libcxx/include/__charconv/to_chars_base_10.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___CHARCONV_TO_CHARS_BASE_10_H
  11 #define _LIBCPP___CHARCONV_TO_CHARS_BASE_10_H
  12
  13 #include <__algorithm/copy_n.h>
  14 #include <__assert>
  15 #include <__charconv/tables.h>
  16 #include <__config>
  17 #include <cstdint>
  18 #include <limits>
  19
  20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  21 #  pragma GCC system_header
  22 #endif
  23
  24 _LIBCPP_PUSH_MACROS
  25 #include <__undef_macros>
  26
  27 _LIBCPP_BEGIN_NAMESPACE_STD
  28
  29 #if _LIBCPP_STD_VER >= 17
  30
  31 namespace __itoa {
  32
  33 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append1(char* __first, uint32_t __value) noexcept {
  34   *__first = '0' + static_cast<char>(__value);
  35   return __first + 1;
  36 }
  37
  38 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append2(char* __first, uint32_t __value) noexcept {
  39   return std::copy_n(&__digits_base_10[__value * 2], 2, __first);
  40 }
  41
  42 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append3(char* __first, uint32_t __value) noexcept {
  43   return __itoa::__append2(__itoa::__append1(__first, __value / 100), __value % 100);
  44 }
  45
  46 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append4(char* __first, uint32_t __value) noexcept {
  47   return __itoa::__append2(__itoa::__append2(__first, __value / 100), __value % 100);
  48 }
  49
  50 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append5(char* __first, uint32_t __value) noexcept {
  51   return __itoa::__append4(__itoa::__append1(__first, __value / 10000), __value % 10000);
  52 }
  53
  54 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append6(char* __first, uint32_t __value) noexcept {
  55   return __itoa::__append4(__itoa::__append2(__first, __value / 10000), __value % 10000);
  56 }
  57
  58 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append7(char* __first, uint32_t __value) noexcept {
  59   return __itoa::__append6(__itoa::__append1(__first, __value / 1000000), __value % 1000000);
  60 }
  61
  62 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append8(char* __first, uint32_t __value) noexcept {
  63   return __itoa::__append6(__itoa::__append2(__first, __value / 1000000), __value % 1000000);
  64 }
  65
  66 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append9(char* __first, uint32_t __value) noexcept {
  67   return __itoa::__append8(__itoa::__append1(__first, __value / 100000000), __value % 100000000);
  68 }
  69
  70 template <class _Tp>
  71 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI char* __append10(char* __first, _Tp __value) noexcept {
  72   return __itoa::__append8(__itoa::__append2(__first, static_cast<uint32_t>(__value / 100000000)),
  73                            static_cast<uint32_t>(__value % 100000000));
  74 }
  75
  76 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char*
  77 __base_10_u32(char* __first, uint32_t __value) noexcept {
  78   if (__value < 1000000) {
  79     if (__value < 10000) {
  80       if (__value < 100) {
  81         // 0 <= __value < 100
  82         if (__value < 10)
  83           return __itoa::__append1(__first, __value);
  84         return __itoa::__append2(__first, __value);
  85       }
  86       // 100 <= __value < 10'000
  87       if (__value < 1000)
  88         return __itoa::__append3(__first, __value);
  89       return __itoa::__append4(__first, __value);
  90     }
  91
  92     // 10'000 <= __value < 1'000'000
  93     if (__value < 100000)
  94       return __itoa::__append5(__first, __value);
  95     return __itoa::__append6(__first, __value);
  96   }
  97
  98   // __value => 1'000'000
  99   if (__value < 100000000) {
 100     // 1'000'000 <= __value < 100'000'000
 101     if (__value < 10000000)
 102       return __itoa::__append7(__first, __value);
 103     return __itoa::__append8(__first, __value);
 104   }
 105
 106   // 100'000'000 <= __value < max
 107   if (__value < 1000000000)
 108     return __itoa::__append9(__first, __value);
 109   return __itoa::__append10(__first, __value);
 110 }
 111
 112 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char*
 113 __base_10_u64(char* __buffer, uint64_t __value) noexcept {
 114   if (__value <= UINT32_MAX)
 115     return __itoa::__base_10_u32(__buffer, static_cast<uint32_t>(__value));
 116
 117   // Numbers in the range UINT32_MAX <= val < 10'000'000'000 always contain 10
 118   // digits and are outputted after this if statement.
