2 * Copyright 2016 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>
26 constexpr T constexpr_max(T a, T b) {
31 constexpr T constexpr_min(T a, T b) {
37 template <typename T, typename = void>
38 struct constexpr_abs_helper {};
41 struct constexpr_abs_helper<
43 typename std::enable_if<std::is_floating_point<T>::value>::type> {
44 static constexpr T go(T t) {
45 return t < static_cast<T>(0) ? -t : t;
50 struct constexpr_abs_helper<
52 typename std::enable_if<
53 std::is_integral<T>::value && !std::is_same<T, bool>::value &&
54 std::is_unsigned<T>::value>::type> {
55 static constexpr T go(T t) {
61 struct constexpr_abs_helper<
63 typename std::enable_if<
64 std::is_integral<T>::value && !std::is_same<T, bool>::value &&
65 std::is_signed<T>::value>::type> {
66 static constexpr typename std::make_unsigned<T>::type go(T t) {
67 return t < static_cast<T>(0) ? -t : t;
73 constexpr auto constexpr_abs(T t)
74 -> decltype(detail::constexpr_abs_helper<T>::go(t)) {
75 return detail::constexpr_abs_helper<T>::go(t);
79 constexpr size_t constexpr_strlen_internal(const char* s, size_t len) {
80 return *s == '\0' ? len : constexpr_strlen_internal(s + 1, len + 1);
82 static_assert(constexpr_strlen_internal("123456789", 0) == 9,
83 "Someone appears to have broken constexpr_strlen...");
86 constexpr size_t constexpr_strlen(const char* s) {
87 #if defined(__clang__)
88 return __builtin_strlen(s);
89 #elif defined(_MSC_VER)
90 return s == nullptr ? 0 : constexpr_strlen_internal(s, 0);
92 return std::strlen(s);