diff --git a/absl/strings/internal/utf8.h b/absl/strings/internal/utf8.h
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+// 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_