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 <__type_traits/is_constant_evaluated.h> 14 #include <__type_traits/is_equality_comparable.h> 15 #include <__type_traits/is_same.h> 16 #include <__type_traits/is_trivially_lexicographically_comparable.h> 17 #include <__type_traits/remove_cv.h> 18 #include <cstddef> 19 20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 21 # pragma GCC system_header 22 #endif 23 24 _LIBCPP_BEGIN_NAMESPACE_STD 25 26 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const char* __str) { 27 // GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation. 28 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816 29 #ifdef _LIBCPP_COMPILER_GCC 30 if (__libcpp_is_constant_evaluated()) { 31 size_t __i = 0; 32 for (; __str[__i] != '\0'; ++__i) 33 ; 34 return __i; 35 } 36 #endif 37 return __builtin_strlen(__str); 38 } 39 40 // Because of __libcpp_is_trivially_lexicographically_comparable we know that comparing the object representations is 41 // equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead 42 // of invoking it on every object individually. 43 template <class _Tp, class _Up> 44 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int 45 __constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, size_t __count) { 46 static_assert(__libcpp_is_trivially_lexicographically_comparable<_Tp, _Up>::value, 47 "_Tp and _Up have to be trivially lexicographically comparable"); 48 49 if (__libcpp_is_constant_evaluated()) { 50 #ifdef _LIBCPP_COMPILER_CLANG_BASED 51 if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value) 52 return __builtin_memcmp(__lhs, __rhs, __count); 53 #endif 54 55 while (__count != 0) { 56 if (*__lhs < *__rhs) 57 return -1; 58 if (*__rhs < *__lhs) 59 return 1; 60 61 __count -= sizeof(_Tp); 62 ++__lhs; 63 ++__rhs; 64 } 65 return 0; 66 } else { 67 return __builtin_memcmp(__lhs, __rhs, __count); 68 } 69 } 70 71 // Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent 72 // to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead 73 // of invoking it on every object individually. 74 template <class _Tp, class _Up> 75 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool 76 __constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, size_t __count) { 77 static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value, 78 "_Tp and _Up have to be trivially equality comparable"); 79 80 if (__libcpp_is_constant_evaluated()) { 81 #ifdef _LIBCPP_COMPILER_CLANG_BASED 82 if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value) 83 return __builtin_memcmp(__lhs, __rhs, __count) == 0; 84 #endif 85 while (__count != 0) { 86 if (*__lhs != *__rhs) 87 return false; 88 89 __count -= sizeof(_Tp); 90 ++__lhs; 91 ++__rhs; 92 } 93 return true; 94 } else { 95 return __builtin_memcmp(__lhs, __rhs, __count) == 0; 96 } 97 } 98 99 template <class _Tp, class _Up> 100 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __constexpr_memchr(_Tp* __str, _Up __value, size_t __count) { 101 static_assert(sizeof(_Tp) == 1 && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value, 102 "Calling memchr on non-trivially equality comparable types is unsafe."); 103 104 if (__libcpp_is_constant_evaluated()) { 105 // use __builtin_char_memchr to optimize constexpr evaluation if we can 106 #if _LIBCPP_STD_VER >= 17 && __has_builtin(__builtin_char_memchr) 107 if constexpr (is_same_v<remove_cv_t<_Tp>, char> && is_same_v<remove_cv_t<_Up>, char>) 108 return __builtin_char_memchr(__str, __value, __count); 109 #endif 110 111 for (; __count; --__count) { 112 if (*__str == __value) 113 return __str; 114 ++__str; 115 } 116 return nullptr; 117 } else { 118 char __value_buffer = 0; 119 __builtin_memcpy(&__value_buffer, &__value, sizeof(char)); 120 return static_cast<_Tp*>(__builtin_memchr(__str, __value_buffer, __count)); 121 } 122 } 123 124 _LIBCPP_END_NAMESPACE_STD 125 126 #endif // _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H 127