Initial Commit

18 files changed, 2960 insertions, 0 deletions

diff --git a/absl/strings/internal/char_map.h b/absl/strings/internal/char_map.h
new file mode 100644
index 000000000000..8d92963a4dea
--- /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
+//
+//      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.
+//
+// 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_test.cc b/absl/strings/internal/char_map_test.cc
new file mode 100644
index 000000000000..2167be975e7d
--- /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
+//
+//      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/char_map.h"
+
+#include <cstdio>
+#include <cstdlib>
+#include <cctype>
+
+#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/escaping_test_common.inc b/absl/strings/internal/escaping_test_common.inc
new file mode 100644
index 000000000000..6f29140e3584
--- /dev/null
+++ b/absl/strings/internal/escaping_test_common.inc
@@ -0,0 +1,113 @@
+// 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.
+//
+// This test contains common things needed by both escaping_test.cc and
+// escaping_benchmark.cc.
+
+namespace {
+
+struct {
+  absl::string_view plaintext;
+  absl::string_view cyphertext;
+} const base64_strings[] = {
+  // 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
+  { "",
+    "" },
+};
+
+}  // namespace
diff --git a/absl/strings/internal/fastmem.h b/absl/strings/internal/fastmem.h
new file mode 100644
index 000000000000..9989b12e34d3
--- /dev/null
+++ b/absl/strings/internal/fastmem.h
@@ -0,0 +1,215 @@
+// 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.
+//
+// Fast memory copying and comparison routines.
+//   strings::fastmemcmp_inlined() replaces memcmp()
+//   strings::memcpy_inlined() replaces memcpy()
+//   strings::memeq(a, b, n) replaces memcmp(a, b, n) == 0
+//
+// strings::*_inlined() routines are inline versions of the
+// routines exported by this module.  Sometimes using the inlined
+// versions is faster.  Measure before using the inlined versions.
+//
+
+#ifndef ABSL_STRINGS_INTERNAL_FASTMEM_H_
+#define ABSL_STRINGS_INTERNAL_FASTMEM_H_
+
+#ifdef __SSE4_1__
+#include <immintrin.h>
+#endif
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstring>
+
+#include "absl/base/internal/unaligned_access.h"
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+
+namespace absl {
+namespace strings_internal {
+
+// Return true if the n bytes at a equal the n bytes at b.
+// The regions are allowed to overlap.
+//
+// The performance is similar to the performance of memcmp(), but faster for
+// moderately-sized inputs, or inputs that share a common prefix and differ
+// somewhere in their last 8 bytes. Further optimizations can be added later
+// if it makes sense to do so.  Alternatively, if the compiler & runtime improve
+// to eliminate the need for this, we can remove it.
+inline bool memeq(const char* a, const char* b, size_t n) {
+  size_t n_rounded_down = n & ~static_cast<size_t>(7);
+  if (ABSL_PREDICT_FALSE(n_rounded_down == 0)) {  // n <= 7
+    return memcmp(a, b, n) == 0;
+  }
+  // n >= 8
+  {
+    uint64_t u =
+        ABSL_INTERNAL_UNALIGNED_LOAD64(a) ^ ABSL_INTERNAL_UNALIGNED_LOAD64(b);
+    uint64_t v = ABSL_INTERNAL_UNALIGNED_LOAD64(a + n - 8) ^
+                 ABSL_INTERNAL_UNALIGNED_LOAD64(b + n - 8);
+    if ((u | v) != 0) {  // The first or last 8 bytes differ.
+      return false;
+    }
+  }
+  // The next line forces n to be a multiple of 8.
+  n = n_rounded_down;
+  if (n >= 80) {
+    // In 2013 or later, this should be fast on long strings.
+    return memcmp(a, b, n) == 0;
+  }
+  // Now force n to be a multiple of 16.  Arguably, a "switch" would be smart
+  // here, but there's a difficult-to-evaluate code size vs. speed issue.  The
+  // current approach often re-compares some bytes (worst case is if n initially
+  // was 16, 32, 48, or 64), but is fairly short.
+  size_t e = n & 8;
+  a += e;
+  b += e;
+  n -= e;
+  // n is now in {0, 16, 32, ...}.  Process 0 or more 16-byte chunks.
