| /* |
| * Copyright 2017 The WebRTC Project Authors. All rights reserved. |
| * |
| * Use of this source code is governed by a BSD-style license |
| * that can be found in the LICENSE file in the root of the source |
| * tree. An additional intellectual property rights grant can be found |
| * in the file PATENTS. All contributing project authors may |
| * be found in the AUTHORS file in the root of the source tree. |
| */ |
| |
| // Minimum and maximum |
| // =================== |
| // |
| // rtc::SafeMin(x, y) |
| // rtc::SafeMax(x, y) |
| // |
| // Accept two arguments of either any two integral or any two floating-point |
| // types, and return the smaller and larger value, respectively, with no |
| // truncation or wrap-around. If only one of the input types is statically |
| // guaranteed to be able to represent the result, the return type is that type; |
| // if either one would do, the result type is the smaller type. (One of these |
| // two cases always applies.) |
| // |
| // (The case with one floating-point and one integral type is not allowed, |
| // because the floating-point type will have greater range, but may not have |
| // sufficient precision to represent the integer value exactly.) |
| // |
| // Requesting a specific return type |
| // ================================= |
| // |
| // Both functions allow callers to explicitly specify the return type as a |
| // template parameter, overriding the default return type. E.g. |
| // |
| // rtc::SafeMin<int>(x, y) // returns an int |
| // |
| // If the requested type is statically guaranteed to be able to represent the |
| // result, then everything's fine, and the return type is as requested. But if |
| // the requested type is too small, a static_assert is triggered. |
| |
| #ifndef WEBRTC_BASE_SAFE_MINMAX_H_ |
| #define WEBRTC_BASE_SAFE_MINMAX_H_ |
| |
| #include <limits> |
| #include <type_traits> |
| |
| #include "webrtc/base/checks.h" |
| #include "webrtc/base/safe_compare.h" |
| #include "webrtc/base/type_traits.h" |
| |
| namespace rtc { |
| |
| namespace safe_minmax_impl { |
| |
| // Make the range of a type available via something other than a constexpr |
| // function, to work around MSVC limitations. See |
| // https://blogs.msdn.microsoft.com/vcblog/2015/12/02/partial-support-for-expression-sfinae-in-vs-2015-update-1/ |
| template <typename T> |
| struct Limits { |
| static constexpr T lowest = std::numeric_limits<T>::lowest(); |
| static constexpr T max = std::numeric_limits<T>::max(); |
| }; |
| |
| template <typename T, bool is_enum = std::is_enum<T>::value> |
| struct UnderlyingType; |
| |
| template <typename T> |
| struct UnderlyingType<T, false> { |
| using type = T; |
| }; |
| |
| template <typename T> |
| struct UnderlyingType<T, true> { |
| using type = typename std::underlying_type<T>::type; |
| }; |
| |
| // Given two types T1 and T2, find types that can hold the smallest (in |
| // ::min_t) and the largest (in ::max_t) of the two values. |
| template <typename T1, |
| typename T2, |
| bool int1 = IsIntlike<T1>::value, |
| bool int2 = IsIntlike<T2>::value> |
| struct MType { |
| static_assert(int1 == int2, |
| "You may not mix integral and floating-point arguments"); |
| }; |
| |
| // Specialization for when neither type is integral (and therefore presumably |
| // floating-point). |
| template <typename T1, typename T2> |
| struct MType<T1, T2, false, false> { |
| using min_t = typename std::common_type<T1, T2>::type; |
| static_assert(std::is_same<min_t, T1>::value || |
| std::is_same<min_t, T2>::value, |
| ""); |
| |
| using max_t = typename std::common_type<T1, T2>::type; |
| static_assert(std::is_same<max_t, T1>::value || |
| std::is_same<max_t, T2>::value, |
| ""); |
| }; |
| |
