EXPECT_EQ(d.find(b), absl::string_view::npos);
+  EXPECT_EQ(e.find(b), absl::string_view::npos);
+  EXPECT_EQ(d.find(b, 4), absl::string_view::npos);
+  EXPECT_EQ(e.find(b, 7), absl::string_view::npos);
+
+  size_t empty_search_pos = std::string().find(std::string());
+  EXPECT_EQ(d.find(d), empty_search_pos);
+  EXPECT_EQ(d.find(e), empty_search_pos);
+  EXPECT_EQ(e.find(d), empty_search_pos);
+  EXPECT_EQ(e.find(e), empty_search_pos);
+  EXPECT_EQ(d.find(d, 4), std::string().find(std::string(), 4));
+  EXPECT_EQ(d.find(e, 4), std::string().find(std::string(), 4));
+  EXPECT_EQ(e.find(d, 4), std::string().find(std::string(), 4));
+  EXPECT_EQ(e.find(e, 4), std::string().find(std::string(), 4));
+
+  EXPECT_EQ(a.find('a'), 0);
+  EXPECT_EQ(a.find('c'), 2);
+  EXPECT_EQ(a.find('z'), 25);
+  EXPECT_EQ(a.find('$'), absl::string_view::npos);
+  EXPECT_EQ(a.find('\0'), absl::string_view::npos);
+  EXPECT_EQ(f.find('\0'), 3);
+  EXPECT_EQ(f.find('3'), 2);
+  EXPECT_EQ(f.find('5'), 5);
+  EXPECT_EQ(g.find('o'), 4);
+  EXPECT_EQ(g.find('o', 4), 4);
+  EXPECT_EQ(g.find('o', 5), 8);
+  EXPECT_EQ(a.find('b', 5), absl::string_view::npos);
+  // empty std::string nonsense
+  EXPECT_EQ(d.find('\0'), absl::string_view::npos);
+  EXPECT_EQ(e.find('\0'), absl::string_view::npos);
+  EXPECT_EQ(d.find('\0', 4), absl::string_view::npos);
+  EXPECT_EQ(e.find('\0', 7), absl::string_view::npos);
+  EXPECT_EQ(d.find('x'), absl::string_view::npos);
+  EXPECT_EQ(e.find('x'), absl::string_view::npos);
+  EXPECT_EQ(d.find('x', 4), absl::string_view::npos);
+  EXPECT_EQ(e.find('x', 7), absl::string_view::npos);
+
+  EXPECT_EQ(a.rfind(b), 0);
+  EXPECT_EQ(a.rfind(b, 1), 0);
+  EXPECT_EQ(a.rfind(c), 23);
+  EXPECT_EQ(a.rfind(c, 22), absl::string_view::npos);
+  EXPECT_EQ(a.rfind(c, 1), absl::string_view::npos);
+  EXPECT_EQ(a.rfind(c, 0), absl::string_view::npos);
+  EXPECT_EQ(b.rfind(c), absl::string_view::npos);
+  EXPECT_EQ(b.rfind(c, 0), absl::string_view::npos);
+  EXPECT_EQ(a.rfind(d), std::string(a).rfind(std::string()));
+  EXPECT_EQ(a.rfind(e), std::string(a).rfind(std::string()));
+  EXPECT_EQ(a.rfind(d, 12), 12);
+  EXPECT_EQ(a.rfind(e, 17), 17);
+  EXPECT_EQ(a.rfind(g), absl::string_view::npos);
+  EXPECT_EQ(d.rfind(b), absl::string_view::npos);
+  EXPECT_EQ(e.rfind(b), absl::string_view::npos);
+  EXPECT_EQ(d.rfind(b, 4), absl::string_view::npos);
+  EXPECT_EQ(e.rfind(b, 7), absl::string_view::npos);
+  // empty std::string nonsense
+  EXPECT_EQ(d.rfind(d, 4), std::string().rfind(std::string()));
+  EXPECT_EQ(e.rfind(d, 7), std::string().rfind(std::string()));
+  EXPECT_EQ(d.rfind(e, 4), std::string().rfind(std::string()));
+  EXPECT_EQ(e.rfind(e, 7), std::string().rfind(std::string()));
+  EXPECT_EQ(d.rfind(d), std::string().rfind(std::string()));
+  EXPECT_EQ(e.rfind(d), std::string().rfind(std::string()));
+  EXPECT_EQ(d.rfind(e), std::string().rfind(std::string()));
+  EXPECT_EQ(e.rfind(e), std::string().rfind(std::string()));
+
+  EXPECT_EQ(g.rfind('o'), 8);
+  EXPECT_EQ(g.rfind('q'), absl::string_view::npos);
+  EXPECT_EQ(g.rfind('o', 8), 8);
+  EXPECT_EQ(g.rfind('o', 7), 4);
+  EXPECT_EQ(g.rfind('o', 3), absl::string_view::npos);
+  EXPECT_EQ(f.rfind('\0'), 3);
+  EXPECT_EQ(f.rfind('\0', 12), 3);
+  EXPECT_EQ(f.rfind('3'), 2);
+  EXPECT_EQ(f.rfind('5'), 5);
+  // empty std::string nonsense
+  EXPECT_EQ(d.rfind('o'), absl::string_view::npos);
+  EXPECT_EQ(e.rfind('o'), absl::string_view::npos);
+  EXPECT_EQ(d.rfind('o', 4), absl::string_view::npos);
+  EXPECT_EQ(e.rfind('o', 7), absl::string_view::npos);
+}
+
+// Continued from STL2
+TEST(StringViewTest, STL2FindFirst) {
+  const absl::string_view a("abcdefghijklmnopqrstuvwxyz");
+  const absl::string_view b("abc");
+  const absl::string_view c("xyz");
+  absl::string_view d("foobar");
+  const absl::string_view e;
+  const absl::string_view f(
+      "123"
+      "\0"
+      "456",
+      7);
+  absl::string_view g("xx not found bb");
+
+  d = absl::string_view();
+  EXPECT_EQ(a.find_first_of(b), 0);
+  EXPECT_EQ(a.find_first_of(b, 0), 0);
+  EXPECT_EQ(a.find_first_of(b, 1), 1);
+  EXPECT_EQ(a.find_first_of(b, 2), 2);
+  EXPECT_EQ(a.find_first_of(b, 3), absl::string_view::npos);
+  EXPECT_EQ(a.find_first_of(c), 23);
+  EXPECT_EQ(a.find_first_of(c, 23), 23);
+  EXPECT_EQ(a.find_first_of(c, 24), 24);
+  EXPECT_EQ(a.find_first_of(c, 25), 25);
+  EXPECT_EQ(a.find_first_of(c, 26), absl::string_view::npos);
+  EXPECT_EQ(g.find_first_of(b), 13);
+  EXPECT_EQ(g.find_first_of(c), 0);
+  EXPECT_EQ(a.find_first_of(f), absl::string_view::npos);
+  EXPECT_EQ(f.find_first_of(a), absl::string_view::npos);
+  // empty std::string nonsense
+  EXPECT_EQ(a.find_first_of(d), absl::string_view::npos);
+  EXPECT_EQ(a.find_first_of(e), absl::string_view::npos);
+  EXPECT_EQ(d.find_first_of(b), absl::string_view::npos);
+  EXPECT_EQ(e.find_first_of(b), absl::string_view::npos);
+  EXPECT_EQ(d.find_first_of(d), absl::string_view::npos);
+  EXPECT_EQ(e.find_first_of(d), absl::string_view::npos);
+  EXPECT_EQ(d.find_first_of(e), absl::string_view::npos);
+  EXPECT_EQ(e.find_first_of(e), absl::string_view::npos);
+
+  EXPECT_EQ(a.find_first_not_of(b), 3);
+  EXPECT_EQ(a.find_first_not_of(c), 0);
+  EXPECT_EQ(b.find_first_not_of(a), absl::string_view::npos);
+  EXPECT_EQ(c.find_first_not_of(a), absl::string_view::npos);
+  EXPECT_EQ(f.find_first_not_of(a), 0);
+  EXPECT_EQ(a.find_first_not_of(f), 0);
+  EXPECT_EQ(a.find_first_not_of(d), 0);
+  EXPECT_EQ(a.find_first_not_of(e), 0);
+  // empty std::string nonsense
+  EXPECT_EQ(a.find_first_not_of(d), 0);
+  EXPECT_EQ(a.find_first_not_of(e), 0);
+  EXPECT_EQ(a.find_first_not_of(d, 1), 1);
+  EXPECT_EQ(a.find_first_not_of(e, 1), 1);
+  EXPECT_EQ(a.find_first_not_of(d, a.size() - 1), a.size() - 1);
+  EXPECT_EQ(a.find_first_not_of(e, a.size() - 1), a.size() - 1);
+  EXPECT_EQ(a.find_first_not_of(d, a.size()), absl::string_view::npos);
+  EXPECT_EQ(a.find_first_not_of(e, a.size()), absl::string_view::npos);
+  EXPECT_EQ(a.find_first_not_of(d, absl::string_view::npos),
+            absl::string_view::npos);
+  EXPECT_EQ(a.find_first_not_of(e, absl::string_view::npos),
+            absl::string_view::npos);
+  EXPECT_EQ(d.find_first_not_of(a), absl::string_view::npos);
+  EXPECT_EQ(e.find_first_not_of(a), absl::string_view::npos);
+  EXPECT_EQ(d.find_first_not_of(d), absl::string_view::npos);
+  EXPECT_EQ(e.find_first_not_of(d), absl::string_view::npos);
+  EXPECT_EQ(d.find_first_not_of(e), absl::string_view::npos);
+  EXPECT_EQ(e.find_first_not_of(e), absl::string_view::npos);
+
+  absl::string_view h("====");
+  EXPECT_EQ(h.find_first_not_of('='), absl::string_view::npos);
+  EXPECT_EQ(h.find_first_not_of('=', 3), absl::string_view::npos);
+  EXPECT_EQ(h.find_first_not_of('\0'), 0);
+  EXPECT_EQ(g.find_first_not_of('x'), 2);
+  EXPECT_EQ(f.find_first_not_of('\0'), 0);
+  EXPECT_EQ(f.find_first_not_of('\0', 3), 4);
+  EXPECT_EQ(f.find_first_not_of('\0', 2), 2);
+  // empty std::string nonsense
+  EXPECT_EQ(d.find_first_not_of('x'), absl::string_view::npos);
+  EXPECT_EQ(e.find_first_not_of('x'), absl::string_view::npos);
+  EXPECT_EQ(d.find_first_not_of('\0'), absl::string_view::npos);
+  EXPECT_EQ(e.find_first_not_of('\0'), absl::string_view::npos);
+}
+
+// Continued from STL2
+TEST(StringViewTest, STL2FindLast) {
+  const absl::string_view a("abcdefghijklmnopqrstuvwxyz");
+  const absl::string_view b("abc");
+  const absl::string_view c("xyz");
+  absl::string_view d("foobar");
+  const absl::string_view e;
+  const absl::string_view f(
+      "123"
+      "\0"
+      "456",
+      7);
+  absl::string_view g("xx not found bb");
+  absl::string_view h("====");
+  absl::string_view i("56");
+
+  d = absl::string_view();
+  EXPECT_EQ(h.find_last_of(a), absl::string_view::npos);
+  EXPECT_EQ(g.find_last_of(a), g.size()-1);
+  EXPECT_EQ(a.find_last_of(b), 2);
+  EXPECT_EQ(a.find_last_of(c), a.size()-1);
+  EXPECT_EQ(f.find_last_of(i), 6);
+  EXPECT_EQ(a.find_last_of('a'), 0);
+  EXPECT_EQ(a.find_last_of('b'), 1);
+  EXPECT_EQ(a.find_last_of('z'), 25);
+  EXPECT_EQ(a.find_last_of('a', 5), 0);
+  EXPECT_EQ(a.find_last_of('b', 5), 1);
+  EXPECT_EQ(a.find_last_of('b', 0), absl::string_view::npos);
+  EXPECT_EQ(a.find_last_of('z', 25), 25);
+  EXPECT_EQ(a.find_last_of('z', 24), absl::string_view::npos);
+  EXPECT_EQ(f.find_last_of(i, 5), 5);
+  EXPECT_EQ(f.find_last_of(i, 6), 6);
+  EXPECT_EQ(f.find_last_of(a, 4), absl::string_view::npos);
+  // empty std::string nonsense
+  EXPECT_EQ(f.find_last_of(d), absl::string_view::npos);
+  EXPECT_EQ(f.find_last_of(e), absl::string_view::npos);
+  EXPECT_EQ(f.find_last_of(d, 4), absl::string_view::npos);
