diff --git a/absl/numeric/int128_test.cc b/absl/numeric/int128_test.cc
new file mode 100644
index 0000000..5e1b5ec
--- /dev/null
+++ b/absl/numeric/int128_test.cc
@@ -0,0 +1,482 @@
+// 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/numeric/int128.h"
+
+#include <algorithm>
+#include <limits>
+#include <random>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "absl/base/internal/cycleclock.h"
+#include "absl/hash/hash_testing.h"
+#include "absl/meta/type_traits.h"
+
+#if defined(_MSC_VER) && _MSC_VER == 1900
+// Disable "unary minus operator applied to unsigned type" warnings in Microsoft
+// Visual C++ 14 (2015).
+#pragma warning(disable:4146)
+#endif
+
+namespace {
+
+template <typename T>
+class Uint128IntegerTraitsTest : public ::testing::Test {};
+typedef ::testing::Types<bool, char, signed char, unsigned char, char16_t,
+                         char32_t, wchar_t,
+                         short,           // NOLINT(runtime/int)
+                         unsigned short,  // NOLINT(runtime/int)
+                         int, unsigned int,
+                         long,                // NOLINT(runtime/int)
+                         unsigned long,       // NOLINT(runtime/int)
+                         long long,           // NOLINT(runtime/int)
+                         unsigned long long>  // NOLINT(runtime/int)
+    IntegerTypes;
+
+template <typename T>
+class Uint128FloatTraitsTest : public ::testing::Test {};
+typedef ::testing::Types<float, double, long double> FloatingPointTypes;
+
+TYPED_TEST_SUITE(Uint128IntegerTraitsTest, IntegerTypes);
+
+TYPED_TEST(Uint128IntegerTraitsTest, ConstructAssignTest) {
+  static_assert(std::is_constructible<absl::uint128, TypeParam>::value,
+                "absl::uint128 must be constructible from TypeParam");
+  static_assert(std::is_assignable<absl::uint128&, TypeParam>::value,
+                "absl::uint128 must be assignable from TypeParam");
+  static_assert(!std::is_assignable<TypeParam&, absl::uint128>::value,
+                "TypeParam must not be assignable from absl::uint128");
+}
+
+TYPED_TEST_SUITE(Uint128FloatTraitsTest, FloatingPointTypes);
+
+TYPED_TEST(Uint128FloatTraitsTest, ConstructAssignTest) {
+  static_assert(std::is_constructible<absl::uint128, TypeParam>::value,
+                "absl::uint128 must be constructible from TypeParam");
+  static_assert(!std::is_assignable<absl::uint128&, TypeParam>::value,
+                "absl::uint128 must not be assignable from TypeParam");
+  static_assert(!std::is_assignable<TypeParam&, absl::uint128>::value,
+                "TypeParam must not be assignable from absl::uint128");
+}
+
+#ifdef ABSL_HAVE_INTRINSIC_INT128
+// These type traits done separately as TYPED_TEST requires typeinfo, and not
+// all platforms have this for __int128 even though they define the type.
+TEST(Uint128, IntrinsicTypeTraitsTest) {
+  static_assert(std::is_constructible<absl::uint128, __int128>::value,
+                "absl::uint128 must be constructible from __int128");
+  static_assert(std::is_assignable<absl::uint128&, __int128>::value,
+                "absl::uint128 must be assignable from __int128");
+  static_assert(!std::is_assignable<__int128&, absl::uint128>::value,
+                "__int128 must not be assignable from absl::uint128");
+
+  static_assert(std::is_constructible<absl::uint128, unsigned __int128>::value,
+                "absl::uint128 must be constructible from unsigned __int128");
+  static_assert(std::is_assignable<absl::uint128&, unsigned __int128>::value,
