absl/strings/numbers.h

// 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
//
//      https://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.
//
// -----------------------------------------------------------------------------
// File: numbers.h
// -----------------------------------------------------------------------------
//
// This package contains functions for converting strings to numbers. For
// converting numbers to strings, use `StrCat()` or `StrAppend()` in str_cat.h,
// which automatically detect and convert most number values appropriately.

#ifndef ABSL_STRINGS_NUMBERS_H_
#define ABSL_STRINGS_NUMBERS_H_

#ifdef __SSSE3__
#include <tmmintrin.h>
#endif

#ifdef _MSC_VER
#include <intrin.h>
#endif

#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <limits>
#include <string>
#include <type_traits>

#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/internal/endian.h"
#include "absl/base/macros.h"
#include "absl/base/nullability.h"
#include "absl/base/optimization.h"
#include "absl/base/port.h"
#include "absl/numeric/bits.h"
#include "absl/numeric/int128.h"
#include "absl/strings/string_view.h"

namespace absl {
ABSL_NAMESPACE_BEGIN

// SimpleAtoi()
//
// Converts the given string (optionally followed or preceded by ASCII
// whitespace) into an integer value, returning `true` if successful. The string
// must reflect a base-10 integer whose value falls within the range of the
// integer type (optionally preceded by a `+` or `-`). If any errors are
// encountered, this function returns `false`, leaving `out` in an unspecified
// state.
template <typename int_type>
ABSL_MUST_USE_RESULT bool SimpleAtoi(absl::string_view str,
                                     absl::Nonnull<int_type*> out);

// SimpleAtof()
//
// Converts the given string (optionally followed or preceded by ASCII
// whitespace) into a float, which may be rounded on overflow or underflow,
// returning `true` if successful.
// See https://en.cppreference.com/w/c/string/byte/strtof for details about the
// allowed formats for `str`, except SimpleAtof() is locale-independent and will
// always use the "C" locale. If any errors are encountered, this function
// returns `false`, leaving `out` in an unspecified state.
ABSL_MUST_USE_RESULT bool SimpleAtof(absl::string_view str,
                                     absl::Nonnull<float*> out);

// SimpleAtod()
//
// Converts the given string (optionally followed or preceded by ASCII
// whitespace) into a double, which may be rounded on overflow or underflow,
// returning `true` if successful.
// See https://en.cppreference.com/w/c/string/byte/strtof for details about the
// allowed formats for `str`, except SimpleAtod is locale-independent and will
// always use the "C" locale. If any errors are encountered, this function
// returns `false`, leaving `out` in an unspecified state.
ABSL_MUST_USE_RESULT bool SimpleAtod(absl::string_view str,
                                     absl::Nonnull<double*> out);

// SimpleAtob()
//
// Converts the given string into a boolean, returning `true` if successful.
// The following case-insensitive strings are interpreted as boolean `true`:
// "true", "t", "yes", "y", "1". The following case-insensitive strings
// are interpreted as boolean `false`: "false", "f", "no", "n", "0". If any
// errors are encountered, this function returns `false`, leaving `out` in an
// unspecified state.
ABSL_MUST_USE_RESULT bool SimpleAtob(absl::string_view str,
                                     absl::Nonnull<bool*> out);

// SimpleHexAtoi()
//
// Converts a hexadecimal string (optionally followed or preceded by ASCII
// whitespace) to an integer, returning `true` if successful. Only valid base-16
// hexadecimal integers whose value falls within the range of the integer type
// (optionally preceded by a `+` or `-`) can be converted. A valid hexadecimal
// value may include both upper and lowercase character symbols, and may
// optionally include a leading "0x" (or "0X") number prefix, which is ignored
// by this function. If any errors are encountered, this function returns
// `false`, leaving `out` in an unspecified state.
template <typename int_type>
ABSL_MUST_USE_RESULT bool SimpleHexAtoi(absl::string_view str,
                                        absl::Nonnull<int_type*> out);

// Overloads of SimpleHexAtoi() for 128 bit integers.
ABSL_MUST_USE_RESULT inline bool SimpleHexAtoi(
    absl::string_view str, absl::Nonnull<absl::int128*> out);
ABSL_MUST_USE_RESULT inline bool SimpleHexAtoi(
    absl::string_view str, absl::Nonnull<absl::uint128*> out);

ABSL_NAMESPACE_END
}  // namespace absl

// End of public API.  Implementation details follow.

