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 > 14
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* __base_10_u32(char* __first, uint32_t __value) noexcept {
76   if (__value < 1000000) {
77     if (__value < 10000) {
78       if (__value < 100) {
79         // 0 <= __value < 100
80         if (__value < 10)
81           return __itoa::__append1(__first, __value);
82         return __itoa::__append2(__first, __value);
83       }
84       // 100 <= __value < 10'000
85       if (__value < 1000)
86         return __itoa::__append3(__first, __value);
87       return __itoa::__append4(__first, __value);
88     }
89 
90     // 10'000 <= __value < 1'000'000
91     if (__value < 100000)
92       return __itoa::__append5(__first, __value);
93     return __itoa::__append6(__first, __value);
94   }
95 
96   // __value => 1'000'000
97   if (__value < 100000000) {
98     // 1'000'000 <= __value < 100'000'000
99     if (__value < 10000000)
100       return __itoa::__append7(__first, __value);
101     return __itoa::__append8(__first, __value);
102   }
103 
104   // 100'000'000 <= __value < max
105   if (__value < 1000000000)
106     return __itoa::__append9(__first, __value);
107   return __itoa::__append10(__first, __value);
108 }
109 
110 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __base_10_u64(char* __buffer, uint64_t __value) noexcept {
111   if (__value <= UINT32_MAX)
112     return __itoa::__base_10_u32(__buffer, static_cast<uint32_t>(__value));
113 
114   // Numbers in the range UINT32_MAX <= val < 10'000'000'000 always contain 10
115   // digits and are outputted after this if statement.
116   if (__value >= 10000000000) {
117     // This function properly deterimines the first non-zero leading digit.
118     __buffer = __itoa::__base_10_u32(__buffer, static_cast<uint32_t>(__value / 10000000000));
119     __value %= 10000000000;
120   }
121   return __itoa::__append10(__buffer, __value);
122 }
123 
124 #  ifndef _LIBCPP_HAS_NO_INT128
125 /// \returns 10^\a exp
126 ///
127 /// \pre \a exp [19, 39]
128 ///
129 /// \note The lookup table contains a partial set of exponents limiting the
130 /// range that can be used. However the range is sufficient for
131 /// \ref __base_10_u128.
132 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline __uint128_t __pow_10(int __exp) noexcept {
133   _LIBCPP_ASSERT(__exp >= __pow10_128_offset, "Index out of bounds");
134   return __pow10_128[__exp - __pow10_128_offset];
135 }
136 
137 _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline char* __base_10_u128(char* __buffer, __uint128_t __value) noexcept {
138   _LIBCPP_ASSERT(
139       __value > numeric_limits<uint64_t>::max(), "The optimizations for this algorithm fail when this isn't true.");
140 
141   // Unlike the 64 to 32 bit case the 128 bit case the "upper half" can't be
142   // stored in the "lower half". Instead we first need to handle the top most
143   // digits separately.
144   //
145   // Maximum unsigned values
146   // 64  bit                             18'446'744'073'709'551'615 (20 digits)
147   // 128 bit    340'282'366'920'938'463'463'374'607'431'768'211'455 (39 digits)
148   // step 1     ^                                                   ([0-1] digits)
149   // step 2      ^^^^^^^^^^^^^^^^^^^^^^^^^                          ([0-19] digits)
150   // step 3                               ^^^^^^^^^^^^^^^^^^^^^^^^^ (19 digits)
151   if (__value >= __itoa::__pow_10(38)) {
152     // step 1
153     __buffer = __itoa::__append1(__buffer, static_cast<uint32_t>(__value / __itoa::__pow_10(38)));
154     __value %= __itoa::__pow_10(38);
155 
156     // step 2 always 19 digits.
157     // They are handled here since leading zeros need to be appended to the buffer,
158     __buffer = __itoa::__append9(__buffer, static_cast<uint32_t>(__value / __itoa::__pow_10(29)));
159     __value %= __itoa::__pow_10(29);
160     __buffer = __itoa::__append10(__buffer, static_cast<uint64_t>(__value / __itoa::__pow_10(19)));
161     __value %= __itoa::__pow_10(19);
162   }
163   else {
164     // step 2
165     // This version needs to determine the position of the leading non-zero digit.
166     __buffer = __base_10_u64(__buffer, static_cast<uint64_t>(__value / __itoa::__pow_10(19)));
167     __value %= __itoa::__pow_10(19);
168   }
169 
170   // Step 3
171   __buffer = __itoa::__append9(__buffer, static_cast<uint32_t>(__value / 10000000000));
172   __buffer = __itoa::__append10(__buffer, static_cast<uint64_t>(__value % 10000000000));
173 
174   return __buffer;
175 }
176 #  endif
177 } // namespace __itoa
178 
179 #endif // _LIBCPP_STD_VER > 14
180 
181 _LIBCPP_END_NAMESPACE_STD
182 
183 _LIBCPP_POP_MACROS
184 
185 #endif // _LIBCPP___CHARCONV_TO_CHARS_BASE_10_H
186