 119   if (__value >= 10000000000) {
 120     // This function properly deterimines the first non-zero leading digit.
 121     __buffer = __itoa::__base_10_u32(__buffer, static_cast<uint32_t>(__value / 10000000000));
 122     __value %= 10000000000;
 123   }
 124   return __itoa::__append10(__buffer, __value);
 125 }
 126
 127 #  if _LIBCPP_HAS_INT128
 128 /// \returns 10^\a exp
 129 ///
 130 /// \pre \a exp [19, 39]
 131 ///
 132 /// \note The lookup table contains a partial set of exponents limiting the
 133 /// range that can be used. However the range is sufficient for
 134 /// \ref __base_10_u128.
 135 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline __uint128_t __pow_10(int __exp) noexcept {
 136   _LIBCPP_ASSERT_INTERNAL(__exp >= __pow10_128_offset, "Index out of bounds");
 137   return __pow10_128[__exp - __pow10_128_offset];
 138 }
 139
 140 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char*
 141 __base_10_u128(char* __buffer, __uint128_t __value) noexcept {
 142   _LIBCPP_ASSERT_INTERNAL(
 143       __value > numeric_limits<uint64_t>::max(), "The optimizations for this algorithm fails when this isn't true.");
 144
 145   // Unlike the 64 to 32 bit case the 128 bit case the "upper half" can't be
 146   // stored in the "lower half". Instead we first need to handle the top most
 147   // digits separately.
 148   //
 149   // Maximum unsigned values
 150   // 64  bit                             18'446'744'073'709'551'615 (20 digits)
 151   // 128 bit    340'282'366'920'938'463'463'374'607'431'768'211'455 (39 digits)
 152   // step 1     ^                                                   ([0-1] digits)
 153   // step 2      ^^^^^^^^^^^^^^^^^^^^^^^^^                          ([0-19] digits)
 154   // step 3                               ^^^^^^^^^^^^^^^^^^^^^^^^^ (19 digits)
 155   if (__value >= __itoa::__pow_10(38)) {
 156     // step 1
 157     __buffer = __itoa::__append1(__buffer, static_cast<uint32_t>(__value / __itoa::__pow_10(38)));
 158     __value %= __itoa::__pow_10(38);
 159
 160     // step 2 always 19 digits.
 161     // They are handled here since leading zeros need to be appended to the buffer,
 162     __buffer = __itoa::__append9(__buffer, static_cast<uint32_t>(__value / __itoa::__pow_10(29)));
 163     __value %= __itoa::__pow_10(29);
 164     __buffer = __itoa::__append10(__buffer, static_cast<uint64_t>(__value / __itoa::__pow_10(19)));
 165     __value %= __itoa::__pow_10(19);
 166   } else {
 167     // step 2
 168     // This version needs to determine the position of the leading non-zero digit.
 169     __buffer = __base_10_u64(__buffer, static_cast<uint64_t>(__value / __itoa::__pow_10(19)));
 170     __value %= __itoa::__pow_10(19);
 171   }
 172
 173   // Step 3
 174   __buffer = __itoa::__append9(__buffer, static_cast<uint32_t>(__value / 10000000000));
 175   __buffer = __itoa::__append10(__buffer, static_cast<uint64_t>(__value % 10000000000));
 176
 177   return __buffer;
 178 }
 179 #  endif
 180 } // namespace __itoa
 181
 182 #endif // _LIBCPP_STD_VER >= 17
 183
 184 _LIBCPP_END_NAMESPACE_STD
 185
 186 _LIBCPP_POP_MACROS
 187
 188 #endif // _LIBCPP___CHARCONV_TO_CHARS_BASE_10_H