+                "absl::uint128 must be assignable from unsigned __int128");
+  static_assert(!std::is_assignable<unsigned __int128&, absl::uint128>::value,
+                "unsigned __int128 must not be assignable from absl::uint128");
+}
+#endif  // ABSL_HAVE_INTRINSIC_INT128
+
+TEST(Uint128, TrivialTraitsTest) {
+  static_assert(absl::is_trivially_default_constructible<absl::uint128>::value,
+                "");
+  static_assert(absl::is_trivially_copy_constructible<absl::uint128>::value,
+                "");
+  static_assert(absl::is_trivially_copy_assignable<absl::uint128>::value, "");
+  static_assert(std::is_trivially_destructible<absl::uint128>::value, "");
+}
+
+TEST(Uint128, AllTests) {
+  absl::uint128 zero = 0;
+  absl::uint128 one = 1;
+  absl::uint128 one_2arg = absl::MakeUint128(0, 1);
+  absl::uint128 two = 2;
+  absl::uint128 three = 3;
+  absl::uint128 big = absl::MakeUint128(2000, 2);
+  absl::uint128 big_minus_one = absl::MakeUint128(2000, 1);
+  absl::uint128 bigger = absl::MakeUint128(2001, 1);
+  absl::uint128 biggest = absl::Uint128Max();
+  absl::uint128 high_low = absl::MakeUint128(1, 0);
+  absl::uint128 low_high =
+      absl::MakeUint128(0, std::numeric_limits<uint64_t>::max());
+  EXPECT_LT(one, two);
+  EXPECT_GT(two, one);
+  EXPECT_LT(one, big);
+  EXPECT_LT(one, big);
+  EXPECT_EQ(one, one_2arg);
+  EXPECT_NE(one, two);
+  EXPECT_GT(big, one);
+  EXPECT_GE(big, two);
+  EXPECT_GE(big, big_minus_one);
+  EXPECT_GT(big, big_minus_one);
+  EXPECT_LT(big_minus_one, big);
+  EXPECT_LE(big_minus_one, big);
+  EXPECT_NE(big_minus_one, big);
+  EXPECT_LT(big, biggest);
+  EXPECT_LE(big, biggest);
+  EXPECT_GT(biggest, big);
+  EXPECT_GE(biggest, big);
+  EXPECT_EQ(big, ~~big);
+  EXPECT_EQ(one, one | one);
+  EXPECT_EQ(big, big | big);
+  EXPECT_EQ(one, one | zero);
+  EXPECT_EQ(one, one & one);
+  EXPECT_EQ(big, big & big);
+  EXPECT_EQ(zero, one & zero);
+  EXPECT_EQ(zero, big & ~big);
+  EXPECT_EQ(zero, one ^ one);
+  EXPECT_EQ(zero, big ^ big);
+  EXPECT_EQ(one, one ^ zero);
+
+  // Shift operators.
+  EXPECT_EQ(big, big << 0);
+  EXPECT_EQ(big, big >> 0);
+  EXPECT_GT(big << 1, big);
+  EXPECT_LT(big >> 1, big);
+  EXPECT_EQ(big, (big << 10) >> 10);
+  EXPECT_EQ(big, (big >> 1) << 1);
+  EXPECT_EQ(one, (one << 80) >> 80);
+  EXPECT_EQ(zero, (one >> 80) << 80);
+
+  // Shift assignments.
+  absl::uint128 big_copy = big;
+  EXPECT_EQ(big << 0, big_copy <<= 0);
+  big_copy = big;
+  EXPECT_EQ(big >> 0, big_copy >>= 0);
+  big_copy = big;
+  EXPECT_EQ(big << 1, big_copy <<= 1);
+  big_copy = big;
+  EXPECT_EQ(big >> 1, big_copy >>= 1);
+  big_copy = big;
+  EXPECT_EQ(big << 10, big_copy <<= 10);
+  big_copy = big;
+  EXPECT_EQ(big >> 10, big_copy >>= 10);
+  big_copy = big;
+  EXPECT_EQ(big << 64, big_copy <<= 64);
+  big_copy = big;
+  EXPECT_EQ(big >> 64, big_copy >>= 64);
+  big_copy = big;
+  EXPECT_EQ(big << 73, big_copy <<= 73);
+  big_copy = big;
+  EXPECT_EQ(big >> 73, big_copy >>= 73);
+
+  EXPECT_EQ(absl::Uint128High64(biggest), std::numeric_limits<uint64_t>::max());
+  EXPECT_EQ(absl::Uint128Low64(biggest), std::numeric_limits<uint64_t>::max());
+  EXPECT_EQ(zero + one, one);
+  EXPECT_EQ(one + one, two);
+  EXPECT_EQ(big_minus_one + one, big);
+  EXPECT_EQ(one - one, zero);
+  EXPECT_EQ(one - zero, one);
+  EXPECT_EQ(zero - one, biggest);
+  EXPECT_EQ(big - big, zero);
+  EXPECT_EQ(big - one, big_minus_one);
+  EXPECT_EQ(big + std::numeric_limits<uint64_t>::max(), bigger);
+  EXPECT_EQ(biggest + 1, zero);