+  while (n > 0) {
+#ifdef __SSE4_1__
+    __m128i u =
+        _mm_xor_si128(_mm_loadu_si128(reinterpret_cast<const __m128i*>(a)),
+                      _mm_loadu_si128(reinterpret_cast<const __m128i*>(b)));
+    if (!_mm_test_all_zeros(u, u)) {
+      return false;
+    }
+#else
+    uint64_t x =
+        ABSL_INTERNAL_UNALIGNED_LOAD64(a) ^ ABSL_INTERNAL_UNALIGNED_LOAD64(b);
+    uint64_t y = ABSL_INTERNAL_UNALIGNED_LOAD64(a + 8) ^
+                 ABSL_INTERNAL_UNALIGNED_LOAD64(b + 8);
+    if ((x | y) != 0) {
+      return false;
+    }
+#endif
+    a += 16;
+    b += 16;
+    n -= 16;
+  }
+  return true;
+}
+
+inline int fastmemcmp_inlined(const void* va, const void* vb, size_t n) {
+  const unsigned char* pa = static_cast<const unsigned char*>(va);
+  const unsigned char* pb = static_cast<const unsigned char*>(vb);
+  switch (n) {
+    default:
+      return memcmp(va, vb, n);
+    case 7:
+      if (*pa != *pb) return *pa < *pb ? -1 : +1;
+      ++pa;
+      ++pb;
+      ABSL_FALLTHROUGH_INTENDED;
+    case 6:
+      if (*pa != *pb) return *pa < *pb ? -1 : +1;
+      ++pa;
+      ++pb;
+      ABSL_FALLTHROUGH_INTENDED;
+    case 5:
+      if (*pa != *pb) return *pa < *pb ? -1 : +1;
+      ++pa;
+      ++pb;
+      ABSL_FALLTHROUGH_INTENDED;
+    case 4:
+      if (*pa != *pb) return *pa < *pb ? -1 : +1;
+      ++pa;
+      ++pb;
+      ABSL_FALLTHROUGH_INTENDED;
+    case 3:
+      if (*pa != *pb) return *pa < *pb ? -1 : +1;
+      ++pa;
+      ++pb;
+      ABSL_FALLTHROUGH_INTENDED;
+    case 2:
+      if (*pa != *pb) return *pa < *pb ? -1 : +1;
+      ++pa;
+      ++pb;
+      ABSL_FALLTHROUGH_INTENDED;
+    case 1:
+      if (*pa != *pb) return *pa < *pb ? -1 : +1;
+      ABSL_FALLTHROUGH_INTENDED;
+    case 0:
+      break;
+  }
+  return 0;
+}
+
+// The standard memcpy operation is slow for variable small sizes.
+// This implementation inlines the optimal realization for sizes 1 to 16.
+// To avoid code bloat don't use it in case of not performance-critical spots,
+// nor when you don't expect very frequent values of size <= 16.
+inline void memcpy_inlined(char* dst, const char* src, size_t size) {
+  // Compiler inlines code with minimal amount of data movement when third
+  // parameter of memcpy is a constant.
+  switch (size) {
+    case 1:
+      memcpy(dst, src, 1);
+      break;
+    case 2:
+      memcpy(dst, src, 2);
+      break;
+    case 3:
+      memcpy(dst, src, 3);
+      break;
+    case 4:
+      memcpy(dst, src, 4);
+      break;
+    case 5:
+      memcpy(dst, src, 5);
+      break;
+    case 6:
+      memcpy(dst, src, 6);
+      break;
+    case 7:
+      memcpy(dst, src, 7);
+      break;
+    case 8:
+      memcpy(dst, src, 8);
+      break;
+    case 9:
+      memcpy(dst, src, 9);
+      break;
+    case 10:
+      memcpy(dst, src, 10);
+      break;
+    case 11:
+      memcpy(dst, src, 11);
+      break;
+    case 12:
+      memcpy(dst, src, 12);
+      break;
+    case 13:
+      memcpy(dst, src, 13);
+      break;
+    case 14:
+      memcpy(dst, src, 14);
+      break;
+    case 15:
+      memcpy(dst, src, 15);
+      break;
+    case 16:
+      memcpy(dst, src, 16);
+      break;
+    default:
+      memcpy(dst, src, size);
+      break;
+  }
+}
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_FASTMEM_H_
diff --git a/absl/strings/internal/fastmem_test.cc b/absl/strings/internal/fastmem_test.cc
new file mode 100644
index 000000000000..7c670f967bb3
--- /dev/null
+++ b/absl/strings/internal/fastmem_test.cc
@@ -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
+//
+//      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
diff --git a/absl/strings/internal/memutil.cc b/absl/strings/internal/memutil.cc
new file mode 100644
index 000000000000..a0de70dffdbd
--- /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
+//
+//      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/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 000000000000..a6f1c69138e3
--- /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
+//
+//      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.
+//
+
+// These routines provide mem versions of standard C std::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 std::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 std::string.h, and their mem analogues.
+// Functions in lowercase are defined in std::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_test.cc b/absl/strings/internal/memutil_test.cc
new file mode 100644
index 000000000000..1ff60f20e0bd
--- /dev/null
+++ b/absl/strings/internal/memutil_test.cc
@@ -0,0 +1,180 @@
+// 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.
