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- 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
This commit is contained in:
Abseil Team 2017-09-24 08:20:48 -07:00 • committed by Derek Mauro
parent 53c239d1fc
commit cf6ab6bb2b
68 changed files with 629 additions and 831 deletions
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387
absl/strings/numbers.cc
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@ -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?