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diff --git a/absl/strings/internal/fastmem_test.cc b/absl/strings/internal/fastmem_test.cc
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+++ b/absl/strings/internal/fastmem_test.cc
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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
+//
+//      http://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/fastmem.h"
+
+#include <memory>
+#include <random>
+#include <string>
+
+#include "base/init_google.h"
+#include "base/logging.h"
+#include "testing/base/public/benchmark.h"
+#include "gtest/gtest.h"
+
+namespace {
+
+using RandomEngine = std::minstd_rand0;
+
+void VerifyResults(const int r1, const int r2, const std::string& a,
+                   const std::string& b) {
+  CHECK_EQ(a.size(), b.size());
+  if (r1 == 0) {
+    EXPECT_EQ(r2, 0) << a << " " << b;
+  } else if (r1 > 0) {
+    EXPECT_GT(r2, 0) << a << " " << b;
+  } else {
+    EXPECT_LT(r2, 0) << a << " " << b;
+  }
+  if ((r1 == 0) == (r2 == 0)) {
+    EXPECT_EQ(r1 == 0,
+              absl::strings_internal::memeq(a.data(), b.data(), a.size()))
+        << r1 << " " << a << " " << b;
+  }
+}
+
+// Check correctness against glibc's memcmp implementation
+void CheckSingle(const std::string& a, const std::string& b) {
+  CHECK_EQ(a.size(), b.size());
+  const int r1 = memcmp(a.data(), b.data(), a.size());
+  const int r2 =
+      absl::strings_internal::fastmemcmp_inlined(a.data(), b.data(), a.size());
+  VerifyResults(r1, r2, a, b);
+}
+
+void GenerateString(size_t len, std::string* s) {
+  s->clear();
+  for (int i = 0; i < len; i++) {
+    *s += ('a' + (i % 26));
+  }
+}
+
+void CheckCompare(const std::string& a, const std::string& b) {
+  CheckSingle(a, b);
+  for (int common = 0; common <= 32; common++) {
+    std::string extra;
+    GenerateString(common, &extra);
+    CheckSingle(extra + a, extra + b);
+    CheckSingle(a + extra, b + extra);
+    for (char c1 = 'a'; c1 <= 'c'; c1++) {
+      for (char c2 = 'a'; c2 <= 'c'; c2++) {
+        CheckSingle(extra + c1 + a, extra + c2 + b);
+      }
+    }
+  }
+}
+
+TEST(FastCompare, Misc) {
+  CheckCompare("", "");
+
+  CheckCompare("a", "a");
+  CheckCompare("ab", "ab");
+  CheckCompare("abc", "abc");
+  CheckCompare("abcd", "abcd");
+  CheckCompare("abcde", "abcde");
+
+  CheckCompare("a", "x");
+  CheckCompare("ab", "xb");
+  CheckCompare("abc", "xbc");
+  CheckCompare("abcd", "xbcd");
+  CheckCompare("abcde", "xbcde");
+
+  CheckCompare("x", "a");
+  CheckCompare("xb", "ab");
+  CheckCompare("xbc", "abc");
+  CheckCompare("xbcd", "abcd");
+  CheckCompare("xbcde", "abcde");
+
+  CheckCompare("a", "x");
+  CheckCompare("ab", "ax");
+  CheckCompare("abc", "abx");
+  CheckCompare("abcd", "abcx");
+  CheckCompare("abcde", "abcdx");
+
+  CheckCompare("x", "a");
+  CheckCompare("ax", "ab");
+  CheckCompare("abx", "abc");
+  CheckCompare("abcx", "abcd");
+  CheckCompare("abcdx", "abcde");
+
+  for (int len = 0; len < 1000; len++) {
+    std::string p(len, 'z');
+    CheckCompare(p + "x", p + "a");
+    CheckCompare(p + "ax", p + "ab");
+    CheckCompare(p + "abx", p + "abc");
+    CheckCompare(p + "abcx", p + "abcd");
+    CheckCompare(p + "abcdx", p + "abcde");
+  }
+}
+
+TEST(FastCompare, TrailingByte) {
+  for (int i = 0; i < 256; i++) {
+    for (int j = 0; j < 256; j++) {
+      std::string a(1, i);
+      std::string b(1, j);
+      CheckSingle(a, b);
+    }
+  }
+}
+
+// Check correctness of memcpy_inlined.
