Changes imported from Abseil "staging" branch:

  - b527a3e4b36b644ac424e3c525b1cd393f6f6c40 Fix some typos in the usage examples by Jorg Brown <jorg@google.com>
  - 82be4a9adf3bb0ddafc0d46274969c99afffe870 Fix typo in optional.h comment. by Abseil Team <absl-team@google.com>
  - d6ee63bf8fc51fba074c23b33cebc28c808d7f07 Remove internal-only identifiers from code. by Daniel Katz <katzdm@google.com>
  - f9c3ad2f0d73f53b21603638af8b4bed636e79f4 Use easier understandable names for absl::StartsWith and ... by Abseil Team <absl-team@google.com>
  - 7c16c14fefee89c927b8789d6043c4691bcffc9b Add -Wno-missing-prototypes back to the LLVM copts. by Derek Mauro <dmauro@google.com>
  - 2f4b7d2e50c7023240242f1e15db60ccd7e8768d IWYU | absl/strings by Juemin Yang <jueminyang@google.com>
  - a99cbcc1daa34a2d6a2bb26de275e05173cc77e9 IWYU | absl/type by Juemin Yang <jueminyang@google.com>
  - 12e1146d0fc76c071d7e0ebaabb62f0a984fae66 Use LLVM_FLAGS and LLVM_TEST_FLAGS when --compiler=llvm. by Derek Mauro <dmauro@google.com>
  - cd6bea616abda558d0bace5bd77455662a233688 IWYU | absl/debugging by Juemin Yang <jueminyang@google.com>
  - d9a7382e59d46a8581b6b7a31cd5a48bb89326e9 IWYU | absl/synchronization by Juemin Yang <jueminyang@google.com>
  - 07ec7d6d5a4a666f4183c5d0ed9c342baa7b24bc IWYU | absl/numeric by Juemin Yang <jueminyang@google.com>
  - 12bfe40051f4270f8707e191af5652f83f2f750c Remove the RoundTrip{Float,Double}ToBuffer routines from ... by Jorg Brown <jorg@google.com>
  - eeb4fd67c9d97f66cb9475c3c5e51ab132f1c810 Adds conversion functions for converting between absl/tim... by Greg Miller <jgm@google.com>
  - 59a2108d05d4ea85dc5cc11e49b2cd2335d4295a Change Substitute to use %.6g formatting rather than 15/1... by Jorg Brown <jorg@google.com>
  - 394becb48e0fcd161642cdaac5120d32567e0ef8 IWYU | absl/meta by Juemin Yang <jueminyang@google.com>
  - 1e5da6e8da336699b2469dcf6dda025b9b0ec4c9 Rewrite atomic_hook.h to not use std::atomic<T*> under Wi... by Greg Falcon <gfalcon@google.com>

GitOrigin-RevId: b527a3e4b36b644ac424e3c525b1cd393f6f6c40
Change-Id: I14e331d91c956ef045ac7927091a9f179716de0c

22 files changed, 61 insertions, 486 deletions

diff --git a/absl/strings/BUILD.bazel b/absl/strings/BUILD.bazel
index 070721cc117c..da441e201aa4 100644
--- a/absl/strings/BUILD.bazel
+++ b/absl/strings/BUILD.bazel
@@ -162,6 +162,7 @@ cc_test(
     deps = [
         ":strings",
         ":internal",
+        "//absl/base:core_headers",
     ] + select(GUNIT_MAIN_DEPS_SELECTOR),
 )
 
diff --git a/absl/strings/escaping.cc b/absl/strings/escaping.cc
index f1576057f849..7d688ac3fac7 100644
--- a/absl/strings/escaping.cc
+++ b/absl/strings/escaping.cc
@@ -14,22 +14,21 @@
 
 #include "absl/strings/escaping.h"
 
+#include <algorithm>
 #include <cassert>
 #include <cstdint>
-#include <cstdio>
 #include <cstring>
+#include <iterator>
 #include <limits>
 #include <string>
-#include <vector>
 
 #include "absl/base/internal/endian.h"
 #include "absl/base/internal/raw_logging.h"
 #include "absl/base/internal/unaligned_access.h"
-#include "absl/base/macros.h"
-#include "absl/base/port.h"
 #include "absl/strings/internal/char_map.h"
 #include "absl/strings/internal/resize_uninitialized.h"
 #include "absl/strings/internal/utf8.h"
+#include "absl/strings/str_cat.h"
 #include "absl/strings/str_join.h"
 #include "absl/strings/string_view.h"
 
diff --git a/absl/strings/escaping_test.cc b/absl/strings/escaping_test.cc
index d464051df020..ecac9ca8c588 100644
--- a/absl/strings/escaping_test.cc
+++ b/absl/strings/escaping_test.cc
@@ -17,11 +17,11 @@
 #include <array>
 #include <cstdio>
 #include <cstring>
+#include <memory>
 #include <vector>
 
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
-#include "absl/base/macros.h"
 #include "absl/container/fixed_array.h"
 #include "absl/strings/str_cat.h"
 
diff --git a/absl/strings/internal/char_map_test.cc b/absl/strings/internal/char_map_test.cc
index 2167be975e7d..c3601e101e2a 100644
--- a/absl/strings/internal/char_map_test.cc
+++ b/absl/strings/internal/char_map_test.cc
@@ -14,9 +14,9 @@
 
