| /* |
| * Copyright 2017 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 <cstdint> |
| #include <cstring> |
| #include <type_traits> |
| |
| namespace folly { |
| |
| // TLDR: Prefer using operator< for ordering. And when |
| // a and b are equivalent objects, we return b to make |
| // sorting stable. |
| // See http://stepanovpapers.com/notes.pdf for details. |
| template <typename T> |
| constexpr T constexpr_max(T a, T b) { |
| return b < a ? a : b; |
| } |
| |
| // When a and b are equivalent objects, we return a to |
| // make sorting stable. |
| template <typename T> |
| constexpr T constexpr_min(T a, T b) { |
| return b < a ? b : a; |
| } |
| |
| namespace detail { |
| |
| template <typename T, typename = void> |
| struct constexpr_abs_helper {}; |
| |
| template <typename T> |
| struct constexpr_abs_helper< |
| T, |
| typename std::enable_if<std::is_floating_point<T>::value>::type> { |
| static constexpr T go(T t) { |
| return t < static_cast<T>(0) ? -t : t; |
| } |
| }; |
| |
| template <typename T> |
| struct constexpr_abs_helper< |
| T, |
| typename std::enable_if< |
| std::is_integral<T>::value && !std::is_same<T, bool>::value && |
| std::is_unsigned<T>::value>::type> { |
| static constexpr T go(T t) { |
| return t; |
| } |
| }; |
| |
| template <typename T> |
| struct constexpr_abs_helper< |
| T, |
| typename std::enable_if< |
| std::is_integral<T>::value && !std::is_same<T, bool>::value && |
| std::is_signed<T>::value>::type> { |
| static constexpr typename std::make_unsigned<T>::type go(T t) { |
| return typename std::make_unsigned<T>::type(t < static_cast<T>(0) ? -t : t); |
| } |
| }; |
| } // namespace detail |
| |
| template <typename T> |
| constexpr auto constexpr_abs(T t) |
| -> decltype(detail::constexpr_abs_helper<T>::go(t)) { |
| return detail::constexpr_abs_helper<T>::go(t); |
| } |
| |
| namespace detail { |
| |
| template <typename Char> |
| constexpr size_t constexpr_strlen_internal(const Char* s, size_t len) { |
| return *s == Char(0) ? len : constexpr_strlen_internal(s + 1, len + 1); |
| } |
| static_assert( |
| constexpr_strlen_internal("123456789", 0) == 9, |
| "Someone appears to have broken constexpr_strlen..."); |
| } // 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 defined(__clang__) |
| return __builtin_strlen(s); |
| #elif defined(_MSC_VER) || defined(__CUDACC__) |
| return detail::constexpr_strlen_internal(s, 0); |
| #else |
| return std::strlen(s); |
| #endif |
| } |
| } |