+
+// Unit test for memutil.cc
+
+#include "absl/strings/internal/memutil.h"
+
+#include <algorithm>
+#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.inc b/absl/strings/internal/numbers_test_common.inc
new file mode 100644
index 000000000000..e165b3bea5c6
--- /dev/null
+++ b/absl/strings/internal/numbers_test_common.inc
@@ -0,0 +1,166 @@
+// 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.
+//
+// This file contains common things needed by numbers_test.cc,
+// numbers_legacy_test.cc and numbers_benchmark.cc.
+
+namespace {
+
+// Previously documented minimum buffer sizes for Fast*ToBuffer functions.
+// NOTE(edk): These should be deleted and uses replaced with kFastToBufferSize
+//            once existing code has been fixed to use kFastToBufferSize.
+enum {
+  kFastInt32ToBufferSize = 12,
+  kFastInt64ToBufferSize = 22,
+  kFastUInt32ToBufferSize = 12,
+  kFastUInt64ToBufferSize = 22
+};
+
+template <typename IntType>
+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;
+} const strtouint32_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},
+};
+
+struct uint64_test_case {
+  const char* str;
+  bool expect_ok;
+  int base;
+  uint64_t expected;
+} const strtouint64_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},
+};
+
+}  // namespace
diff --git a/absl/strings/internal/ostringstream.h b/absl/strings/internal/ostringstream.h
new file mode 100644
index 000000000000..017632a9292e
--- /dev/null
+++ b/absl/strings/internal/ostringstream.h
@@ -0,0 +1,97 @@
+// 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.
+
+#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 = Buf::traits_type::eof()) override {
+    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 xsputn(const char* s, std::streamsize n) override {
+    assert(s_);
+    s_->append(s, n);
+    return n;
+  }
+
+  std::string* s_;
+};
+
+}  // namespace strings_internal
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
diff --git a/absl/strings/internal/ostringstream_test.cc b/absl/strings/internal/ostringstream_test.cc
new file mode 100644
index 000000000000..0047ec822e8b
--- /dev/null
+++ b/absl/strings/internal/ostringstream_test.cc
@@ -0,0 +1,103 @@
+// 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/ostringstream.h"
+
+#include <memory>
+#include <ostream>
+#include <sstream>
+#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/resize_uninitialized.h b/absl/strings/internal/resize_uninitialized.h
new file mode 100644
index 000000000000..0157ca0245f3
--- /dev/null
+++ b/absl/strings/internal/resize_uninitialized.h
@@ -0,0 +1,69 @@
+//
+// 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.
+//
+
+#ifndef ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_
+#define ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_
+
+#include <string>
+#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_uninitialized member.
+template <typename T, typename = void>
+struct HasResizeUninitialized : std::false_type {};
+template <typename T>
+struct HasResizeUninitialized<
+    T, absl::void_t<decltype(std::declval<T>().resize_uninitialized(237))>>
+    : std::true_type {};
+
+template <typename string_type>
+void ResizeUninit(string_type* s, size_t new_size, std::true_type) {
+  s->resize_uninitialized(new_size);
+}
+template <typename string_type>
+void ResizeUninit(string_type* s, size_t new_size, std::false_type) {
+  s->resize(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 HasResizeUninitialized<string_type>();
+}
+
+// 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. Uses a Google extension to std::string.
+template <typename string_type, typename = void>
+inline void STLStringResizeUninitialized(string_type* s, size_t new_size) {
+  ResizeUninit(s, new_size, HasResizeUninitialized<string_type>());
+}
+
+}  // 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 000000000000..ad282efcd9bb
--- /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
+//
+//      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/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_uninitialized_call_count = 0;
+
+struct resize_uninitializable_string {
+  void resize(size_t) { resize_call_count += 1; }
+  void resize_uninitialized(size_t) { resize_uninitialized_call_count += 1; }
+};
+
+TEST(ResizeUninit, WithAndWithout) {
+  resize_call_count = 0;
+  resize_uninitialized_call_count = 0;
+  {
+    resizable_string rs;
+
+    EXPECT_EQ(resize_call_count, 0);
+    EXPECT_EQ(resize_uninitialized_call_count, 0);
+    EXPECT_FALSE(
+        absl::strings_internal::STLStringSupportsNontrashingResize(&rs));
+    EXPECT_EQ(resize_call_count, 0);
+    EXPECT_EQ(resize_uninitialized_call_count, 0);
+    absl::strings_internal::STLStringResizeUninitialized(&rs, 237);
+    EXPECT_EQ(resize_call_count, 1);
+    EXPECT_EQ(resize_uninitialized_call_count, 0);
+  }
+
+  resize_call_count = 0;
+  resize_uninitialized_call_count = 0;
+  {
+    resize_uninitializable_string rus;
+
+    EXPECT_EQ(resize_call_count, 0);
+    EXPECT_EQ(resize_uninitialized_call_count, 0);
+    EXPECT_TRUE(
+        absl::strings_internal::STLStringSupportsNontrashingResize(&rus));
+    EXPECT_EQ(resize_call_count, 0);
+    EXPECT_EQ(resize_uninitialized_call_count, 0);
+    absl::strings_internal::STLStringResizeUninitialized(&rus, 237);
+    EXPECT_EQ(resize_call_count, 0);
+    EXPECT_EQ(resize_uninitialized_call_count, 1);
+  }
+}
+
+}  // namespace
diff --git a/absl/strings/internal/str_join_internal.h b/absl/strings/internal/str_join_internal.h
new file mode 100644
index 000000000000..e73f1dde403d
--- /dev/null
+++ b/absl/strings/internal/str_join_internal.h
@@ -0,0 +1,314 @@
+//
+// 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.
