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115 lines
3.7 KiB
C++
115 lines
3.7 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef Utils_h
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#define Utils_h
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#include <type_traits>
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#include "mozilla/CheckedInt.h"
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#include "mozilla/TemplateLib.h"
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// Helper for log2 of powers of 2 at compile time.
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template <size_t N>
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struct Log2 : mozilla::tl::CeilingLog2<N> {
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using mozilla::tl::CeilingLog2<N>::value;
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static_assert(1ULL << value == N, "Number is not a power of 2");
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};
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#define LOG2(N) Log2<N>::value
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enum class Order {
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eLess = -1,
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eEqual = 0,
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eGreater = 1,
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};
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// Compare two integers. Returns whether the first integer is Less,
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// Equal or Greater than the second integer.
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template <typename T>
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Order CompareInt(T aValue1, T aValue2) {
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static_assert(std::is_integral_v<T>, "Type must be integral");
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if (aValue1 < aValue2) {
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return Order::eLess;
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}
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if (aValue1 > aValue2) {
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return Order::eGreater;
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}
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return Order::eEqual;
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}
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// Compare two addresses. Returns whether the first address is Less,
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// Equal or Greater than the second address.
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template <typename T>
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Order CompareAddr(T* aAddr1, T* aAddr2) {
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return CompareInt(uintptr_t(aAddr1), uintptr_t(aAddr2));
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}
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// Helper for (fast) comparison of fractions without involving divisions or
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// floats.
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class Fraction {
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public:
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explicit constexpr Fraction(size_t aNumerator, size_t aDenominator)
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: mNumerator(aNumerator), mDenominator(aDenominator) {}
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MOZ_IMPLICIT constexpr Fraction(long double aValue)
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// We use an arbitrary power of two as denominator that provides enough
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// precision for our use case.
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: mNumerator(aValue * 4096), mDenominator(4096) {}
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inline bool operator<(const Fraction& aOther) const {
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#ifndef MOZ_DEBUG
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// We are comparing A / B < C / D, with all A, B, C and D being positive
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// numbers. Multiplying both sides with B * D, we have:
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// (A * B * D) / B < (C * B * D) / D, which can then be simplified as
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// A * D < C * B. When can thus compare our fractions without actually
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// doing any division.
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// This however assumes the multiplied quantities are small enough not
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// to overflow the multiplication. We use CheckedInt on debug builds
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// to enforce the assumption.
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return mNumerator * aOther.mDenominator < aOther.mNumerator * mDenominator;
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#else
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mozilla::CheckedInt<size_t> numerator(mNumerator);
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mozilla::CheckedInt<size_t> denominator(mDenominator);
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// value() asserts when the multiplication overflowed.
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size_t lhs = (numerator * aOther.mDenominator).value();
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size_t rhs = (aOther.mNumerator * denominator).value();
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return lhs < rhs;
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#endif
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}
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inline bool operator>(const Fraction& aOther) const { return aOther < *this; }
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inline bool operator>=(const Fraction& aOther) const {
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return !(*this < aOther);
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}
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inline bool operator<=(const Fraction& aOther) const {
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return !(*this > aOther);
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}
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inline bool operator==(const Fraction& aOther) const {
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#ifndef MOZ_DEBUG
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// Same logic as operator<
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return mNumerator * aOther.mDenominator == aOther.mNumerator * mDenominator;
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#else
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mozilla::CheckedInt<size_t> numerator(mNumerator);
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mozilla::CheckedInt<size_t> denominator(mDenominator);
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size_t lhs = (numerator * aOther.mDenominator).value();
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size_t rhs = (aOther.mNumerator * denominator).value();
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return lhs == rhs;
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#endif
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}
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inline bool operator!=(const Fraction& aOther) const {
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return !(*this == aOther);
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}
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private:
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size_t mNumerator;
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size_t mDenominator;
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};
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#endif
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