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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
#ifndef mozilla_StickyTimeDuration_h
#define mozilla_StickyTimeDuration_h
#include <cmath>
#include "mozilla/TimeStamp.h"
#include "mozilla/FloatingPoint.h"
namespace mozilla {
/**
* A ValueCalculator class that performs additional checks before performing
* arithmetic operations such that if either operand is Forever (or the
* negative equivalent) the result remains Forever (or the negative equivalent
* as appropriate).
*
* Currently this only checks if either argument to each operation is
* Forever/-Forever. However, it is possible that, for example,
* aA + aB > INT64_MAX (or < INT64_MIN).
*
* We currently don't check for that case since we don't expect that to
* happen often except under test conditions in which case the wrapping
* behavior is probably acceptable.
*/
class StickyTimeDurationValueCalculator {
public:
static int64_t Add(int64_t aA, int64_t aB) {
MOZ_ASSERT((aA != INT64_MAX || aB != INT64_MIN) &&
(aA != INT64_MIN || aB != INT64_MAX),
"'Infinity + -Infinity' and '-Infinity + Infinity'"
" are undefined");
// Forever + x = Forever
// x + Forever = Forever
if (aA == INT64_MAX || aB == INT64_MAX) {
return INT64_MAX;
}
// -Forever + x = -Forever
// x + -Forever = -Forever
if (aA == INT64_MIN || aB == INT64_MIN) {
return INT64_MIN;
}
return aA + aB;
}
// Note that we can't just define Add and have BaseTimeDuration call Add with
// negative arguments since INT64_MAX != -INT64_MIN so the saturating logic
// won't work.
static int64_t Subtract(int64_t aA, int64_t aB) {
MOZ_ASSERT((aA != INT64_MAX && aA != INT64_MIN) || aA != aB,
"'Infinity - Infinity' and '-Infinity - -Infinity'"
" are undefined");
// Forever - x = Forever
// x - -Forever = Forever
if (aA == INT64_MAX || aB == INT64_MIN) {
return INT64_MAX;
}
// -Forever - x = -Forever
// x - Forever = -Forever
if (aA == INT64_MIN || aB == INT64_MAX) {
return INT64_MIN;
}
return aA - aB;
}
template <typename T>
static int64_t Multiply(int64_t aA, T aB) {
// Specializations for double, float, and int64_t are provided following.
return Multiply(aA, static_cast<int64_t>(aB));
}
static int64_t Divide(int64_t aA, int64_t aB) {
MOZ_ASSERT(aB != 0, "Division by zero");
MOZ_ASSERT((aA != INT64_MAX && aA != INT64_MIN) ||
(aB != INT64_MAX && aB != INT64_MIN),
"Dividing +/-Infinity by +/-Infinity is undefined");
// Forever / +x = Forever
// Forever / -x = -Forever
// -Forever / +x = -Forever
// -Forever / -x = Forever
if (aA == INT64_MAX || aA == INT64_MIN) {
return (aA >= 0) ^ (aB >= 0) ? INT64_MIN : INT64_MAX;
}
// x / Forever = 0
// x / -Forever = 0
if (aB == INT64_MAX || aB == INT64_MIN) {
return 0;
}
return aA / aB;
}
static double DivideDouble(int64_t aA, int64_t aB) {
MOZ_ASSERT(aB != 0, "Division by zero");
MOZ_ASSERT((aA != INT64_MAX && aA != INT64_MIN) ||
(aB != INT64_MAX && aB != INT64_MIN),
"Dividing +/-Infinity by +/-Infinity is undefined");
// Forever / +x = Forever
// Forever / -x = -Forever
// -Forever / +x = -Forever
// -Forever / -x = Forever
if (aA == INT64_MAX || aA == INT64_MIN) {
return (aA >= 0) ^ (aB >= 0) ? NegativeInfinity<double>()
: PositiveInfinity<double>();
}
// x / Forever = 0
// x / -Forever = 0
if (aB == INT64_MAX || aB == INT64_MIN) {
return 0.0;
}
return static_cast<double>(aA) / aB;
}
static int64_t Modulo(int64_t aA, int64_t aB) {
MOZ_ASSERT(aA != INT64_MAX && aA != INT64_MIN,
"Infinity modulo x is undefined");
return aA % aB;
}
};
template <>
inline int64_t StickyTimeDurationValueCalculator::Multiply<int64_t>(
int64_t aA, int64_t aB) {
MOZ_ASSERT((aA != 0 || (aB != INT64_MIN && aB != INT64_MAX)) &&
((aA != INT64_MIN && aA != INT64_MAX) || aB != 0),
"Multiplication of infinity by zero");
// Forever * +x = Forever
// Forever * -x = -Forever
// -Forever * +x = -Forever
// -Forever * -x = Forever
//
// i.e. If one or more of the arguments is +/-Forever, then
// return -Forever if the signs differ, or +Forever otherwise.
