2 * Copyright 2017 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
21 #include <type_traits>
27 template <typename Char>
28 constexpr size_t constexpr_strlen_internal(const Char* s, size_t len) {
29 return *s == Char(0) ? len : constexpr_strlen_internal(s + 1, len + 1);
32 constexpr_strlen_internal("123456789", 0) == 9,
33 "Someone appears to have broken constexpr_strlen...");
36 template <typename Char>
37 constexpr size_t constexpr_strlen(const Char* s) {
38 return detail::constexpr_strlen_internal(s, 0);
42 constexpr size_t constexpr_strlen(const char* s) {
43 #if defined(__clang__)
44 return __builtin_strlen(s);
45 #elif defined(_MSC_VER) || defined(__CUDACC__)
46 return detail::constexpr_strlen_internal(s, 0);
48 return std::strlen(s);