fc8dc48020
git-subtree-dir: third_party/abseil_cpp git-subtree-mainline:ffb2ae54begit-subtree-split:768eb2ca28
266 lines
11 KiB
C++
266 lines
11 KiB
C++
//
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// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// -----------------------------------------------------------------------------
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// File: numbers.h
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// -----------------------------------------------------------------------------
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//
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// This package contains functions for converting strings to numbers. For
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// converting numbers to strings, use `StrCat()` or `StrAppend()` in str_cat.h,
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// which automatically detect and convert most number values appropriately.
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#ifndef ABSL_STRINGS_NUMBERS_H_
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#define ABSL_STRINGS_NUMBERS_H_
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#ifdef __SSE4_2__
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#include <x86intrin.h>
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#endif
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#include <cstddef>
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#include <cstdlib>
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#include <cstring>
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#include <ctime>
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#include <limits>
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#include <string>
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#include <type_traits>
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#include "absl/base/config.h"
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#include "absl/base/internal/bits.h"
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#ifdef __SSE4_2__
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// TODO(jorg): Remove this when we figure out the right way
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// to swap bytes on SSE 4.2 that works with the compilers
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// we claim to support. Also, add tests for the compiler
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// that doesn't support the Intel _bswap64 intrinsic but
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// does support all the SSE 4.2 intrinsics
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#include "absl/base/internal/endian.h"
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#endif
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#include "absl/base/macros.h"
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#include "absl/base/port.h"
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#include "absl/numeric/int128.h"
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#include "absl/strings/string_view.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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// SimpleAtoi()
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//
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// Converts the given string (optionally followed or preceded by ASCII
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// whitespace) into an integer value, returning `true` if successful. The string
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// must reflect a base-10 integer whose value falls within the range of the
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// integer type (optionally preceded by a `+` or `-`). If any errors are
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// encountered, this function returns `false`, leaving `out` in an unspecified
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// state.
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template <typename int_type>
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ABSL_MUST_USE_RESULT bool SimpleAtoi(absl::string_view str, int_type* out);
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// SimpleAtof()
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//
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// Converts the given string (optionally followed or preceded by ASCII
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// whitespace) into a float, which may be rounded on overflow or underflow,
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// returning `true` if successful.
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// See https://en.cppreference.com/w/c/string/byte/strtof for details about the
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// allowed formats for `str`, except SimpleAtof() is locale-independent and will
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// always use the "C" locale. If any errors are encountered, this function
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// returns `false`, leaving `out` in an unspecified state.
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ABSL_MUST_USE_RESULT bool SimpleAtof(absl::string_view str, float* out);
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// SimpleAtod()
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//
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// Converts the given string (optionally followed or preceded by ASCII
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// whitespace) into a double, which may be rounded on overflow or underflow,
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// returning `true` if successful.
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// See https://en.cppreference.com/w/c/string/byte/strtof for details about the
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// allowed formats for `str`, except SimpleAtod is locale-independent and will
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// always use the "C" locale. If any errors are encountered, this function
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// returns `false`, leaving `out` in an unspecified state.
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ABSL_MUST_USE_RESULT bool SimpleAtod(absl::string_view str, double* out);
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// SimpleAtob()
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//
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// Converts the given string into a boolean, returning `true` if successful.
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// The following case-insensitive strings are interpreted as boolean `true`:
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// "true", "t", "yes", "y", "1". The following case-insensitive strings
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// are interpreted as boolean `false`: "false", "f", "no", "n", "0". If any
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// errors are encountered, this function returns `false`, leaving `out` in an
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// unspecified state.
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ABSL_MUST_USE_RESULT bool SimpleAtob(absl::string_view str, bool* out);
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ABSL_NAMESPACE_END
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} // namespace absl
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// End of public API. Implementation details follow.
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace numbers_internal {
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// Digit conversion.
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ABSL_DLL extern const char kHexChar[17]; // 0123456789abcdef
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ABSL_DLL extern const char
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kHexTable[513]; // 000102030405060708090a0b0c0d0e0f1011...
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ABSL_DLL extern const char
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two_ASCII_digits[100][2]; // 00, 01, 02, 03...
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// Writes a two-character representation of 'i' to 'buf'. 'i' must be in the
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// range 0 <= i < 100, and buf must have space for two characters. Example:
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// char buf[2];
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// PutTwoDigits(42, buf);
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// // buf[0] == '4'
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// // buf[1] == '2'
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inline void PutTwoDigits(size_t i, char* buf) {
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assert(i < 100);
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memcpy(buf, two_ASCII_digits[i], 2);
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}
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// safe_strto?() functions for implementing SimpleAtoi()
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bool safe_strto32_base(absl::string_view text, int32_t* value, int base);
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bool safe_strto64_base(absl::string_view text, int64_t* value, int base);
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bool safe_strtou32_base(absl::string_view text, uint32_t* value, int base);
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bool safe_strtou64_base(absl::string_view text, uint64_t* value, int base);
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bool safe_strtou128_base(absl::string_view text, absl::uint128* value,
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int base);
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static const int kFastToBufferSize = 32;
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static const int kSixDigitsToBufferSize = 16;
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// Helper function for fast formatting of floating-point values.
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// The result is the same as printf's "%g", a.k.a. "%.6g"; that is, six
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// significant digits are returned, trailing zeros are removed, and numbers
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// outside the range 0.0001-999999 are output using scientific notation
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// (1.23456e+06). This routine is heavily optimized.
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// Required buffer size is `kSixDigitsToBufferSize`.
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size_t SixDigitsToBuffer(double d, char* buffer);
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// These functions are intended for speed. All functions take an output buffer
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// as an argument and return a pointer to the last byte they wrote, which is the
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// terminating '\0'. At most `kFastToBufferSize` bytes are written.
