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 <__memory/addressof.h>
14 #include <__memory/construct_at.h>
15 #include <__type_traits/datasizeof.h>
16 #include <__type_traits/is_always_bitcastable.h>
17 #include <__type_traits/is_assignable.h>
18 #include <__type_traits/is_constant_evaluated.h>
19 #include <__type_traits/is_constructible.h>
20 #include <__type_traits/is_equality_comparable.h>
21 #include <__type_traits/is_same.h>
22 #include <__type_traits/is_trivially_copyable.h>
23 #include <__type_traits/is_trivially_lexicographically_comparable.h>
24 #include <__type_traits/remove_cv.h>
25 #include <__utility/is_pointer_in_range.h>
26 #include <cstddef>
27
28 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
29 # pragma GCC system_header
30 #endif
31
32 _LIBCPP_BEGIN_NAMESPACE_STD
33
34 // Type used to encode that a function takes an integer that represents a number
35 // of elements as opposed to a number of bytes.
36 enum class __element_count : size_t {};
37
38 template <class _Tp>
39 inline const bool __is_char_type = false;
40
41 template <>
42 inline const bool __is_char_type<char> = true;
43
44 #ifndef _LIBCPP_HAS_NO_CHAR8_T
45 template <>
46 inline const bool __is_char_type<char8_t> = true;
47 #endif
48
49 template <class _Tp>
__constexpr_strlen(const _Tp * __str)50 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const _Tp* __str) _NOEXCEPT {
51 static_assert(__is_char_type<_Tp>, "__constexpr_strlen only works with char and char8_t");
52 // GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation.
53 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816
54 if (__libcpp_is_constant_evaluated()) {
55 #if _LIBCPP_STD_VER >= 17 && defined(_LIBCPP_COMPILER_CLANG_BASED)
56 if constexpr (is_same_v<_Tp, char>)
57 return __builtin_strlen(__str);
58 #endif
59 size_t __i = 0;
60 for (; __str[__i] != '\0'; ++__i)
61 ;
62 return __i;
63 }
64 return __builtin_strlen(reinterpret_cast<const char*>(__str));
65 }
66
67 // Because of __libcpp_is_trivially_lexicographically_comparable we know that comparing the object representations is
68 // equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead
69 // of invoking it on every object individually.
70 template <class _Tp, class _Up>
71 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int
__constexpr_memcmp(const _Tp * __lhs,const _Up * __rhs,__element_count __n)72 __constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {
73 static_assert(__libcpp_is_trivially_lexicographically_comparable<_Tp, _Up>::value,
74 "_Tp and _Up have to be trivially lexicographically comparable");
75
76 auto __count = static_cast<size_t>(__n);
77
78 if (__libcpp_is_constant_evaluated()) {
79 #ifdef _LIBCPP_COMPILER_CLANG_BASED
80 if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value)
81 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));
82 #endif
83
84 while (__count != 0) {
85 if (*__lhs < *__rhs)
86 return -1;
87 if (*__rhs < *__lhs)
88 return 1;
89
90 --__count;
91 ++__lhs;
92 ++__rhs;
93 }
94 return 0;
95 } else {
96 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));
97 }
98 }
99
100 // Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent
101 // to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead
102 // of invoking it on every object individually.
103 template <class _Tp, class _Up>
104 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
__constexpr_memcmp_equal(const _Tp * __lhs,const _Up * __rhs,__element_count __n)105 __constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {
106 static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
107 "_Tp and _Up have to be trivially equality comparable");
108
109 auto __count = static_cast<size_t>(__n);
110
111 if (__libcpp_is_constant_evaluated()) {
112 #ifdef _LIBCPP_COMPILER_CLANG_BASED
113 if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value)
114 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;
115 #endif
116 while (__count != 0) {
117 if (*__lhs != *__rhs)
118 return false;
119
120 --__count;
121 ++__lhs;
122 ++__rhs;
123 }
124 return true;
125 } else {
126 return ::__builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;
127 }
128 }
129
130 template <class _Tp, class _Up>
__constexpr_memchr(_Tp * __str,_Up __value,size_t __count)131 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __constexpr_memchr(_Tp* __str, _Up __value, size_t __count) {
132 static_assert(sizeof(_Tp) == 1 && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
133 "Calling memchr on non-trivially equality comparable types is unsafe.");
134
135 if (__libcpp_is_constant_evaluated()) {
136 // use __builtin_char_memchr to optimize constexpr evaluation if we can
137 #if _LIBCPP_STD_VER >= 17 && __has_builtin(__builtin_char_memchr)
138 if constexpr (is_same_v<remove_cv_t<_Tp>, char> && is_same_v<remove_cv_t<_Up>, char>)
139 return __builtin_char_memchr(__str, __value, __count);
140 #endif
141
142 for (; __count; --__count) {
143 if (*__str == __value)
144 return __str;
145 ++__str;
146 }
147 return nullptr;
148 } else {
149 char __value_buffer = 0;
150 __builtin_memcpy(&__value_buffer, &__value, sizeof(char));
151 return static_cast<_Tp*>(__builtin_memchr(__str, __value_buffer, __count));
152 }
153 }
154
155 // This function performs an assignment to an existing, already alive TriviallyCopyable object
156 // from another TriviallyCopyable object.
