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tvl-depot/absl/strings/numbers.cc

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Initial Commit
2017-09-19 22:54:40 +02:00
// This file contains std::string processing functions related to
// numeric values.
#include "absl/strings/numbers.h"
#include <cassert>
#include <cctype>
#include <cfloat> // for DBL_DIG and FLT_DIG
#include <cmath> // for HUGE_VAL
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <limits>
#include <memory>
#include <string>
#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"
namespace absl {
bool SimpleAtof(absl::string_view str, float* value) {
*value = 0.0;
if (str.empty()) return false;
char buf[32];
std::unique_ptr<char[]> bigbuf;
char* ptr = buf;
if (str.size() > sizeof(buf) - 1) {
bigbuf.reset(new char[str.size() + 1]);
ptr = bigbuf.get();
}
memcpy(ptr, str.data(), str.size());
ptr[str.size()] = '\0';
char* endptr;
*value = strtof(ptr, &endptr);
if (endptr != ptr) {
while (absl::ascii_isspace(*endptr)) ++endptr;
}
// Ignore range errors from strtod/strtof.
// The values it returns on underflow and
// overflow are the right fallback in a
// robust setting.
return *ptr != '\0' && *endptr == '\0';
}
bool SimpleAtod(absl::string_view str, double* value) {
*value = 0.0;
if (str.empty()) return false;
char buf[32];
std::unique_ptr<char[]> bigbuf;
char* ptr = buf;
if (str.size() > sizeof(buf) - 1) {
bigbuf.reset(new char[str.size() + 1]);
ptr = bigbuf.get();
}
memcpy(ptr, str.data(), str.size());
ptr[str.size()] = '\0';
char* endptr;
*value = strtod(ptr, &endptr);
if (endptr != ptr) {
while (absl::ascii_isspace(*endptr)) ++endptr;
}
// Ignore range errors from strtod. The values it
// returns on underflow and overflow are the right
// fallback in a robust setting.
return *ptr != '\0' && *endptr == '\0';
}
namespace {
// TODO(rogeeff): replace with the real released thing once we figure out what
// it is.
inline bool CaseEqual(absl::string_view piece1, absl::string_view piece2) {
return (piece1.size() == piece2.size() &&
0 == strings_internal::memcasecmp(piece1.data(), piece2.data(),
piece1.size()));
}
// Writes a two-character representation of 'i' to 'buf'. 'i' must be in the
// range 0 <= i < 100, and buf must have space for two characters. Example:
// char buf[2];
// PutTwoDigits(42, buf);
// // buf[0] == '4'
// // buf[1] == '2'
inline void PutTwoDigits(size_t i, char* buf) {
static const char two_ASCII_digits[100][2] = {
{'0', '0'}, {'0', '1'}, {'0', '2'}, {'0', '3'}, {'0', '4'},
{'0', '5'}, {'0', '6'}, {'0', '7'}, {'0', '8'}, {'0', '9'},
{'1', '0'}, {'1', '1'}, {'1', '2'}, {'1', '3'}, {'1', '4'},
{'1', '5'}, {'1', '6'}, {'1', '7'}, {'1', '8'}, {'1', '9'},
{'2', '0'}, {'2', '1'}, {'2', '2'}, {'2', '3'}, {'2', '4'},
{'2', '5'}, {'2', '6'}, {'2', '7'}, {'2', '8'}, {'2', '9'},
