746cf7e38c
Reviewed By: ldionne, #libc Spies: libcxx-commits Differential Revision: https://reviews.llvm.org/D148553
117 lines
3.9 KiB
C++
117 lines
3.9 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H
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#define _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H
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#include <__config>
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#include <__type_traits/is_constant_evaluated.h>
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#include <__type_traits/is_equality_comparable.h>
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#include <__type_traits/is_same.h>
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#include <__type_traits/is_trivially_lexicographically_comparable.h>
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#include <cstddef>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const char* __str) {
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// GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation.
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// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816
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#ifdef _LIBCPP_COMPILER_GCC
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if (__libcpp_is_constant_evaluated()) {
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size_t __i = 0;
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for (; __str[__i] != '\0'; ++__i)
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;
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return __i;
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}
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#endif
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return __builtin_strlen(__str);
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}
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// Because of __libcpp_is_trivially_lexicographically_comparable we know that comparing the object representations is
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// equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead
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// of invoking it on every object individually.
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template <class _Tp, class _Up>
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int
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__constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, size_t __count) {
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static_assert(__libcpp_is_trivially_lexicographically_comparable<_Tp, _Up>::value,
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"_Tp and _Up have to be trivially lexicographically comparable");
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if (__libcpp_is_constant_evaluated()) {
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#ifdef _LIBCPP_COMPILER_CLANG_BASED
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if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value)
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return __builtin_memcmp(__lhs, __rhs, __count);
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#endif
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while (__count != 0) {
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if (*__lhs < *__rhs)
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return -1;
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if (*__rhs < *__lhs)
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return 1;
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__count -= sizeof(_Tp);
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++__lhs;
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++__rhs;
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}
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return 0;
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} else {
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return __builtin_memcmp(__lhs, __rhs, __count);
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}
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}
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// Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent
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// to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead
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// of invoking it on every object individually.
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template <class _Tp, class _Up>
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
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__constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, size_t __count) {
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static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
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"_Tp and _Up have to be trivially equality comparable");
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if (__libcpp_is_constant_evaluated()) {
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#ifdef _LIBCPP_COMPILER_CLANG_BASED
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if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value)
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return __builtin_memcmp(__lhs, __rhs, __count) == 0;
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#endif
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while (__count != 0) {
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if (*__lhs != *__rhs)
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return false;
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__count -= sizeof(_Tp);
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++__lhs;
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++__rhs;
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}
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return true;
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} else {
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return __builtin_memcmp(__lhs, __rhs, __count) == 0;
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}
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}
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inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const char*
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__constexpr_char_memchr(const char* __str, int __char, size_t __count) {
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#if __has_builtin(__builtin_char_memchr)
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return __builtin_char_memchr(__str, __char, __count);
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#else
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if (!__libcpp_is_constant_evaluated())
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return static_cast<const char*>(__builtin_memchr(__str, __char, __count));
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for (; __count; --__count) {
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if (*__str == __char)
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return __str;
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++__str;
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}
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return nullptr;
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#endif
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}
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H
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