109 lines
3.1 KiB
C++
109 lines
3.1 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <folly/CPortability.h>
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#include <cstdint>
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#include <cstring>
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namespace folly {
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namespace detail {
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#if FOLLY_HAS_FEATURE(cxx_constexpr_string_builtins) || \
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FOLLY_HAS_BUILTIN(__builtin_strlen) || defined(_MSC_VER)
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#define FOLLY_DETAIL_STRLEN __builtin_strlen
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#else
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#define FOLLY_DETAIL_STRLEN ::std::strlen
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#endif
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#if FOLLY_HAS_FEATURE(cxx_constexpr_string_builtins) || \
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FOLLY_HAS_BUILTIN(__builtin_strcmp)
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#define FOLLY_DETAIL_STRCMP __builtin_strcmp
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#else
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#define FOLLY_DETAIL_STRCMP ::std::strcmp
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#endif
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// This overload is preferred if Char is char and if FOLLY_DETAIL_STRLEN
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// yields a compile-time constant.
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template <
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typename Char,
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std::size_t = FOLLY_DETAIL_STRLEN(static_cast<const Char*>(""))>
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constexpr std::size_t constexpr_strlen_internal(const Char* s, int) noexcept {
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return FOLLY_DETAIL_STRLEN(s);
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}
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template <typename Char>
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constexpr std::size_t constexpr_strlen_internal(
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const Char* s, unsigned) noexcept {
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std::size_t ret = 0;
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while (*s++) {
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++ret;
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}
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return ret;
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}
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template <typename Char>
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constexpr std::size_t constexpr_strlen_fallback(const Char* s) noexcept {
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return constexpr_strlen_internal(s, 0u);
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}
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static_assert(
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constexpr_strlen_fallback("123456789") == 9,
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"Someone appears to have broken constexpr_strlen...");
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// This overload is preferred if Char is char and if FOLLY_DETAIL_STRCMP
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// yields a compile-time constant.
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template <
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typename Char,
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int = FOLLY_DETAIL_STRCMP(static_cast<const Char*>(""), "")>
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constexpr int constexpr_strcmp_internal(
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const Char* s1, const Char* s2, int) noexcept {
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return FOLLY_DETAIL_STRCMP(s1, s2);
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}
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template <typename Char>
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constexpr int constexpr_strcmp_internal(
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const Char* s1, const Char* s2, unsigned) noexcept {
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while (*s1 && *s1 == *s2) {
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++s1, ++s2;
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}
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// NOTE: `int(*s1 - *s2)` may cause signed arithmetics overflow which is UB.
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return int(*s2 < *s1) - int(*s1 < *s2);
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}
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template <typename Char>
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constexpr int constexpr_strcmp_fallback(
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const Char* s1, const Char* s2) noexcept {
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return constexpr_strcmp_internal(s1, s2, 0u);
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}
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#undef FOLLY_DETAIL_STRCMP
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#undef FOLLY_DETAIL_STRLEN
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} // namespace detail
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template <typename Char>
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constexpr std::size_t constexpr_strlen(const Char* s) noexcept {
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return detail::constexpr_strlen_internal(s, 0);
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}
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template <typename Char>
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constexpr int constexpr_strcmp(const Char* s1, const Char* s2) noexcept {
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return detail::constexpr_strcmp_internal(s1, s2, 0);
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}
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} // namespace folly
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