+void CheckSingleMemcpyInlined(const std::string& a) {
+  std::unique_ptr<char[]> destination(new char[a.size() + 2]);
+  destination[0] = 'x';
+  destination[a.size() + 1] = 'x';
+  absl::strings_internal::memcpy_inlined(destination.get() + 1, a.data(),
+                                         a.size());
+  CHECK_EQ('x', destination[0]);
+  CHECK_EQ('x', destination[a.size() + 1]);
+  CHECK_EQ(0, memcmp(a.data(), destination.get() + 1, a.size()));
+}
+
+TEST(MemCpyInlined, Misc) {
+  CheckSingleMemcpyInlined("");
+  CheckSingleMemcpyInlined("0");
+  CheckSingleMemcpyInlined("012");
+  CheckSingleMemcpyInlined("0123");
+  CheckSingleMemcpyInlined("01234");
+  CheckSingleMemcpyInlined("012345");
+  CheckSingleMemcpyInlined("0123456");
+  CheckSingleMemcpyInlined("01234567");
+  CheckSingleMemcpyInlined("012345678");
+  CheckSingleMemcpyInlined("0123456789");
+  CheckSingleMemcpyInlined("0123456789a");
+  CheckSingleMemcpyInlined("0123456789ab");
+  CheckSingleMemcpyInlined("0123456789abc");
+  CheckSingleMemcpyInlined("0123456789abcd");
+  CheckSingleMemcpyInlined("0123456789abcde");
+  CheckSingleMemcpyInlined("0123456789abcdef");
+  CheckSingleMemcpyInlined("0123456789abcdefg");
+}
+
+template <typename Function>
+inline void CopyLoop(benchmark::State& state, int size, Function func) {
+  char* src = new char[size];
+  char* dst = new char[size];
+  memset(src, 'x', size);
+  memset(dst, 'y', size);
+  for (auto _ : state) {
+    func(dst, src, size);
+  }
+  state.SetBytesProcessed(static_cast<int64_t>(state.iterations()) * size);
+  CHECK_EQ(dst[0], 'x');
+  delete[] src;
+  delete[] dst;
+}
+
+void BM_memcpy(benchmark::State& state) {
+  CopyLoop(state, state.range(0), memcpy);
+}
+BENCHMARK(BM_memcpy)->DenseRange(1, 18)->Range(32, 8 << 20);
+
+void BM_memcpy_inlined(benchmark::State& state) {
+  CopyLoop(state, state.range(0), absl::strings_internal::memcpy_inlined);
+}
+BENCHMARK(BM_memcpy_inlined)->DenseRange(1, 18)->Range(32, 8 << 20);
+
+// unaligned memcpy
+void BM_unaligned_memcpy(benchmark::State& state) {
+  const int n = state.range(0);
+  const int kMaxOffset = 32;
+  char* src = new char[n + kMaxOffset];
+  char* dst = new char[n + kMaxOffset];
+  memset(src, 'x', n + kMaxOffset);
+  int r = 0, i = 0;
+  for (auto _ : state) {
+    memcpy(dst + (i % kMaxOffset), src + ((i + 5) % kMaxOffset), n);
+    r += dst[0];
+    ++i;
+  }
+  state.SetBytesProcessed(static_cast<int64_t>(state.iterations()) * n);
+  delete[] src;
+  delete[] dst;
+  benchmark::DoNotOptimize(r);
+}
+BENCHMARK(BM_unaligned_memcpy)->DenseRange(1, 18)->Range(32, 8 << 20);
+
+// memmove worst case: heavy overlap, but not always by the same amount.
+// Also, the source and destination will often be unaligned.
+void BM_memmove_worst_case(benchmark::State& state) {
+  const int n = state.range(0);
+  const int32_t kDeterministicSeed = 301;
+  const int kMaxOffset = 32;
+  char* src = new char[n + kMaxOffset];
+  memset(src, 'x', n + kMaxOffset);
+  size_t offsets[64];
+  RandomEngine rng(kDeterministicSeed);
+  std::uniform_int_distribution<size_t> random_to_max_offset(0, kMaxOffset);
+  for (size_t& offset : offsets) {
+    offset = random_to_max_offset(rng);
+  }
+  int r = 0, i = 0;
+  for (auto _ : state) {
+    memmove(src + offsets[i], src + offsets[i + 1], n);
+    r += src[0];
+    i = (i + 2) % arraysize(offsets);
+  }
+  state.SetBytesProcessed(static_cast<int64_t>(state.iterations()) * n);
+  delete[] src;
+  benchmark::DoNotOptimize(r);
+}
+BENCHMARK(BM_memmove_worst_case)->DenseRange(1, 18)->Range(32, 8 << 20);
+
+// memmove cache-friendly: aligned and overlapping with 4k
+// between the source and destination addresses.