+  EXPECT_EQ(zero - 1, biggest);
+  EXPECT_EQ(high_low - one, low_high);
+  EXPECT_EQ(low_high + one, high_low);
+  EXPECT_EQ(absl::Uint128High64((absl::uint128(1) << 64) - 1), 0);
+  EXPECT_EQ(absl::Uint128Low64((absl::uint128(1) << 64) - 1),
+            std::numeric_limits<uint64_t>::max());
+  EXPECT_TRUE(!!one);
+  EXPECT_TRUE(!!high_low);
+  EXPECT_FALSE(!!zero);
+  EXPECT_FALSE(!one);
+  EXPECT_FALSE(!high_low);
+  EXPECT_TRUE(!zero);
+  EXPECT_TRUE(zero == 0);       // NOLINT(readability/check)
+  EXPECT_FALSE(zero != 0);      // NOLINT(readability/check)
+  EXPECT_FALSE(one == 0);       // NOLINT(readability/check)
+  EXPECT_TRUE(one != 0);        // NOLINT(readability/check)
+  EXPECT_FALSE(high_low == 0);  // NOLINT(readability/check)
+  EXPECT_TRUE(high_low != 0);   // NOLINT(readability/check)
+
+  absl::uint128 test = zero;
+  EXPECT_EQ(++test, one);
+  EXPECT_EQ(test, one);
+  EXPECT_EQ(test++, one);
+  EXPECT_EQ(test, two);
+  EXPECT_EQ(test -= 2, zero);
+  EXPECT_EQ(test, zero);
+  EXPECT_EQ(test += 2, two);
+  EXPECT_EQ(test, two);
+  EXPECT_EQ(--test, one);
+  EXPECT_EQ(test, one);
+  EXPECT_EQ(test--, one);
+  EXPECT_EQ(test, zero);
+  EXPECT_EQ(test |= three, three);
+  EXPECT_EQ(test &= one, one);
+  EXPECT_EQ(test ^= three, two);
+  EXPECT_EQ(test >>= 1, one);
+  EXPECT_EQ(test <<= 1, two);
+
+  EXPECT_EQ(big, -(-big));
+  EXPECT_EQ(two, -((-one) - 1));
+  EXPECT_EQ(absl::Uint128Max(), -one);
+  EXPECT_EQ(zero, -zero);
+
+  EXPECT_EQ(absl::Uint128Max(), absl::kuint128max);
+}
+
+TEST(Uint128, ConversionTests) {
+  EXPECT_TRUE(absl::MakeUint128(1, 0));
+
+#ifdef ABSL_HAVE_INTRINSIC_INT128
+  unsigned __int128 intrinsic =
+      (static_cast<unsigned __int128>(0x3a5b76c209de76f6) << 64) +
+      0x1f25e1d63a2b46c5;
+  absl::uint128 custom =
+      absl::MakeUint128(0x3a5b76c209de76f6, 0x1f25e1d63a2b46c5);
+
+  EXPECT_EQ(custom, absl::uint128(intrinsic));
+  EXPECT_EQ(custom, absl::uint128(static_cast<__int128>(intrinsic)));
+  EXPECT_EQ(intrinsic, static_cast<unsigned __int128>(custom));
+  EXPECT_EQ(intrinsic, static_cast<__int128>(custom));
+#endif  // ABSL_HAVE_INTRINSIC_INT128
+
+  // verify that an integer greater than 2**64 that can be stored precisely
+  // inside a double is converted to a absl::uint128 without loss of
+  // information.
+  double precise_double = 0x530e * std::pow(2.0, 64.0) + 0xda74000000000000;
+  absl::uint128 from_precise_double(precise_double);
+  absl::uint128 from_precise_ints =
+      absl::MakeUint128(0x530e, 0xda74000000000000);
+  EXPECT_EQ(from_precise_double, from_precise_ints);
+  EXPECT_DOUBLE_EQ(static_cast<double>(from_precise_ints), precise_double);
+
+  double approx_double = 0xffffeeeeddddcccc * std::pow(2.0, 64.0) +
+                         0xbbbbaaaa99998888;
+  absl::uint128 from_approx_double(approx_double);
+  EXPECT_DOUBLE_EQ(static_cast<double>(from_approx_double), approx_double);
+
+  double round_to_zero = 0.7;
+  double round_to_five = 5.8;
+  double round_to_nine = 9.3;
+  EXPECT_EQ(static_cast<absl::uint128>(round_to_zero), 0);
+  EXPECT_EQ(static_cast<absl::uint128>(round_to_five), 5);
+  EXPECT_EQ(static_cast<absl::uint128>(round_to_nine), 9);
+
+  absl::uint128 highest_precision_in_long_double =
+      ~absl::uint128{} >> (128 - std::numeric_limits<long double>::digits);
+  EXPECT_EQ(highest_precision_in_long_double,
+            static_cast<absl::uint128>(
+                static_cast<long double>(highest_precision_in_long_double)));
+  // Apply a mask just to make sure all the bits are the right place.
