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 188