{'3', '0'}, {'3', '1'}, {'3', '2'}, {'3', '3'}, {'3', '4'},
{'3', '5'}, {'3', '6'}, {'3', '7'}, {'3', '8'}, {'3', '9'},
{'4', '0'}, {'4', '1'}, {'4', '2'}, {'4', '3'}, {'4', '4'},
{'4', '5'}, {'4', '6'}, {'4', '7'}, {'4', '8'}, {'4', '9'},
{'5', '0'}, {'5', '1'}, {'5', '2'}, {'5', '3'}, {'5', '4'},
{'5', '5'}, {'5', '6'}, {'5', '7'}, {'5', '8'}, {'5', '9'},
{'6', '0'}, {'6', '1'}, {'6', '2'}, {'6', '3'}, {'6', '4'},
{'6', '5'}, {'6', '6'}, {'6', '7'}, {'6', '8'}, {'6', '9'},
{'7', '0'}, {'7', '1'}, {'7', '2'}, {'7', '3'}, {'7', '4'},
{'7', '5'}, {'7', '6'}, {'7', '7'}, {'7', '8'}, {'7', '9'},
{'8', '0'}, {'8', '1'}, {'8', '2'}, {'8', '3'}, {'8', '4'},
{'8', '5'}, {'8', '6'}, {'8', '7'}, {'8', '8'}, {'8', '9'},
{'9', '0'}, {'9', '1'}, {'9', '2'}, {'9', '3'}, {'9', '4'},
{'9', '5'}, {'9', '6'}, {'9', '7'}, {'9', '8'}, {'9', '9'}
};
assert(i < 100);
memcpy(buf, two_ASCII_digits[i], 2);
}
} // namespace
bool SimpleAtob(absl::string_view str, bool* value) {
ABSL_RAW_CHECK(value != nullptr, "Output pointer must not be nullptr.");
if (CaseEqual(str, "true") || CaseEqual(str, "t") ||
CaseEqual(str, "yes") || CaseEqual(str, "y") ||
CaseEqual(str, "1")) {
*value = true;
return true;
}
if (CaseEqual(str, "false") || CaseEqual(str, "f") ||
CaseEqual(str, "no") || CaseEqual(str, "n") ||
CaseEqual(str, "0")) {
*value = false;
return true;
}
return false;
}
// ----------------------------------------------------------------------
// FastInt32ToBuffer()
// FastUInt32ToBuffer()
// FastInt64ToBuffer()
// FastUInt64ToBuffer()
//
// Like the Fast*ToBuffer() functions above, these are intended for speed.
// Unlike the Fast*ToBuffer() functions, however, these functions write
// their output to the beginning of the buffer (hence the name, as the
// output is left-aligned). The caller is responsible for ensuring that
// the buffer has enough space to hold the output.
//
// Returns a pointer to the end of the std::string (i.e. the null character
// terminating the std::string).
// ----------------------------------------------------------------------
namespace {
// Used to optimize printing a decimal number's final digit.
const char one_ASCII_final_digits[10][2] {
{'0', 0}, {'1', 0}, {'2', 0}, {'3', 0}, {'4', 0},
{'5', 0}, {'6', 0}, {'7', 0}, {'8', 0}, {'9', 0},
};
} // namespace
char* numbers_internal::FastUInt32ToBuffer(uint32_t i, char* buffer) {
uint32_t digits;
// The idea of this implementation is to trim the number of divides to as few
// as possible, and also reducing memory stores and branches, by going in
// steps of two digits at a time rather than one whenever possible.
// The huge-number case is first, in the hopes that the compiler will output
// that case in one branch-free block of code, and only output conditional
// branches into it from below.