+  const absl::uint128 arbitrary_mask =
+      absl::MakeUint128(0xa29f622677ded751, 0xf8ca66add076f468);
+  EXPECT_EQ(highest_precision_in_long_double & arbitrary_mask,
+            static_cast<absl::uint128>(static_cast<long double>(
+                highest_precision_in_long_double & arbitrary_mask)));
+
+  EXPECT_EQ(static_cast<absl::uint128>(-0.1L), 0);
+}
+
+TEST(Uint128, OperatorAssignReturnRef) {
+  absl::uint128 v(1);
+  (v += 4) -= 3;
+  EXPECT_EQ(2, v);
+}
+
+TEST(Uint128, Multiply) {
+  absl::uint128 a, b, c;
+
+  // Zero test.
+  a = 0;
+  b = 0;
+  c = a * b;
+  EXPECT_EQ(0, c);
+
+  // Max carries.
+  a = absl::uint128(0) - 1;
+  b = absl::uint128(0) - 1;
+  c = a * b;
+  EXPECT_EQ(1, c);
+
+  // Self-operation with max carries.
+  c = absl::uint128(0) - 1;
+  c *= c;
+  EXPECT_EQ(1, c);
+
+  // 1-bit x 1-bit.
+  for (int i = 0; i < 64; ++i) {
+    for (int j = 0; j < 64; ++j) {
+      a = absl::uint128(1) << i;
+      b = absl::uint128(1) << j;
+      c = a * b;
+      EXPECT_EQ(absl::uint128(1) << (i + j), c);
+    }
+  }
+
+  // Verified with dc.
+  a = absl::MakeUint128(0xffffeeeeddddcccc, 0xbbbbaaaa99998888);
+  b = absl::MakeUint128(0x7777666655554444, 0x3333222211110000);
+  c = a * b;
+  EXPECT_EQ(absl::MakeUint128(0x530EDA741C71D4C3, 0xBF25975319080000), c);
+  EXPECT_EQ(0, c - b * a);
+  EXPECT_EQ(a*a - b*b, (a+b) * (a-b));
+
+  // Verified with dc.
+  a = absl::MakeUint128(0x0123456789abcdef, 0xfedcba9876543210);
+  b = absl::MakeUint128(0x02468ace13579bdf, 0xfdb97531eca86420);
+  c = a * b;
+  EXPECT_EQ(absl::MakeUint128(0x97a87f4f261ba3f2, 0x342d0bbf48948200), c);
+  EXPECT_EQ(0, c - b * a);
+  EXPECT_EQ(a*a - b*b, (a+b) * (a-b));
+}
+
+TEST(Uint128, AliasTests) {
+  absl::uint128 x1 = absl::MakeUint128(1, 2);
+  absl::uint128 x2 = absl::MakeUint128(2, 4);
+  x1 += x1;
+  EXPECT_EQ(x2, x1);
+
+  absl::uint128 x3 = absl::MakeUint128(1, static_cast<uint64_t>(1) << 63);
+  absl::uint128 x4 = absl::MakeUint128(3, 0);
+  x3 += x3;
+  EXPECT_EQ(x4, x3);
+}
+
+TEST(Uint128, DivideAndMod) {
+  using std::swap;
+
+  // a := q * b + r
+  absl::uint128 a, b, q, r;
+
+  // Zero test.
+  a = 0;
+  b = 123;
+  q = a / b;
+  r = a % b;
+  EXPECT_EQ(0, q);
+  EXPECT_EQ(0, r);
+
+  a = absl::MakeUint128(0x530eda741c71d4c3, 0xbf25975319080000);
+  q = absl::MakeUint128(0x4de2cab081, 0x14c34ab4676e4bab);
+  b = absl::uint128(0x1110001);
+  r = absl::uint128(0x3eb455);
+  ASSERT_EQ(a, q * b + r);  // Sanity-check.