+  EXPECT_EQ(f.find_last_of(e, 4), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_of(d), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_of(e), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_of(d), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_of(e), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_of(f), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_of(f), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_of(d, 4), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_of(e, 4), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_of(d, 4), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_of(e, 4), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_of(f, 4), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_of(f, 4), absl::string_view::npos);
+
+  EXPECT_EQ(a.find_last_not_of(b), a.size()-1);
+  EXPECT_EQ(a.find_last_not_of(c), 22);
+  EXPECT_EQ(b.find_last_not_of(a), absl::string_view::npos);
+  EXPECT_EQ(b.find_last_not_of(b), absl::string_view::npos);
+  EXPECT_EQ(f.find_last_not_of(i), 4);
+  EXPECT_EQ(a.find_last_not_of(c, 24), 22);
+  EXPECT_EQ(a.find_last_not_of(b, 3), 3);
+  EXPECT_EQ(a.find_last_not_of(b, 2), absl::string_view::npos);
+  // empty std::string nonsense
+  EXPECT_EQ(f.find_last_not_of(d), f.size()-1);
+  EXPECT_EQ(f.find_last_not_of(e), f.size()-1);
+  EXPECT_EQ(f.find_last_not_of(d, 4), 4);
+  EXPECT_EQ(f.find_last_not_of(e, 4), 4);
+  EXPECT_EQ(d.find_last_not_of(d), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_not_of(e), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_not_of(d), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_not_of(e), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_not_of(f), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_not_of(f), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_not_of(d, 4), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_not_of(e, 4), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_not_of(d, 4), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_not_of(e, 4), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_not_of(f, 4), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_not_of(f, 4), absl::string_view::npos);
+
+  EXPECT_EQ(h.find_last_not_of('x'), h.size() - 1);
+  EXPECT_EQ(h.find_last_not_of('='), absl::string_view::npos);
+  EXPECT_EQ(b.find_last_not_of('c'), 1);
+  EXPECT_EQ(h.find_last_not_of('x', 2), 2);
+  EXPECT_EQ(h.find_last_not_of('=', 2), absl::string_view::npos);
+  EXPECT_EQ(b.find_last_not_of('b', 1), 0);
+  // empty std::string nonsense
+  EXPECT_EQ(d.find_last_not_of('x'), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_not_of('x'), absl::string_view::npos);
+  EXPECT_EQ(d.find_last_not_of('\0'), absl::string_view::npos);
+  EXPECT_EQ(e.find_last_not_of('\0'), absl::string_view::npos);
+}
+
+// Continued from STL2
+TEST(StringViewTest, STL2Substr) {
+  const absl::string_view a("abcdefghijklmnopqrstuvwxyz");
+  const absl::string_view b("abc");
+  const absl::string_view c("xyz");
+  absl::string_view d("foobar");
+  const absl::string_view e;
+
+  d = absl::string_view();
+  EXPECT_EQ(a.substr(0, 3), b);
+  EXPECT_EQ(a.substr(23), c);
+  EXPECT_EQ(a.substr(23, 3), c);
+  EXPECT_EQ(a.substr(23, 99), c);
+  EXPECT_EQ(a.substr(0), a);
+  EXPECT_EQ(a.substr(3, 2), "de");
+  // empty std::string nonsense
+  EXPECT_EQ(d.substr(0, 99), e);
+  // use of npos
+  EXPECT_EQ(a.substr(0, absl::string_view::npos), a);
+  EXPECT_EQ(a.substr(23, absl::string_view::npos), c);
+  // throw exception
+#ifdef ABSL_HAVE_EXCEPTIONS
+  EXPECT_THROW((void)a.substr(99, 2), std::out_of_range);
+#else
+  ABSL_EXPECT_DEATH_IF_SUPPORTED((void)a.substr(99, 2),
+                                 "absl::string_view::substr");
+#endif
+}
+
+TEST(StringViewTest, TruncSubstr) {
+  const absl::string_view hi("hi");
+  EXPECT_EQ("", absl::ClippedSubstr(hi, 0, 0));
+  EXPECT_EQ("h", absl::ClippedSubstr(hi, 0, 1));
+  EXPECT_EQ("hi", absl::ClippedSubstr(hi, 0));
+  EXPECT_EQ("i", absl::ClippedSubstr(hi, 1));
+  EXPECT_EQ("", absl::ClippedSubstr(hi, 2));
+  EXPECT_EQ("", absl::ClippedSubstr(hi, 3));  // truncation
+  EXPECT_EQ("", absl::ClippedSubstr(hi, 3, 2));  // truncation
+}
+
+TEST(StringViewTest, UTF8) {
+  std::string utf8 = "\u00E1";
+  std::string utf8_twice = utf8 + " " + utf8;
+  int utf8_len = strlen(utf8.data());
+  EXPECT_EQ(utf8_len, absl::string_view(utf8_twice).find_first_of(" "));
+  EXPECT_EQ(utf8_len, absl::string_view(utf8_twice).find_first_of(" \t"));
+}
+
+TEST(StringViewTest, FindConformance) {
+  struct {
+    std::string haystack;
+    std::string needle;
+  } specs[] = {
+    {"", ""},
+    {"", "a"},
+    {"a", ""},
+    {"a", "a"},
+    {"a", "b"},
+    {"aa", ""},
+    {"aa", "a"},
+    {"aa", "b"},
+    {"ab", "a"},
+    {"ab", "b"},
+    {"abcd", ""},
+    {"abcd", "a"},
+    {"abcd", "d"},
+    {"abcd", "ab"},
+    {"abcd", "bc"},
+    {"abcd", "cd"},
+    {"abcd", "abcd"},
+  };
+  for (const auto& s : specs) {
+    SCOPED_TRACE(s.haystack);
+    SCOPED_TRACE(s.needle);
+    std::string st = s.haystack;
+    absl::string_view sp = s.haystack;
+    for (size_t i = 0; i <= sp.size(); ++i) {
+      size_t pos = (i == sp.size()) ? absl::string_view::npos : i;
+      SCOPED_TRACE(pos);
+      EXPECT_EQ(sp.find(s.needle, pos),
+                st.find(s.needle, pos));
+      EXPECT_EQ(sp.rfind(s.needle, pos),
+                st.rfind(s.needle, pos));
+      EXPECT_EQ(sp.find_first_of(s.needle, pos),
+                st.find_first_of(s.needle, pos));
+      EXPECT_EQ(sp.find_first_not_of(s.needle, pos),
+                st.find_first_not_of(s.needle, pos));
+      EXPECT_EQ(sp.find_last_of(s.needle, pos),
+                st.find_last_of(s.needle, pos));
+      EXPECT_EQ(sp.find_last_not_of(s.needle, pos),
+                st.find_last_not_of(s.needle, pos));
+    }
+  }
+}
+
+TEST(StringViewTest, Remove) {
+  absl::string_view a("foobar");
+  std::string s1("123");
+  s1 += '\0';
+  s1 += "456";
+  absl::string_view e;
+  std::string s2;
+
+  // remove_prefix
+  absl::string_view c(a);
+  c.remove_prefix(3);
+  EXPECT_EQ(c, "bar");
+  c = a;
+  c.remove_prefix(0);
+  EXPECT_EQ(c, a);
+  c.remove_prefix(c.size());
+  EXPECT_EQ(c, e);
+
+  // remove_suffix
+  c = a;
+  c.remove_suffix(3);
+  EXPECT_EQ(c, "foo");
+  c = a;
+  c.remove_suffix(0);
+  EXPECT_EQ(c, a);
+  c.remove_suffix(c.size());
+  EXPECT_EQ(c, e);
+}
+
+TEST(StringViewTest, Set) {
+  absl::string_view a("foobar");
+  absl::string_view empty;
+  absl::string_view b;
+
+  // set
+  b = absl::string_view("foobar", 6);
+  EXPECT_EQ(b, a);
+  b = absl::string_view("foobar", 0);
+  EXPECT_EQ(b, empty);
+  b = absl::string_view("foobar", 7);
+  EXPECT_NE(b, a);
+
+  b = absl::string_view("foobar");
+  EXPECT_EQ(b, a);
+}
+
+TEST(StringViewTest, FrontBack) {
+  static const char arr[] = "abcd";
+  const absl::string_view csp(arr, 4);
+  EXPECT_EQ(&arr[0], &csp.front());
+  EXPECT_EQ(&arr[3], &csp.back());
+}
+
+TEST(StringViewTest, FrontBackSingleChar) {
+  static const char c = 'a';
+  const absl::string_view csp(&c, 1);
+  EXPECT_EQ(&c, &csp.front());
+  EXPECT_EQ(&c, &csp.back());
+}
+
+// `std::string_view::string_view(const char*)` calls
+// `std::char_traits<char>::length(const char*)` to get the string length. In
+// libc++, it doesn't allow `nullptr` in the constexpr context, with the error
+// "read of dereferenced null pointer is not allowed in a constant expression".
+// At run time, the behavior of `std::char_traits::length()` on `nullptr` is
+// undefined by the standard and usually results in crash with libc++.
+// GCC also started rejected this in libstdc++ starting in GCC9.
+// In MSVC, creating a constexpr string_view from nullptr also triggers an
+// "unevaluable pointer value" error. This compiler implementation conforms
+// to the standard, but `absl::string_view` implements a different
+// behavior for historical reasons. We work around tests that construct
+// `string_view` from `nullptr` when using libc++.
+#if !defined(ABSL_HAVE_STD_STRING_VIEW) ||                    \
+    (!(defined(_GLIBCXX_RELEASE) && _GLIBCXX_RELEASE >= 9) && \
+     !defined(_LIBCPP_VERSION) && !defined(_MSC_VER))
+#define ABSL_HAVE_STRING_VIEW_FROM_NULLPTR 1
+#endif
+
+TEST(StringViewTest, NULLInput) {
+  absl::string_view s;
+  EXPECT_EQ(s.data(), nullptr);
+  EXPECT_EQ(s.size(), 0);
+
+#ifdef ABSL_HAVE_STRING_VIEW_FROM_NULLPTR
+  s = absl::string_view(nullptr);
+  EXPECT_EQ(s.data(), nullptr);
+  EXPECT_EQ(s.size(), 0);
+
+  // .ToString() on a absl::string_view with nullptr should produce the empty
+  // std::string.
