mfbt/Saturate.h
author Jim Chen <nchen@mozilla.com>
Wed, 20 Jun 2018 16:46:20 -0400
changeset 423113 2806729c61eaac199ad4670788c4008079a99f34
parent 420862 b54db66223586b4e04f5cb926fccdacf8a176b91
child 448947 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1469683 - 1. Fix crash tests; r=esawin Specify individual sessions in crash tests (i.e. "mainSession.waitUntilCalled" instead of "sessionRule.waitUntilCalled"), so that the tests assert behavior on the correct session, and not inadvertently on the cached session. Also, under x86 debug builds, Gecko installs an "ah_crap_handler" for SIGSEGV that waits for a long time, which causes our crash tests to time out. Therefore, ignore crash tests under x86 debug. MozReview-Commit-ID: DdtmRBLmPGp

/* -*- 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 "mozilla/Attributes.h"
#include "mozilla/Move.h"
#include "mozilla/TypeTraits.h"

#include <limits>

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(IsIntegral<T>::value,
                  "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
 * build 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