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>
25 // TLDR: Prefer using operator< for ordering. And when
26 // a and b are equivalent objects, we return b to make
28 // See http://stepanovpapers.com/notes.pdf for details.
30 constexpr T constexpr_max(T a, T b) {
34 // When a and b are equivalent objects, we return a to
35 // make sorting stable.
37 constexpr T constexpr_min(T a, T b) {
43 template <typename T, typename = void>
44 struct constexpr_abs_helper {};
47 struct constexpr_abs_helper<
49 typename std::enable_if<std::is_floating_point<T>::value>::type> {
50 static constexpr T go(T t) {
51 return t < static_cast<T>(0) ? -t : t;
56 struct constexpr_abs_helper<
58 typename std::enable_if<
59 std::is_integral<T>::value && !std::is_same<T, bool>::value &&
60 std::is_unsigned<T>::value>::type> {
61 static constexpr T go(T t) {
67 struct constexpr_abs_helper<
69 typename std::enable_if<
70 std::is_integral<T>::value && !std::is_same<T, bool>::value &&
71 std::is_signed<T>::value>::type> {
72 static constexpr typename std::make_unsigned<T>::type go(T t) {
73 return typename std::make_unsigned<T>::type(t < static_cast<T>(0) ? -t : t);
79 constexpr auto constexpr_abs(T t)
80 -> decltype(detail::constexpr_abs_helper<T>::go(t)) {
81 return detail::constexpr_abs_helper<T>::go(t);
86 template <typename Char>
87 constexpr size_t constexpr_strlen_internal(const Char* s, size_t len) {
88 return *s == Char(0) ? len : constexpr_strlen_internal(s + 1, len + 1);
91 constexpr_strlen_internal("123456789", 0) == 9,
92 "Someone appears to have broken constexpr_strlen...");
95 template <typename Char>
96 constexpr size_t constexpr_strlen(const Char* s) {
97 return detail::constexpr_strlen_internal(s, 0);
101 constexpr size_t constexpr_strlen(const char* s) {
102 #if defined(__clang__)
103 return __builtin_strlen(s);
104 #elif defined(_MSC_VER)
105 return detail::constexpr_strlen_internal(s, 0);
107 return std::strlen(s);