+  EXPECT_EQ("", std::string(s));
+#endif  // ABSL_HAVE_STRING_VIEW_FROM_NULLPTR
+}
+
+TEST(StringViewTest, Comparisons2) {
+  // The `compare` member has 6 overloads (v: string_view, s: const char*):
+  //  (1) compare(v)
+  //  (2) compare(pos1, count1, v)
+  //  (3) compare(pos1, count1, v, pos2, count2)
+  //  (4) compare(s)
+  //  (5) compare(pos1, count1, s)
+  //  (6) compare(pos1, count1, s, count2)
+
+  absl::string_view abc("abcdefghijklmnopqrstuvwxyz");
+
+  // check comparison operations on strings longer than 4 bytes.
+  EXPECT_EQ(abc, absl::string_view("abcdefghijklmnopqrstuvwxyz"));
+  EXPECT_EQ(abc.compare(absl::string_view("abcdefghijklmnopqrstuvwxyz")), 0);
+
+  EXPECT_LT(abc, absl::string_view("abcdefghijklmnopqrstuvwxzz"));
+  EXPECT_LT(abc.compare(absl::string_view("abcdefghijklmnopqrstuvwxzz")), 0);
+
+  EXPECT_GT(abc, absl::string_view("abcdefghijklmnopqrstuvwxyy"));
+  EXPECT_GT(abc.compare(absl::string_view("abcdefghijklmnopqrstuvwxyy")), 0);
+
+  // The "substr" variants of `compare`.
+  absl::string_view digits("0123456789");
+  auto npos = absl::string_view::npos;
+
+  // Taking string_view
+  EXPECT_EQ(digits.compare(3, npos, absl::string_view("3456789")), 0);  // 2
+  EXPECT_EQ(digits.compare(3, 4, absl::string_view("3456")), 0);        // 2
+  EXPECT_EQ(digits.compare(10, 0, absl::string_view()), 0);             // 2
+  EXPECT_EQ(digits.compare(3, 4, absl::string_view("0123456789"), 3, 4),
+            0);  // 3
+  EXPECT_LT(digits.compare(3, 4, absl::string_view("0123456789"), 3, 5),
+            0);  // 3
+  EXPECT_LT(digits.compare(0, npos, absl::string_view("0123456789"), 3, 5),
+            0);  // 3
+  // Taking const char*
+  EXPECT_EQ(digits.compare(3, 4, "3456"), 0);                 // 5
+  EXPECT_EQ(digits.compare(3, npos, "3456789"), 0);           // 5
+  EXPECT_EQ(digits.compare(10, 0, ""), 0);                    // 5
+  EXPECT_EQ(digits.compare(3, 4, "0123456789", 3, 4), 0);     // 6
+  EXPECT_LT(digits.compare(3, 4, "0123456789", 3, 5), 0);     // 6
+  EXPECT_LT(digits.compare(0, npos, "0123456789", 3, 5), 0);  // 6
+}
+
+TEST(StringViewTest, At) {
+  absl::string_view abc = "abc";
+  EXPECT_EQ(abc.at(0), 'a');
+  EXPECT_EQ(abc.at(1), 'b');
+  EXPECT_EQ(abc.at(2), 'c');
+#ifdef ABSL_HAVE_EXCEPTIONS
+  EXPECT_THROW(abc.at(3), std::out_of_range);
+#else
+  ABSL_EXPECT_DEATH_IF_SUPPORTED(abc.at(3), "absl::string_view::at");
+#endif
+}
+
+struct MyCharAlloc : std::allocator<char> {};
+
+TEST(StringViewTest, ExplicitConversionOperator) {
+  absl::string_view sp = "hi";
+  EXPECT_EQ(sp, std::string(sp));
+}
+
+TEST(StringViewTest, NullSafeStringView) {
+  {
+    absl::string_view s = absl::NullSafeStringView(nullptr);
+    EXPECT_EQ(nullptr, s.data());
+    EXPECT_EQ(0, s.size());
+    EXPECT_EQ(absl::string_view(), s);
+  }
+  {
+    static const char kHi[] = "hi";
+    absl::string_view s = absl::NullSafeStringView(kHi);
+    EXPECT_EQ(kHi, s.data());
+    EXPECT_EQ(strlen(kHi), s.size());
+    EXPECT_EQ(absl::string_view("hi"), s);
+  }
+}
+
+TEST(StringViewTest, ConstexprCompiles) {
+  constexpr absl::string_view sp;
+#ifdef ABSL_HAVE_STRING_VIEW_FROM_NULLPTR
+  constexpr absl::string_view cstr(nullptr);
+#endif
+  constexpr absl::string_view cstr_len("cstr", 4);
+
+#if defined(ABSL_HAVE_STD_STRING_VIEW)
+  // In libstdc++ (as of 7.2), `std::string_view::string_view(const char*)`
+  // calls `std::char_traits<char>::length(const char*)` to get the std::string
+  // length, but it is not marked constexpr yet. See GCC bug:
+  // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78156
+  // Also, there is a LWG issue that adds constexpr to length() which was just
+  // resolved 2017-06-02. See
+  // http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2232
+  // TODO(zhangxy): Update the condition when libstdc++ adopts the constexpr
+  // length().
+#if !defined(__GLIBCXX__)
+#define ABSL_HAVE_CONSTEXPR_STRING_VIEW_FROM_CSTR 1
+#endif  // !__GLIBCXX__
+
+#else  // ABSL_HAVE_STD_STRING_VIEW
+
+// This duplicates the check for __builtin_strlen in the header.
+#if ABSL_HAVE_BUILTIN(__builtin_strlen) || \
+    (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_HAVE_CONSTEXPR_STRING_VIEW_FROM_CSTR 1
+#elif defined(__GNUC__)  // GCC or clang
+#error GCC/clang should have constexpr string_view.
+#endif
+
+// MSVC 2017+ should be able to construct a constexpr string_view from a cstr.
+#if defined(_MSC_VER) && _MSC_VER >= 1910
+#define ABSL_HAVE_CONSTEXPR_STRING_VIEW_FROM_CSTR 1
+#endif
+
+#endif  // ABSL_HAVE_STD_STRING_VIEW
+
+#ifdef ABSL_HAVE_CONSTEXPR_STRING_VIEW_FROM_CSTR
+  constexpr absl::string_view cstr_strlen("foo");
+  EXPECT_EQ(cstr_strlen.length(), 3);
+  constexpr absl::string_view cstr_strlen2 = "bar";
+  EXPECT_EQ(cstr_strlen2, "bar");
+#endif
+
+#if !defined(__clang__) || 3 < __clang_major__ || \
+  (3 == __clang_major__ && 4 < __clang_minor__)
+  // older clang versions (< 3.5) complain that:
+  //   "cannot perform pointer arithmetic on null pointer"
+  constexpr absl::string_view::iterator const_begin_empty = sp.begin();
+  constexpr absl::string_view::iterator const_end_empty = sp.end();
+  EXPECT_EQ(const_begin_empty, const_end_empty);
+
+#ifdef ABSL_HAVE_STRING_VIEW_FROM_NULLPTR
+  constexpr absl::string_view::iterator const_begin_nullptr = cstr.begin();
+  constexpr absl::string_view::iterator const_end_nullptr = cstr.end();
+  EXPECT_EQ(const_begin_nullptr, const_end_nullptr);
+#endif  // ABSL_HAVE_STRING_VIEW_FROM_NULLPTR
+#endif  // !defined(__clang__) || ...
+
+  constexpr absl::string_view::iterator const_begin = cstr_len.begin();
+  constexpr absl::string_view::iterator const_end = cstr_len.end();
+  constexpr absl::string_view::size_type const_size = cstr_len.size();
+  constexpr absl::string_view::size_type const_length = cstr_len.length();
+  static_assert(const_begin + const_size == const_end,
+                "pointer arithmetic check");
+  static_assert(const_begin + const_length == const_end,
+                "pointer arithmetic check");
+#ifndef _MSC_VER
+  // MSVC has bugs doing constexpr pointer arithmetic.
+  // https://developercommunity.visualstudio.com/content/problem/482192/bad-pointer-arithmetic-in-constepxr-2019-rc1-svc1.html
+  EXPECT_EQ(const_begin + const_size, const_end);
+  EXPECT_EQ(const_begin + const_length, const_end);
+#endif
+
+  constexpr bool isempty = sp.empty();
+  EXPECT_TRUE(isempty);
+
+  constexpr const char c = cstr_len[2];
+  EXPECT_EQ(c, 't');
+
+  constexpr const char cfront = cstr_len.front();
+  constexpr const char cback = cstr_len.back();
+  EXPECT_EQ(cfront, 'c');
+  EXPECT_EQ(cback, 'r');
+
+  constexpr const char* np = sp.data();
+  constexpr const char* cstr_ptr = cstr_len.data();
+  EXPECT_EQ(np, nullptr);
+  EXPECT_NE(cstr_ptr, nullptr);
+
+  constexpr size_t sp_npos = sp.npos;
+  EXPECT_EQ(sp_npos, -1);
+}
+
+TEST(StringViewTest, Noexcept) {
+  EXPECT_TRUE((std::is_nothrow_constructible<absl::string_view,
+                                             const std::string&>::value));
+  EXPECT_TRUE((std::is_nothrow_constructible<absl::string_view,
+                                             const std::string&>::value));
+  EXPECT_TRUE(std::is_nothrow_constructible<absl::string_view>::value);
+  constexpr absl::string_view sp;
+  EXPECT_TRUE(noexcept(sp.begin()));
+  EXPECT_TRUE(noexcept(sp.end()));
+  EXPECT_TRUE(noexcept(sp.cbegin()));
+  EXPECT_TRUE(noexcept(sp.cend()));
+  EXPECT_TRUE(noexcept(sp.rbegin()));
+  EXPECT_TRUE(noexcept(sp.rend()));
+  EXPECT_TRUE(noexcept(sp.crbegin()));
+  EXPECT_TRUE(noexcept(sp.crend()));
+  EXPECT_TRUE(noexcept(sp.size()));
+  EXPECT_TRUE(noexcept(sp.length()));
+  EXPECT_TRUE(noexcept(sp.empty()));
+  EXPECT_TRUE(noexcept(sp.data()));
+  EXPECT_TRUE(noexcept(sp.compare(sp)));
+  EXPECT_TRUE(noexcept(sp.find(sp)));
+  EXPECT_TRUE(noexcept(sp.find('f')));
+  EXPECT_TRUE(noexcept(sp.rfind(sp)));
+  EXPECT_TRUE(noexcept(sp.rfind('f')));
+  EXPECT_TRUE(noexcept(sp.find_first_of(sp)));
+  EXPECT_TRUE(noexcept(sp.find_first_of('f')));
+  EXPECT_TRUE(noexcept(sp.find_last_of(sp)));
+  EXPECT_TRUE(noexcept(sp.find_last_of('f')));
+  EXPECT_TRUE(noexcept(sp.find_first_not_of(sp)));
+  EXPECT_TRUE(noexcept(sp.find_first_not_of('f')));
+  EXPECT_TRUE(noexcept(sp.find_last_not_of(sp)));
+  EXPECT_TRUE(noexcept(sp.find_last_not_of('f')));
+}
+
+TEST(ComparisonOpsTest, StringCompareNotAmbiguous) {
+  EXPECT_EQ("hello", std::string("hello"));
+  EXPECT_LT("hello", std::string("world"));
+}
+
+TEST(ComparisonOpsTest, HeterogenousStringViewEquals) {
+  EXPECT_EQ(absl::string_view("hello"), std::string("hello"));
+  EXPECT_EQ("hello", absl::string_view("hello"));
+}
+
+TEST(FindOneCharTest, EdgeCases) {
+  absl::string_view a("xxyyyxx");
+
+  // Set a = "xyyyx".