if (i >= 1000000000) { // >= 1,000,000,000
digits = i / 100000000; // 100,000,000
i -= digits * 100000000;
PutTwoDigits(digits, buffer);
buffer += 2;
lt100_000_000:
digits = i / 1000000; // 1,000,000
i -= digits * 1000000;
PutTwoDigits(digits, buffer);
buffer += 2;
lt1_000_000:
digits = i / 10000; // 10,000
i -= digits * 10000;
PutTwoDigits(digits, buffer);
buffer += 2;
lt10_000:
digits = i / 100;
i -= digits * 100;
PutTwoDigits(digits, buffer);
buffer += 2;
lt100:
digits = i;
PutTwoDigits(digits, buffer);
buffer += 2;
*buffer = 0;
return buffer;
}
if (i < 100) {
digits = i;
if (i >= 10) goto lt100;
memcpy(buffer, one_ASCII_final_digits[i], 2);
return buffer + 1;
}
if (i < 10000) { // 10,000
if (i >= 1000) goto lt10_000;
digits = i / 100;
i -= digits * 100;
*buffer++ = '0' + digits;
goto lt100;
}
if (i < 1000000) { // 1,000,000
if (i >= 100000) goto lt1_000_000;
digits = i / 10000; // 10,000
i -= digits * 10000;
*buffer++ = '0' + digits;
goto lt10_000;
}
if (i < 100000000) { // 100,000,000
if (i >= 10000000) goto lt100_000_000;
digits = i / 1000000; // 1,000,000
i -= digits * 1000000;
*buffer++ = '0' + digits;
goto lt1_000_000;
}
// we already know that i < 1,000,000,000
digits = i / 100000000; // 100,000,000
i -= digits * 100000000;
*buffer++ = '0' + digits;
goto lt100_000_000;
}
char* numbers_internal::FastInt32ToBuffer(int32_t i, char* buffer) {
uint32_t u = i;
if (i < 0) {
*buffer++ = '-';
// We need to do the negation in modular (i.e., "unsigned")
// arithmetic; MSVC++ apprently warns for plain "-u", so
// we write the equivalent expression "0 - u" instead.
u = 0 - u;
}
return numbers_internal::FastUInt32ToBuffer(u, buffer);
}
char* numbers_internal::FastUInt64ToBuffer(uint64_t i, char* buffer) {
uint32_t u32 = static_cast<uint32_t>(i);
if (u32 == i) return numbers_internal::FastUInt32ToBuffer(u32, buffer);
// Here we know i has at least 10 decimal digits.
uint64_t top_1to11 = i / 1000000000;
u32 = static_cast<uint32_t>(i - top_1to11 * 1000000000);
uint32_t top_1to11_32 = static_cast<uint32_t>(top_1to11);
if (top_1to11_32 == top_1to11) {
buffer = numbers_internal::FastUInt32ToBuffer(top_1to11_32, buffer);
} else {
// top_1to11 has more than 32 bits too; print it in two steps.
uint32_t top_8to9 = static_cast<uint32_t>(top_1to11 / 100);
uint32_t mid_2 = static_cast<uint32_t>(top_1to11 - top_8to9 * 100);
buffer = numbers_internal::FastUInt32ToBuffer(top_8to9, buffer);
PutTwoDigits(mid_2, buffer);
buffer += 2;
}
// We have only 9 digits now, again the maximum uint32_t can handle fully.
uint32_t digits = u32 / 10000000; // 10,000,000
u32 -= digits * 10000000;
PutTwoDigits(digits, buffer);
buffer += 2;
digits = u32 / 100000; // 100,000
u32 -= digits * 100000;
PutTwoDigits(digits, buffer);
buffer += 2;
digits = u32 / 1000; // 1,000
u32 -= digits * 1000;
PutTwoDigits(digits, buffer);
buffer += 2;
digits = u32 / 10;
u32 -= digits * 10;
PutTwoDigits(digits, buffer);
buffer += 2;
memcpy(buffer, one_ASCII_final_digits[u32], 2);
return buffer + 1;
}
char* numbers_internal::FastInt64ToBuffer(int64_t i, char* buffer) {
uint64_t u = i;
if (i < 0) {
*buffer++ = '-';
u = 0 - u;
}
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?
static inline int CountLeadingZeros64(uint64_t n) {
int zeroes = 60;
if (n >> 32) zeroes -= 32, n >>= 32;
if (n >> 16) zeroes -= 16, n >>= 16;
if (n >> 8) zeroes -= 8, n >>= 8;
if (n >> 4) zeroes -= 4, n >>= 4;
return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0\0"[n] + zeroes;
}
// Given a 128-bit number expressed as a pair of uint64_t, high half first,
// return that number multiplied by the given 32-bit value. If the result is
// too large to fit in a 128-bit number, divide it by 2 until it fits.
static std::pair<uint64_t, uint64_t> Mul32(std::pair<uint64_t, uint64_t> num,
uint32_t mul) {
uint64_t bits0_31 = num.second & 0xFFFFFFFF;
uint64_t bits32_63 = num.second >> 32;
uint64_t bits64_95 = num.first & 0xFFFFFFFF;
uint64_t bits96_127 = num.first >> 32;
// The picture so far: each of these 64-bit values has only the lower 32 bits
// filled in.