 #include "absl/strings/internal/char_map.h"
 
-#include <cstdio>
-#include <cstdlib>
 #include <cctype>
+#include <string>
+#include <vector>
 
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
diff --git a/absl/strings/internal/memutil_test.cc b/absl/strings/internal/memutil_test.cc
index 1ff60f20e0bd..09424de9a477 100644
--- a/absl/strings/internal/memutil_test.cc
+++ b/absl/strings/internal/memutil_test.cc
@@ -16,7 +16,6 @@
 
 #include "absl/strings/internal/memutil.h"
 
-#include <algorithm>
 #include <cstdlib>
 
 #include "gtest/gtest.h"
diff --git a/absl/strings/internal/ostringstream_test.cc b/absl/strings/internal/ostringstream_test.cc
index 0047ec822e8b..069a0e1fbbb1 100644
--- a/absl/strings/internal/ostringstream_test.cc
+++ b/absl/strings/internal/ostringstream_test.cc
@@ -16,7 +16,6 @@
 
 #include <memory>
 #include <ostream>
-#include <sstream>
 #include <string>
 #include <type_traits>
 
diff --git a/absl/strings/internal/utf8_test.cc b/absl/strings/internal/utf8_test.cc
index 4d437427a88a..64cec70df7e1 100644
--- a/absl/strings/internal/utf8_test.cc
+++ b/absl/strings/internal/utf8_test.cc
@@ -14,12 +14,11 @@
 
 #include "absl/strings/internal/utf8.h"
 
-#include <cctype>
-#include <cstdlib>
-#include <cstring>
 #include <cstdint>
+#include <utility>
 
 #include "gtest/gtest.h"
+#include "absl/base/port.h"
 
 namespace {
 
diff --git a/absl/strings/match.cc b/absl/strings/match.cc
index 53881bdd3f3c..25bd7f0b828b 100644
--- a/absl/strings/match.cc
+++ b/absl/strings/match.cc
@@ -27,9 +27,9 @@ bool CaseEqual(absl::string_view piece1, absl::string_view piece2) {
 }
 }  // namespace
 
-bool StartsWithIgnoreCase(absl::string_view text, absl::string_view preffix) {
-  return (text.size() >= preffix.size()) &&
-         CaseEqual(text.substr(0, preffix.size()), preffix);
+bool StartsWithIgnoreCase(absl::string_view text, absl::string_view prefix) {
+  return (text.size() >= prefix.size()) &&
+         CaseEqual(text.substr(0, prefix.size()), prefix);
 }
 
 bool EndsWithIgnoreCase(absl::string_view text, absl::string_view suffix) {
diff --git a/absl/strings/match.h b/absl/strings/match.h
index 4a5d1c0342cd..4ac35f192e00 100644
--- a/absl/strings/match.h
+++ b/absl/strings/match.h
@@ -41,40 +41,42 @@ namespace absl {
 
 // StrContains()
 //
-// Returns whether a given std::string `s` contains the substring `x`.
-inline bool StrContains(absl::string_view s, absl::string_view x) {
-  return static_cast<absl::string_view::size_type>(s.find(x, 0)) != s.npos;
+// Returns whether a given std::string `haystack` contains the substring `needle`.
+inline bool StrContains(absl::string_view haystack, absl::string_view needle) {
+  return static_cast<absl::string_view::size_type>(haystack.find(needle, 0)) !=
+         haystack.npos;
 }
 
 // StartsWith()
 //
-// Returns whether a given std::string `s` begins with `x`.
-inline bool StartsWith(absl::string_view s, absl::string_view x) {
-  return x.empty() ||
-         (s.size() >= x.size() && memcmp(s.data(), x.data(), x.size()) == 0);
+// Returns whether a given std::string `text` begins with `prefix`.
+inline bool StartsWith(absl::string_view text, absl::string_view prefix) {
+  return prefix.empty() ||
+         (text.size() >= prefix.size() &&
+         memcmp(text.data(), prefix.data(), prefix.size()) == 0);
 }
 
 // EndsWith()
 //
-// Returns whether a given std::string `s` ends `x`.
-inline bool EndsWith(absl::string_view s, absl::string_view x) {
-  return x.empty() ||
-         (s.size() >= x.size() &&
-          memcmp(s.data() + (s.size() - x.size()), x.data(), x.size()) == 0);
+// Returns whether a given std::string `text` ends with `suffix`.
+inline bool EndsWith(absl::string_view text, absl::string_view suffix) {
+  return suffix.empty() ||
+         (text.size() >= suffix.size() &&
+          memcmp(text.data() + (text.size() - suffix.size()), suffix.data(),
+  suffix.size()) == 0);
 }
 
 // StartsWithIgnoreCase()
 //
 // Returns whether a given std::string `text` starts with `starts_with`, ignoring
 // case in the comparison.
-bool StartsWithIgnoreCase(absl::string_view text,
-                          absl::string_view starts_with);
+bool StartsWithIgnoreCase(absl::string_view text, absl::string_view prefix);
 
 // EndsWithIgnoreCase()
 //
 // Returns whether a given std::string `text` ends with `ends_with`, ignoring case
 // in the comparison.
-bool EndsWithIgnoreCase(absl::string_view text, absl::string_view ends_with);
+bool EndsWithIgnoreCase(absl::string_view text, absl::string_view suffix);
 