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace numbers_internal {

// Digit conversion.
ABSL_DLL extern const char kHexChar[17];  // 0123456789abcdef
ABSL_DLL extern const char
    kHexTable[513];  // 000102030405060708090a0b0c0d0e0f1011...

// 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'
void PutTwoDigits(uint32_t i, absl::Nonnull<char*> buf);

// safe_strto?() functions for implementing SimpleAtoi()

bool safe_strto32_base(absl::string_view text, absl::Nonnull<int32_t*> value,
                       int base);
bool safe_strto64_base(absl::string_view text, absl::Nonnull<int64_t*> value,
                       int base);
bool safe_strto128_base(absl::string_view text,
                        absl::Nonnull<absl::int128*> value, int base);
bool safe_strtou32_base(absl::string_view text, absl::Nonnull<uint32_t*> value,
                        int base);
bool safe_strtou64_base(absl::string_view text, absl::Nonnull<uint64_t*> value,
                        int base);
bool safe_strtou128_base(absl::string_view text,
                         absl::Nonnull<absl::uint128*> value, int base);

static const int kFastToBufferSize = 32;
static const int kSixDigitsToBufferSize = 16;

template <class T>
std::enable_if_t<!std::is_unsigned<T>::value, bool> IsNegative(const T& v) {
  return v < T();
}

template <class T>
std::enable_if_t<std::is_unsigned<T>::value, std::false_type> IsNegative(
    const T&) {
  // The integer is unsigned, so return a compile-time constant.
  // This can help the optimizer avoid having to prove bool to be false later.
  return std::false_type();
}

template <class T>
std::enable_if_t<std::is_unsigned<std::decay_t<T>>::value, T&&>
UnsignedAbsoluteValue(T&& v ABSL_ATTRIBUTE_LIFETIME_BOUND) {
  // The value is unsigned; just return the original.
  return std::forward<T>(v);
}

template <class T>
ABSL_ATTRIBUTE_CONST_FUNCTION
    std::enable_if_t<!std::is_unsigned<T>::value, std::make_unsigned_t<T>>
    UnsignedAbsoluteValue(T v) {
  using U = std::make_unsigned_t<T>;
  return IsNegative(v) ? U() - static_cast<U>(v) : static_cast<U>(v);
}

// Returns the number of base-10 digits in the given number.
// Note that this strictly counts digits. It does not count the sign.
// The `initial_digits` parameter is the starting point, which is normally equal
// to 1 because the number of digits in 0 is 1 (a special case).
// However, callers may e.g. wish to change it to 2 to account for the sign.
template <typename T>
std::enable_if_t<std::is_unsigned<T>::value, uint32_t> Base10Digits(
    T v, const uint32_t initial_digits = 1) {
  uint32_t r = initial_digits;
  // If code size becomes an issue, the 'if' stage can be removed for a minor
  // performance loss.
  for (;;) {
    if (ABSL_PREDICT_TRUE(v < 10 * 10)) {
      r += (v >= 10);
      break;
    }
    if (ABSL_PREDICT_TRUE(v < 1000 * 10)) {
      r += (v >= 1000) + 2;
      break;
    }
    if (ABSL_PREDICT_TRUE(v < 100000 * 10)) {
      r += (v >= 100000) + 4;
      break;
    }
    r += 6;
    v = static_cast<T>(v / 1000000);
  }
  return r;
}

template <typename T>
std::enable_if_t<std::is_signed<T>::value, uint32_t> Base10Digits(
    T v, uint32_t r = 1) {
  // Branchlessly add 1 to account for a minus sign.
  r += static_cast<uint32_t>(IsNegative(v));
  return Base10Digits(UnsignedAbsoluteValue(v), r);
}