// bits96_127: [ 00000000 xxxxxxxx ]
// bits64_95: [ 00000000 xxxxxxxx ]
// bits32_63: [ 00000000 xxxxxxxx ]
// bits0_31: [ 00000000 xxxxxxxx ]
bits0_31 *= mul;
bits32_63 *= mul;
bits64_95 *= mul;
bits96_127 *= mul;
// Now the top halves may also have value, though all 64 of their bits will
// never be set at the same time, since they are a result of a 32x32 bit
// multiply. This makes the carry calculation slightly easier.
// bits96_127: [ mmmmmmmm | mmmmmmmm ]
// bits64_95: [ | mmmmmmmm mmmmmmmm | ]
// bits32_63: | [ mmmmmmmm | mmmmmmmm ]
// bits0_31: | [ | mmmmmmmm mmmmmmmm ]
// eventually: [ bits128_up | ...bits64_127.... | ..bits0_63... ]
uint64_t bits0_63 = bits0_31 + (bits32_63 << 32);
uint64_t bits64_127 = bits64_95 + (bits96_127 << 32) + (bits32_63 >> 32) +
(bits0_63 < bits0_31);
uint64_t bits128_up = (bits96_127 >> 32) + (bits64_127 < bits64_95);
if (bits128_up == 0) return {bits64_127, bits0_63};
int shift = 64 - CountLeadingZeros64(bits128_up);
uint64_t lo = (bits0_63 >> shift) + (bits64_127 << (64 - shift));
uint64_t hi = (bits64_127 >> shift) + (bits128_up << (64 - shift));
return {hi, lo};
}
// Compute num * 5 ^ expfive, and return the first 128 bits of the result,
// where the first bit is always a one. So PowFive(1, 0) starts 0b100000,
// PowFive(1, 1) starts 0b101000, PowFive(1, 2) starts 0b110010, etc.
static std::pair<uint64_t, uint64_t> PowFive(uint64_t num, int expfive) {
std::pair<uint64_t, uint64_t> result = {num, 0};
while (expfive >= 13) {
// 5^13 is the highest power of five that will fit in a 32-bit integer.
result = Mul32(result, 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5);
expfive -= 13;
}
constexpr int powers_of_five[13] = {
1,
5,
5 * 5,
5 * 5 * 5,
5 * 5 * 5 * 5,
5 * 5 * 5 * 5 * 5,
5 * 5 * 5 * 5 * 5 * 5,
5 * 5 * 5 * 5 * 5 * 5 * 5,
5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5};
result = Mul32(result, powers_of_five[expfive & 15]);
int shift = CountLeadingZeros64(result.first);
if (shift != 0) {
result.first = (result.first << shift) + (result.second >> (64 - shift));
result.second = (result.second << shift);
}
return result;
}
struct ExpDigits {
int32_t exponent;
char digits[6];
};
// SplitToSix converts value, a positive double-precision floating-point number,
// into a base-10 exponent and 6 ASCII digits, where the first digit is never
// zero. For example, SplitToSix(1) returns an exponent of zero and a digits
// array of {'1', '0', '0', '0', '0', '0'}. If value is exactly halfway between
// two possible representations, e.g. value = 100000.5, then "round to even" is
// performed.
static ExpDigits SplitToSix(const double value) {
ExpDigits exp_dig;
int exp = 5;
double d = value;
// First step: calculate a close approximation of the output, where the
// value d will be between 100,000 and 999,999, representing the digits
// in the output ASCII array, and exp is the base-10 exponent. It would be
// faster to use a table here, and to look up the base-2 exponent of value,
// however value is an IEEE-754 64-bit number, so the table would have 2,000
// entries, which is not cache-friendly.