 }  // namespace absl
 
diff --git a/absl/strings/numbers.cc b/absl/strings/numbers.cc
index 3b093b98c6f4..ac73f5308225 100644
--- a/absl/strings/numbers.cc
+++ b/absl/strings/numbers.cc
@@ -3,19 +3,20 @@
 
 #include "absl/strings/numbers.h"
 
+#include <algorithm>
 #include <cassert>
-#include <cctype>
 #include <cfloat>          // for DBL_DIG and FLT_DIG
 #include <cmath>           // for HUGE_VAL
+#include <cstdint>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
+#include <iterator>
 #include <limits>
 #include <memory>
-#include <string>
+#include <utility>
 
 #include "absl/base/internal/raw_logging.h"
-#include "absl/numeric/int128.h"
 #include "absl/strings/ascii.h"
 #include "absl/strings/internal/memutil.h"
 #include "absl/strings/str_cat.h"
@@ -291,386 +292,6 @@ char* numbers_internal::FastInt64ToBuffer(int64_t i, char* buffer) {
   return numbers_internal::FastUInt64ToBuffer(u, buffer);
 }
 
-// Although DBL_DIG is typically 15, DBL_MAX is normally represented with 17
-// digits of precision. When converted to a std::string value with fewer digits
-// of precision using strtod(), the result can be bigger than DBL_MAX due to
-// a rounding error. Converting this value back to a double will produce an
-// Inf which will trigger a SIGFPE if FP exceptions are enabled. We skip
-// the precision check for sufficiently large values to avoid the SIGFPE.
-static const double kDoublePrecisionCheckMax = DBL_MAX / 1.000000000000001;
-
-char* numbers_internal::RoundTripDoubleToBuffer(double d, char* buffer) {
-  // DBL_DIG is 15 for IEEE-754 doubles, which are used on almost all
-  // platforms these days.  Just in case some system exists where DBL_DIG
-  // is significantly larger -- and risks overflowing our buffer -- we have
-  // this assert.
-  static_assert(DBL_DIG < 20, "DBL_DIG is too big");
-
-  bool full_precision_needed = true;
-  if (std::abs(d) <= kDoublePrecisionCheckMax) {
-    int snprintf_result = snprintf(buffer, numbers_internal::kFastToBufferSize,
-                                   "%.*g", DBL_DIG, d);
-
-    // The snprintf should never overflow because the buffer is significantly
-    // larger than the precision we asked for.
-    assert(snprintf_result > 0 &&
-           snprintf_result < numbers_internal::kFastToBufferSize);
-    (void)snprintf_result;
-
-    full_precision_needed = strtod(buffer, nullptr) != d;
-  }
-
-  if (full_precision_needed) {
-    int snprintf_result = snprintf(buffer, numbers_internal::kFastToBufferSize,
-                                   "%.*g", DBL_DIG + 2, d);
-
-    // Should never overflow; see above.
-    assert(snprintf_result > 0 &&
-           snprintf_result < numbers_internal::kFastToBufferSize);
-    (void)snprintf_result;
-  }
-  return buffer;
-}
-// This table is used to quickly calculate the base-ten exponent of a given
-// float, and then to provide a multiplier to bring that number into the
-// range 1-999,999,999, that is, into uint32_t range.  Finally, the exp
-// std::string is made available so there is one less int-to-std::string conversion
-// to be done.
-
-struct Spec {
-  double min_range;
-  double multiplier;
-  const char expstr[5];
-};
-const Spec neg_exp_table[] = {
-    {1.4e-45f, 1e+55, "e-45"},  //
-    {1e-44f, 1e+54, "e-44"},    //
-    {1e-43f, 1e+53, "e-43"},    //
-    {1e-42f, 1e+52, "e-42"},    //
-    {1e-41f, 1e+51, "e-41"},    //
-    {1e-40f, 1e+50, "e-40"},    //
-    {1e-39f, 1e+49, "e-39"},    //
-    {1e-38f, 1e+48, "e-38"},    //
-    {1e-37f, 1e+47, "e-37"},    //
-    {1e-36f, 1e+46, "e-36"},    //
-    {1e-35f, 1e+45, "e-35"},    //
-    {1e-34f, 1e+44, "e-34"},    //
-    {1e-33f, 1e+43, "e-33"},    //
-    {1e-32f, 1e+42, "e-32"},    //
-    {1e-31f, 1e+41, "e-31"},    //
-    {1e-30f, 1e+40, "e-30"},    //
-    {1e-29f, 1e+39, "e-29"},    //
-    {1e-28f, 1e+38, "e-28"},    //
-    {1e-27f, 1e+37, "e-27"},    //
-    {1e-26f, 1e+36, "e-26"},    //
-    {1e-25f, 1e+35, "e-25"},    //
-    {1e-24f, 1e+34, "e-24"},    //
-    {1e-23f, 1e+33, "e-23"},    //
-    {1e-22f, 1e+32, "e-22"},    //
-    {1e-21f, 1e+31, "e-21"},    //
-    {1e-20f, 1e+30, "e-20"},    //
-    {1e-19f, 1e+29, "e-19"},    //
-    {1e-18f, 1e+28, "e-18"},    //
-    {1e-17f, 1e+27, "e-17"},    //
-    {1e-16f, 1e+26, "e-16"},    //
-    {1e-15f, 1e+25, "e-15"},    //
-    {1e-14f, 1e+24, "e-14"},    //
-    {1e-13f, 1e+23, "e-13"},    //
-    {1e-12f, 1e+22, "e-12"},    //
-    {1e-11f, 1e+21, "e-11"},    //
-    {1e-10f, 1e+20, "e-10"},    //
-    {1e-09f, 1e+19, "e-09"},    //
-    {1e-08f, 1e+18, "e-08"},    //
-    {1e-07f, 1e+17, "e-07"},    //
-    {1e-06f, 1e+16, "e-06"},    //
-    {1e-05f, 1e+15, "e-05"},    //
-    {1e-04f, 1e+14, "e-04"},    //
-};
-
-const Spec pos_exp_table[] = {
-    {1e+08f, 1e+02, "e+08"},  //
-    {1e+09f, 1e+01, "e+09"},  //
-    {1e+10f, 1e+00, "e+10"},  //
-    {1e+11f, 1e-01, "e+11"},  //
-    {1e+12f, 1e-02, "e+12"},  //
-    {1e+13f, 1e-03, "e+13"},  //
-    {1e+14f, 1e-04, "e+14"},  //
-    {1e+15f, 1e-05, "e+15"},  //
-    {1e+16f, 1e-06, "e+16"},  //
-    {1e+17f, 1e-07, "e+17"},  //
-    {1e+18f, 1e-08, "e+18"},  //
-    {1e+19f, 1e-09, "e+19"},  //
