tor-browser

Saturate.h (6197B)

---

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* Provides saturation arithmetics for scalar types. */

#ifndef mozilla_Saturate_h
#define mozilla_Saturate_h

#include <limits>
#include <stdint.h>
#include <type_traits>
#include <utility>

#include "mozilla/Attributes.h"
#include "mozilla/CheckedArithmetic.h"

namespace mozilla {
namespace detail {

/**
* |SaturateOp<T>| wraps scalar values for saturation arithmetics. Usage:
*
*    uint32_t value = 1;
*
*    ++SaturateOp<uint32_t>(value); // value is 2
*    --SaturateOp<uint32_t>(value); // value is 1
*    --SaturateOp<uint32_t>(value); // value is 0
*    --SaturateOp<uint32_t>(value); // value is still 0
*
* Please add new operators when required.
*
* |SaturateOp<T>| will saturate at the minimum and maximum values of
* type T. If you need other bounds, implement a clamped-type class and
* specialize the type traits accordingly.
*/
template <typename T>
class SaturateOp {
public:
 explicit SaturateOp(T& aValue) : mValue(aValue) {
   // We should actually check for |std::is_scalar<T>::value| to be
   // true, but this type trait is not available everywhere. Relax
   // this assertion if you want to use floating point values as well.
   static_assert(std::is_integral_v<T>,
                 "Integral type required in instantiation");
 }

 // Add and subtract operators

 T operator+(const T& aRhs) const { return T(mValue) += aRhs; }

 T operator-(const T& aRhs) const { return T(mValue) -= aRhs; }

 // Compound operators
 const T& operator+=(const T& aRhs) const {
   constexpr T min = std::numeric_limits<T>::min();
   constexpr T max = std::numeric_limits<T>::max();
   if (!mozilla::SafeAdd(mValue, aRhs, &mValue)) {
     return mValue = (aRhs > 0 ? max : min);
   }
   return mValue;
 }

 const T& operator-=(const T& aRhs) const {
   constexpr T min = std::numeric_limits<T>::min();
   constexpr T max = std::numeric_limits<T>::max();
   if (!mozilla::SafeSub(mValue, aRhs, &mValue)) {
     return mValue = (aRhs > 0 ? min : max);
   }
   return mValue;
 }

 // Increment and decrement operators

 const T& operator++() const  // prefix
 {
   return operator+=(static_cast<T>(1));
 }

 T operator++(int) const  // postfix
 {
   const T value(mValue);
   operator++();
   return value;
 }

 const T& operator--() const  // prefix
 {
   return operator-=(static_cast<T>(1));
 }

 T operator--(int) const  // postfix
 {
   const T value(mValue);
   operator--();
   return value;
 }

private:
 SaturateOp(const SaturateOp<T>&) = delete;
 SaturateOp(SaturateOp<T>&&) = delete;
 SaturateOp& operator=(const SaturateOp<T>&) = delete;
 SaturateOp& operator=(SaturateOp<T>&&) = delete;

 T& mValue;
};

/**
* |Saturate<T>| is a value type for saturation arithmetics. It's
* built on top of |SaturateOp<T>|.
*/
template <typename T>
class Saturate {
public:
 Saturate() = default;
 MOZ_IMPLICIT Saturate(const Saturate<T>&) = default;

 MOZ_IMPLICIT Saturate(Saturate<T>&& aValue) {
   mValue = std::move(aValue.mValue);
 }

 explicit Saturate(const T& aValue) : mValue(aValue) {}

 const T& value() const { return mValue; }

 // Compare operators

 bool operator==(const Saturate<T>& aRhs) const {
   return mValue == aRhs.mValue;
 }

 bool operator!=(const Saturate<T>& aRhs) const { return !operator==(aRhs); }

 bool operator==(const T& aRhs) const { return mValue == aRhs; }

 bool operator!=(const T& aRhs) const { return !operator==(aRhs); }

 // Assignment operators

 Saturate<T>& operator=(const Saturate<T>&) = default;

 Saturate<T>& operator=(Saturate<T>&& aRhs) {
   mValue = std::move(aRhs.mValue);
   return *this;
 }

 // Add and subtract operators

 Saturate<T> operator+(const Saturate<T>& aRhs) const {
   Saturate<T> lhs(mValue);
   return lhs += aRhs.mValue;
 }

 Saturate<T> operator+(const T& aRhs) const {
   Saturate<T> lhs(mValue);
   return lhs += aRhs;
 }

 Saturate<T> operator-(const Saturate<T>& aRhs) const {
   Saturate<T> lhs(mValue);
   return lhs -= aRhs.mValue;
 }

 Saturate<T> operator-(const T& aRhs) const {
   Saturate<T> lhs(mValue);
   return lhs -= aRhs;
 }

 // Compound operators

 Saturate<T>& operator+=(const Saturate<T>& aRhs) {
   SaturateOp<T>(mValue) += aRhs.mValue;
   return *this;
 }

 Saturate<T>& operator+=(const T& aRhs) {
   SaturateOp<T>(mValue) += aRhs;
   return *this;
 }

 Saturate<T>& operator-=(const Saturate<T>& aRhs) {
   SaturateOp<T>(mValue) -= aRhs.mValue;
   return *this;
 }

 Saturate<T>& operator-=(const T& aRhs) {
   SaturateOp<T>(mValue) -= aRhs;
   return *this;
 }

 // Increment and decrement operators

 Saturate<T>& operator++()  // prefix
 {
   ++SaturateOp<T>(mValue);
   return *this;
 }

 Saturate<T> operator++(int)  // postfix
 {
   return Saturate<T>(SaturateOp<T>(mValue)++);
 }

 Saturate<T>& operator--()  // prefix
 {
   --SaturateOp<T>(mValue);
   return *this;
 }

 Saturate<T> operator--(int)  // postfix
 {
   return Saturate<T>(SaturateOp<T>(mValue)--);
 }

private:
 T mValue;
};

}  // namespace detail

typedef detail::Saturate<int8_t> SaturateInt8;
typedef detail::Saturate<int16_t> SaturateInt16;
typedef detail::Saturate<int32_t> SaturateInt32;
typedef detail::Saturate<uint8_t> SaturateUint8;
typedef detail::Saturate<uint16_t> SaturateUint16;
typedef detail::Saturate<uint32_t> SaturateUint32;
typedef detail::Saturate<intptr_t> SaturateIntPtr;
typedef detail::Saturate<uintptr_t> SaturateUintPtr;

using detail::Saturate;

}  // namespace mozilla

template <typename LhsT, typename RhsT>
bool operator==(LhsT aLhs, const mozilla::detail::Saturate<RhsT>& aRhs) {
 return aRhs.operator==(static_cast<RhsT>(aLhs));
}

template <typename LhsT, typename RhsT>
bool operator!=(LhsT aLhs, const mozilla::detail::Saturate<RhsT>& aRhs) {
 return !(aLhs == aRhs);
}

#endif  // mozilla_Saturate_h