+  a.remove_prefix(1);
+  a.remove_suffix(1);
+
+  EXPECT_EQ(0, a.find('x'));
+  EXPECT_EQ(0, a.find('x', 0));
+  EXPECT_EQ(4, a.find('x', 1));
+  EXPECT_EQ(4, a.find('x', 4));
+  EXPECT_EQ(absl::string_view::npos, a.find('x', 5));
+
+  EXPECT_EQ(4, a.rfind('x'));
+  EXPECT_EQ(4, a.rfind('x', 5));
+  EXPECT_EQ(4, a.rfind('x', 4));
+  EXPECT_EQ(0, a.rfind('x', 3));
+  EXPECT_EQ(0, a.rfind('x', 0));
+
+  // Set a = "yyy".
+  a.remove_prefix(1);
+  a.remove_suffix(1);
+
+  EXPECT_EQ(absl::string_view::npos, a.find('x'));
+  EXPECT_EQ(absl::string_view::npos, a.rfind('x'));
+}
+
+#ifndef THREAD_SANITIZER  // Allocates too much memory for tsan.
+TEST(HugeStringView, TwoPointTwoGB) {
+  if (sizeof(size_t) <= 4 || RunningOnValgrind())
+    return;
+  // Try a huge std::string piece.
+  const size_t size = size_t{2200} * 1000 * 1000;
+  std::string s(size, 'a');
+  absl::string_view sp(s);
+  EXPECT_EQ(size, sp.length());
+  sp.remove_prefix(1);
+  EXPECT_EQ(size - 1, sp.length());
+  sp.remove_suffix(2);
+  EXPECT_EQ(size - 1 - 2, sp.length());
+}
+#endif  // THREAD_SANITIZER
+
+#if !defined(NDEBUG) && !defined(ABSL_HAVE_STD_STRING_VIEW)
+TEST(NonNegativeLenTest, NonNegativeLen) {
+  ABSL_EXPECT_DEATH_IF_SUPPORTED(absl::string_view("xyz", -1),
+                                 "len <= kMaxSize");
+}
+
+TEST(LenExceedsMaxSizeTest, LenExceedsMaxSize) {
+  auto max_size = absl::string_view().max_size();
+
+  // This should construct ok (although the view itself is obviously invalid).
+  absl::string_view ok_view("", max_size);
+
+  // Adding one to the max should trigger an assertion.
+  ABSL_EXPECT_DEATH_IF_SUPPORTED(absl::string_view("", max_size + 1),
+                                 "len <= kMaxSize");
+}
+#endif  // !defined(NDEBUG) && !defined(ABSL_HAVE_STD_STRING_VIEW)
+
+class StringViewStreamTest : public ::testing::Test {
+ public:
+  // Set negative 'width' for right justification.
+  template <typename T>
+  std::string Pad(const T& s, int width, char fill = 0) {
+    std::ostringstream oss;
+    if (fill != 0) {
+      oss << std::setfill(fill);
+    }
+    if (width < 0) {
+      width = -width;
+      oss << std::right;
+    }
+    oss << std::setw(width) << s;
+    return oss.str();
+  }
+};
+
+TEST_F(StringViewStreamTest, Padding) {
+  std::string s("hello");
+  absl::string_view sp(s);
+  for (int w = -64; w < 64; ++w) {
+    SCOPED_TRACE(w);
+    EXPECT_EQ(Pad(s, w), Pad(sp, w));
+  }
+  for (int w = -64; w < 64; ++w) {
+    SCOPED_TRACE(w);
+    EXPECT_EQ(Pad(s, w, '#'), Pad(sp, w, '#'));
+  }
+}
+
+TEST_F(StringViewStreamTest, ResetsWidth) {
+  // Width should reset after one formatted write.
+  // If we weren't resetting width after formatting the string_view,
+  // we'd have width=5 carrying over to the printing of the "]",
+  // creating "[###hi####]".
+  std::string s = "hi";
+  absl::string_view sp = s;
+  {
+    std::ostringstream oss;
+    oss << "[" << std::setfill('#') << std::setw(5) << s << "]";
+    ASSERT_EQ("[###hi]", oss.str());
+  }
+  {
+    std::ostringstream oss;
+    oss << "[" << std::setfill('#') << std::setw(5) << sp << "]";
+    EXPECT_EQ("[###hi]", oss.str());
+  }
+}
+
+}  // namespace
diff --git a/absl/strings/strip.h b/absl/strings/strip.h
new file mode 100644
index 0000000..e1341e0
--- /dev/null
+++ b/absl/strings/strip.h
@@ -0,0 +1,89 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: strip.h
+// -----------------------------------------------------------------------------
+//
+// This file contains various functions for stripping substrings from a string.
+#ifndef ABSL_STRINGS_STRIP_H_
+#define ABSL_STRINGS_STRIP_H_
+
+#include <cstddef>
+#include <string>
+
+#include "absl/base/macros.h"
+#include "absl/strings/ascii.h"
+#include "absl/strings/match.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+
+// ConsumePrefix()
+//
+// Strips the `expected` prefix from the start of the given string, returning
+// `true` if the strip operation succeeded or false otherwise.
+//
+// Example:
+//
+//   absl::string_view input("abc");
+//   EXPECT_TRUE(absl::ConsumePrefix(&input, "a"));
+//   EXPECT_EQ(input, "bc");
+inline bool ConsumePrefix(absl::string_view* str, absl::string_view expected) {
+  if (!absl::StartsWith(*str, expected)) return false;
+  str->remove_prefix(expected.size());
+  return true;
+}
+// ConsumeSuffix()
+//
+// Strips the `expected` suffix from the end of the given string, returning
+// `true` if the strip operation succeeded or false otherwise.
+//
+// Example:
+//
+//   absl::string_view input("abcdef");
+//   EXPECT_TRUE(absl::ConsumeSuffix(&input, "def"));
+//   EXPECT_EQ(input, "abc");
+inline bool ConsumeSuffix(absl::string_view* str, absl::string_view expected) {
+  if (!absl::EndsWith(*str, expected)) return false;
+  str->remove_suffix(expected.size());
+  return true;
+}
+
+// StripPrefix()
+//
+// Returns a view into the input string 'str' with the given 'prefix' removed,
+// but leaving the original string intact. If the prefix does not match at the
+// start of the string, returns the original string instead.
+ABSL_MUST_USE_RESULT inline absl::string_view StripPrefix(
+    absl::string_view str, absl::string_view prefix) {
+  if (absl::StartsWith(str, prefix)) str.remove_prefix(prefix.size());
+  return str;
+}
+
+// StripSuffix()
+//
+// Returns a view into the input string 'str' with the given 'suffix' removed,
+// but leaving the original string intact. If the suffix does not match at the
+// end of the string, returns the original string instead.
+ABSL_MUST_USE_RESULT inline absl::string_view StripSuffix(
+    absl::string_view str, absl::string_view suffix) {
+  if (absl::EndsWith(str, suffix)) str.remove_suffix(suffix.size());
+  return str;
+}
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_STRIP_H_
diff --git a/absl/strings/strip_test.cc b/absl/strings/strip_test.cc
new file mode 100644
index 0000000..e4e00cb
--- /dev/null
+++ b/absl/strings/strip_test.cc
@@ -0,0 +1,198 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file contains functions that remove a defined part from the string,
+// i.e., strip the string.
+
+#include "absl/strings/strip.h"
+
+#include <cassert>
+#include <cstdio>
+#include <cstring>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/strings/string_view.h"
+
+namespace {
+
+TEST(Strip, ConsumePrefixOneChar) {
+  absl::string_view input("abc");
+  EXPECT_TRUE(absl::ConsumePrefix(&input, "a"));
+  EXPECT_EQ(input, "bc");
+
+  EXPECT_FALSE(absl::ConsumePrefix(&input, "x"));
+  EXPECT_EQ(input, "bc");
+
+  EXPECT_TRUE(absl::ConsumePrefix(&input, "b"));
+  EXPECT_EQ(input, "c");
+
+  EXPECT_TRUE(absl::ConsumePrefix(&input, "c"));
+  EXPECT_EQ(input, "");
+
+  EXPECT_FALSE(absl::ConsumePrefix(&input, "a"));
+  EXPECT_EQ(input, "");
+}
+
+TEST(Strip, ConsumePrefix) {
+  absl::string_view input("abcdef");
+  EXPECT_FALSE(absl::ConsumePrefix(&input, "abcdefg"));
+  EXPECT_EQ(input, "abcdef");
+
+  EXPECT_FALSE(absl::ConsumePrefix(&input, "abce"));
+  EXPECT_EQ(input, "abcdef");
+
+  EXPECT_TRUE(absl::ConsumePrefix(&input, ""));
+  EXPECT_EQ(input, "abcdef");
+
+  EXPECT_FALSE(absl::ConsumePrefix(&input, "abcdeg"));
+  EXPECT_EQ(input, "abcdef");
+
+  EXPECT_TRUE(absl::ConsumePrefix(&input, "abcdef"));
+  EXPECT_EQ(input, "");
+
+  input = "abcdef";
+  EXPECT_TRUE(absl::ConsumePrefix(&input, "abcde"));
+  EXPECT_EQ(input, "f");
+}
+
+TEST(Strip, ConsumeSuffix) {
+  absl::string_view input("abcdef");
+  EXPECT_FALSE(absl::ConsumeSuffix(&input, "abcdefg"));
+  EXPECT_EQ(input, "abcdef");
+
+  EXPECT_TRUE(absl::ConsumeSuffix(&input, ""));
+  EXPECT_EQ(input, "abcdef");
+
+  EXPECT_TRUE(absl::ConsumeSuffix(&input, "def"));
+  EXPECT_EQ(input, "abc");
+
+  input = "abcdef";
+  EXPECT_FALSE(absl::ConsumeSuffix(&input, "abcdeg"));
+  EXPECT_EQ(input, "abcdef");
+
+  EXPECT_TRUE(absl::ConsumeSuffix(&input, "f"));
+  EXPECT_EQ(input, "abcde");
+
+  EXPECT_TRUE(absl::ConsumeSuffix(&input, "abcde"));
+  EXPECT_EQ(input, "");
+}
+
+TEST(Strip, StripPrefix) {
+  const absl::string_view null_str;
+
+  EXPECT_EQ(absl::StripPrefix("foobar", "foo"), "bar");
+  EXPECT_EQ(absl::StripPrefix("foobar", ""), "foobar");
+  EXPECT_EQ(absl::StripPrefix("foobar", null_str), "foobar");
+  EXPECT_EQ(absl::StripPrefix("foobar", "foobar"), "");
+  EXPECT_EQ(absl::StripPrefix("foobar", "bar"), "foobar");
+  EXPECT_EQ(absl::StripPrefix("foobar", "foobarr"), "foobar");
+  EXPECT_EQ(absl::StripPrefix("", ""), "");
+}
+
+TEST(Strip, StripSuffix) {
+  const absl::string_view null_str;
+
+  EXPECT_EQ(absl::StripSuffix("foobar", "bar"), "foo");
+  EXPECT_EQ(absl::StripSuffix("foobar", ""), "foobar");
+  EXPECT_EQ(absl::StripSuffix("foobar", null_str), "foobar");
+  EXPECT_EQ(absl::StripSuffix("foobar", "foobar"), "");
+  EXPECT_EQ(absl::StripSuffix("foobar", "foo"), "foobar");
+  EXPECT_EQ(absl::StripSuffix("foobar", "ffoobar"), "foobar");
+  EXPECT_EQ(absl::StripSuffix("", ""), "");
+}
+
+TEST(Strip, RemoveExtraAsciiWhitespace) {
+  const char* inputs[] = {
+      "No extra space",
+      "  Leading whitespace",
+      "Trailing whitespace  ",
+      "  Leading and trailing  ",
+      " Whitespace \t  in\v   middle  ",
+      "'Eeeeep!  \n Newlines!\n",
+      "nospaces",
+  };
+  const char* outputs[] = {
+      "No extra space",
+      "Leading whitespace",
+      "Trailing whitespace",
+      "Leading and trailing",
+      "Whitespace in middle",
+      "'Eeeeep! Newlines!",
+      "nospaces",
+  };
+  int NUM_TESTS = 7;
+
+  for (int i = 0; i < NUM_TESTS; i++) {
+    std::string s(inputs[i]);
+    absl::RemoveExtraAsciiWhitespace(&s);