-    {1e+20f, 1e-10, "e+20"},  //
-    {1e+21f, 1e-11, "e+21"},  //
-    {1e+22f, 1e-12, "e+22"},  //
-    {1e+23f, 1e-13, "e+23"},  //
-    {1e+24f, 1e-14, "e+24"},  //
-    {1e+25f, 1e-15, "e+25"},  //
-    {1e+26f, 1e-16, "e+26"},  //
-    {1e+27f, 1e-17, "e+27"},  //
-    {1e+28f, 1e-18, "e+28"},  //
-    {1e+29f, 1e-19, "e+29"},  //
-    {1e+30f, 1e-20, "e+30"},  //
-    {1e+31f, 1e-21, "e+31"},  //
-    {1e+32f, 1e-22, "e+32"},  //
-    {1e+33f, 1e-23, "e+33"},  //
-    {1e+34f, 1e-24, "e+34"},  //
-    {1e+35f, 1e-25, "e+35"},  //
-    {1e+36f, 1e-26, "e+36"},  //
-    {1e+37f, 1e-27, "e+37"},  //
-    {1e+38f, 1e-28, "e+38"},  //
-    {1e+39,  1e-29, "e+39"},  //
-};
-
-struct ExpCompare {
-  bool operator()(const Spec& spec, double d) const {
-    return spec.min_range < d;
-  }
-};
-
-// Utility routine(s) for RoundTripFloatToBuffer:
-// OutputNecessaryDigits takes two 11-digit numbers, whose integer portion
-// represents the fractional part of a floating-point number, and outputs a
-// number that is in-between them, with the fewest digits possible. For
-// instance, given 12345678900 and 12345876900, it would output "0123457".
-// When there are multiple final digits that would satisfy this requirement,
-// this routine attempts to use a digit that would represent the average of
-// lower_double and upper_double.
-//
-// Although the routine works using integers, all callers use doubles, so
-// for their convenience this routine accepts doubles.
-static char* OutputNecessaryDigits(double lower_double, double upper_double,
-                                   char* out) {
-  assert(lower_double > 0);
-  assert(lower_double < upper_double - 10);
-  assert(upper_double < 100000000000.0);
-
-  // Narrow the range a bit; without this bias, an input of lower=87654320010.0
-  // and upper=87654320100.0 would produce an output of 876543201
-  //
-  // We do this in three steps: first, we lower the upper bound and truncate it
-  // to an integer.  Then, we increase the lower bound by exactly the amount we
-  // just decreased the upper bound by - at that point, the midpoint is exactly
-  // where it used to be.  Then we truncate the lower bound.
-
-  uint64_t upper64 = upper_double - (1.0 / 1024);
-  double shrink = upper_double - upper64;
-  uint64_t lower64 = lower_double + shrink;
-
-  // Theory of operation: we convert the lower number to ascii representation,
-  // two digits at a time.  As we go, we remove the same digits from the upper
-  // number.  When we see the upper number does not share those same digits, we
-  // know we can stop converting. When we stop, the last digit we output is
-  // taken from the average of upper and lower values, rounded up.
-  char buf[2];
-  uint32_t lodigits =
-      static_cast<uint32_t>(lower64 / 1000000000);  // 1,000,000,000
-  uint64_t mul64 = lodigits * uint64_t{1000000000};
-
-  PutTwoDigits(lodigits, out);
-  out += 2;
-  if (upper64 - mul64 >= 1000000000) {  // digit mismatch!
-    PutTwoDigits(upper64 / 1000000000, buf);
-    if (out[-2] != buf[0]) {
-      out[-2] = '0' + (upper64 + lower64 + 10000000000) / 20000000000;
-      --out;
-    } else {
-      PutTwoDigits((upper64 + lower64 + 1000000000) / 2000000000, out - 2);
-    }
-    *out = '\0';
-    return out;
-  }
-  uint32_t lower = static_cast<uint32_t>(lower64 - mul64);
-  uint32_t upper = static_cast<uint32_t>(upper64 - mul64);
-
-  lodigits = lower / 10000000;  // 10,000,000
-  uint32_t mul = lodigits * 10000000;
-  PutTwoDigits(lodigits, out);
-  out += 2;
-  if (upper - mul >= 10000000) {  // digit mismatch!
-    PutTwoDigits(upper / 10000000, buf);
-    if (out[-2] != buf[0]) {
-      out[-2] = '0' + (upper + lower + 100000000) / 200000000;
-      --out;
-    } else {
-      PutTwoDigits((upper + lower + 10000000) / 20000000, out - 2);
-    }
-    *out = '\0';
-    return out;
-  }
-  lower -= mul;
-  upper -= mul;
-
-  lodigits = lower / 100000;  // 100,000
-  mul = lodigits * 100000;
-  PutTwoDigits(lodigits, out);
-  out += 2;
-  if (upper - mul >= 100000) {  // digit mismatch!
-    PutTwoDigits(upper / 100000, buf);
-    if (out[-2] != buf[0]) {
-      out[-2] = '0' + (upper + lower + 1000000) / 2000000;
-      --out;
-    } else {
-      PutTwoDigits((upper + lower + 100000) / 200000, out - 2);
-    }
-    *out = '\0';
-    return out;
-  }
-  lower -= mul;
-  upper -= mul;
-
-  lodigits = lower / 1000;
-  mul = lodigits * 1000;
-  PutTwoDigits(lodigits, out);
-  out += 2;
-  if (upper - mul >= 1000) {  // digit mismatch!
-    PutTwoDigits(upper / 1000, buf);
-    if (out[-2] != buf[0]) {
-      out[-2] = '0' + (upper + lower + 10000) / 20000;
-      --out;
-    } else {
-      PutTwoDigits((upper + lower + 1000) / 2000, out - 2);
-    }
-    *out = '\0';
-    return out;
-  }
-  lower -= mul;
-  upper -= mul;
-
-  PutTwoDigits(lower / 10, out);
-  out += 2;
-  PutTwoDigits(upper / 10, buf);
-  if (out[-2] != buf[0]) {
-    out[-2] = '0' + (upper + lower + 100) / 200;
-    --out;
-  } else {
-    PutTwoDigits((upper + lower + 10) / 20, out - 2);
-  }
-  *out = '\0';
-  return out;
-}
-
-// RoundTripFloatToBuffer converts the given float into a std::string which, if