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char* FastIntToBuffer(int32_t, char*);
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char* FastIntToBuffer(uint32_t, char*);
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char* FastIntToBuffer(int64_t, char*);
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char* FastIntToBuffer(uint64_t, char*);
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// For enums and integer types that are not an exact match for the types above,
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// use templates to call the appropriate one of the four overloads above.
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template <typename int_type>
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char* FastIntToBuffer(int_type i, char* buffer) {
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static_assert(sizeof(i) <= 64 / 8,
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"FastIntToBuffer works only with 64-bit-or-less integers.");
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// TODO(jorg): This signed-ness check is used because it works correctly
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// with enums, and it also serves to check that int_type is not a pointer.
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// If one day something like std::is_signed<enum E> works, switch to it.
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if (static_cast<int_type>(1) - 2 < 0) { // Signed
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if (sizeof(i) > 32 / 8) { // 33-bit to 64-bit
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return FastIntToBuffer(static_cast<int64_t>(i), buffer);
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} else { // 32-bit or less
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return FastIntToBuffer(static_cast<int32_t>(i), buffer);
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}
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} else { // Unsigned
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if (sizeof(i) > 32 / 8) { // 33-bit to 64-bit
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return FastIntToBuffer(static_cast<uint64_t>(i), buffer);
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} else { // 32-bit or less
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return FastIntToBuffer(static_cast<uint32_t>(i), buffer);
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}
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}
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}
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// Implementation of SimpleAtoi, generalized to support arbitrary base (used
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// with base different from 10 elsewhere in Abseil implementation).
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template <typename int_type>
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ABSL_MUST_USE_RESULT bool safe_strtoi_base(absl::string_view s, int_type* out,
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int base) {
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static_assert(sizeof(*out) == 4 || sizeof(*out) == 8,
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"SimpleAtoi works only with 32-bit or 64-bit integers.");
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static_assert(!std::is_floating_point<int_type>::value,
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"Use SimpleAtof or SimpleAtod instead.");
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bool parsed;
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// TODO(jorg): This signed-ness check is used because it works correctly
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// with enums, and it also serves to check that int_type is not a pointer.
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// If one day something like std::is_signed<enum E> works, switch to it.
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if (static_cast<int_type>(1) - 2 < 0) { // Signed
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if (sizeof(*out) == 64 / 8) { // 64-bit
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int64_t val;
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parsed = numbers_internal::safe_strto64_base(s, &val, base);
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*out = static_cast<int_type>(val);
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} else { // 32-bit
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int32_t val;
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parsed = numbers_internal::safe_strto32_base(s, &val, base);
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*out = static_cast<int_type>(val);
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}
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} else { // Unsigned
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if (sizeof(*out) == 64 / 8) { // 64-bit
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uint64_t val;
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parsed = numbers_internal::safe_strtou64_base(s, &val, base);
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*out = static_cast<int_type>(val);
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} else { // 32-bit
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uint32_t val;
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parsed = numbers_internal::safe_strtou32_base(s, &val, base);
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*out = static_cast<int_type>(val);
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}
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}
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return parsed;
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}
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// FastHexToBufferZeroPad16()
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//
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// Outputs `val` into `out` as if by `snprintf(out, 17, "%016x", val)` but
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// without the terminating null character. Thus `out` must be of length >= 16.
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// Returns the number of non-pad digits of the output (it can never be zero
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// since 0 has one digit).
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inline size_t FastHexToBufferZeroPad16(uint64_t val, char* out) {
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#ifdef __SSE4_2__
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uint64_t be = absl::big_endian::FromHost64(val);
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const auto kNibbleMask = _mm_set1_epi8(0xf);
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const auto kHexDigits = _mm_setr_epi8('0', '1', '2', '3', '4', '5', '6', '7',
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'8', '9', 'a', 'b', 'c', 'd', 'e', 'f');
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auto v = _mm_loadl_epi64(reinterpret_cast<__m128i*>(&be)); // load lo dword
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auto v4 = _mm_srli_epi64(v, 4); // shift 4 right
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auto il = _mm_unpacklo_epi8(v4, v); // interleave bytes
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auto m = _mm_and_si128(il, kNibbleMask); // mask out nibbles
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auto hexchars = _mm_shuffle_epi8(kHexDigits, m); // hex chars
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_mm_storeu_si128(reinterpret_cast<__m128i*>(out), hexchars);
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#else
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for (int i = 0; i < 8; ++i) {
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auto byte = (val >> (56 - 8 * i)) & 0xFF;
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auto* hex = &absl::numbers_internal::kHexTable[byte * 2];
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std::memcpy(out + 2 * i, hex, 2);
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}
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#endif
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// | 0x1 so that even 0 has 1 digit.
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return 16 - absl::base_internal::CountLeadingZeros64(val | 0x1) / 4;
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}
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} // namespace numbers_internal
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// SimpleAtoi()
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//
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// Converts a string to an integer, using `safe_strto?()` functions for actual
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// parsing, returning `true` if successful. The `safe_strto?()` functions apply
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// strict checking; the string must be a base-10 integer, optionally followed or
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// preceded by ASCII whitespace, with a value in the range of the corresponding
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// integer type.
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template <typename int_type>
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ABSL_MUST_USE_RESULT bool SimpleAtoi(absl::string_view str, int_type* out) {
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return numbers_internal::safe_strtoi_base(str, out, 10);
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}
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ABSL_MUST_USE_RESULT inline bool SimpleAtoi(absl::string_view str,
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absl::uint128* out) {
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return numbers_internal::safe_strtou128_base(str, out, 10);
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}
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_STRINGS_NUMBERS_H_
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