// These functions return the number of base-10 digits, but multiplied by -1 if
// the input itself is negative. This is handy and efficient for later usage,
// since the bitwise complement of the result becomes equal to the number of
// characters required.
ABSL_ATTRIBUTE_CONST_FUNCTION int GetNumDigitsOrNegativeIfNegative(
    signed char v);
ABSL_ATTRIBUTE_CONST_FUNCTION int GetNumDigitsOrNegativeIfNegative(
    unsigned char v);
ABSL_ATTRIBUTE_CONST_FUNCTION int GetNumDigitsOrNegativeIfNegative(
    short v);  // NOLINT
ABSL_ATTRIBUTE_CONST_FUNCTION int GetNumDigitsOrNegativeIfNegative(
    unsigned short v);  // NOLINT
ABSL_ATTRIBUTE_CONST_FUNCTION int GetNumDigitsOrNegativeIfNegative(int v);
ABSL_ATTRIBUTE_CONST_FUNCTION int GetNumDigitsOrNegativeIfNegative(
    unsigned int v);
ABSL_ATTRIBUTE_CONST_FUNCTION int GetNumDigitsOrNegativeIfNegative(
    long v);  // NOLINT
ABSL_ATTRIBUTE_CONST_FUNCTION int GetNumDigitsOrNegativeIfNegative(
    unsigned long v);  // NOLINT
ABSL_ATTRIBUTE_CONST_FUNCTION int GetNumDigitsOrNegativeIfNegative(
    long long v);  // NOLINT
ABSL_ATTRIBUTE_CONST_FUNCTION int GetNumDigitsOrNegativeIfNegative(
    unsigned long long v);  // NOLINT

// Helper function for fast formatting of floating-point values.
// The result is the same as printf's "%g", a.k.a. "%.6g"; that is, six
// significant digits are returned, trailing zeros are removed, and numbers
// outside the range 0.0001-999999 are output using scientific notation
// (1.23456e+06). This routine is heavily optimized.
// Required buffer size is `kSixDigitsToBufferSize`.
size_t SixDigitsToBuffer(double d, absl::Nonnull<char*> buffer);

// All of these functions take an output buffer
// as an argument and return a pointer to the last byte they wrote, which is the
// terminating '\0'. At most `kFastToBufferSize` bytes are written.
absl::Nonnull<char*> FastIntToBuffer(int32_t i, absl::Nonnull<char*> buffer);
absl::Nonnull<char*> FastIntToBuffer(uint32_t i, absl::Nonnull<char*> buffer);
absl::Nonnull<char*> FastIntToBuffer(int64_t i, absl::Nonnull<char*> buffer);
absl::Nonnull<char*> FastIntToBuffer(uint64_t i, absl::Nonnull<char*> buffer);

// For enums and integer types that are not an exact match for the types above,
// use templates to call the appropriate one of the four overloads above.
template <typename int_type>
absl::Nonnull<char*> FastIntToBuffer(int_type i, absl::Nonnull<char*> buffer) {
  static_assert(sizeof(i) <= 64 / 8,
                "FastIntToBuffer works only with 64-bit-or-less integers.");
  // TODO(jorg): This signed-ness check is used because it works correctly
  // with enums, and it also serves to check that int_type is not a pointer.
  // If one day something like std::is_signed<enum E> works, switch to it.
  // These conditions are constexpr bools to suppress MSVC warning C4127.
  constexpr bool kIsSigned = static_cast<int_type>(1) - 2 < 0;
  constexpr bool kUse64Bit = sizeof(i) > 32 / 8;
  if (kIsSigned) {
    if (kUse64Bit) {
      return FastIntToBuffer(static_cast<int64_t>(i), buffer);
    } else {
      return FastIntToBuffer(static_cast<int32_t>(i), buffer);
    }
  } else {
    if (kUse64Bit) {
      return FastIntToBuffer(static_cast<uint64_t>(i), buffer);
    } else {
      return FastIntToBuffer(static_cast<uint32_t>(i), buffer);
    }
  }
}

