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 <__charconv/tables.h>
  15 #include <__config>
  16 #include <cstdint>
  17 #include <limits>
  18
  19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  20 #  pragma GCC system_header
  21 #endif
  22
  23 _LIBCPP_PUSH_MACROS
  24 #include <__undef_macros>
  25
  26 _LIBCPP_BEGIN_NAMESPACE_STD
  27
  28 #if _LIBCPP_STD_VER >= 17
  29
  30 namespace __itoa {
  31
  32 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append1(char* __first, uint32_t __value) noexcept {
  33   *__first = '0' + static_cast<char>(__value);
  34   return __first + 1;
  35 }
  36
  37 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append2(char* __first, uint32_t __value) noexcept {
  38   return std::copy_n(&__digits_base_10[__value * 2], 2, __first);
  39 }
  40
  41 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append3(char* __first, uint32_t __value) noexcept {
  42   return __itoa::__append2(__itoa::__append1(__first, __value / 100), __value % 100);
  43 }
  44
  45 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append4(char* __first, uint32_t __value) noexcept {
  46   return __itoa::__append2(__itoa::__append2(__first, __value / 100), __value % 100);
  47 }
  48
  49 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append5(char* __first, uint32_t __value) noexcept {
  50   return __itoa::__append4(__itoa::__append1(__first, __value / 10000), __value % 10000);
  51 }
  52
  53 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append6(char* __first, uint32_t __value) noexcept {
  54   return __itoa::__append4(__itoa::__append2(__first, __value / 10000), __value % 10000);
  55 }
  56
  57 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append7(char* __first, uint32_t __value) noexcept {
  58   return __itoa::__append6(__itoa::__append1(__first, __value / 1000000), __value % 1000000);
  59 }
  60
  61 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append8(char* __first, uint32_t __value) noexcept {
  62   return __itoa::__append6(__itoa::__append2(__first, __value / 1000000), __value % 1000000);
  63 }
  64
  65 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __append9(char* __first, uint32_t __value) noexcept {
  66   return __itoa::__append8(__itoa::__append1(__first, __value / 100000000), __value % 100000000);
  67 }
  68
  69 template <class _Tp>
  70 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI char* __append10(char* __first, _Tp __value) noexcept {
  71   return __itoa::__append8(__itoa::__append2(__first, static_cast<uint32_t>(__value / 100000000)),
  72                            static_cast<uint32_t>(__value % 100000000));
  73 }
  74
  75 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char*
  76 __base_10_u32(char* __first, uint32_t __value) noexcept {
  77   if (__value < 1000000) {
  78     if (__value < 10000) {
  79       if (__value < 100) {
  80         // 0 <= __value < 100
  81         if (__value < 10)
  82           return __itoa::__append1(__first, __value);
  83         return __itoa::__append2(__first, __value);
  84       }
  85       // 100 <= __value < 10'000
  86       if (__value < 1000)
  87         return __itoa::__append3(__first, __value);
  88       return __itoa::__append4(__first, __value);
  89     }
  90
  91     // 10'000 <= __value < 1'000'000
  92     if (__value < 100000)
  93       return __itoa::__append5(__first, __value);
  94     return __itoa::__append6(__first, __value);
  95   }
  96
  97   // __value => 1'000'000
  98   if (__value < 100000000) {
  99     // 1'000'000 <= __value < 100'000'000
 100     if (__value < 10000000)
 101       return __itoa::__append7(__first, __value);
 102     return __itoa::__append8(__first, __value);
 103   }
 104
 105   // 100'000'000 <= __value < max
 106   if (__value < 1000000000)
 107     return __itoa::__append9(__first, __value);
 108   return __itoa::__append10(__first, __value);
 109 }
 110
 111 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char*
 112 __base_10_u64(char* __buffer, uint64_t __value) noexcept {
 113   if (__value <= UINT32_MAX)
 114     return __itoa::__base_10_u32(__buffer, static_cast<uint32_t>(__value));
 115
 116   // Numbers in the range UINT32_MAX <= val < 10'000'000'000 always contain 10
 117   // digits and are outputted after this if statement.
