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1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H
10#define _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H
11
12#include <__config>
13#include <__cstddef/size_t.h>
14#include <__memory/addressof.h>
15#include <__memory/construct_at.h>
16#include <__type_traits/datasizeof.h>
17#include <__type_traits/enable_if.h>
18#include <__type_traits/is_always_bitcastable.h>
19#include <__type_traits/is_assignable.h>
20#include <__type_traits/is_constant_evaluated.h>
21#include <__type_traits/is_constructible.h>
22#include <__type_traits/is_equality_comparable.h>
23#include <__type_traits/is_integral.h>
24#include <__type_traits/is_same.h>
25#include <__type_traits/is_trivially_copyable.h>
26#include <__type_traits/is_trivially_lexicographically_comparable.h>
27#include <__type_traits/remove_cv.h>
28#include <__utility/element_count.h>
29#include <__utility/is_pointer_in_range.h>
30
31#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
32# pragma GCC system_header
33#endif
34
35_LIBCPP_BEGIN_NAMESPACE_STD
36
37template <class _Tp>
38inline const bool __is_char_type = false;
39
40template <>
41inline const bool __is_char_type<char> = true;
42
43#if _LIBCPP_HAS_CHAR8_T
44template <>
45inline const bool __is_char_type<char8_t> = true;
46#endif
47
48template <class _Tp>
49inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const _Tp* __str) _NOEXCEPT {
50 static_assert(__is_char_type<_Tp>, "__constexpr_strlen only works with char and char8_t");
51 // GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation.
52 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816
53 if (__libcpp_is_constant_evaluated()) {
54#if _LIBCPP_STD_VER >= 17 && defined(_LIBCPP_COMPILER_CLANG_BASED)
55 if constexpr (is_same_v<_Tp, char>)
56 return __builtin_strlen(__str);
57#endif
58 size_t __i = 0;
59 for (; __str[__i] != '\0'; ++__i)
60 ;
61 return __i;
62 }
63 return __builtin_strlen(reinterpret_cast<const char*>(__str));
64}
65
66// Because of __is_trivially_lexicographically_comparable_v we know that comparing the object representations is
67// equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead
68// of invoking it on every object individually.
69template <class _Tp, class _Up>
70_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int
71__constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {
72 static_assert(__is_trivially_lexicographically_comparable_v<_Tp, _Up>,
73 "_Tp and _Up have to be trivially lexicographically comparable");
74
75 auto __count = static_cast<size_t>(__n);
76
77 if (__libcpp_is_constant_evaluated()) {
78#ifdef _LIBCPP_COMPILER_CLANG_BASED
79 if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value)
80 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));
81#endif
82
83 while (__count != 0) {
84 if (*__lhs < *__rhs)
85 return -1;
86 if (*__rhs < *__lhs)
87 return 1;
88
89 --__count;
90 ++__lhs;
91 ++__rhs;
92 }
93 return 0;
94 } else {
95 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));
96 }
97}
98
99// Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent
100// to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead
101// of invoking it on every object individually.
102template <class _Tp, class _Up>
103_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
104__constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {
105 static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
106 "_Tp and _Up have to be trivially equality comparable");
107
108 auto __count = static_cast<size_t>(__n);
109
110 if (__libcpp_is_constant_evaluated()) {
111#ifdef _LIBCPP_COMPILER_CLANG_BASED
112 if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value)
113 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;
114#endif
115 while (__count != 0) {
116 if (*__lhs != *__rhs)
117 return false;
118
119 --__count;
120 ++__lhs;
121 ++__rhs;
122 }
123 return true;
124 } else {
125 return ::__builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;
126 }
127}
128
129template <class _Tp, class _Up>
130_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __constexpr_memchr(_Tp* __str, _Up __value, size_t __count) {
131 static_assert(sizeof(_Tp) == 1 && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
132 "Calling memchr on non-trivially equality comparable types is unsafe.");
133
134 if (__libcpp_is_constant_evaluated()) {
135// use __builtin_char_memchr to optimize constexpr evaluation if we can
136#if _LIBCPP_STD_VER >= 17 && __has_builtin(__builtin_char_memchr)
137 if constexpr (is_same_v<remove_cv_t<_Tp>, char> && is_same_v<remove_cv_t<_Up>, char>)
138 return __builtin_char_memchr(__str, __value, __count);
139#endif
140
141 for (; __count; --__count) {
142 if (*__str == __value)
143 return __str;
144 ++__str;
145 }
146 return nullptr;
147 } else {
148 char __value_buffer = 0;
149 __builtin_memcpy(&__value_buffer, std::addressof(__value), sizeof(char));
150 return static_cast<_Tp*>(__builtin_memchr(__str, __value_buffer, __count));
151 }
152}
153
154// This function performs an assignment to an existing, already alive TriviallyCopyable object
155// from another TriviallyCopyable object.
