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/* -*- 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
/* 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"
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 {
const T min = std::numeric_limits<T>::min();
const T max = std::numeric_limits<T>::max();
if (aRhs > static_cast<T>(0)) {
mValue = (max - aRhs) < mValue ? max : mValue + aRhs;
} else {
mValue = (min - aRhs) > mValue ? min : mValue + aRhs;
}
return mValue;
}
const T& operator-=(const T& aRhs) const {
const T min = std::numeric_limits<T>::min();
const T max = std::numeric_limits<T>::max();
if (aRhs > static_cast<T>(0)) {
mValue = (min + aRhs) > mValue ? min : mValue - aRhs;
} else {
mValue = (max + aRhs) < mValue ? max : mValue - aRhs;
}
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;
} // 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