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

1 files changed, 4 insertions, 383 deletions

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?