92 lines
2.7 KiB
C
92 lines
2.7 KiB
C
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/*
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* Copyright 2016-present Facebook, Inc.
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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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#include <type_traits>
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namespace folly {
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namespace detail {
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template <typename Char>
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constexpr size_t constexpr_strlen_internal(const Char* s, size_t len) {
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// clang-format off
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return
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*(s + 0) == Char(0) ? len + 0 :
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*(s + 1) == Char(0) ? len + 1 :
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*(s + 2) == Char(0) ? len + 2 :
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*(s + 3) == Char(0) ? len + 3 :
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*(s + 4) == Char(0) ? len + 4 :
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*(s + 5) == Char(0) ? len + 5 :
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*(s + 6) == Char(0) ? len + 6 :
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*(s + 7) == Char(0) ? len + 7 :
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constexpr_strlen_internal(s + 8, len + 8);
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// clang-format on
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}
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static_assert(
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constexpr_strlen_internal("123456789", 0) == 9,
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"Someone appears to have broken constexpr_strlen...");
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template <typename Char>
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constexpr int constexpr_strcmp_internal(const Char* s1, const Char* s2) {
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return (*s1 == '\0' || *s1 != *s2)
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? (static_cast<int>(*s1 - *s2))
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: constexpr_strcmp_internal(s1 + 1, s2 + 1);
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}
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} // namespace detail
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template <typename Char>
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constexpr size_t constexpr_strlen(const Char* s) {
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return detail::constexpr_strlen_internal(s, 0);
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}
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template <>
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constexpr size_t constexpr_strlen(const char* s) {
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#if FOLLY_HAS_FEATURE(cxx_constexpr_string_builtins)
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// clang provides a constexpr builtin
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return __builtin_strlen(s);
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#elif defined(__GNUC__) && !defined(__clang__)
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// strlen() happens to already be constexpr under gcc
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return std::strlen(s);
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#else
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return detail::constexpr_strlen_internal(s, 0);
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#endif
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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) {
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return detail::constexpr_strcmp_internal(s1, s2);
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}
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template <>
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constexpr int constexpr_strcmp(const char* s1, const char* s2) {
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#if FOLLY_HAS_FEATURE(cxx_constexpr_string_builtins)
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// clang provides a constexpr builtin
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return __builtin_strcmp(s1, s2);
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#elif defined(__GNUC__) && !defined(__clang__)
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// strcmp() happens to already be constexpr under gcc
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return std::strcmp(s1, s2);
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#else
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return detail::constexpr_strcmp_internal(s1, s2);
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#endif
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}
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} // namespace folly
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