Cleanup `//absl/strings/internal/memutil.h`

`memmatch()` is only used in `string_view.cc`, so move it there.
The moving of `memmatch()` to `string_view.cc` decouples `string_view`
from `memutil`, which will allow us to move `string_view` into its
own target in a followup.

The only other function that is used is `memcasecmp()`, so delete
all other functions.

PiperOrigin-RevId: 547238386
Change-Id: Id6fad47dd24191c8e8f26dd923fffa1007c8db4a

5 files changed, 34 insertions, 528 deletions

diff --git a/absl/strings/internal/memutil.cc b/absl/strings/internal/memutil.cc
index 44996a75..e2e7347c 100644
--- a/absl/strings/internal/memutil.cc
+++ b/absl/strings/internal/memutil.cc
@@ -16,6 +16,8 @@
 
 #include <cstdlib>
 
+#include "absl/strings/ascii.h"
+
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace strings_internal {
@@ -33,83 +35,6 @@ int memcasecmp(const char* s1, const char* s2, size_t len) {
   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 static_cast<size_t>(p - 1 - s);
-  for (spanp = accept; (sc = *spanp++) != '\0';)
-    if (sc == c) goto cont;
-  return static_cast<size_t>(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 static_cast<size_t>(p - 1 - s);
-  }
-  return static_cast<size_t>(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], static_cast<size_t>(hayend - phaystack))))) {
-    if (memcmp(match, pneedle, neelen) == 0)
-      return match;
-    else
-      phaystack = match + 1;
-  }
-  return nullptr;
-}
-
 }  // namespace strings_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
diff --git a/absl/strings/internal/memutil.h b/absl/strings/internal/memutil.h
index 9ad05358..b5911a01 100644
--- a/absl/strings/internal/memutil.h
+++ b/absl/strings/internal/memutil.h
@@ -14,51 +14,6 @@
 // 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_
 
@@ -72,74 +27,11 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 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));
-}
-
+// Performs a byte-by-byte comparison of `len` bytes of the strings `s1` and
+// `s2`, ignoring the case of the characters. It returns an integer less than,
+// equal to, or greater than zero if `s1` is found, respectively, to be less
+// than, to match, or be greater than `s2`.
 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
 ABSL_NAMESPACE_END
diff --git a/absl/strings/internal/memutil_benchmark.cc b/absl/strings/internal/memutil_benchmark.cc
index dc95c3e5..61e323a4 100644
--- a/absl/strings/internal/memutil_benchmark.cc
+++ b/absl/strings/internal/memutil_benchmark.cc
@@ -25,62 +25,6 @@
 // - 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 {
 
@@ -94,96 +38,10 @@ const char* MakeHaystack() {
 }
 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,
@@ -241,34 +99,6 @@ const char* memcasematch(const char* phaystack, size_t haylen,
   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));
@@ -295,29 +125,4 @@ void BM_MemcasematchPathological(benchmark::State& state) {
 }
 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
index d8681ddf..277be2c4 100644
--- a/absl/strings/internal/memutil_test.cc
+++ b/absl/strings/internal/memutil_test.cc
@@ -19,42 +19,12 @@
 #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) {
+TEST(MemUtil, memcasecmp) {
   // 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);
+  const char a[] = "hello there";
 
   EXPECT_EQ(absl::strings_internal::memcasecmp(a, "heLLO there",
                                                sizeof("hello there") - 1),
@@ -66,114 +36,6 @@ TEST(MemUtilTest, AllTests) {
                                                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/string_view.cc b/absl/strings/string_view.cc
index e2261625..f20ff530 100644
--- a/absl/strings/string_view.cc
+++ b/absl/strings/string_view.cc
@@ -21,12 +21,35 @@
 #include <cstring>
 #include <ostream>
 
-#include "absl/strings/internal/memutil.h"
-
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 
 namespace {
+
+// This is significantly faster for case-sensitive matches with very
+// few possible matches.
+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], static_cast<size_t>(hayend - phaystack))))) {
+    if (memcmp(match, pneedle, neelen) == 0)
+      return match;
+    else
+      phaystack = match + 1;
+  }
+  return nullptr;
+}
+
 void WritePadding(std::ostream& o, size_t pad) {
   char fill_buf[32];
   memset(fill_buf, o.fill(), sizeof(fill_buf));
@@ -84,8 +107,7 @@ string_view::size_type string_view::find(string_view s,
     if (empty() && pos == 0 && s.empty()) return 0;
     return npos;
   }
-  const char* result =
-      strings_internal::memmatch(ptr_ + pos, length_ - pos, s.ptr_, s.length_);
+  const char* result = memmatch(ptr_ + pos, length_ - pos, s.ptr_, s.length_);
   return result ? static_cast<size_type>(result - ptr_) : npos;
 }