if (d >= 999999.5) {
if (d >= 1e+261) exp += 256, d *= 1e-256;
if (d >= 1e+133) exp += 128, d *= 1e-128;
if (d >= 1e+69) exp += 64, d *= 1e-64;
if (d >= 1e+37) exp += 32, d *= 1e-32;
if (d >= 1e+21) exp += 16, d *= 1e-16;
if (d >= 1e+13) exp += 8, d *= 1e-8;
if (d >= 1e+9) exp += 4, d *= 1e-4;
if (d >= 1e+7) exp += 2, d *= 1e-2;
if (d >= 1e+6) exp += 1, d *= 1e-1;
} else {
if (d < 1e-250) exp -= 256, d *= 1e256;
if (d < 1e-122) exp -= 128, d *= 1e128;
if (d < 1e-58) exp -= 64, d *= 1e64;
if (d < 1e-26) exp -= 32, d *= 1e32;
if (d < 1e-10) exp -= 16, d *= 1e16;
if (d < 1e-2) exp -= 8, d *= 1e8;
if (d < 1e+2) exp -= 4, d *= 1e4;
if (d < 1e+4) exp -= 2, d *= 1e2;
if (d < 1e+5) exp -= 1, d *= 1e1;
}
// At this point, d is in the range [99999.5..999999.5) and exp is in the
// range [-324..308]. Since we need to round d up, we want to add a half
// and truncate.
// However, the technique above may have lost some precision, due to its
// repeated multiplication by constants that each may be off by half a bit
// of precision. This only matters if we're close to the edge though.
// Since we'd like to know if the fractional part of d is close to a half,
// we multiply it by 65536 and see if the fractional part is close to 32768.
// (The number doesn't have to be a power of two,but powers of two are faster)
uint64_t d64k = d * 65536;
int dddddd; // A 6-digit decimal integer.
if ((d64k % 65536) == 32767 || (d64k % 65536) == 32768) {
// OK, it's fairly likely that precision was lost above, which is
// not a surprise given only 52 mantissa bits are available. Therefore
// redo the calculation using 128-bit numbers. (64 bits are not enough).
// Start out with digits rounded down; maybe add one below.
dddddd = static_cast<int>(d64k / 65536);
// mantissa is a 64-bit integer representing M.mmm... * 2^63. The actual
// value we're representing, of course, is M.mmm... * 2^exp2.
int exp2;
double m = std::frexp(value, &exp2);
uint64_t mantissa = m * (32768.0 * 65536.0 * 65536.0 * 65536.0);
// std::frexp returns an m value in the range [0.5, 1.0), however we
// can't multiply it by 2^64 and convert to an integer because some FPUs
// throw an exception when converting an number higher than 2^63 into an
// integer - even an unsigned 64-bit integer! Fortunately it doesn't matter
// since m only has 52 significant bits anyway.
mantissa <<= 1;
exp2 -= 64; // not needed, but nice for debugging
// OK, we are here to compare:
// (dddddd + 0.5) * 10^(exp-5) vs. mantissa * 2^exp2
// so we can round up dddddd if appropriate. Those values span the full
// range of 600 orders of magnitude of IEE 64-bit floating-point.
// Fortunately, we already know they are very close, so we don't need to
// track the base-2 exponent of both sides. This greatly simplifies the
// the math since the 2^exp2 calculation is unnecessary and the power-of-10
// calculation can become a power-of-5 instead.
std::pair<uint64_t, uint64_t> edge, val;
if (exp >= 6) {
// Compare (dddddd + 0.5) * 5 ^ (exp - 5) to mantissa
// Since we're tossing powers of two, 2 * dddddd + 1 is the
// same as dddddd + 0.5
edge = PowFive(2 * dddddd + 1, exp - 5);
val.first = mantissa;
val.second = 0;
} else {
// We can't compare (dddddd + 0.5) * 5 ^ (exp - 5) to mantissa as we did
// above because (exp - 5) is negative. So we compare (dddddd + 0.5) to
// mantissa * 5 ^ (5 - exp)
edge = PowFive(2 * dddddd + 1, 0);
val = PowFive(mantissa, 5 - exp);
}
// printf("exp=%d %016lx %016lx vs %016lx %016lx\n", exp, val.first,
// val.second, edge.first, edge.second);
if (val > edge) {
dddddd++;
} else if (val == edge) {
dddddd += (dddddd & 1);
}
} else {
// Here, we are not close to the edge.