-// passed to strtof, will produce the exact same original float.  It does this
-// by computing the range of possible doubles which map to the given float, and
-// then examining the digits of the doubles in that range.  If all the doubles
-// in the range start with "2.37", then clearly our float does, too.  As soon as
-// they diverge, only one more digit is needed.
-char* numbers_internal::RoundTripFloatToBuffer(float f, char* buffer) {
-  static_assert(std::numeric_limits<float>::is_iec559,
-                "IEEE-754/IEC-559 support only");
-
-  char* out = buffer;  // we write data to out, incrementing as we go, but
-                       // FloatToBuffer always returns the address of the buffer
-                       // passed in.
-
-  if (std::isnan(f)) {
-    strcpy(out, "nan");  // NOLINT(runtime/printf)
-    return buffer;
-  }
-  if (f == 0) {  // +0 and -0 are handled here
-    if (std::signbit(f)) {
-      strcpy(out, "-0");  // NOLINT(runtime/printf)
-    } else {
-      strcpy(out, "0");  // NOLINT(runtime/printf)
-    }
-    return buffer;
-  }
-  if (f < 0) {
-    *out++ = '-';
-    f = -f;
-  }
-  if (std::isinf(f)) {
-    strcpy(out, "inf");  // NOLINT(runtime/printf)
-    return buffer;
-  }
-
-  double next_lower = nextafterf(f, 0.0f);
-  // For all doubles in the range lower_bound < f < upper_bound, the
-  // nearest float is f.
-  double lower_bound = (f + next_lower) * 0.5;
-  double upper_bound = f + (f - lower_bound);
-  // Note: because std::nextafter is slow, we calculate upper_bound
-  // assuming that it is the same distance from f as lower_bound is.
-  // For exact powers of two, upper_bound is actually twice as far
-  // from f as lower_bound is, but this turns out not to matter.
-
-  // Most callers pass floats that are either 0 or within the
-  // range 0.0001 through 100,000,000, so handle those first,
-  // since they don't need exponential notation.
-  const Spec* spec = nullptr;
-  if (f < 1.0) {
-    if (f >= 0.0001f) {
-      // for fractional values, we set up the multiplier at the same
-      // time as we output the leading "0." / "0.0" / "0.00" / "0.000"
-      double multiplier = 1e+11;
-      *out++ = '0';
-      *out++ = '.';
-      if (f < 0.1f) {
-        multiplier = 1e+12;
-        *out++ = '0';
-        if (f < 0.01f) {
-          multiplier = 1e+13;
-          *out++ = '0';
-          if (f < 0.001f) {
-            multiplier = 1e+14;
-            *out++ = '0';
-          }
-        }
-      }
-      OutputNecessaryDigits(lower_bound * multiplier, upper_bound * multiplier,
-                            out);
-      return buffer;
-    }
-    spec = std::lower_bound(std::begin(neg_exp_table), std::end(neg_exp_table),
-                            double{f}, ExpCompare());
-    if (spec == std::end(neg_exp_table)) --spec;
-  } else if (f < 1e8) {
-    // Handling non-exponential format greater than 1.0 is similar to the above,
-    // but instead of 0.0 / 0.00 / 0.000, the prefix is simply the truncated
-    // integer part of f.
-    int32_t as_int = f;
-    out = numbers_internal::FastUInt32ToBuffer(as_int, out);
-    // Easy: if the integer part is within (lower_bound, upper_bound), then we
-    // are already done.
-    if (as_int > lower_bound && as_int < upper_bound) {
-      return buffer;
-    }
-    *out++ = '.';
-    OutputNecessaryDigits((lower_bound - as_int) * 1e11,
-                          (upper_bound - as_int) * 1e11, out);
-    return buffer;
-  } else {
-    spec = std::lower_bound(std::begin(pos_exp_table),
-                            std::end(pos_exp_table),
-                            double{f}, ExpCompare());
-    if (spec == std::end(pos_exp_table)) --spec;
-  }
-  // Exponential notation from here on.  "spec" was computed using lower_bound,
-  // which means it's the first spec from the table where min_range is greater
-  // or equal to f.
-  // Unfortunately that's not quite what we want; we want a min_range that is
-  // less or equal.  So first thing, if it was greater, back up one entry.
-  if (spec->min_range > f) --spec;
-
-  // The digits might be "237000123", but we want "2.37000123",
-  // so we output the digits one character later, and then move the first
-  // digit back so we can stick the "." in.
-  char* start = out;
-  out = OutputNecessaryDigits(lower_bound * spec->multiplier,
-                              upper_bound * spec->multiplier, start + 1);
-  start[0] = start[1];
-  start[1] = '.';
-
-  // If it turns out there was only one digit output, then back up over the '.'
-  if (out == &start[2]) --out;
-
-  // Now add the "e+NN" part.
-  memcpy(out, spec->expstr, 4);
-  out[4] = '\0';
-  return buffer;
-}
-
 // Returns the number of leading 0 bits in a 64-bit value.
 // TODO(jorg): Replace with builtin_clzll if available.
 // Are we shipping util/bits in absl?
diff --git a/absl/strings/numbers.h b/absl/strings/numbers.h
index f17dc97b2b1c..74aebc8028ea 100644
--- a/absl/strings/numbers.h
+++ b/absl/strings/numbers.h
@@ -92,9 +92,6 @@ char* FastUInt64ToBuffer(uint64_t i, char* buffer);
 static const int kFastToBufferSize = 32;
 static const int kSixDigitsToBufferSize = 16;
 