157 //
158 // It basically works around the fact that TriviallyCopyable objects are not required to be
159 // syntactically copy/move constructible or copy/move assignable. Technically, only one of the
160 // four operations is required to be syntactically valid -- but at least one definitely has to
161 // be valid.
162 //
163 // This is necessary in order to implement __constexpr_memmove below in a way that mirrors as
164 // closely as possible what the compiler's __builtin_memmove is able to do.
165 template <class _Tp, class _Up, __enable_if_t<is_assignable<_Tp&, _Up const&>::value, int> = 0>
__assign_trivially_copyable(_Tp & __dest,_Up const & __src)166 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {
167 __dest = __src;
168 return __dest;
169 }
170
171 // clang-format off
172 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
173 is_assignable<_Tp&, _Up&&>::value, int> = 0>
174 // clang-format on
__assign_trivially_copyable(_Tp & __dest,_Up & __src)175 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {
176 __dest =
177 static_cast<_Up&&>(__src); // this is safe, we're not actually moving anything since the assignment is trivial
178 return __dest;
179 }
180
181 // clang-format off
182 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
183 !is_assignable<_Tp&, _Up&&>::value &&
184 is_constructible<_Tp, _Up const&>::value, int> = 0>
185 // clang-format on
__assign_trivially_copyable(_Tp & __dest,_Up const & __src)186 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {
187 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object
188 // that was there previously
189 std::__construct_at(std::addressof(__dest), __src);
190 return __dest;
191 }
192
193 // clang-format off
194 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
195 !is_assignable<_Tp&, _Up&&>::value &&
196 !is_constructible<_Tp, _Up const&>::value &&
197 is_constructible<_Tp, _Up&&>::value, int> = 0>
198 // clang-format on
__assign_trivially_copyable(_Tp & __dest,_Up & __src)199 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {
200 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object
201 // that was there previously
202 std::__construct_at(
203 std::addressof(__dest),
204 static_cast<_Up&&>(__src)); // this is safe, we're not actually moving anything since the constructor is trivial
205 return __dest;
206 }
207
208 template <class _Tp, class _Up, __enable_if_t<__is_always_bitcastable<_Up, _Tp>::value, int> = 0>
209 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp*
__constexpr_memmove(_Tp * __dest,_Up * __src,__element_count __n)210 __constexpr_memmove(_Tp* __dest, _Up* __src, __element_count __n) {
211 size_t __count = static_cast<size_t>(__n);
212 if (__libcpp_is_constant_evaluated()) {
213 #ifdef _LIBCPP_COMPILER_CLANG_BASED
214 if (is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >::value) {
215 ::__builtin_memmove(__dest, __src, __count * sizeof(_Tp));
216 return __dest;
217 }
218 #endif
219 if (std::__is_pointer_in_range(__src, __src + __count, __dest)) {
220 for (; __count > 0; --__count)
221 std::__assign_trivially_copyable(__dest[__count - 1], __src[__count - 1]);
222 } else {
223 for (size_t __i = 0; __i != __count; ++__i)
224 std::__assign_trivially_copyable(__dest[__i], __src[__i]);
225 }
226 } else if (__count > 0) {
227 ::__builtin_memmove(__dest, __src, (__count - 1) * sizeof(_Tp) + __datasizeof_v<_Tp>);
228 }
229 return __dest;
230 }
231
232 _LIBCPP_END_NAMESPACE_STD
233
234 #endif // _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H
235