dddddd = static_cast<int>((d64k + 32768) / 65536);
}
if (dddddd == 1000000) {
dddddd = 100000;
exp += 1;
}
exp_dig.exponent = exp;
int two_digits = dddddd / 10000;
dddddd -= two_digits * 10000;
PutTwoDigits(two_digits, &exp_dig.digits[0]);
two_digits = dddddd / 100;
dddddd -= two_digits * 100;
PutTwoDigits(two_digits, &exp_dig.digits[2]);
PutTwoDigits(dddddd, &exp_dig.digits[4]);
return exp_dig;
}
// Helper function for fast formatting of floating-point.
// The result is the same as "%g", a.k.a. "%.6g".
size_t numbers_internal::SixDigitsToBuffer(double d, char* const 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(d)) {
strcpy(out, "nan"); // NOLINT(runtime/printf)
return 3;
}
if (d == 0) { // +0 and -0 are handled here
if (std::signbit(d)) *out++ = '-';
*out++ = '0';
*out = 0;
return out - buffer;
}
if (d < 0) {
*out++ = '-';
d = -d;
}
if (std::isinf(d)) {
strcpy(out, "inf"); // NOLINT(runtime/printf)
return out + 3 - buffer;
}
auto exp_dig = SplitToSix(d);
int exp = exp_dig.exponent;
const char* digits = exp_dig.digits;
out[0] = '0';
out[1] = '.';
switch (exp) {
case 5:
memcpy(out, &digits[0], 6), out += 6;
*out = 0;
return out - buffer;
case 4:
memcpy(out, &digits[0], 5), out += 5;
if (digits[5] != '0') {
*out++ = '.';
*out++ = digits[5];
}
*out = 0;
return out - buffer;
case 3:
memcpy(out, &digits[0], 4), out += 4;
if ((digits[5] | digits[4]) != '0') {
*out++ = '.';
*out++ = digits[4];
if (digits[5] != '0') *out++ = digits[5];
}
*out = 0;
return out - buffer;
case 2:
memcpy(out, &digits[0], 3), out += 3;
*out++ = '.';
memcpy(out, &digits[3], 3);
out += 3;
while (out[-1] == '0') --out;
if (out[-1] == '.') --out;
*out = 0;
return out - buffer;
case 1:
memcpy(out, &digits[0], 2), out += 2;
*out++ = '.';
memcpy(out, &digits[2], 4);
out += 4;
while (out[-1] == '0') --out;
if (out[-1] == '.') --out;
*out = 0;
return out - buffer;
case 0:
memcpy(out, &digits[0], 1), out += 1;
*out++ = '.';
memcpy(out, &digits[1], 5);
out += 5;
while (out[-1] == '0') --out;
if (out[-1] == '.') --out;
*out = 0;
return out - buffer;
case -4:
out[2] = '0';
++out;
ABSL_FALLTHROUGH_INTENDED;
case -3:
out[2] = '0';
++out;
ABSL_FALLTHROUGH_INTENDED;
case -2:
out[2] = '0';
++out;
ABSL_FALLTHROUGH_INTENDED;
case -1:
out += 2;
memcpy(out, &digits[0], 6);
out += 6;
while (out[-1] == '0') --out;
*out = 0;
return out - buffer;
}
assert(exp < -4 || exp >= 6);
out[0] = digits[0];
assert(out[1] == '.');
out += 2;
memcpy(out, &digits[1], 5), out += 5;
while (out[-1] == '0') --out;
if (out[-1] == '.') --out;
*out++ = 'e';
if (exp > 0) {
*out++ = '+';
} else {
*out++ = '-';
exp = -exp;
}
if (exp > 99) {
int dig1 = exp / 100;
exp -= dig1 * 100;
*out++ = '0' + dig1;
}
PutTwoDigits(exp, out);
out += 2;
*out = 0;
return out - buffer;
}
namespace {
// Represents integer values of digits.