-char* RoundTripDoubleToBuffer(double d, char* buffer);
-char* RoundTripFloatToBuffer(float f, char* buffer);
-
 // Helper function for fast formatting of floating-point values.
 // The result is the same as printf's "%g", a.k.a. "%.6g"; that is, six
 // significant digits are returned, trailing zeros are removed, and numbers
diff --git a/absl/strings/numbers_test.cc b/absl/strings/numbers_test.cc
index 9b74d67b87c8..817604d78c7f 100644
--- a/absl/strings/numbers_test.cc
+++ b/absl/strings/numbers_test.cc
@@ -3,10 +3,7 @@
 #include "absl/strings/numbers.h"
 
 #include <sys/types.h>
-#include <algorithm>
-#include <cctype>
 #include <cfenv>  // NOLINT(build/c++11)
-#include <cfloat>
 #include <cinttypes>
 #include <climits>
 #include <cmath>
@@ -25,7 +22,6 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "absl/base/internal/raw_logging.h"
-#include "absl/base/port.h"
 #include "absl/strings/str_cat.h"
 
 #include "absl/strings/internal/numbers_test_common.inc"
@@ -42,7 +38,6 @@ using absl::numbers_internal::safe_strto32_base;
 using absl::numbers_internal::safe_strto64_base;
 using absl::numbers_internal::safe_strtou32_base;
 using absl::numbers_internal::safe_strtou64_base;
-using absl::numbers_internal::RoundTripFloatToBuffer;
 using absl::numbers_internal::SixDigitsToBuffer;
 using absl::SimpleAtoi;
 using testing::Eq;
@@ -776,42 +771,6 @@ void ExhaustiveFloat(uint32_t cases, R&& runnable) {
   }
 }
 