156//
157// It basically works around the fact that TriviallyCopyable objects are not required to be
158// syntactically copy/move constructible or copy/move assignable. Technically, only one of the
159// four operations is required to be syntactically valid -- but at least one definitely has to
160// be valid.
161//
162// This is necessary in order to implement __constexpr_memmove below in a way that mirrors as
163// closely as possible what the compiler's __builtin_memmove is able to do.
164template <class _Tp, class _Up, __enable_if_t<is_assignable<_Tp&, _Up const&>::value, int> = 0>
165_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {
166 __dest = __src;
167 return __dest;
168}
169
170// clang-format off
171template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
172 is_assignable<_Tp&, _Up&&>::value, int> = 0>
173// clang-format on
174_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {
175 __dest =
176 static_cast<_Up&&>(__src); // this is safe, we're not actually moving anything since the assignment is trivial
177 return __dest;
178}
179
180// clang-format off
181template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
182 !is_assignable<_Tp&, _Up&&>::value &&
183 is_constructible<_Tp, _Up const&>::value, int> = 0>
184// clang-format on
185_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {
186 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object
187 // that was there previously
188 std::__construct_at(std::addressof(__dest), __src);
189 return __dest;
190}
191
192// clang-format off
193template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
194 !is_assignable<_Tp&, _Up&&>::value &&
195 !is_constructible<_Tp, _Up const&>::value &&
196 is_constructible<_Tp, _Up&&>::value, int> = 0>
197// clang-format on
198_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {
199 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object
200 // that was there previously
201 std::__construct_at(
202 std::addressof(__dest),
203 static_cast<_Up&&>(__src)); // this is safe, we're not actually moving anything since the constructor is trivial
204 return __dest;
205}
206
207template <class _Tp, class _Up>
208_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp*
209__constexpr_memmove(_Tp* __dest, _Up* __src, __element_count __n) {
210 static_assert(__is_always_bitcastable<_Up, _Tp>::value);
211 size_t __count = static_cast<size_t>(__n);
212 if (__libcpp_is_constant_evaluated()) {
213#ifdef _LIBCPP_COMPILER_CLANG_BASED
214 if _LIBCPP_CONSTEXPR (is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >::value) {
215 ::__builtin_memmove(__dest, __src, __count * sizeof(_Tp));
216 return __dest;
217 } else
218#endif
219 {
220 if (std::__is_pointer_in_range(__src, __src + __count, __dest)) {
221 for (; __count > 0; --__count)
222 std::__assign_trivially_copyable(__dest[__count - 1], __src[__count - 1]);
223 } else {
224 for (size_t __i = 0; __i != __count; ++__i)
225 std::__assign_trivially_copyable(__dest[__i], __src[__i]);
226 }
227 }
228 } else if (__count > 0) {
229 ::__builtin_memmove(__dest, __src, (__count - 1) * sizeof(_Tp) + __datasizeof_v<_Tp>);
230 }
231 return __dest;
232}
233
234_LIBCPP_END_NAMESPACE_STD
235
236#endif // _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H