+void BM_memmove_cache_friendly(benchmark::State& state) {
+  const int n = state.range(0);
+  char* src = new char[n + 4096];
+  memset(src, 'x', n);
+  int r = 0;
+  while (state.KeepRunningBatch(2)) {  // count each memmove as an iteration
+    memmove(src + 4096, src, n);
+    memmove(src, src + 4096, n);
+    r += src[0];
+  }
+  state.SetBytesProcessed(static_cast<int64_t>(state.iterations()) * n);
+  delete[] src;
+  benchmark::DoNotOptimize(r);
+}
+BENCHMARK(BM_memmove_cache_friendly)
+    ->Arg(5 * 1024)
+    ->Arg(10 * 1024)
+    ->Range(16 << 10, 8 << 20);
+
+// memmove best(?) case: aligned and non-overlapping.
+void BM_memmove_aligned_non_overlapping(benchmark::State& state) {
+  CopyLoop(state, state.range(0), memmove);
+}
+BENCHMARK(BM_memmove_aligned_non_overlapping)
+    ->DenseRange(1, 18)
+    ->Range(32, 8 << 20);
+
+// memset speed
+void BM_memset(benchmark::State& state) {
+  const int n = state.range(0);
+  char* dst = new char[n];
+  int r = 0;
+  for (auto _ : state) {
+    memset(dst, 'x', n);
+    r += dst[0];
+  }
+  state.SetBytesProcessed(static_cast<int64_t>(state.iterations()) * n);
+  delete[] dst;
+  benchmark::DoNotOptimize(r);
+}
+BENCHMARK(BM_memset)->Range(8, 4096 << 10);
+
+// Bandwidth (vectorization?) test: the ideal generated code will be limited
+// by memory bandwidth.  Even so-so generated code will max out memory bandwidth
+// on some machines.
+void BM_membandwidth(benchmark::State& state) {
+  const int n = state.range(0);
+  CHECK_EQ(n % 32, 0);  // We will read 32 bytes per iter.
+  char* dst = new char[n];
+  int r = 0;
+  for (auto _ : state) {
+    const uint32_t* p = reinterpret_cast<uint32_t*>(dst);
+    const uint32_t* limit = reinterpret_cast<uint32_t*>(dst + n);
+    uint32_t x = 0;
+    while (p < limit) {
+      x += p[0];
+      x += p[1];
+      x += p[2];
+      x += p[3];
+      x += p[4];
+      x += p[5];
+      x += p[6];
+      x += p[7];
+      p += 8;
+    }
+    r += x;
+  }
+  state.SetBytesProcessed(static_cast<int64_t>(state.iterations()) * n);
+  delete[] dst;
+  benchmark::DoNotOptimize(r);
+}
+BENCHMARK(BM_membandwidth)->Range(32, 16384 << 10);
+
+// Helper for benchmarks.  Repeatedly compares two strings that are
+// either equal or different only in one character.  If test_equal_strings
+// is false then position_to_modify determines where the difference will be.
+template <typename Function>
+ABSL_ATTRIBUTE_ALWAYS_INLINE inline void StringCompareLoop(
+    benchmark::State& state, bool test_equal_strings,
+    std::string::size_type position_to_modify, int size, Function func) {
+  const int kIterMult = 4;  // Iteration multiplier for better timing resolution
+  CHECK_GT(size, 0);
+  const bool position_to_modify_is_valid =
+      position_to_modify != std::string::npos && position_to_modify < size;
+  CHECK_NE(position_to_modify_is_valid, test_equal_strings);
+  if (!position_to_modify_is_valid) {
+    position_to_modify = 0;
+  }
+  std::string sa(size, 'a');
+  std::string sb = sa;
+  char last = sa[size - 1];
+  int num = 0;
+  for (auto _ : state) {
+    for (int i = 0; i < kIterMult; ++i) {
+      sb[position_to_modify] = test_equal_strings ? last : last ^ 1;
+      num += func(sa, sb);
+    }
+  }
+  state.SetBytesProcessed(static_cast<int64_t>(state.iterations()) * size);
+  benchmark::DoNotOptimize(num);
+}
+
+// Helper for benchmarks.  Repeatedly compares two memory regions that are
+// either equal or different only in their final character.