-TEST_F(SimpleDtoaTest, ExhaustiveFloatToBuffer) {
-  uint64_t test_count = 0;
-  std::vector<float> mismatches;
-  ExhaustiveFloat(kFloatNumCases, [&](float f) {
-    if (f != f) return;  // rule out NaNs
-    ++test_count;
-    char fastbuf[kFastToBufferSize];
-    RoundTripFloatToBuffer(f, fastbuf);
-    float round_trip = strtof(fastbuf, nullptr);
-    if (f != round_trip) {
-      mismatches.push_back(f);
-      if (mismatches.size() < 10) {
-        ABSL_RAW_LOG(ERROR, "%s",
-                     absl::StrCat("Round-trip failure with float.  ", "f=", f,
-                                  "=", ToNineDigits(f), " fast=", fastbuf,
-                                  " strtof=", ToNineDigits(round_trip))
-                         .c_str());
-      }
-    }
-  });
-  if (!mismatches.empty()) {
-    EXPECT_EQ(mismatches.size(), 0);
-    for (size_t i = 0; i < mismatches.size(); ++i) {
-      if (i > 100) i = mismatches.size() - 1;
-      float f = mismatches[i];
-      std::string msg =
-          absl::StrCat("Mismatch #", i, "  f=", f, " (", ToNineDigits(f), ")");
-      char buf[kFastToBufferSize];
-      absl::StrAppend(&msg, " fast='", RoundTripFloatToBuffer(f, buf), "'");
-      float rt = strtof(buf, nullptr);
-      absl::StrAppend(&msg, " rt=", ToNineDigits(rt));
-      ABSL_RAW_LOG(ERROR, "%s", msg.c_str());
-    }
-  }
-}
-
 TEST_F(SimpleDtoaTest, ExhaustiveDoubleToSixDigits) {
   uint64_t test_count = 0;
   std::vector<double> mismatches;
diff --git a/absl/strings/str_cat.cc b/absl/strings/str_cat.cc
index 0c75655c993f..99eb28908c19 100644
--- a/absl/strings/str_cat.cc
+++ b/absl/strings/str_cat.cc
@@ -14,9 +14,9 @@
 
 #include "absl/strings/str_cat.h"
 
-#include <cstdarg>
+#include <assert.h>
+#include <algorithm>
 #include <cstdint>
-#include <cstdio>
 #include <cstring>
 
 #include "absl/strings/ascii.h"
diff --git a/absl/strings/str_join_test.cc b/absl/strings/str_join_test.cc
index 7c2ed09b91d6..03b60f03c82e 100644
--- a/absl/strings/str_join_test.cc
+++ b/absl/strings/str_join_test.cc
@@ -16,22 +16,21 @@
 
 #include "absl/strings/str_join.h"
 
-#include <algorithm>
 #include <cstddef>
 #include <cstdint>
 #include <cstdio>
+#include <functional>
 #include <initializer_list>
 #include <map>
+#include <memory>
 #include <ostream>
-#include <random>
 #include <set>
 #include <tuple>
+#include <type_traits>
 #include <vector>
 
-#include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "absl/base/macros.h"
-#include "absl/base/port.h"
 #include "absl/memory/memory.h"
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_split.h"
diff --git a/absl/strings/str_replace_test.cc b/absl/strings/str_replace_test.cc
index f49c7e1c32cf..5d003a224a4f 100644
--- a/absl/strings/str_replace_test.cc
+++ b/absl/strings/str_replace_test.cc
@@ -15,11 +15,12 @@
 #include "absl/strings/str_replace.h"
 
 #include <list>
+#include <map>
 #include <tuple>
 
 #include "gtest/gtest.h"
-#include "absl/strings/str_split.h"
 #include "absl/strings/str_cat.h"
+#include "absl/strings/str_split.h"
 
 TEST(StrReplaceAll, OneReplacement) {
   std::string s;
diff --git a/absl/strings/str_split.cc b/absl/strings/str_split.cc
index 910a67cf2840..0207213c26ba 100644
--- a/absl/strings/str_split.cc
+++ b/absl/strings/str_split.cc
@@ -14,11 +14,14 @@
 
 #include "absl/strings/str_split.h"
 
+#include <algorithm>
 #include <cassert>
+#include <cstdint>
 #include <cstdlib>
 #include <cstring>
 #include <iterator>
 #include <limits>
+#include <memory>
 
 #include "absl/base/internal/raw_logging.h"
 #include "absl/strings/ascii.h"
diff --git a/absl/strings/str_split_test.cc b/absl/strings/str_split_test.cc
index a95a0fbd3596..22a68d0f8339 100644
--- a/absl/strings/str_split_test.cc
+++ b/absl/strings/str_split_test.cc
@@ -14,15 +14,13 @@
 
 #include "absl/strings/str_split.h"
 
-#include <climits>
-#include <cstdlib>
-#include <cstring>
 #include <deque>
-#include <limits>
+#include <initializer_list>
 #include <list>
 #include <map>
 #include <memory>
 #include <string>
+#include <type_traits>
 #include <unordered_map>
 #include <unordered_set>
 #include <vector>
@@ -31,7 +29,6 @@
 #include "gtest/gtest.h"
 #include "absl/base/dynamic_annotations.h"  // for RunningOnValgrind
 #include "absl/base/macros.h"
-#include "absl/base/port.h"
 #include "absl/strings/numbers.h"
 
 namespace {
diff --git a/absl/strings/string_view.cc b/absl/strings/string_view.cc
index 4d4ba6c1741f..0e1729546a5f 100644
--- a/absl/strings/string_view.cc
+++ b/absl/strings/string_view.cc
@@ -20,7 +20,6 @@
 #include <climits>
 #include <cstring>
 #include <ostream>
-#include <string>
 