+    EXPECT_STREQ(outputs[i], s.c_str());
+  }
+
+  // Test that absl::RemoveExtraAsciiWhitespace returns immediately for empty
+  // strings (It was adding the \0 character to the C++ std::string, which broke
+  // tests involving empty())
+  std::string zero_string = "";
+  assert(zero_string.empty());
+  absl::RemoveExtraAsciiWhitespace(&zero_string);
+  EXPECT_EQ(zero_string.size(), 0);
+  EXPECT_TRUE(zero_string.empty());
+}
+
+TEST(Strip, StripTrailingAsciiWhitespace) {
+  std::string test = "foo  ";
+  absl::StripTrailingAsciiWhitespace(&test);
+  EXPECT_EQ(test, "foo");
+
+  test = "   ";
+  absl::StripTrailingAsciiWhitespace(&test);
+  EXPECT_EQ(test, "");
+
+  test = "";
+  absl::StripTrailingAsciiWhitespace(&test);
+  EXPECT_EQ(test, "");
+
+  test = " abc\t";
+  absl::StripTrailingAsciiWhitespace(&test);
+  EXPECT_EQ(test, " abc");
+}
+
+TEST(String, StripLeadingAsciiWhitespace) {
+  absl::string_view orig = "\t  \n\f\r\n\vfoo";
+  EXPECT_EQ("foo", absl::StripLeadingAsciiWhitespace(orig));
+  orig = "\t  \n\f\r\v\n\t  \n\f\r\v\n";
+  EXPECT_EQ(absl::string_view(), absl::StripLeadingAsciiWhitespace(orig));
+}
+
+TEST(Strip, StripAsciiWhitespace) {
+  std::string test2 = "\t  \f\r\n\vfoo \t\f\r\v\n";
+  absl::StripAsciiWhitespace(&test2);
+  EXPECT_EQ(test2, "foo");
+  std::string test3 = "bar";
+  absl::StripAsciiWhitespace(&test3);
+  EXPECT_EQ(test3, "bar");
+  std::string test4 = "\t  \f\r\n\vfoo";
+  absl::StripAsciiWhitespace(&test4);
+  EXPECT_EQ(test4, "foo");
+  std::string test5 = "foo \t\f\r\v\n";
+  absl::StripAsciiWhitespace(&test5);
+  EXPECT_EQ(test5, "foo");
+  absl::string_view test6("\t  \f\r\n\vfoo \t\f\r\v\n");
+  test6 = absl::StripAsciiWhitespace(test6);
+  EXPECT_EQ(test6, "foo");
+  test6 = absl::StripAsciiWhitespace(test6);
+  EXPECT_EQ(test6, "foo");  // already stripped
+}
+
+}  // namespace
diff --git a/absl/strings/substitute.cc b/absl/strings/substitute.cc
new file mode 100644
index 0000000..bc17695
--- /dev/null
+++ b/absl/strings/substitute.cc
@@ -0,0 +1,170 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/substitute.h"
+
+#include <algorithm>
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/strings/ascii.h"
+#include "absl/strings/escaping.h"
+#include "absl/strings/internal/resize_uninitialized.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+namespace substitute_internal {
+
+void SubstituteAndAppendArray(std::string* output, absl::string_view format,
+                              const absl::string_view* args_array,
+                              size_t num_args) {
+  // Determine total size needed.
+  size_t size = 0;
+  for (size_t i = 0; i < format.size(); i++) {
+    if (format[i] == '$') {
+      if (i + 1 >= format.size()) {
+#ifndef NDEBUG
+        ABSL_RAW_LOG(FATAL,
+                     "Invalid strings::Substitute() format std::string: \"%s\".",
+                     absl::CEscape(format).c_str());
+#endif
+        return;
+      } else if (absl::ascii_isdigit(format[i + 1])) {
+        int index = format[i + 1] - '0';
+        if (static_cast<size_t>(index) >= num_args) {
+#ifndef NDEBUG
+          ABSL_RAW_LOG(
+              FATAL,
+              "Invalid strings::Substitute() format std::string: asked for \"$"
+              "%d\", but only %d args were given.  Full format std::string was: "
+              "\"%s\".",
+              index, static_cast<int>(num_args), absl::CEscape(format).c_str());
+#endif
+          return;
+        }
+        size += args_array[index].size();
+        ++i;  // Skip next char.
+      } else if (format[i + 1] == '$') {
+        ++size;
+        ++i;  // Skip next char.
+      } else {
+#ifndef NDEBUG
+        ABSL_RAW_LOG(FATAL,
+                     "Invalid strings::Substitute() format std::string: \"%s\".",
+                     absl::CEscape(format).c_str());
+#endif
+        return;
+      }
+    } else {
+      ++size;
+    }
+  }
+
+  if (size == 0) return;
+
+  // Build the std::string.
+  size_t original_size = output->size();
+  strings_internal::STLStringResizeUninitialized(output, original_size + size);
+  char* target = &(*output)[original_size];
+  for (size_t i = 0; i < format.size(); i++) {
+    if (format[i] == '$') {
+      if (absl::ascii_isdigit(format[i + 1])) {
+        const absl::string_view src = args_array[format[i + 1] - '0'];
+        target = std::copy(src.begin(), src.end(), target);
+        ++i;  // Skip next char.
+      } else if (format[i + 1] == '$') {
+        *target++ = '$';
+        ++i;  // Skip next char.
+      }
+    } else {
+      *target++ = format[i];
+    }
+  }
+
+  assert(target == output->data() + output->size());
+}
+
+static const char kHexDigits[] = "0123456789abcdef";
+Arg::Arg(const void* value) {
+  static_assert(sizeof(scratch_) >= sizeof(value) * 2 + 2,
+                "fix sizeof(scratch_)");
+  if (value == nullptr) {
+    piece_ = "NULL";
+  } else {
+    char* ptr = scratch_ + sizeof(scratch_);
+    uintptr_t num = reinterpret_cast<uintptr_t>(value);
+    do {
+      *--ptr = kHexDigits[num & 0xf];
+      num >>= 4;
+    } while (num != 0);
+    *--ptr = 'x';
+    *--ptr = '0';
+    piece_ = absl::string_view(ptr, scratch_ + sizeof(scratch_) - ptr);
+  }
+}
+
+// TODO(jorg): Don't duplicate so much code between here and str_cat.cc
+Arg::Arg(Hex hex) {
+  char* const end = &scratch_[numbers_internal::kFastToBufferSize];
+  char* writer = end;
+  uint64_t value = hex.value;
+  do {
+    *--writer = kHexDigits[value & 0xF];
+    value >>= 4;
+  } while (value != 0);
+
+  char* beg;
+  if (end - writer < hex.width) {
+    beg = end - hex.width;
+    std::fill_n(beg, writer - beg, hex.fill);
+  } else {
+    beg = writer;
+  }
+
+  piece_ = absl::string_view(beg, end - beg);
+}
+
+// TODO(jorg): Don't duplicate so much code between here and str_cat.cc
+Arg::Arg(Dec dec) {
+  assert(dec.width <= numbers_internal::kFastToBufferSize);
+  char* const end = &scratch_[numbers_internal::kFastToBufferSize];
+  char* const minfill = end - dec.width;
+  char* writer = end;
+  uint64_t value = dec.value;
+  bool neg = dec.neg;
+  while (value > 9) {
+    *--writer = '0' + (value % 10);
+    value /= 10;
+  }
+  *--writer = '0' + value;
+  if (neg) *--writer = '-';
+
+  ptrdiff_t fillers = writer - minfill;
+  if (fillers > 0) {
+    // Tricky: if the fill character is ' ', then it's <fill><+/-><digits>
+    // But...: if the fill character is '0', then it's <+/-><fill><digits>
+    bool add_sign_again = false;
+    if (neg && dec.fill == '0') {  // If filling with '0',
+      ++writer;                    // ignore the sign we just added
+      add_sign_again = true;       // and re-add the sign later.
+    }
+    writer -= fillers;
+    std::fill_n(writer, fillers, dec.fill);
+    if (add_sign_again) *--writer = '-';
+  }
+
+  piece_ = absl::string_view(writer, end - writer);
+}
+
+}  // namespace substitute_internal
+}  // namespace absl
diff --git a/absl/strings/substitute.h b/absl/strings/substitute.h
new file mode 100644
index 0000000..233e9dc
--- /dev/null
+++ b/absl/strings/substitute.h
@@ -0,0 +1,686 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: substitute.h
+// -----------------------------------------------------------------------------
+//
+// This package contains functions for efficiently performing string
+// substitutions using a format string with positional notation:
+// `Substitute()` and `SubstituteAndAppend()`.
+//
+// Unlike printf-style format specifiers, `Substitute()` functions do not need
+// to specify the type of the substitution arguments. Supported arguments
+// following the format string, such as strings, string_views, ints,
+// floats, and bools, are automatically converted to strings during the
+// substitution process. (See below for a full list of supported types.)
+//
+// `Substitute()` does not allow you to specify *how* to format a value, beyond
+// the default conversion to string. For example, you cannot format an integer
+// in hex.
+//
+// The format string uses positional identifiers indicated by a dollar sign ($)
+// and single digit positional ids to indicate which substitution arguments to
+// use at that location within the format string.
+//
+// A '$$' sequence in the format string causes a literal '$' character to be
+// output.
+//
+// Example 1:
+//   std::string s = Substitute("$1 purchased $0 $2 for $$10. Thanks $1!",
+//                              5, "Bob", "Apples");
+//   EXPECT_EQ("Bob purchased 5 Apples for $10. Thanks Bob!", s);
+//
+// Example 2:
+//   std::string s = "Hi. ";
+//   SubstituteAndAppend(&s, "My name is $0 and I am $1 years old.", "Bob", 5);
+//   EXPECT_EQ("Hi. My name is Bob and I am 5 years old.", s);
+//
+// Supported types:
+//   * absl::string_view, std::string, const char* (null is equivalent to "")
+//   * int32_t, int64_t, uint32_t, uint64
+//   * float, double
+//   * bool (Printed as "true" or "false")
+//   * pointer types other than char* (Printed as "0x<lower case hex string>",
+//     except that null is printed as "NULL")
+//
+// If an invalid format string is provided, Substitute returns an empty string
+// and SubstituteAndAppend does not change the provided output string.
+// A format string is invalid if it:
+//   * ends in an unescaped $ character,
+//     e.g. "Hello $", or
+//   * calls for a position argument which is not provided,
+//     e.g. Substitute("Hello $2", "world"), or
+//   * specifies a non-digit, non-$ character after an unescaped $ character,
+//     e.g. "Hello $f".
+// In debug mode, i.e. #ifndef NDEBUG, such errors terminate the program.
