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lokinet/vendor/abseil-cpp/absl/strings/numbers.cc
Michael 41f9f5fad6
Import abseil LTS 20181200
2019-02-03 01:56:38 +00:00

915 lines
30 KiB
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// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// This file contains string processing functions related to
// numeric values.
#include "absl/strings/numbers.h"
#include <algorithm>
#include <cassert>
#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 <utility>
#include "absl/base/internal/bits.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/strings/ascii.h"
#include "absl/strings/charconv.h"
#include "absl/strings/internal/memutil.h"
#include "absl/strings/str_cat.h"
namespace absl {
inline namespace lts_2018_12_18 {
bool SimpleAtof(absl::string_view str, float* value) {
*value = 0.0;
str = StripAsciiWhitespace(str);
if (!str.empty() && str[0] == '+') {
str.remove_prefix(1);
}
auto result = absl::from_chars(str.data(), str.data() + str.size(), *value);
if (result.ec == std::errc::invalid_argument) {
return false;
}
if (result.ptr != str.data() + str.size()) {
// not all non-whitespace characters consumed
return false;
}
// from_chars() with DR 3801's current wording will return max() on
// overflow. SimpleAtof returns infinity instead.
if (result.ec == std::errc::result_out_of_range) {
if (*value > 1.0) {
*value = std::numeric_limits<float>::infinity();
} else if (*value < -1.0) {
*value = -std::numeric_limits<float>::infinity();
}
}
return true;
}
bool SimpleAtod(absl::string_view str, double* value) {
*value = 0.0;
str = StripAsciiWhitespace(str);
if (!str.empty() && str[0] == '+') {
str.remove_prefix(1);
}
auto result = absl::from_chars(str.data(), str.data() + str.size(), *value);
if (result.ec == std::errc::invalid_argument) {
return false;
}
if (result.ptr != str.data() + str.size()) {
// not all non-whitespace characters consumed
return false;
}
// from_chars() with DR 3801's current wording will return max() on
// overflow. SimpleAtod returns infinity instead.
if (result.ec == std::errc::result_out_of_range) {
if (*value > 1.0) {
*value = std::numeric_limits<double>::infinity();
} else if (*value < -1.0) {
*value = -std::numeric_limits<double>::infinity();
}
}
return true;
}
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;
}
// ----------------------------------------------------------------------
// FastIntToBuffer() overloads
//
// 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. The caller is responsible
// for ensuring that the buffer has enough space to hold the output.
//
// Returns a pointer to the end of the string (i.e. the null character
// terminating the 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::FastIntToBuffer(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::FastIntToBuffer(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::FastIntToBuffer(u, buffer);
}
char* numbers_internal::FastIntToBuffer(uint64_t i, char* buffer) {
uint32_t u32 = static_cast<uint32_t>(i);
if (u32 == i) return numbers_internal::FastIntToBuffer(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::FastIntToBuffer(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::FastIntToBuffer(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::FastIntToBuffer(int64_t i, char* buffer) {
uint64_t u = i;
if (i < 0) {
*buffer++ = '-';
u = 0 - u;
}
return numbers_internal::FastIntToBuffer(u, buffer);
}
// 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 - base_internal::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 = base_internal::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
} // inline namespace lts_2018_12_18
} // namespace absl
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