+
+  absl::uint128 result_q, result_r;
+  result_q = a / b;
+  result_r = a % b;
+  EXPECT_EQ(q, result_q);
+  EXPECT_EQ(r, result_r);
+
+  // Try the other way around.
+  swap(q, b);
+  result_q = a / b;
+  result_r = a % b;
+  EXPECT_EQ(q, result_q);
+  EXPECT_EQ(r, result_r);
+  // Restore.
+  swap(b, q);
+
+  // Dividend < divisor; result should be q:0 r:<dividend>.
+  swap(a, b);
+  result_q = a / b;
+  result_r = a % b;
+  EXPECT_EQ(0, result_q);
+  EXPECT_EQ(a, result_r);
+  // Try the other way around.
+  swap(a, q);
+  result_q = a / b;
+  result_r = a % b;
+  EXPECT_EQ(0, result_q);
+  EXPECT_EQ(a, result_r);
+  // Restore.
+  swap(q, a);
+  swap(b, a);
+
+  // Try a large remainder.
+  b = a / 2 + 1;
+  absl::uint128 expected_r =
+      absl::MakeUint128(0x29876d3a0e38ea61, 0xdf92cba98c83ffff);
+  // Sanity checks.
+  ASSERT_EQ(a / 2 - 1, expected_r);
+  ASSERT_EQ(a, b + expected_r);
+  result_q = a / b;
+  result_r = a % b;
+  EXPECT_EQ(1, result_q);
+  EXPECT_EQ(expected_r, result_r);
+}
+
+TEST(Uint128, DivideAndModRandomInputs) {
+  const int kNumIters = 1 << 18;
+  std::minstd_rand random(testing::UnitTest::GetInstance()->random_seed());
+  std::uniform_int_distribution<uint64_t> uniform_uint64;
+  for (int i = 0; i < kNumIters; ++i) {
+    const absl::uint128 a =
+        absl::MakeUint128(uniform_uint64(random), uniform_uint64(random));
+    const absl::uint128 b =
+        absl::MakeUint128(uniform_uint64(random), uniform_uint64(random));
+    if (b == 0) {
+      continue;  // Avoid a div-by-zero.
+    }
+    const absl::uint128 q = a / b;
+    const absl::uint128 r = a % b;
+    ASSERT_EQ(a, b * q + r);
+  }
+}
+
+TEST(Uint128, ConstexprTest) {
+  constexpr absl::uint128 zero = absl::uint128();
+  constexpr absl::uint128 one = 1;
+  constexpr absl::uint128 minus_two = -2;
+  EXPECT_EQ(zero, absl::uint128(0));
+  EXPECT_EQ(one, absl::uint128(1));
+  EXPECT_EQ(minus_two, absl::MakeUint128(-1, -2));
+}
+
+TEST(Uint128, NumericLimitsTest) {
+  static_assert(std::numeric_limits<absl::uint128>::is_specialized, "");
+  static_assert(!std::numeric_limits<absl::uint128>::is_signed, "");
+  static_assert(std::numeric_limits<absl::uint128>::is_integer, "");
+  EXPECT_EQ(static_cast<int>(128 * std::log10(2)),
+            std::numeric_limits<absl::uint128>::digits10);
+  EXPECT_EQ(0, std::numeric_limits<absl::uint128>::min());
+  EXPECT_EQ(0, std::numeric_limits<absl::uint128>::lowest());
+  EXPECT_EQ(absl::Uint128Max(), std::numeric_limits<absl::uint128>::max());
+}
+
+TEST(Uint128, Hash) {
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly({
+      // Some simple values
+      absl::uint128{0},
+      absl::uint128{1},
+      ~absl::uint128{},
+      // 64 bit limits
+      absl::uint128{std::numeric_limits<int64_t>::max()},
+      absl::uint128{std::numeric_limits<uint64_t>::max()} + 0,
+      absl::uint128{std::numeric_limits<uint64_t>::max()} + 1,
+      absl::uint128{std::numeric_limits<uint64_t>::max()} + 2,
+      // Keeping high same
+      absl::uint128{1} << 62,
+      absl::uint128{1} << 63,
+      // Keeping low same
+      absl::uint128{1} << 64,
+      absl::uint128{1} << 65,
+      // 128 bit limits
+      std::numeric_limits<absl::uint128>::max(),
+      std::numeric_limits<absl::uint128>::max() - 1,
+      std::numeric_limits<absl::uint128>::min() + 1,
+      std::numeric_limits<absl::uint128>::min(),
+  }));
+}
+
+}  // namespace