+
+#ifndef ABSL_STRINGS_SUBSTITUTE_H_
+#define ABSL_STRINGS_SUBSTITUTE_H_
+
+#include <cstring>
+#include <string>
+#include <type_traits>
+#include <vector>
+
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+#include "absl/strings/ascii.h"
+#include "absl/strings/escaping.h"
+#include "absl/strings/numbers.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_split.h"
+#include "absl/strings/string_view.h"
+#include "absl/strings/strip.h"
+
+namespace absl {
+namespace substitute_internal {
+
+// Arg
+//
+// This class provides an argument type for `absl::Substitute()` and
+// `absl::SubstituteAndAppend()`. `Arg` handles implicit conversion of various
+// types to a string. (`Arg` is very similar to the `AlphaNum` class in
+// `StrCat()`.)
+//
+// This class has implicit constructors.
+class Arg {
+ public:
+  // Overloads for std::string-y things
+  //
+  // Explicitly overload `const char*` so the compiler doesn't cast to `bool`.
+  Arg(const char* value)  // NOLINT(runtime/explicit)
+      : piece_(absl::NullSafeStringView(value)) {}
+  template <typename Allocator>
+  Arg(  // NOLINT
+      const std::basic_string<char, std::char_traits<char>, Allocator>&
+          value) noexcept
+      : piece_(value) {}
+  Arg(absl::string_view value)  // NOLINT(runtime/explicit)
+      : piece_(value) {}
+
+  // Overloads for primitives
+  //
+  // No overloads are available for signed and unsigned char because if people
+  // are explicitly declaring their chars as signed or unsigned then they are
+  // probably using them as 8-bit integers and would probably prefer an integer
+  // representation. However, we can't really know, so we make the caller decide
+  // what to do.
+  Arg(char value)  // NOLINT(runtime/explicit)
+      : piece_(scratch_, 1) { scratch_[0] = value; }
+  Arg(short value)  // NOLINT(*)
+      : piece_(scratch_,
+               numbers_internal::FastIntToBuffer(value, scratch_) - scratch_) {}
+  Arg(unsigned short value)  // NOLINT(*)
+      : piece_(scratch_,
+               numbers_internal::FastIntToBuffer(value, scratch_) - scratch_) {}
+  Arg(int value)  // NOLINT(runtime/explicit)
+      : piece_(scratch_,
+               numbers_internal::FastIntToBuffer(value, scratch_) - scratch_) {}
+  Arg(unsigned int value)  // NOLINT(runtime/explicit)
+      : piece_(scratch_,
+               numbers_internal::FastIntToBuffer(value, scratch_) - scratch_) {}
+  Arg(long value)  // NOLINT(*)
+      : piece_(scratch_,
+               numbers_internal::FastIntToBuffer(value, scratch_) - scratch_) {}
+  Arg(unsigned long value)  // NOLINT(*)
+      : piece_(scratch_,
+               numbers_internal::FastIntToBuffer(value, scratch_) - scratch_) {}
+  Arg(long long value)  // NOLINT(*)
+      : piece_(scratch_,
+               numbers_internal::FastIntToBuffer(value, scratch_) - scratch_) {}
+  Arg(unsigned long long value)  // NOLINT(*)
+      : piece_(scratch_,
+               numbers_internal::FastIntToBuffer(value, scratch_) - scratch_) {}
+  Arg(float value)  // NOLINT(runtime/explicit)
+      : piece_(scratch_, numbers_internal::SixDigitsToBuffer(value, scratch_)) {
+  }
+  Arg(double value)  // NOLINT(runtime/explicit)
+      : piece_(scratch_, numbers_internal::SixDigitsToBuffer(value, scratch_)) {
+  }
+  Arg(bool value)  // NOLINT(runtime/explicit)
+      : piece_(value ? "true" : "false") {}
+
+  Arg(Hex hex);  // NOLINT(runtime/explicit)
+  Arg(Dec dec);  // NOLINT(runtime/explicit)
+
+  // vector<bool>::reference and const_reference require special help to
+  // convert to `AlphaNum` because it requires two user defined conversions.
+  template <typename T,
+            absl::enable_if_t<
+                std::is_class<T>::value &&
+                (std::is_same<T, std::vector<bool>::reference>::value ||
+                 std::is_same<T, std::vector<bool>::const_reference>::value)>* =
+                nullptr>
+  Arg(T value)  // NOLINT(google-explicit-constructor)
+      : Arg(static_cast<bool>(value)) {}
+
+  // `void*` values, with the exception of `char*`, are printed as
+  // "0x<hex value>". However, in the case of `nullptr`, "NULL" is printed.
+  Arg(const void* value);  // NOLINT(runtime/explicit)
+
+  Arg(const Arg&) = delete;
+  Arg& operator=(const Arg&) = delete;
+
+  absl::string_view piece() const { return piece_; }
+
+ private:
+  absl::string_view piece_;
+  char scratch_[numbers_internal::kFastToBufferSize];
+};
+
+// Internal helper function. Don't call this from outside this implementation.
+// This interface may change without notice.
+void SubstituteAndAppendArray(std::string* output, absl::string_view format,
+                              const absl::string_view* args_array,
+                              size_t num_args);
+
+#if defined(ABSL_BAD_CALL_IF)
+constexpr int CalculateOneBit(const char* format) {
+  return (*format < '0' || *format > '9') ? 0 : (1 << (*format - '0'));
+}
+
+constexpr const char* SkipNumber(const char* format) {
+  return !*format ? format : (format + 1);
+}
+
+constexpr int PlaceholderBitmask(const char* format) {
+  return !*format ? 0 : *format != '$'
+                             ? PlaceholderBitmask(format + 1)
+                             : (CalculateOneBit(format + 1) |
+                                   PlaceholderBitmask(SkipNumber(format + 1)));
+}
+#endif  // ABSL_BAD_CALL_IF
+
+}  // namespace substitute_internal
+
+//
+// PUBLIC API
+//
+
+// SubstituteAndAppend()
+//
+// Substitutes variables into a given format string and appends to a given
+// output string. See file comments above for usage.
+//
+// The declarations of `SubstituteAndAppend()` below consist of overloads
+// for passing 0 to 10 arguments, respectively.
+//
+// NOTE: A zero-argument `SubstituteAndAppend()` may be used within variadic
+// templates to allow a variable number of arguments.
+//
+// Example:
+//  template <typename... Args>
+//  void VarMsg(std::string* boilerplate, absl::string_view format,
+//      const Args&... args) {
+//    absl::SubstituteAndAppend(boilerplate, format, args...);
+//  }
+//
+inline void SubstituteAndAppend(std::string* output, absl::string_view format) {
+  substitute_internal::SubstituteAndAppendArray(output, format, nullptr, 0);
+}
+
+inline void SubstituteAndAppend(std::string* output, absl::string_view format,
+                                const substitute_internal::Arg& a0) {
+  const absl::string_view args[] = {a0.piece()};
+  substitute_internal::SubstituteAndAppendArray(output, format, args,
+                                                ABSL_ARRAYSIZE(args));
+}
+
+inline void SubstituteAndAppend(std::string* output, absl::string_view format,
+                                const substitute_internal::Arg& a0,
+                                const substitute_internal::Arg& a1) {
+  const absl::string_view args[] = {a0.piece(), a1.piece()};
+  substitute_internal::SubstituteAndAppendArray(output, format, args,
+                                                ABSL_ARRAYSIZE(args));
+}
+
+inline void SubstituteAndAppend(std::string* output, absl::string_view format,
+                                const substitute_internal::Arg& a0,
+                                const substitute_internal::Arg& a1,
+                                const substitute_internal::Arg& a2) {
+  const absl::string_view args[] = {a0.piece(), a1.piece(), a2.piece()};
+  substitute_internal::SubstituteAndAppendArray(output, format, args,
+                                                ABSL_ARRAYSIZE(args));
+}
+
+inline void SubstituteAndAppend(std::string* output, absl::string_view format,
+                                const substitute_internal::Arg& a0,
+                                const substitute_internal::Arg& a1,
+                                const substitute_internal::Arg& a2,
+                                const substitute_internal::Arg& a3) {
+  const absl::string_view args[] = {a0.piece(), a1.piece(), a2.piece(),
+                                    a3.piece()};
+  substitute_internal::SubstituteAndAppendArray(output, format, args,
+                                                ABSL_ARRAYSIZE(args));
+}
+
+inline void SubstituteAndAppend(std::string* output, absl::string_view format,
+                                const substitute_internal::Arg& a0,
+                                const substitute_internal::Arg& a1,
+                                const substitute_internal::Arg& a2,
+                                const substitute_internal::Arg& a3,
+                                const substitute_internal::Arg& a4) {
+  const absl::string_view args[] = {a0.piece(), a1.piece(), a2.piece(),
+                                    a3.piece(), a4.piece()};
+  substitute_internal::SubstituteAndAppendArray(output, format, args,
+                                                ABSL_ARRAYSIZE(args));
+}
+
+inline void SubstituteAndAppend(std::string* output, absl::string_view format,
+                                const substitute_internal::Arg& a0,
+                                const substitute_internal::Arg& a1,
+                                const substitute_internal::Arg& a2,
+                                const substitute_internal::Arg& a3,
+                                const substitute_internal::Arg& a4,
+                                const substitute_internal::Arg& a5) {
+  const absl::string_view args[] = {a0.piece(), a1.piece(), a2.piece(),
+                                    a3.piece(), a4.piece(), a5.piece()};
+  substitute_internal::SubstituteAndAppendArray(output, format, args,
+                                                ABSL_ARRAYSIZE(args));
+}
+
+inline void SubstituteAndAppend(std::string* output, absl::string_view format,
+                                const substitute_internal::Arg& a0,
+                                const substitute_internal::Arg& a1,
+                                const substitute_internal::Arg& a2,
+                                const substitute_internal::Arg& a3,
+                                const substitute_internal::Arg& a4,
+                                const substitute_internal::Arg& a5,
+                                const substitute_internal::Arg& a6) {
+  const absl::string_view args[] = {a0.piece(), a1.piece(), a2.piece(),
+                                    a3.piece(), a4.piece(), a5.piece(),
+                                    a6.piece()};
+  substitute_internal::SubstituteAndAppendArray(output, format, args,
+                                                ABSL_ARRAYSIZE(args));
+}
+
+inline void SubstituteAndAppend(
+    std::string* output, absl::string_view format,
+    const substitute_internal::Arg& a0, const substitute_internal::Arg& a1,
+    const substitute_internal::Arg& a2, const substitute_internal::Arg& a3,
+    const substitute_internal::Arg& a4, const substitute_internal::Arg& a5,
+    const substitute_internal::Arg& a6, const substitute_internal::Arg& a7) {
+  const absl::string_view args[] = {a0.piece(), a1.piece(), a2.piece(),
+                                    a3.piece(), a4.piece(), a5.piece(),
+                                    a6.piece(), a7.piece()};
+  substitute_internal::SubstituteAndAppendArray(output, format, args,
+                                                ABSL_ARRAYSIZE(args));
+}
+
+inline void SubstituteAndAppend(
+    std::string* output, absl::string_view format,
+    const substitute_internal::Arg& a0, const substitute_internal::Arg& a1,
+    const substitute_internal::Arg& a2, const substitute_internal::Arg& a3,
+    const substitute_internal::Arg& a4, const substitute_internal::Arg& a5,
+    const substitute_internal::Arg& a6, const substitute_internal::Arg& a7,
+    const substitute_internal::Arg& a8) {
+  const absl::string_view args[] = {a0.piece(), a1.piece(), a2.piece(),
+                                    a3.piece(), a4.piece(), a5.piece(),
+                                    a6.piece(), a7.piece(), a8.piece()};
+  substitute_internal::SubstituteAndAppendArray(output, format, args,
+                                                ABSL_ARRAYSIZE(args));
+}
+
+inline void SubstituteAndAppend(
+    std::string* output, absl::string_view format,
+    const substitute_internal::Arg& a0, const substitute_internal::Arg& a1,
+    const substitute_internal::Arg& a2, const substitute_internal::Arg& a3,
+    const substitute_internal::Arg& a4, const substitute_internal::Arg& a5,
+    const substitute_internal::Arg& a6, const substitute_internal::Arg& a7,
+    const substitute_internal::Arg& a8, const substitute_internal::Arg& a9) {
+  const absl::string_view args[] = {
+      a0.piece(), a1.piece(), a2.piece(), a3.piece(), a4.piece(),
+      a5.piece(), a6.piece(), a7.piece(), a8.piece(), a9.piece()};
+  substitute_internal::SubstituteAndAppendArray(output, format, args,
+                                                ABSL_ARRAYSIZE(args));
+}
+
+#if defined(ABSL_BAD_CALL_IF)
+// This body of functions catches cases where the number of placeholders
+// doesn't match the number of data arguments.