// Uses 36 to indicate an invalid character since we support
// bases up to 36.
static const int8_t kAsciiToInt[256] = {
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, // 16 36s.
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 0, 1, 2, 3, 4, 5,
6, 7, 8, 9, 36, 36, 36, 36, 36, 36, 36, 10, 11, 12, 13, 14, 15, 16, 17,
18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
36, 36, 36, 36, 36, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 36, 36, 36, 36, 36, 36,
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36,
36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36};
// Parse the sign and optional hex or oct prefix in text.
inline bool safe_parse_sign_and_base(absl::string_view* text /*inout*/,
int* base_ptr /*inout*/,
bool* negative_ptr /*output*/) {
if (text->data() == nullptr) {
return false;
}
const char* start = text->data();
const char* end = start + text->size();
int base = *base_ptr;
// Consume whitespace.
while (start < end && absl::ascii_isspace(start[0])) {
++start;
}
while (start < end && absl::ascii_isspace(end[-1])) {
--end;
}
if (start >= end) {
return false;
}
// Consume sign.
*negative_ptr = (start[0] == '-');
if (*negative_ptr || start[0] == '+') {
++start;
if (start >= end) {
return false;
}
}
// Consume base-dependent prefix.
// base 0: "0x" -> base 16, "0" -> base 8, default -> base 10
// base 16: "0x" -> base 16
// Also validate the base.
if (base == 0) {
if (end - start >= 2 && start[0] == '0' &&
(start[1] == 'x' || start[1] == 'X')) {
base = 16;
start += 2;
if (start >= end) {
// "0x" with no digits after is invalid.
return false;
}
} else if (end - start >= 1 && start[0] == '0') {
base = 8;
start += 1;
} else {
base = 10;
}
} else if (base == 16) {
if (end - start >= 2 && start[0] == '0' &&
(start[1] == 'x' || start[1] == 'X')) {
start += 2;
if (start >= end) {
// "0x" with no digits after is invalid.
return false;
}
}
} else if (base >= 2 && base <= 36) {
// okay
} else {
return false;
}
*text = absl::string_view(start, end - start);
*base_ptr = base;
return true;
}
// Consume digits.
//
// The classic loop:
//
// for each digit
// value = value * base + digit
// value *= sign
//
// The classic loop needs overflow checking. It also fails on the most
// negative integer, -2147483648 in 32-bit two's complement representation.
//
// My improved loop:
//
// if (!negative)
// for each digit
// value = value * base
// value = value + digit
// else
// for each digit
// value = value * base
// value = value - digit
//
// Overflow checking becomes simple.
// Lookup tables per IntType:
// vmax/base and vmin/base are precomputed because division costs at least 8ns.
// TODO(junyer): Doing this per base instead (i.e. an array of structs, not a
// struct of arrays) would probably be better in terms of d-cache for the most
// commonly used bases.
template <typename IntType>
struct LookupTables {
static const IntType kVmaxOverBase[];
static const IntType kVminOverBase[];
};
// An array initializer macro for X/base where base in [0, 36].
// However, note that lookups for base in [0, 1] should never happen because
// base has been validated to be in [2, 36] by safe_parse_sign_and_base().