 #include "absl/strings/internal/memutil.h"
 #include "absl/strings/internal/resize_uninitialized.h"
diff --git a/absl/strings/string_view.h b/absl/strings/string_view.h
index e2609f174f93..8e37acb8d870 100644
--- a/absl/strings/string_view.h
+++ b/absl/strings/string_view.h
@@ -180,9 +180,9 @@ class string_view {
   constexpr string_view(const char* data, size_type len)
       : ptr_(data), length_(CheckLengthInternal(len)) {}
 
-  // NOTE(b/36227513): harmlessly omitted to work around gdb bug.
-  // constexpr string_view(const string_view&) noexcept = default;
-  // string_view& operator=(const string_view&) noexcept = default;
+  // NOTE: Harmlessly omitted to work around gdb bug.
+  //   constexpr string_view(const string_view&) noexcept = default;
+  //   string_view& operator=(const string_view&) noexcept = default;
 
   // Iterators
 
@@ -550,8 +550,7 @@ namespace absl {
 // ClippedSubstr()
 //
 // Like `s.substr(pos, n)`, but clips `pos` to an upper bound of `s.size()`.
-// Provided because std::string_view::substr throws if `pos > size()`,
-// to support b/37991613.
+// Provided because std::string_view::substr throws if `pos > size()`
 inline string_view ClippedSubstr(string_view s, size_t pos,
                                  size_t n = string_view::npos) {
   pos = std::min(pos, static_cast<size_t>(s.size()));
diff --git a/absl/strings/string_view_test.cc b/absl/strings/string_view_test.cc
index 439d6499730e..6be6f3b82b11 100644
--- a/absl/strings/string_view_test.cc
+++ b/absl/strings/string_view_test.cc
@@ -14,12 +14,13 @@
 
 #include "absl/strings/string_view.h"
 
-#include <algorithm>
+#include <stdlib.h>
 #include <iomanip>
 #include <iterator>
+#include <limits>
 #include <map>
-#include <random>
 #include <sstream>
+#include <stdexcept>
 #include <string>
 #include <type_traits>
 #include <utility>
@@ -27,7 +28,6 @@
 #include "gtest/gtest.h"
 #include "absl/base/config.h"
 #include "absl/base/dynamic_annotations.h"
-#include "absl/base/port.h"
 
 namespace {
 
diff --git a/absl/strings/strip.cc b/absl/strings/strip.cc
index 968c09c6fd31..adc219f16b8c 100644
--- a/absl/strings/strip.cc
+++ b/absl/strings/strip.cc
@@ -18,7 +18,6 @@
 #include "absl/strings/strip.h"
 
 #include <algorithm>
-#include <cassert>
 #include <cstring>
 #include <string>
 
diff --git a/absl/strings/substitute.h b/absl/strings/substitute.h
index 5d6bfd90c2fb..3fc4ac4cdcc4 100644
--- a/absl/strings/substitute.h
+++ b/absl/strings/substitute.h
@@ -73,7 +73,7 @@
 //   * calls for a position argument which is not provided,
 //     e.g. Substitute("Hello $2", "world"), or
 //   * specifies a non-digit, non-$ character after an unescaped $ character,
-//     e.g. "Hello %f".
+//     e.g. "Hello $f".
 // In debug mode, i.e. #ifndef NDEBUG, such errors terminate the program.
 
 #ifndef ABSL_STRINGS_SUBSTITUTE_H_
@@ -149,9 +149,11 @@ class Arg {
       : piece_(scratch_,
                numbers_internal::FastIntToBuffer(value, scratch_) - scratch_) {}
   Arg(float value)  // NOLINT(runtime/explicit)
-      : piece_(numbers_internal::RoundTripFloatToBuffer(value, scratch_)) {}
+      : piece_(scratch_, numbers_internal::SixDigitsToBuffer(value, scratch_)) {
+  }
   Arg(double value)  // NOLINT(runtime/explicit)
-      : piece_(numbers_internal::RoundTripDoubleToBuffer(value, scratch_)) {}
+      : piece_(scratch_, numbers_internal::SixDigitsToBuffer(value, scratch_)) {
+  }
   Arg(bool value)  // NOLINT(runtime/explicit)
       : piece_(value ? "true" : "false") {}
   // `void*` values, with the exception of `char*`, are printed as
@@ -211,9 +213,9 @@ constexpr int PlaceholderBitmask(const char* format) {
 //
 // Example:
 //  template <typename... Args>
-//  void VarMsg(std::string* boilerplate, const std::string& format,
+//  void VarMsg(std::string* boilerplate, absl::string_view format,
 //      const Args&... args) {
-//    std::string s = absl::SubstituteAndAppend(boilerplate, format, args...)";
+//    absl::SubstituteAndAppend(boilerplate, format, args...);
 //  }
 //
 inline void SubstituteAndAppend(std::string* output, absl::string_view format) {
@@ -458,8 +460,8 @@ void SubstituteAndAppend(
 //
 // Example:
 //  template <typename... Args>
-//  void VarMsg(const std::string& format, const Args&... args) {
-//    std::string s = absl::Substitute(format, args...)";
+//  void VarMsg(absl::string_view format, const Args&... args) {
+//    std::string s = absl::Substitute(format, args...);
 
 ABSL_MUST_USE_RESULT inline std::string Substitute(absl::string_view format) {
   std::string result;