/* -*- 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/. */
#ifndef Utils_h
#define Utils_h
#include <type_traits>
#include "mozilla/CheckedInt.h"
#include "mozilla/TemplateLib.h"
// Helper for log2 of powers of 2 at compile time.
template <size_t N>
struct Log2 : mozilla::tl::CeilingLog2<N> {
using mozilla::tl::CeilingLog2<N>::value;
static_assert(1ULL << value == N,
"Number is not a power of 2");
};
#define LOG2(N) Log2<N>::value
enum class Order {
eLess = -1,
eEqual = 0,
eGreater = 1,
};
// Compare two integers. Returns whether the first integer is Less,
// Equal or Greater than the second integer.
template <
typename T>
Order CompareInt(T aValue1, T aValue2) {
static_assert(std::is_integral_v<T>,
"Type must be integral");
if (aValue1 < aValue2) {
return Order::eLess;
}
if (aValue1 > aValue2) {
return Order::eGreater;
}
return Order::eEqual;
}
// Compare two addresses. Returns whether the first address is Less,
// Equal or Greater than the second address.
template <
typename T>
Order CompareAddr(T* aAddr1, T* aAddr2) {
return CompareInt(uintptr_t(aAddr1), uintptr_t(aAddr2));
}
// Helper for (fast) comparison of fractions without involving divisions or
// floats.
class Fraction {
public:
explicit constexpr Fraction(size_t aNumerator, size_t aDenominator)
: mNumerator(aNumerator), mDenominator(aDenominator) {}
MOZ_IMPLICIT constexpr Fraction(
long double aValue)
// We use an arbitrary power of two as denominator that provides enough
// precision for our use case.
: mNumerator(aValue * 4096), mDenominator(4096) {}
inline bool operator<(
const Fraction& aOther)
const {
#ifndef MOZ_DEBUG
// We are comparing A / B < C / D, with all A, B, C and D being positive
// numbers. Multiplying both sides with B * D, we have:
// (A * B * D) / B < (C * B * D) / D, which can then be simplified as
// A * D < C * B. When can thus compare our fractions without actually
// doing any division.
// This however assumes the multiplied quantities are small enough not
// to overflow the multiplication. We use CheckedInt on debug builds
// to enforce the assumption.
return mNumerator * aOther.mDenominator < aOther.mNumerator * mDenominator;
#else
mozilla::CheckedInt<size_t> numerator(mNumerator);
mozilla::CheckedInt<size_t> denominator(mDenominator);
// value() asserts when the multiplication overflowed.
size_t lhs = (numerator * aOther.mDenominator).value();
size_t rhs = (aOther.mNumerator * denominator).value();
return lhs < rhs;
#endif
}
inline bool operator>(
const Fraction& aOther)
const {
return aOther < *
this; }
inline bool operator>=(
const Fraction& aOther)
const {
return !(*
this < aOther);
}
inline bool operator<=(
const Fraction& aOther)
const {
return !(*
this > aOther);
}
inline bool operator==(
const Fraction& aOther)
const {
#ifndef MOZ_DEBUG
// Same logic as operator<
return mNumerator * aOther.mDenominator == aOther.mNumerator * mDenominator;
#else
mozilla::CheckedInt<size_t> numerator(mNumerator);
mozilla::CheckedInt<size_t> denominator(mDenominator);
size_t lhs = (numerator * aOther.mDenominator).value();
size_t rhs = (aOther.mNumerator * denominator).value();
return lhs == rhs;
#endif
}
inline bool operator!=(
const Fraction& aOther)
const {
return !(*
this == aOther);
}
private:
size_t mNumerator;
size_t mDenominator;
};
#endif
