| /* |
| * 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) |
| // |
| // (These are both constexpr.) |
| // |
| // 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.) |
| // |
| // Clamp (a.k.a. constrain to a given interval) |
| // ============================================ |
| // |
| // rtc::SafeClamp(x, a, b) |
| // |
| // Accepts three arguments of any mix of integral types or any mix of |
| // floating-point types, and returns the value in the closed interval [a, b] |
| // that is closest to x (that is, if x < a it returns a; if x > b it returns b; |
| // and if a <= x <= b it returns x). As for SafeMin() and SafeMax(), there is |
| // no truncation or wrap-around. The result type |
| // |
| // 1. is statically guaranteed to be able to represent the result; |
| // |
| // 2. is no larger than the largest of the three argument types; and |
| // |
| // 3. has the same signedness as the type of the third argument, if this is |
| // possible without violating the First or Second Law. |
| // |
| // There is always at least one type that meets criteria 1 and 2. If more than |
| // one type meets these criteria equally well, the result type is one of the |
| // types that is smallest. Note that unlike SafeMin() and SafeMax(), |
| // SafeClamp() will sometimes pick a return type that isn't the type of any of |
| // its arguments. |
| // |
| // * In this context, a type A is smaller than a type B if it has a smaller |
| // range; that is, if A::max() - A::min() < B::max() - B::min(). For |
| // example, int8_t < int16_t == uint16_t < int32_t, and all integral types |
| // are smaller than all floating-point types.) |
| // |
| // * As for SafeMin and SafeMax, mixing integer and floating-point arguments |
| // is not allowed, because floating-point types have greater range than |
| // integer types, but do not have sufficient precision to represent the |
| // values of most integer types exactly. |
| // |
| // Requesting a specific return type |
| // ================================= |
| // |
| // All three 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_RTC_BASE_SAFE_MINMAX_H_ |
| #define WEBRTC_RTC_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< |
| SafeLt(Limits<T1>::lowest, Limits<T2>::lowest), |
| T1, |
| typename std::conditional< |
| SafeGt(Limits<T1>::lowest, Limits<T2>::lowest), |
| T2, |
| typename std::conditional<SafeLe(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(SafeNe(Limits<T1>::max, Limits<T2>::max) || |
| SafeEq(Limits<T1>::lowest, Limits<T2>::lowest), |
| "integer types with the same max should have the same min"); |
| using max_t = typename std:: |
| conditional<SafeGe(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(SafeLe(Limits<type>::lowest, Limits<B>::lowest) && |
| SafeGe(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::MType< |
| typename safe_minmax_impl::UnderlyingType<T1>::type, |
| typename safe_minmax_impl::UnderlyingType<T2>::type>::min_t>::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 SafeLt(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::MType< |
| typename safe_minmax_impl::UnderlyingType<T1>::type, |
| typename safe_minmax_impl::UnderlyingType<T2>::type>::max_t>::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 SafeGt(a, b) ? static_cast<R2>(a) : static_cast<R2>(b); |
| } |
| |
| namespace safe_minmax_impl { |
| |
| // Given three types T, L, and H, let ::type be a suitable return value for |
| // SafeClamp(T, L, H). See the docs at the top of this file for details. |
| template <typename T, |
| typename L, |
| typename H, |
| bool int1 = IsIntlike<T>::value, |
| bool int2 = IsIntlike<L>::value, |
| bool int3 = IsIntlike<H>::value> |
| struct ClampType { |
| static_assert(int1 == int2 && int1 == int3, |
| "You may not mix integral and floating-point arguments"); |
| }; |
| |
| // Specialization for when all three types are floating-point. |
| template <typename T, typename L, typename H> |
| struct ClampType<T, L, H, false, false, false> { |
| using type = typename std::common_type<T, L, H>::type; |
| }; |
| |
| // Specialization for when all three types are integral. |
| template <typename T, typename L, typename H> |
| struct ClampType<T, L, H, true, true, true> { |
| private: |
| // Range of the return value. The return type must be able to represent this |
| // full range. |
| static constexpr auto r_min = |
| SafeMax(Limits<L>::lowest, SafeMin(Limits<H>::lowest, Limits<T>::lowest)); |
| static constexpr auto r_max = |
| SafeMin(Limits<H>::max, SafeMax(Limits<L>::max, Limits<T>::max)); |
| |
| // Is the given type an acceptable return type? (That is, can it represent |
| // all possible return values, and is it no larger than the largest of the |
| // input types?) |
| template <typename A> |
| struct AcceptableType { |
| private: |
| static constexpr bool not_too_large = sizeof(A) <= sizeof(L) || |
| sizeof(A) <= sizeof(H) || |
| sizeof(A) <= sizeof(T); |
| static constexpr bool range_contained = |
| SafeLe(Limits<A>::lowest, r_min) && SafeLe(r_max, Limits<A>::max); |
| |
| public: |
| static constexpr bool value = not_too_large && range_contained; |
| }; |
| |
| using best_signed_type = typename std::conditional< |
| AcceptableType<int8_t>::value, |
| int8_t, |
| typename std::conditional< |
| AcceptableType<int16_t>::value, |
| int16_t, |
| typename std::conditional<AcceptableType<int32_t>::value, |
| int32_t, |
| int64_t>::type>::type>::type; |
| |
| using best_unsigned_type = typename std::conditional< |
| AcceptableType<uint8_t>::value, |
| uint8_t, |
| typename std::conditional< |
| AcceptableType<uint16_t>::value, |
| uint16_t, |
| typename std::conditional<AcceptableType<uint32_t>::value, |
| uint32_t, |
| uint64_t>::type>::type>::type; |
| |
| public: |
| // Pick the best type, preferring the same signedness as T but falling back |
| // to the other one if necessary. |
| using type = typename std::conditional< |
| std::is_signed<T>::value, |
| typename std::conditional<AcceptableType<best_signed_type>::value, |
| best_signed_type, |
| best_unsigned_type>::type, |
| typename std::conditional<AcceptableType<best_unsigned_type>::value, |
| best_unsigned_type, |
| best_signed_type>::type>::type; |
| static_assert(AcceptableType<type>::value, ""); |
| }; |
| |
| } // namespace safe_minmax_impl |
| |
| template < |
| typename R = safe_minmax_impl::DefaultType, |
| typename T = safe_minmax_impl::DefaultType, |
| typename L = safe_minmax_impl::DefaultType, |
| typename H = safe_minmax_impl::DefaultType, |
| typename R2 = typename safe_minmax_impl::TypeOr< |
| R, |
| typename safe_minmax_impl::ClampType< |
| typename safe_minmax_impl::UnderlyingType<T>::type, |
| typename safe_minmax_impl::UnderlyingType<L>::type, |
| typename safe_minmax_impl::UnderlyingType<H>::type>::type>::type> |
| R2 SafeClamp(T x, L min, H max) { |
| static_assert(IsIntlike<H>::value || std::is_floating_point<H>::value, |
| "The first argument must be integral or floating-point"); |
| static_assert(IsIntlike<T>::value || std::is_floating_point<T>::value, |
| "The second argument must be integral or floating-point"); |
| static_assert(IsIntlike<L>::value || std::is_floating_point<L>::value, |
| "The third argument must be integral or floating-point"); |
| RTC_DCHECK_LE(min, max); |
| return SafeLe(x, min) |
| ? static_cast<R2>(min) |
| : SafeGe(x, max) ? static_cast<R2>(max) : static_cast<R2>(x); |
| } |
| |
| } // namespace rtc |
| |
| #endif // WEBRTC_RTC_BASE_SAFE_MINMAX_H_ |