// These functions do NOT add any null-terminator.
// They return a pointer to the beginning of the written string.
// The digit counts provided must *exactly* match the number of base-10 digits
// in the number, or the behavior is undefined.
// (i.e. do NOT count the minus sign, or over- or under-count the digits.)
absl::Nonnull<char*> FastIntToBufferBackward(int32_t i,
                                             absl::Nonnull<char*> buffer_end,
                                             uint32_t exact_digit_count);
absl::Nonnull<char*> FastIntToBufferBackward(uint32_t i,
                                             absl::Nonnull<char*> buffer_end,
                                             uint32_t exact_digit_count);
absl::Nonnull<char*> FastIntToBufferBackward(int64_t i,
                                             absl::Nonnull<char*> buffer_end,
                                             uint32_t exact_digit_count);
absl::Nonnull<char*> FastIntToBufferBackward(uint64_t i,
                                             absl::Nonnull<char*> buffer_end,
                                             uint32_t exact_digit_count);

// For enums and integer types that are not an exact match for the types above,
// use templates to call the appropriate one of the four overloads above.
template <typename int_type>
absl::Nonnull<char*> FastIntToBufferBackward(int_type i,
                                             absl::Nonnull<char*> buffer_end,
                                             uint32_t exact_digit_count) {
  static_assert(
      sizeof(i) <= 64 / 8,
      "FastIntToBufferBackward works only with 64-bit-or-less integers.");
  // This signed-ness check is used because it works correctly
  // with enums, and it also serves to check that int_type is not a pointer.
  // If one day something like std::is_signed<enum E> works, switch to it.
  // These conditions are constexpr bools to suppress MSVC warning C4127.
  constexpr bool kIsSigned = static_cast<int_type>(1) - 2 < 0;
  constexpr bool kUse64Bit = sizeof(i) > 32 / 8;
  if (kIsSigned) {
    if (kUse64Bit) {
      return FastIntToBufferBackward(static_cast<int64_t>(i), buffer_end,
                                     exact_digit_count);
    } else {
      return FastIntToBufferBackward(static_cast<int32_t>(i), buffer_end,
                                     exact_digit_count);
    }
  } else {
    if (kUse64Bit) {
      return FastIntToBufferBackward(static_cast<uint64_t>(i), buffer_end,
                                     exact_digit_count);
    } else {
      return FastIntToBufferBackward(static_cast<uint32_t>(i), buffer_end,
                                     exact_digit_count);
    }
  }
}

// Implementation of SimpleAtoi, generalized to support arbitrary base (used
// with base different from 10 elsewhere in Abseil implementation).
template <typename int_type>
ABSL_MUST_USE_RESULT bool safe_strtoi_base(absl::string_view s,
                                           absl::Nonnull<int_type*> out,
                                           int base) {
  static_assert(sizeof(*out) == 4 || sizeof(*out) == 8,
                "SimpleAtoi works only with 32-bit or 64-bit integers.");
  static_assert(!std::is_floating_point<int_type>::value,
                "Use SimpleAtof or SimpleAtod instead.");
  bool parsed;
  // TODO(jorg): This signed-ness check is used because it works correctly
  // with enums, and it also serves to check that int_type is not a pointer.
  // If one day something like std::is_signed<enum E> works, switch to it.
  // These conditions are constexpr bools to suppress MSVC warning C4127.
  constexpr bool kIsSigned = static_cast<int_type>(1) - 2 < 0;
  constexpr bool kUse64Bit = sizeof(*out) == 64 / 8;
  if (kIsSigned) {
    if (kUse64Bit) {
      int64_t val;
      parsed = numbers_internal::safe_strto64_base(s, &val, base);
      *out = static_cast<int_type>(val);
    } else {
      int32_t val;
      parsed = numbers_internal::safe_strto32_base(s, &val, base);
      *out = static_cast<int_type>(val);
    }
  } else {
    if (kUse64Bit) {
      uint64_t val;
      parsed = numbers_internal::safe_strtou64_base(s, &val, base);
      *out = static_cast<int_type>(val);
    } else {
      uint32_t val;
      parsed = numbers_internal::safe_strtou32_base(s, &val, base);
      *out = static_cast<int_type>(val);
    }
  }
  return parsed;
}