+//
+
+// 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 <cassert>
+#include <iterator>
+#include <memory>
+#include <string>
+#include <utility>
+
+#include "absl/strings/internal/ostringstream.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 std::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;
+}
+
+// No-op placeholder for input iterators which can not be iterated over.
+template <typename Iterator>
+size_t GetResultSize(Iterator, Iterator, size_t, std::input_iterator_tag) {
+  return 0;
+}
+
+// Calculates space to reserve, if the iterator supports multiple passes.
+template <typename Iterator>
+size_t GetResultSize(Iterator it, Iterator end, size_t separator_size,
+                     std::forward_iterator_tag) {
+  assert(it != end);
+  size_t length = it->size();
+  while (++it != end) {
+    length += separator_size;
+    length += it->size();
+  }
+  return length;
+}
+
+// A joining algorithm that's optimized for an iterator range of std::string-like
+// objects that do not need any additional formatting. This is to optimize the
+// common case of joining, say, a std::vector<std::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 std::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
+// std::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 std::string.
+template <typename Iterator>
+std::string JoinAlgorithm(Iterator start, Iterator end, absl::string_view s,
+                     NoFormatter) {
+  std::string result;
+  if (start != end) {
+    typename std::iterator_traits<Iterator>::iterator_category iterator_tag;
+    result.reserve(GetResultSize(start, end, s.size(), iterator_tag));
+
+    // Joins strings
+    absl::string_view sep("", 0);
+    for (Iterator it = start; it != end; ++it) {
+      result.append(sep.data(), sep.size());
+      result.append(it->data(), it->size());
+      sep = s;
+    }
+  }
+
+  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 000000000000..dc31a8ef9090
--- /dev/null
+++ b/absl/strings/internal/str_split_internal.h
@@ -0,0 +1,439 @@
+// 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.
+//
+
+// 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_
+
+#ifdef _GLIBCXX_DEBUG
+#include <glibcxx_debug_traits.h>
+#endif  // _GLIBCXX_DEBUG
+
+#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"
+
+namespace absl {
+namespace strings_internal {
+
+#ifdef _GLIBCXX_DEBUG
+using ::glibcxx_debug_traits::IsStrictlyDebugWrapperBase;
+#else  // _GLIBCXX_DEBUG
+template <typename T> struct IsStrictlyDebugWrapperBase : std::false_type {};
+#endif  // _GLIBCXX_DEBUG
+
+// This class is implicitly constructible from everything that absl::string_view
+// is implicitly constructible from. If it's constructed from a temporary
+// std::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 std::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.end()) 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>
+struct SplitterIsConvertibleTo
+    : std::enable_if<
+          !IsStrictlyDebugWrapperBase<C>::value &&
+          !IsInitializerList<C>::value &&
+          HasValueType<C>::value &&
+          HasConstIterator<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 OnlyIf = typename SplitterIsConvertibleTo<Container>::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 000000000000..2415c2ccc45c
--- /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
+//
+//      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.
+
+// 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 000000000000..705eea7f16ab
--- /dev/null
+++ b/absl/strings/internal/utf8.h
@@ -0,0 +1,52 @@
+// 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.
+//
+// UTF8 utilities, implemented to reduce dependencies.
+//
+// If you need Unicode specific processing (for example being aware of
+// Unicode character boundaries, or knowledge of Unicode casing rules,
+// or various forms of equivalence and normalization), take a look at
+// files in i18n/utf8.
+
+#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 000000000000..4d437427a88a
--- /dev/null
+++ b/absl/strings/internal/utf8_test.cc
@@ -0,0 +1,58 @@
+// 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/utf8.h"
+
+#include <cctype>
+#include <cstdlib>
+#include <cstring>
+#include <cstdint>
+
+#include "gtest/gtest.h"
+
+namespace {
+
+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);
+}
+
+}  // namespace