#define X_OVER_BASE_INITIALIZER(X) \
{ \
0, 0, X / 2, X / 3, X / 4, X / 5, X / 6, X / 7, X / 8, X / 9, X / 10, \
X / 11, X / 12, X / 13, X / 14, X / 15, X / 16, X / 17, X / 18, \
X / 19, X / 20, X / 21, X / 22, X / 23, X / 24, X / 25, X / 26, \
X / 27, X / 28, X / 29, X / 30, X / 31, X / 32, X / 33, X / 34, \
X / 35, X / 36, \
}
template <typename IntType>
const IntType LookupTables<IntType>::kVmaxOverBase[] =
X_OVER_BASE_INITIALIZER(std::numeric_limits<IntType>::max());
template <typename IntType>
const IntType LookupTables<IntType>::kVminOverBase[] =
X_OVER_BASE_INITIALIZER(std::numeric_limits<IntType>::min());
#undef X_OVER_BASE_INITIALIZER
template <typename IntType>
inline bool safe_parse_positive_int(absl::string_view text, int base,
IntType* value_p) {
IntType value = 0;
const IntType vmax = std::numeric_limits<IntType>::max();
assert(vmax > 0);
assert(base >= 0);
assert(vmax >= static_cast<IntType>(base));
const IntType vmax_over_base = LookupTables<IntType>::kVmaxOverBase[base];
const char* start = text.data();
const char* end = start + text.size();
// loop over digits
for (; start < end; ++start) {
unsigned char c = static_cast<unsigned char>(start[0]);
int digit = kAsciiToInt[c];
if (digit >= base) {
*value_p = value;
return false;
}
if (value > vmax_over_base) {
*value_p = vmax;
return false;
}
value *= base;
if (value > vmax - digit) {
*value_p = vmax;
return false;
}
value += digit;
}
*value_p = value;
return true;
}
template <typename IntType>
inline bool safe_parse_negative_int(absl::string_view text, int base,
IntType* value_p) {
IntType value = 0;
const IntType vmin = std::numeric_limits<IntType>::min();
assert(vmin < 0);
assert(vmin <= 0 - base);
IntType vmin_over_base = LookupTables<IntType>::kVminOverBase[base];
// 2003 c++ standard [expr.mul]
// "... the sign of the remainder is implementation-defined."
// Although (vmin/base)*base + vmin%base is always vmin.
// 2011 c++ standard tightens the spec but we cannot rely on it.
// TODO(junyer): Handle this in the lookup table generation.
if (vmin % base > 0) {
vmin_over_base += 1;
}
const char* start = text.data();
const char* end = start + text.size();
// loop over digits
for (; start < end; ++start) {
unsigned char c = static_cast<unsigned char>(start[0]);
int digit = kAsciiToInt[c];
if (digit >= base) {
*value_p = value;
return false;
}
if (value < vmin_over_base) {
*value_p = vmin;
return false;
}
value *= base;
if (value < vmin + digit) {
*value_p = vmin;
return false;
}
value -= digit;
}
*value_p = value;
return true;
}
// Input format based on POSIX.1-2008 strtol
// http://pubs.opengroup.org/onlinepubs/9699919799/functions/strtol.html
template <typename IntType>
inline bool safe_int_internal(absl::string_view text, IntType* value_p,
int base) {
*value_p = 0;
bool negative;
if (!safe_parse_sign_and_base(&text, &base, &negative)) {
return false;
}
if (!negative) {
return safe_parse_positive_int(text, base, value_p);
} else {
return safe_parse_negative_int(text, base, value_p);
}
}
template <typename IntType>
inline bool safe_uint_internal(absl::string_view text, IntType* value_p,
int base) {
*value_p = 0;
bool negative;
if (!safe_parse_sign_and_base(&text, &base, &negative) || negative) {
return false;
}
return safe_parse_positive_int(text, base, value_p);
}
} // anonymous namespace
namespace numbers_internal {
bool safe_strto32_base(absl::string_view text, int32_t* value, int base) {
return safe_int_internal<int32_t>(text, value, base);
}
bool safe_strto64_base(absl::string_view text, int64_t* value, int base) {
return safe_int_internal<int64_t>(text, value, base);
}
bool safe_strtou32_base(absl::string_view text, uint32_t* value, int base) {
return safe_uint_internal<uint32_t>(text, value, base);
}
bool safe_strtou64_base(absl::string_view text, uint64_t* value, int base) {
return safe_uint_internal<uint64_t>(text, value, base);
}
} // namespace numbers_internal
} // namespace absl
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