 118   if (__value >= 10000000000) {
 119     // This function properly deterimines the first non-zero leading digit.
 120     __buffer = __itoa::__base_10_u32(__buffer, static_cast<uint32_t>(__value / 10000000000));
 121     __value %= 10000000000;
 122   }
 123   return __itoa::__append10(__buffer, __value);
 124 }
 125
 126 #  ifndef _LIBCPP_HAS_NO_INT128
 127 /// \returns 10^\a exp
 128 ///
 129 /// \pre \a exp [19, 39]
 130 ///
 131 /// \note The lookup table contains a partial set of exponents limiting the
 132 /// range that can be used. However the range is sufficient for
 133 /// \ref __base_10_u128.
 134 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline __uint128_t __pow_10(int __exp) noexcept {
 135   _LIBCPP_ASSERT_UNCATEGORIZED(__exp >= __pow10_128_offset, "Index out of bounds");
 136   return __pow10_128[__exp - __pow10_128_offset];
 137 }
 138
 139 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char*
 140 __base_10_u128(char* __buffer, __uint128_t __value) noexcept {
 141   _LIBCPP_ASSERT_UNCATEGORIZED(
 142       __value > numeric_limits<uint64_t>::max(), "The optimizations for this algorithm fail when this isn't true.");
 143
 144   // Unlike the 64 to 32 bit case the 128 bit case the "upper half" can't be
 145   // stored in the "lower half". Instead we first need to handle the top most
 146   // digits separately.
 147   //
 148   // Maximum unsigned values
 149   // 64  bit                             18'446'744'073'709'551'615 (20 digits)
 150   // 128 bit    340'282'366'920'938'463'463'374'607'431'768'211'455 (39 digits)
 151   // step 1     ^                                                   ([0-1] digits)
 152   // step 2      ^^^^^^^^^^^^^^^^^^^^^^^^^                          ([0-19] digits)
 153   // step 3                               ^^^^^^^^^^^^^^^^^^^^^^^^^ (19 digits)
 154   if (__value >= __itoa::__pow_10(38)) {
 155     // step 1
 156     __buffer = __itoa::__append1(__buffer, static_cast<uint32_t>(__value / __itoa::__pow_10(38)));
 157     __value %= __itoa::__pow_10(38);
 158
 159     // step 2 always 19 digits.
 160     // They are handled here since leading zeros need to be appended to the buffer,
 161     __buffer = __itoa::__append9(__buffer, static_cast<uint32_t>(__value / __itoa::__pow_10(29)));
 162     __value %= __itoa::__pow_10(29);
 163     __buffer = __itoa::__append10(__buffer, static_cast<uint64_t>(__value / __itoa::__pow_10(19)));
 164     __value %= __itoa::__pow_10(19);
 165   } else {
 166     // step 2
 167     // This version needs to determine the position of the leading non-zero digit.
 168     __buffer = __base_10_u64(__buffer, static_cast<uint64_t>(__value / __itoa::__pow_10(19)));
 169     __value %= __itoa::__pow_10(19);
 170   }
 171
 172   // Step 3
 173   __buffer = __itoa::__append9(__buffer, static_cast<uint32_t>(__value / 10000000000));
 174   __buffer = __itoa::__append10(__buffer, static_cast<uint64_t>(__value % 10000000000));
 175
 176   return __buffer;
 177 }
 178 #  endif
 179 } // namespace __itoa
 180
 181 #endif // _LIBCPP_STD_VER >= 17
 182
 183 _LIBCPP_END_NAMESPACE_STD
 184
 185 _LIBCPP_POP_MACROS
 186
 187 #endif // _LIBCPP___CHARCONV_TO_CHARS_BASE_10_H