+void SubstituteAndAppend(std::string* output, const char* format)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 0,
+                     "There were no substitution arguments "
+                     "but this format std::string has a $[0-9] in it");
+
+void SubstituteAndAppend(std::string* output, const char* format,
+                         const substitute_internal::Arg& a0)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 1,
+                     "There was 1 substitution argument given, but "
+                     "this format std::string is either missing its $0, or "
+                     "contains one of $1-$9");
+
+void SubstituteAndAppend(std::string* output, const char* format,
+                         const substitute_internal::Arg& a0,
+                         const substitute_internal::Arg& a1)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 3,
+                     "There were 2 substitution arguments given, but "
+                     "this format std::string is either missing its $0/$1, or "
+                     "contains one of $2-$9");
+
+void SubstituteAndAppend(std::string* output, const char* format,
+                         const substitute_internal::Arg& a0,
+                         const substitute_internal::Arg& a1,
+                         const substitute_internal::Arg& a2)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 7,
+                     "There were 3 substitution arguments given, but "
+                     "this format std::string is either missing its $0/$1/$2, or "
+                     "contains one of $3-$9");
+
+void SubstituteAndAppend(std::string* output, const char* format,
+                         const substitute_internal::Arg& a0,
+                         const substitute_internal::Arg& a1,
+                         const substitute_internal::Arg& a2,
+                         const substitute_internal::Arg& a3)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 15,
+                     "There were 4 substitution arguments given, but "
+                     "this format std::string is either missing its $0-$3, or "
+                     "contains one of $4-$9");
+
+void SubstituteAndAppend(std::string* output, const char* format,
+                         const substitute_internal::Arg& a0,
+                         const substitute_internal::Arg& a1,
+                         const substitute_internal::Arg& a2,
+                         const substitute_internal::Arg& a3,
+                         const substitute_internal::Arg& a4)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 31,
+                     "There were 5 substitution arguments given, but "
+                     "this format std::string is either missing its $0-$4, or "
+                     "contains one of $5-$9");
+
+void SubstituteAndAppend(std::string* output, const char* format,
+                         const substitute_internal::Arg& a0,
+                         const substitute_internal::Arg& a1,
+                         const substitute_internal::Arg& a2,
+                         const substitute_internal::Arg& a3,
+                         const substitute_internal::Arg& a4,
+                         const substitute_internal::Arg& a5)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 63,
+                     "There were 6 substitution arguments given, but "
+                     "this format std::string is either missing its $0-$5, or "
+                     "contains one of $6-$9");
+
+void SubstituteAndAppend(
+    std::string* output, const char* format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5, const substitute_internal::Arg& a6)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 127,
+                     "There were 7 substitution arguments given, but "
+                     "this format std::string is either missing its $0-$6, or "
+                     "contains one of $7-$9");
+
+void SubstituteAndAppend(
+    std::string* output, const char* format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5, const substitute_internal::Arg& a6,
+    const substitute_internal::Arg& a7)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 255,
+                     "There were 8 substitution arguments given, but "
+                     "this format std::string is either missing its $0-$7, or "
+                     "contains one of $8-$9");
+
+void SubstituteAndAppend(
+    std::string* output, const char* format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5, const substitute_internal::Arg& a6,
+    const substitute_internal::Arg& a7, const substitute_internal::Arg& a8)
+    ABSL_BAD_CALL_IF(
+        substitute_internal::PlaceholderBitmask(format) != 511,
+        "There were 9 substitution arguments given, but "
+        "this format std::string is either missing its $0-$8, or contains a $9");
+
+void SubstituteAndAppend(
+    std::string* output, const char* format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5, const substitute_internal::Arg& a6,
+    const substitute_internal::Arg& a7, const substitute_internal::Arg& a8,
+    const substitute_internal::Arg& a9)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 1023,
+                     "There were 10 substitution arguments given, but this "
+                     "format std::string doesn't contain all of $0 through $9");
+#endif  // ABSL_BAD_CALL_IF
+
+// Substitute()
+//
+// Substitutes variables into a given format string. See file comments above
+// for usage.
+//
+// The declarations of `Substitute()` below consist of overloads for passing 0
+// to 10 arguments, respectively.
+//
+// NOTE: A zero-argument `Substitute()` may be used within variadic templates to
+// allow a variable number of arguments.
+//
+// Example:
+//  template <typename... Args>
+//  void VarMsg(absl::string_view format, const Args&... args) {
+//    std::string s = absl::Substitute(format, args...);
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(absl::string_view format) {
+  std::string result;
+  SubstituteAndAppend(&result, format);
+  return result;
+}
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(
+    absl::string_view format, const substitute_internal::Arg& a0) {
+  std::string result;
+  SubstituteAndAppend(&result, format, a0);
+  return result;
+}
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(
+    absl::string_view format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1) {
+  std::string result;
+  SubstituteAndAppend(&result, format, a0, a1);
+  return result;
+}
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(
+    absl::string_view format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2) {
+  std::string result;
+  SubstituteAndAppend(&result, format, a0, a1, a2);
+  return result;
+}
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(
+    absl::string_view format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3) {
+  std::string result;
+  SubstituteAndAppend(&result, format, a0, a1, a2, a3);
+  return result;
+}
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(
+    absl::string_view format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4) {
+  std::string result;
+  SubstituteAndAppend(&result, format, a0, a1, a2, a3, a4);
+  return result;
+}
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(
+    absl::string_view format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5) {
+  std::string result;
+  SubstituteAndAppend(&result, format, a0, a1, a2, a3, a4, a5);
+  return result;
+}
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(
+    absl::string_view format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5, const substitute_internal::Arg& a6) {
+  std::string result;
+  SubstituteAndAppend(&result, format, a0, a1, a2, a3, a4, a5, a6);
+  return result;
+}
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(
+    absl::string_view format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5, const substitute_internal::Arg& a6,
+    const substitute_internal::Arg& a7) {
+  std::string result;
+  SubstituteAndAppend(&result, format, a0, a1, a2, a3, a4, a5, a6, a7);
+  return result;
+}
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(
+    absl::string_view format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5, const substitute_internal::Arg& a6,
+    const substitute_internal::Arg& a7, const substitute_internal::Arg& a8) {
+  std::string result;
+  SubstituteAndAppend(&result, format, a0, a1, a2, a3, a4, a5, a6, a7, a8);
+  return result;
+}
+
+ABSL_MUST_USE_RESULT inline std::string Substitute(
+    absl::string_view format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5, const substitute_internal::Arg& a6,
+    const substitute_internal::Arg& a7, const substitute_internal::Arg& a8,
+    const substitute_internal::Arg& a9) {
+  std::string result;
+  SubstituteAndAppend(&result, format, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9);
+  return result;
+}
+
+#if defined(ABSL_BAD_CALL_IF)
+// This body of functions catches cases where the number of placeholders
+// doesn't match the number of data arguments.
+std::string Substitute(const char* format)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 0,
+                     "There were no substitution arguments "
+                     "but this format std::string has a $[0-9] in it");
+
+std::string Substitute(const char* format, const substitute_internal::Arg& a0)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 1,
+                     "There was 1 substitution argument given, but "
+                     "this format std::string is either missing its $0, or "
+                     "contains one of $1-$9");
+
+std::string Substitute(const char* format, const substitute_internal::Arg& a0,
+                       const substitute_internal::Arg& a1)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 3,
+                     "There were 2 substitution arguments given, but "
+                     "this format std::string is either missing its $0/$1, or "
+                     "contains one of $2-$9");
+
+std::string Substitute(const char* format, const substitute_internal::Arg& a0,
+                       const substitute_internal::Arg& a1,
+                       const substitute_internal::Arg& a2)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 7,
+                     "There were 3 substitution arguments given, but "
+                     "this format std::string is either missing its $0/$1/$2, or "
+                     "contains one of $3-$9");
+
+std::string Substitute(const char* format, const substitute_internal::Arg& a0,
+                       const substitute_internal::Arg& a1,
+                       const substitute_internal::Arg& a2,
+                       const substitute_internal::Arg& a3)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 15,
+                     "There were 4 substitution arguments given, but "
+                     "this format std::string is either missing its $0-$3, or "
+                     "contains one of $4-$9");
+
+std::string Substitute(const char* format, const substitute_internal::Arg& a0,
+                       const substitute_internal::Arg& a1,
+                       const substitute_internal::Arg& a2,
+                       const substitute_internal::Arg& a3,
+                       const substitute_internal::Arg& a4)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 31,
+                     "There were 5 substitution arguments given, but "
+                     "this format std::string is either missing its $0-$4, or "
+                     "contains one of $5-$9");
+
+std::string Substitute(const char* format, const substitute_internal::Arg& a0,
+                       const substitute_internal::Arg& a1,
+                       const substitute_internal::Arg& a2,
+                       const substitute_internal::Arg& a3,
+                       const substitute_internal::Arg& a4,
+                       const substitute_internal::Arg& a5)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 63,
+                     "There were 6 substitution arguments given, but "
+                     "this format std::string is either missing its $0-$5, or "
+                     "contains one of $6-$9");
+
+std::string Substitute(const char* format, const substitute_internal::Arg& a0,
+                       const substitute_internal::Arg& a1,
+                       const substitute_internal::Arg& a2,
+                       const substitute_internal::Arg& a3,
+                       const substitute_internal::Arg& a4,
+                       const substitute_internal::Arg& a5,
+                       const substitute_internal::Arg& a6)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 127,
+                     "There were 7 substitution arguments given, but "
+                     "this format std::string is either missing its $0-$6, or "
+                     "contains one of $7-$9");
+
+std::string Substitute(const char* format, const substitute_internal::Arg& a0,
+                       const substitute_internal::Arg& a1,
+                       const substitute_internal::Arg& a2,
+                       const substitute_internal::Arg& a3,
+                       const substitute_internal::Arg& a4,
+                       const substitute_internal::Arg& a5,
+                       const substitute_internal::Arg& a6,
+                       const substitute_internal::Arg& a7)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 255,
+                     "There were 8 substitution arguments given, but "
+                     "this format std::string is either missing its $0-$7, or "
+                     "contains one of $8-$9");
+
+std::string Substitute(
+    const char* format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5, const substitute_internal::Arg& a6,
+    const substitute_internal::Arg& a7, const substitute_internal::Arg& a8)
+    ABSL_BAD_CALL_IF(
+        substitute_internal::PlaceholderBitmask(format) != 511,
+        "There were 9 substitution arguments given, but "
+        "this format std::string is either missing its $0-$8, or contains a $9");
+
+std::string Substitute(
+    const char* format, const substitute_internal::Arg& a0,
+    const substitute_internal::Arg& a1, const substitute_internal::Arg& a2,
+    const substitute_internal::Arg& a3, const substitute_internal::Arg& a4,
+    const substitute_internal::Arg& a5, const substitute_internal::Arg& a6,
+    const substitute_internal::Arg& a7, const substitute_internal::Arg& a8,
+    const substitute_internal::Arg& a9)
+    ABSL_BAD_CALL_IF(substitute_internal::PlaceholderBitmask(format) != 1023,
+                     "There were 10 substitution arguments given, but this "
+                     "format std::string doesn't contain all of $0 through $9");
+#endif  // ABSL_BAD_CALL_IF
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_SUBSTITUTE_H_
diff --git a/absl/strings/substitute_test.cc b/absl/strings/substitute_test.cc
new file mode 100644
index 0000000..e27abb1
--- /dev/null
+++ b/absl/strings/substitute_test.cc
@@ -0,0 +1,204 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/substitute.h"
+
+#include <cstdint>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "absl/strings/str_cat.h"
+
+namespace {
+
+TEST(SubstituteTest, Substitute) {
+  // Basic.