// FastHexToBufferZeroPad16()
//
// Outputs `val` into `out` as if by `snprintf(out, 17, "%016x", val)` but
// without the terminating null character. Thus `out` must be of length >= 16.
// Returns the number of non-pad digits of the output (it can never be zero
// since 0 has one digit).
inline size_t FastHexToBufferZeroPad16(uint64_t val, absl::Nonnull<char*> out) {
#ifdef ABSL_INTERNAL_HAVE_SSSE3
  uint64_t be = absl::big_endian::FromHost64(val);
  const auto kNibbleMask = _mm_set1_epi8(0xf);
  const auto kHexDigits = _mm_setr_epi8('0', '1', '2', '3', '4', '5', '6', '7',
                                        '8', '9', 'a', 'b', 'c', 'd', 'e', 'f');
  auto v = _mm_loadl_epi64(reinterpret_cast<__m128i*>(&be));  // load lo dword
  auto v4 = _mm_srli_epi64(v, 4);                            // shift 4 right
  auto il = _mm_unpacklo_epi8(v4, v);                        // interleave bytes
  auto m = _mm_and_si128(il, kNibbleMask);                   // mask out nibbles
  auto hexchars = _mm_shuffle_epi8(kHexDigits, m);           // hex chars
  _mm_storeu_si128(reinterpret_cast<__m128i*>(out), hexchars);
#else
  for (int i = 0; i < 8; ++i) {
    auto byte = (val >> (56 - 8 * i)) & 0xFF;
    auto* hex = &absl::numbers_internal::kHexTable[byte * 2];
    std::memcpy(out + 2 * i, hex, 2);
  }
#endif
  // | 0x1 so that even 0 has 1 digit.
  return 16 - static_cast<size_t>(countl_zero(val | 0x1) / 4);
}

}  // namespace numbers_internal

template <typename int_type>
ABSL_MUST_USE_RESULT bool SimpleAtoi(absl::string_view str,
                                     absl::Nonnull<int_type*> out) {
  return numbers_internal::safe_strtoi_base(str, out, 10);
}

ABSL_MUST_USE_RESULT inline bool SimpleAtoi(absl::string_view str,
                                            absl::Nonnull<absl::int128*> out) {
  return numbers_internal::safe_strto128_base(str, out, 10);
}

ABSL_MUST_USE_RESULT inline bool SimpleAtoi(absl::string_view str,
                                            absl::Nonnull<absl::uint128*> out) {
  return numbers_internal::safe_strtou128_base(str, out, 10);
}

template <typename int_type>
ABSL_MUST_USE_RESULT bool SimpleHexAtoi(absl::string_view str,
                                        absl::Nonnull<int_type*> out) {
  return numbers_internal::safe_strtoi_base(str, out, 16);
}

ABSL_MUST_USE_RESULT inline bool SimpleHexAtoi(
    absl::string_view str, absl::Nonnull<absl::int128*> out) {
  return numbers_internal::safe_strto128_base(str, out, 16);
}

ABSL_MUST_USE_RESULT inline bool SimpleHexAtoi(
    absl::string_view str, absl::Nonnull<absl::uint128*> out) {
  return numbers_internal::safe_strtou128_base(str, out, 16);
}

ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_STRINGS_NUMBERS_H_