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
__append1(char * __first,uint32_t __value)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
__append2(char * __first,uint32_t __value)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
__append3(char * __first,uint32_t __value)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
__append4(char * __first,uint32_t __value)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
__append5(char * __first,uint32_t __value)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
__append6(char * __first,uint32_t __value)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
__append7(char * __first,uint32_t __value)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
__append8(char * __first,uint32_t __value)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
__append9(char * __first,uint32_t __value)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>
__append10(char * __first,_Tp __value)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*
__base_10_u32(char * __first,uint32_t __value)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*
__base_10_u64(char * __buffer,uint64_t __value)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 # ifndef _LIBCPP_HAS_NO_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.
__pow_10(int __exp)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*
__base_10_u128(char * __buffer,__uint128_t __value)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
189