+  EXPECT_EQ("Hello, world!", absl::Substitute("$0, $1!", "Hello", "world"));
+
+  // Non-char* types.
+  EXPECT_EQ("123 0.2 0.1 foo true false x",
+            absl::Substitute("$0 $1 $2 $3 $4 $5 $6", 123, 0.2, 0.1f,
+                             std::string("foo"), true, false, 'x'));
+
+  // All int types.
+  EXPECT_EQ(
+      "-32767 65535 "
+      "-1234567890 3234567890 "
+      "-1234567890 3234567890 "
+      "-1234567890123456789 9234567890123456789",
+      absl::Substitute(
+          "$0 $1 $2 $3 $4 $5 $6 $7",
+          static_cast<short>(-32767),          // NOLINT(runtime/int)
+          static_cast<unsigned short>(65535),  // NOLINT(runtime/int)
+          -1234567890, 3234567890U, -1234567890L, 3234567890UL,
+          -int64_t{1234567890123456789}, uint64_t{9234567890123456789u}));
+
+  // Hex format
+  EXPECT_EQ("0 1 f ffff0ffff 0123456789abcdef",
+            absl::Substitute("$0$1$2$3$4 $5",  //
+                             absl::Hex(0), absl::Hex(1, absl::kSpacePad2),
+                             absl::Hex(0xf, absl::kSpacePad2),
+                             absl::Hex(int16_t{-1}, absl::kSpacePad5),
+                             absl::Hex(int16_t{-1}, absl::kZeroPad5),
+                             absl::Hex(0x123456789abcdef, absl::kZeroPad16)));
+
+  // Dec format
+  EXPECT_EQ("0 115   -1-0001 81985529216486895",
+            absl::Substitute("$0$1$2$3$4 $5",  //
+                             absl::Dec(0), absl::Dec(1, absl::kSpacePad2),
+                             absl::Dec(0xf, absl::kSpacePad2),
+                             absl::Dec(int16_t{-1}, absl::kSpacePad5),
+                             absl::Dec(int16_t{-1}, absl::kZeroPad5),
+                             absl::Dec(0x123456789abcdef, absl::kZeroPad16)));
+
+  // Pointer.
+  const int* int_p = reinterpret_cast<const int*>(0x12345);
+  std::string str = absl::Substitute("$0", int_p);
+  EXPECT_EQ(absl::StrCat("0x", absl::Hex(int_p)), str);
+
+  // Volatile Pointer.
+  // Like C++ streamed I/O, such pointers implicitly become bool
+  volatile int vol = 237;
+  volatile int *volatile volptr = &vol;
+  str = absl::Substitute("$0", volptr);
+  EXPECT_EQ("true", str);
+
+  // null is special. StrCat prints 0x0. Substitute prints NULL.
+  const uint64_t* null_p = nullptr;
+  str = absl::Substitute("$0", null_p);
+  EXPECT_EQ("NULL", str);
+
+  // char* is also special.
+  const char* char_p = "print me";
+  str = absl::Substitute("$0", char_p);
+  EXPECT_EQ("print me", str);
+
+  char char_buf[16];
+  strncpy(char_buf, "print me too", sizeof(char_buf));
+  str = absl::Substitute("$0", char_buf);
+  EXPECT_EQ("print me too", str);
+
+  // null char* is "doubly" special. Represented as the empty std::string.
+  char_p = nullptr;
+  str = absl::Substitute("$0", char_p);
+  EXPECT_EQ("", str);
+
+  // Out-of-order.
+  EXPECT_EQ("b, a, c, b", absl::Substitute("$1, $0, $2, $1", "a", "b", "c"));
+
+  // Literal $
+  EXPECT_EQ("$", absl::Substitute("$$"));
+
+  EXPECT_EQ("$1", absl::Substitute("$$1"));
+
+  // Test all overloads.
+  EXPECT_EQ("a", absl::Substitute("$0", "a"));
+  EXPECT_EQ("a b", absl::Substitute("$0 $1", "a", "b"));
+  EXPECT_EQ("a b c", absl::Substitute("$0 $1 $2", "a", "b", "c"));
+  EXPECT_EQ("a b c d", absl::Substitute("$0 $1 $2 $3", "a", "b", "c", "d"));
+  EXPECT_EQ("a b c d e",
+            absl::Substitute("$0 $1 $2 $3 $4", "a", "b", "c", "d", "e"));
+  EXPECT_EQ("a b c d e f", absl::Substitute("$0 $1 $2 $3 $4 $5", "a", "b", "c",
+                                            "d", "e", "f"));
+  EXPECT_EQ("a b c d e f g", absl::Substitute("$0 $1 $2 $3 $4 $5 $6", "a", "b",
+                                              "c", "d", "e", "f", "g"));
+  EXPECT_EQ("a b c d e f g h",
+            absl::Substitute("$0 $1 $2 $3 $4 $5 $6 $7", "a", "b", "c", "d", "e",
+                             "f", "g", "h"));
+  EXPECT_EQ("a b c d e f g h i",
+            absl::Substitute("$0 $1 $2 $3 $4 $5 $6 $7 $8", "a", "b", "c", "d",
+                             "e", "f", "g", "h", "i"));
+  EXPECT_EQ("a b c d e f g h i j",
+            absl::Substitute("$0 $1 $2 $3 $4 $5 $6 $7 $8 $9", "a", "b", "c",
+                             "d", "e", "f", "g", "h", "i", "j"));
+  EXPECT_EQ("a b c d e f g h i j b0",
+            absl::Substitute("$0 $1 $2 $3 $4 $5 $6 $7 $8 $9 $10", "a", "b", "c",
+                             "d", "e", "f", "g", "h", "i", "j"));
+
+  const char* null_cstring = nullptr;
+  EXPECT_EQ("Text: ''", absl::Substitute("Text: '$0'", null_cstring));
+}
+
+TEST(SubstituteTest, SubstituteAndAppend) {
+  std::string str = "Hello";
+  absl::SubstituteAndAppend(&str, ", $0!", "world");
+  EXPECT_EQ("Hello, world!", str);
+
+  // Test all overloads.
+  str.clear();
+  absl::SubstituteAndAppend(&str, "$0", "a");
+  EXPECT_EQ("a", str);
+  str.clear();
+  absl::SubstituteAndAppend(&str, "$0 $1", "a", "b");
+  EXPECT_EQ("a b", str);
+  str.clear();
+  absl::SubstituteAndAppend(&str, "$0 $1 $2", "a", "b", "c");
+  EXPECT_EQ("a b c", str);
+  str.clear();
+  absl::SubstituteAndAppend(&str, "$0 $1 $2 $3", "a", "b", "c", "d");
+  EXPECT_EQ("a b c d", str);
+  str.clear();
+  absl::SubstituteAndAppend(&str, "$0 $1 $2 $3 $4", "a", "b", "c", "d", "e");
+  EXPECT_EQ("a b c d e", str);
+  str.clear();
+  absl::SubstituteAndAppend(&str, "$0 $1 $2 $3 $4 $5", "a", "b", "c", "d", "e",
+                            "f");
+  EXPECT_EQ("a b c d e f", str);
+  str.clear();
+  absl::SubstituteAndAppend(&str, "$0 $1 $2 $3 $4 $5 $6", "a", "b", "c", "d",
+                            "e", "f", "g");
+  EXPECT_EQ("a b c d e f g", str);
+  str.clear();
+  absl::SubstituteAndAppend(&str, "$0 $1 $2 $3 $4 $5 $6 $7", "a", "b", "c", "d",
+                            "e", "f", "g", "h");
+  EXPECT_EQ("a b c d e f g h", str);
+  str.clear();
+  absl::SubstituteAndAppend(&str, "$0 $1 $2 $3 $4 $5 $6 $7 $8", "a", "b", "c",
+                            "d", "e", "f", "g", "h", "i");
+  EXPECT_EQ("a b c d e f g h i", str);
+  str.clear();
+  absl::SubstituteAndAppend(&str, "$0 $1 $2 $3 $4 $5 $6 $7 $8 $9", "a", "b",
+                            "c", "d", "e", "f", "g", "h", "i", "j");
+  EXPECT_EQ("a b c d e f g h i j", str);
+}
+
+TEST(SubstituteTest, VectorBoolRef) {
+  std::vector<bool> v = {true, false};
+  const auto& cv = v;
+  EXPECT_EQ("true false true false",
+            absl::Substitute("$0 $1 $2 $3", v[0], v[1], cv[0], cv[1]));
+
+  std::string str = "Logic be like: ";
+  absl::SubstituteAndAppend(&str, "$0 $1 $2 $3", v[0], v[1], cv[0], cv[1]);
+  EXPECT_EQ("Logic be like: true false true false", str);
+}
+
+#ifdef GTEST_HAS_DEATH_TEST
+
+TEST(SubstituteDeathTest, SubstituteDeath) {
+  EXPECT_DEBUG_DEATH(
+      static_cast<void>(absl::Substitute(absl::string_view("-$2"), "a", "b")),
+      "Invalid strings::Substitute\\(\\) format std::string: asked for \"\\$2\", "
+      "but only 2 args were given.");
+  EXPECT_DEBUG_DEATH(
+      static_cast<void>(absl::Substitute("-$z-")),
+      "Invalid strings::Substitute\\(\\) format std::string: \"-\\$z-\"");
+  EXPECT_DEBUG_DEATH(
+      static_cast<void>(absl::Substitute("-$")),
+      "Invalid strings::Substitute\\(\\) format std::string: \"-\\$\"");
+}
+
+#endif  // GTEST_HAS_DEATH_TEST
+
+}  // namespace
diff --git a/absl/strings/testdata/getline-1.txt b/absl/strings/testdata/getline-1.txt
new file mode 100644
index 0000000..19b9097
--- /dev/null
+++ b/absl/strings/testdata/getline-1.txt
@@ -0,0 +1,3 @@
+alpha
+
+beta gamma
diff --git a/absl/strings/testdata/getline-2.txt b/absl/strings/testdata/getline-2.txt
new file mode 100644
index 0000000..d6842d8
--- /dev/null
+++ b/absl/strings/testdata/getline-2.txt
@@ -0,0 +1 @@
+one.two.three