+template <typename Function>
+ABSL_ATTRIBUTE_ALWAYS_INLINE inline void CompareLoop(benchmark::State& state,
+                                                     bool test_equal_strings,
+                                                     int size, Function func) {
+  const int kIterMult = 4;  // Iteration multiplier for better timing resolution
+  CHECK_GT(size, 0);
+  char* data = static_cast<char*>(malloc(size * 2));
+  memset(data, 'a', size * 2);
+  char* a = data;
+  char* b = data + size;
+  char last = a[size - 1];
+  int num = 0;
+  for (auto _ : state) {
+    for (int i = 0; i < kIterMult; ++i) {
+      b[size - 1] = test_equal_strings ? last : last ^ 1;
+      num += func(a, b, size);
+    }
+  }
+  state.SetBytesProcessed(static_cast<int64_t>(state.iterations()) * size);
+  benchmark::DoNotOptimize(num);
+  free(data);
+}
+
+void BM_memcmp(benchmark::State& state) {
+  CompareLoop(state, false, state.range(0), memcmp);
+}
+BENCHMARK(BM_memcmp)->DenseRange(1, 9)->Range(32, 8 << 20);
+
+void BM_fastmemcmp_inlined(benchmark::State& state) {
+  CompareLoop(state, false, state.range(0),
+              absl::strings_internal::fastmemcmp_inlined);
+}
+BENCHMARK(BM_fastmemcmp_inlined)->DenseRange(1, 9)->Range(32, 8 << 20);
+
+void BM_memeq(benchmark::State& state) {
+  CompareLoop(state, false, state.range(0), absl::strings_internal::memeq);
+}
+BENCHMARK(BM_memeq)->DenseRange(1, 9)->Range(32, 8 << 20);
+
+void BM_memeq_equal(benchmark::State& state) {
+  CompareLoop(state, true, state.range(0), absl::strings_internal::memeq);
+}
+BENCHMARK(BM_memeq_equal)->DenseRange(1, 9)->Range(32, 8 << 20);
+
+bool StringLess(const std::string& x, const std::string& y) { return x < y; }
+bool StringEqual(const std::string& x, const std::string& y) { return x == y; }
+bool StdEqual(const std::string& x, const std::string& y) {
+  return x.size() == y.size() &&
+         std::equal(x.data(), x.data() + x.size(), y.data());
+}
+
+// Benchmark for x < y, where x and y are strings that differ in only their
+// final char.  That should be more-or-less the worst case for <.
+void BM_string_less(benchmark::State& state) {
+  StringCompareLoop(state, false, state.range(0) - 1, state.range(0),
+                    StringLess);
+}
+BENCHMARK(BM_string_less)->DenseRange(1, 9)->Range(32, 1 << 20);
+
+// Benchmark for x < y, where x and y are strings that differ in only their
+// first char.  That should be more-or-less the best case for <.
+void BM_string_less_easy(benchmark::State& state) {
+  StringCompareLoop(state, false, 0, state.range(0), StringLess);
+}
+BENCHMARK(BM_string_less_easy)->DenseRange(1, 9)->Range(32, 1 << 20);
+
+void BM_string_equal(benchmark::State& state) {
+  StringCompareLoop(state, false, state.range(0) - 1, state.range(0),
+                    StringEqual);
+}
+BENCHMARK(BM_string_equal)->DenseRange(1, 9)->Range(32, 1 << 20);
+
+void BM_string_equal_equal(benchmark::State& state) {
+  StringCompareLoop(state, true, std::string::npos, state.range(0), StringEqual);
+}
+BENCHMARK(BM_string_equal_equal)->DenseRange(1, 9)->Range(32, 1 << 20);
+
+void BM_std_equal(benchmark::State& state) {
+  StringCompareLoop(state, false, state.range(0) - 1, state.range(0), StdEqual);
+}
+BENCHMARK(BM_std_equal)->DenseRange(1, 9)->Range(32, 1 << 20);
+
+void BM_std_equal_equal(benchmark::State& state) {
+  StringCompareLoop(state, true, std::string::npos, state.range(0), StdEqual);
+}
+BENCHMARK(BM_std_equal_equal)->DenseRange(1, 9)->Range(32, 1 << 20);
+
+void BM_string_equal_unequal_lengths(benchmark::State& state) {
+  const int size = state.range(0);
+  std::string a(size, 'a');
+  std::string b(size + 1, 'a');
+  int count = 0;
+  for (auto _ : state) {
+    b[size - 1] = 'a';
+    count += (a == b);
+  }
+  benchmark::DoNotOptimize(count);
+}
+BENCHMARK(BM_string_equal_unequal_lengths)->Arg(1)->Arg(1 << 20);
+
+void BM_stdstring_equal_unequal_lengths(benchmark::State& state) {
+  const int size = state.range(0);
+  std::string a(size, 'a');
+  std::string b(size + 1, 'a');
+  int count = 0;
+  for (auto _ : state) {
+    b[size - 1] = 'a';
+    count += (a == b);
+  }
+  benchmark::DoNotOptimize(count);
+}
+BENCHMARK(BM_stdstring_equal_unequal_lengths)->Arg(1)->Arg(1 << 20);
+
+}  // namespace