if (aA == INT64_MAX || aA == INT64_MIN || aB == INT64_MAX ||
aB == INT64_MIN) {
return (aA >= 0) ^ (aB >= 0) ? INT64_MIN : INT64_MAX;
}
return aA * aB;
}
template <>
inline int64_t StickyTimeDurationValueCalculator::Multiply<double>(int64_t aA,
double aB) {
MOZ_ASSERT((aA != 0 || (!std::isinf(aB))) &&
((aA != INT64_MIN && aA != INT64_MAX) || aB != 0.0),
"Multiplication of infinity by zero");
// As with Multiply<int64_t>, if one or more of the arguments is
// +/-Forever or +/-Infinity, then return -Forever if the signs differ,
// or +Forever otherwise.
if (aA == INT64_MAX || aA == INT64_MIN || std::isinf(aB)) {
return (aA >= 0) ^ (aB >= 0.0) ? INT64_MIN : INT64_MAX;
}
return aA * aB;
}
template <>
inline int64_t StickyTimeDurationValueCalculator::Multiply<float>(int64_t aA,
float aB) {
MOZ_ASSERT(std::isinf(aB) == std::isinf(static_cast<double>(aB)),
"Casting to float loses infinite-ness");
return Multiply(aA, static_cast<double>(aB));
}
/**
* Specialization of BaseTimeDuration that uses
* StickyTimeDurationValueCalculator for arithmetic on the mValue member.
*
* Use this class when you need a time duration that is expected to hold values
* of Forever (or the negative equivalent) *and* when you expect that
* time duration to be used in arithmetic operations (and not just value
* comparisons).
*/
typedef BaseTimeDuration<StickyTimeDurationValueCalculator> StickyTimeDuration;
// Template specializations to allow arithmetic between StickyTimeDuration
// and TimeDuration objects by falling back to the safe behavior.
inline StickyTimeDuration operator+(const TimeDuration& aA,
const StickyTimeDuration& aB) {
return StickyTimeDuration(aA) + aB;
}
inline StickyTimeDuration operator+(const StickyTimeDuration& aA,
const TimeDuration& aB) {
return aA + StickyTimeDuration(aB);
}
inline StickyTimeDuration operator-(const TimeDuration& aA,
const StickyTimeDuration& aB) {
return StickyTimeDuration(aA) - aB;
}
inline StickyTimeDuration operator-(const StickyTimeDuration& aA,
const TimeDuration& aB) {
return aA - StickyTimeDuration(aB);
}
inline StickyTimeDuration& operator+=(StickyTimeDuration& aA,
const TimeDuration& aB) {
return aA += StickyTimeDuration(aB);
}
inline StickyTimeDuration& operator-=(StickyTimeDuration& aA,
const TimeDuration& aB) {
return aA -= StickyTimeDuration(aB);
}
inline double operator/(const TimeDuration& aA, const StickyTimeDuration& aB) {
return StickyTimeDuration(aA) / aB;
}
inline double operator/(const StickyTimeDuration& aA, const TimeDuration& aB) {
return aA / StickyTimeDuration(aB);
}
inline StickyTimeDuration operator%(const TimeDuration& aA,
const StickyTimeDuration& aB) {
return StickyTimeDuration(aA) % aB;
}
inline StickyTimeDuration operator%(const StickyTimeDuration& aA,
const TimeDuration& aB) {
return aA % StickyTimeDuration(aB);
}
} // namespace mozilla
#endif /* mozilla_StickyTimeDuration_h */