224 lines · c
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-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP___CXX03___STRING_CONSTEXPR_C_FUNCTIONS_H10#define _LIBCPP___CXX03___STRING_CONSTEXPR_C_FUNCTIONS_H11 12#include <__cxx03/__config>13#include <__cxx03/__memory/addressof.h>14#include <__cxx03/__memory/construct_at.h>15#include <__cxx03/__type_traits/datasizeof.h>16#include <__cxx03/__type_traits/is_always_bitcastable.h>17#include <__cxx03/__type_traits/is_assignable.h>18#include <__cxx03/__type_traits/is_constant_evaluated.h>19#include <__cxx03/__type_traits/is_constructible.h>20#include <__cxx03/__type_traits/is_equality_comparable.h>21#include <__cxx03/__type_traits/is_same.h>22#include <__cxx03/__type_traits/is_trivially_copyable.h>23#include <__cxx03/__type_traits/is_trivially_lexicographically_comparable.h>24#include <__cxx03/__type_traits/remove_cv.h>25#include <__cxx03/__utility/is_pointer_in_range.h>26#include <__cxx03/cstddef>27 28#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)29# pragma GCC system_header30#endif31 32_LIBCPP_BEGIN_NAMESPACE_STD33 34// Type used to encode that a function takes an integer that represents a number35// of elements as opposed to a number of bytes.36enum class __element_count : size_t {};37 38template <class _Tp>39inline const bool __is_char_type = false;40 41template <>42inline const bool __is_char_type<char> = true;43 44#ifndef _LIBCPP_HAS_NO_CHAR8_T45template <>46inline const bool __is_char_type<char8_t> = true;47#endif48 49template <class _Tp>50inline _LIBCPP_HIDE_FROM_ABI 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=7081654 if (__libcpp_is_constant_evaluated()) {55 size_t __i = 0;56 for (; __str[__i] != '\0'; ++__i)57 ;58 return __i;59 }60 return __builtin_strlen(reinterpret_cast<const char*>(__str));61}62 63// Because of __libcpp_is_trivially_lexicographically_comparable we know that comparing the object representations is64// equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead65// of invoking it on every object individually.66template <class _Tp, class _Up>67_LIBCPP_HIDE_FROM_ABI int __constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {68 static_assert(__libcpp_is_trivially_lexicographically_comparable<_Tp, _Up>::value,69 "_Tp and _Up have to be trivially lexicographically comparable");70 71 auto __count = static_cast<size_t>(__n);72 73 if (__libcpp_is_constant_evaluated()) {74#ifdef _LIBCPP_COMPILER_CLANG_BASED75 if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value)76 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));77#endif78 79 while (__count != 0) {80 if (*__lhs < *__rhs)81 return -1;82 if (*__rhs < *__lhs)83 return 1;84 85 --__count;86 ++__lhs;87 ++__rhs;88 }89 return 0;90 } else {91 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));92 }93}94 95// Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent96// to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead97// of invoking it on every object individually.98template <class _Tp, class _Up>99_LIBCPP_HIDE_FROM_ABI bool __constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {100 static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,101 "_Tp and _Up have to be trivially equality comparable");102 103 auto __count = static_cast<size_t>(__n);104 105 if (__libcpp_is_constant_evaluated()) {106#ifdef _LIBCPP_COMPILER_CLANG_BASED107 if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value)108 return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;109#endif110 while (__count != 0) {111 if (*__lhs != *__rhs)112 return false;113 114 --__count;115 ++__lhs;116 ++__rhs;117 }118 return true;119 } else {120 return ::__builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;121 }122}123 124template <class _Tp, class _Up>125_LIBCPP_HIDE_FROM_ABI _Tp* __constexpr_memchr(_Tp* __str, _Up __value, size_t __count) {126 static_assert(sizeof(_Tp) == 1 && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,127 "Calling memchr on non-trivially equality comparable types is unsafe.");128 129 if (__libcpp_is_constant_evaluated()) {130 // use __builtin_char_memchr to optimize constexpr evaluation if we can131 132 for (; __count; --__count) {133 if (*__str == __value)134 return __str;135 ++__str;136 }137 return nullptr;138 } else {139 char __value_buffer = 0;140 __builtin_memcpy(&__value_buffer, &__value, sizeof(char));141 return static_cast<_Tp*>(__builtin_memchr(__str, __value_buffer, __count));142 }143}144 145// This function performs an assignment to an existing, already alive TriviallyCopyable object146// from another TriviallyCopyable object.147//148// It basically works around the fact that TriviallyCopyable objects are not required to be149// syntactically copy/move constructible or copy/move assignable. Technically, only one of the150// four operations is required to be syntactically valid -- but at least one definitely has to151// be valid.152//153// This is necessary in order to implement __constexpr_memmove below in a way that mirrors as154// closely as possible what the compiler's __builtin_memmove is able to do.155template <class _Tp, class _Up, __enable_if_t<is_assignable<_Tp&, _Up const&>::value, int> = 0>156_LIBCPP_HIDE_FROM_ABI _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {157 __dest = __src;158 return __dest;159}160 161// clang-format off162template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&163 is_assignable<_Tp&, _Up&&>::value, int> = 0>164// clang-format on165_LIBCPP_HIDE_FROM_ABI _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {166 __dest =167 static_cast<_Up&&>(__src); // this is safe, we're not actually moving anything since the assignment is trivial168 return __dest;169}170 171// clang-format off172template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&173 !is_assignable<_Tp&, _Up&&>::value &&174 is_constructible<_Tp, _Up const&>::value, int> = 0>175// clang-format on176_LIBCPP_HIDE_FROM_ABI _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {177 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object178 // that was there previously179 std::__construct_at(std::addressof(__dest), __src);180 return __dest;181}182 183// clang-format off184template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&185 !is_assignable<_Tp&, _Up&&>::value &&186 !is_constructible<_Tp, _Up const&>::value &&187 is_constructible<_Tp, _Up&&>::value, int> = 0>188// clang-format on189_LIBCPP_HIDE_FROM_ABI _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {190 // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object191 // that was there previously192 std::__construct_at(193 std::addressof(__dest),194 static_cast<_Up&&>(__src)); // this is safe, we're not actually moving anything since the constructor is trivial195 return __dest;196}197 198template <class _Tp, class _Up, __enable_if_t<__is_always_bitcastable<_Up, _Tp>::value, int> = 0>199_LIBCPP_HIDE_FROM_ABI _Tp* __constexpr_memmove(_Tp* __dest, _Up* __src, __element_count __n) {200 size_t __count = static_cast<size_t>(__n);201 if (__libcpp_is_constant_evaluated()) {202#ifdef _LIBCPP_COMPILER_CLANG_BASED203 if (is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >::value) {204 ::__builtin_memmove(__dest, __src, __count * sizeof(_Tp));205 return __dest;206 }207#endif208 if (std::__is_pointer_in_range(__src, __src + __count, __dest)) {209 for (; __count > 0; --__count)210 std::__assign_trivially_copyable(__dest[__count - 1], __src[__count - 1]);211 } else {212 for (size_t __i = 0; __i != __count; ++__i)213 std::__assign_trivially_copyable(__dest[__i], __src[__i]);214 }215 } else if (__count > 0) {216 ::__builtin_memmove(__dest, __src, (__count - 1) * sizeof(_Tp) + __datasizeof_v<_Tp>);217 }218 return __dest;219}220 221_LIBCPP_END_NAMESPACE_STD222 223#endif // _LIBCPP___CXX03___STRING_CONSTEXPR_C_FUNCTIONS_H224