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- /*
- * Copyright 2016-present Facebook, Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- #pragma once
- #include <folly/CPortability.h>
- #include <cstdint>
- #include <cstring>
- #include <type_traits>
- namespace folly {
- namespace detail {
- template <typename Char>
- constexpr size_t constexpr_strlen_internal(const Char* s, size_t len) {
- // clang-format off
- return
- *(s + 0) == Char(0) ? len + 0 :
- *(s + 1) == Char(0) ? len + 1 :
- *(s + 2) == Char(0) ? len + 2 :
- *(s + 3) == Char(0) ? len + 3 :
- *(s + 4) == Char(0) ? len + 4 :
- *(s + 5) == Char(0) ? len + 5 :
- *(s + 6) == Char(0) ? len + 6 :
- *(s + 7) == Char(0) ? len + 7 :
- constexpr_strlen_internal(s + 8, len + 8);
- // clang-format on
- }
- static_assert(
- constexpr_strlen_internal("123456789", 0) == 9,
- "Someone appears to have broken constexpr_strlen...");
- template <typename Char>
- constexpr int constexpr_strcmp_internal(const Char* s1, const Char* s2) {
- return (*s1 == '\0' || *s1 != *s2)
- ? (static_cast<int>(*s1 - *s2))
- : constexpr_strcmp_internal(s1 + 1, s2 + 1);
- }
- } // namespace detail
- template <typename Char>
- constexpr size_t constexpr_strlen(const Char* s) {
- return detail::constexpr_strlen_internal(s, 0);
- }
- template <>
- constexpr size_t constexpr_strlen(const char* s) {
- #if FOLLY_HAS_FEATURE(cxx_constexpr_string_builtins)
- // clang provides a constexpr builtin
- return __builtin_strlen(s);
- #elif defined(__GNUC__) && !defined(__clang__)
- // strlen() happens to already be constexpr under gcc
- return std::strlen(s);
- #else
- return detail::constexpr_strlen_internal(s, 0);
- #endif
- }
- template <typename Char>
- constexpr int constexpr_strcmp(const Char* s1, const Char* s2) {
- return detail::constexpr_strcmp_internal(s1, s2);
- }
- template <>
- constexpr int constexpr_strcmp(const char* s1, const char* s2) {
- #if FOLLY_HAS_FEATURE(cxx_constexpr_string_builtins)
- // clang provides a constexpr builtin
- return __builtin_strcmp(s1, s2);
- #elif defined(__GNUC__) && !defined(__clang__)
- // strcmp() happens to already be constexpr under gcc
- return std::strcmp(s1, s2);
- #else
- return detail::constexpr_strcmp_internal(s1, s2);
- #endif
- }
- } // namespace folly
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