| // Specialization for when both types are integral. |
| template <typename T1, typename T2> |
| struct MType<T1, T2, true, true> { |
| // The type with the lowest minimum value. In case of a tie, the type with |
| // the lowest maximum value. In case that too is a tie, the types have the |
| // same range, and we arbitrarily pick T1. |
| using min_t = typename std::conditional< |
| safe_cmp::Lt(Limits<T1>::lowest, Limits<T2>::lowest), |
| T1, |
| typename std::conditional< |
| safe_cmp::Gt(Limits<T1>::lowest, Limits<T2>::lowest), |
| T2, |
| typename std::conditional<safe_cmp::Le(Limits<T1>::max, |
| Limits<T2>::max), |
| T1, |
| T2>::type>::type>::type; |
| static_assert(std::is_same<min_t, T1>::value || |
| std::is_same<min_t, T2>::value, |
| ""); |
| |
| // The type with the highest maximum value. In case of a tie, the types have |
| // the same range (because in C++, integer types with the same maximum also |
| // have the same minimum). |
| static_assert(safe_cmp::Ne(Limits<T1>::max, Limits<T2>::max) || |
| safe_cmp::Eq(Limits<T1>::lowest, Limits<T2>::lowest), |
| "integer types with the same max should have the same min"); |
| using max_t = typename std:: |
| conditional<safe_cmp::Ge(Limits<T1>::max, Limits<T2>::max), T1, T2>::type; |
| static_assert(std::is_same<max_t, T1>::value || |
| std::is_same<max_t, T2>::value, |
| ""); |
| }; |
| |
| // A dummy type that we pass around at compile time but never actually use. |
| // Declared but not defined. |
| struct DefaultType; |
| |
| // ::type is A, except we fall back to B if A is DefaultType. We static_assert |
| // that the chosen type can hold all values that B can hold. |
| template <typename A, typename B> |
| struct TypeOr { |
| using type = typename std:: |
| conditional<std::is_same<A, DefaultType>::value, B, A>::type; |
| static_assert(safe_cmp::Le(Limits<type>::lowest, Limits<B>::lowest) && |
| safe_cmp::Ge(Limits<type>::max, Limits<B>::max), |
| "The specified type isn't large enough"); |
| static_assert(IsIntlike<type>::value == IsIntlike<B>::value && |
| std::is_floating_point<type>::value == |
| std::is_floating_point<type>::value, |
| "float<->int conversions not allowed"); |
| }; |
| |
| } // namespace safe_minmax_impl |
| |
| template <typename R = safe_minmax_impl::DefaultType, |
| typename T1 = safe_minmax_impl::DefaultType, |
| typename T2 = safe_minmax_impl::DefaultType, |
| typename R2 = typename safe_minmax_impl::TypeOr< |
| R, |
| typename safe_minmax_impl::UnderlyingType< |
| typename safe_minmax_impl::MType<T1, T2>::min_t>::type>::type> |
| constexpr R2 SafeMin(T1 a, T2 b) { |
| static_assert(IsIntlike<T1>::value || std::is_floating_point<T1>::value, |
| "The first argument must be integral or floating-point"); |
| static_assert(IsIntlike<T2>::value || std::is_floating_point<T2>::value, |
| "The second argument must be integral or floating-point"); |
| return safe_cmp::Lt(a, b) ? static_cast<R2>(a) : static_cast<R2>(b); |
| } |
| |
| template <typename R = safe_minmax_impl::DefaultType, |
| typename T1 = safe_minmax_impl::DefaultType, |
| typename T2 = safe_minmax_impl::DefaultType, |
| typename R2 = typename safe_minmax_impl::TypeOr< |
| R, |
| typename safe_minmax_impl::UnderlyingType< |
| typename safe_minmax_impl::MType<T1, T2>::max_t>::type>::type> |
| constexpr R2 SafeMax(T1 a, T2 b) { |
| static_assert(IsIntlike<T1>::value || std::is_floating_point<T1>::value, |
| "The first argument must be integral or floating-point"); |
| static_assert(IsIntlike<T2>::value || std::is_floating_point<T2>::value, |
| "The second argument must be integral or floating-point"); |
| return safe_cmp::Gt(a, b) ? static_cast<R2>(a) : static_cast<R2>(b); |
| } |
| |
| } // namespace rtc |
| |
| #endif // WEBRTC_BASE_SAFE_MINMAX_H_ |
