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-rw-r--r--memory/build/Utils.h136
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diff --git a/memory/build/Utils.h b/memory/build/Utils.h
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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
+ * 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));
+}
+
+// User-defined literals to make constants more legible
+constexpr size_t operator"" _KiB(unsigned long long int aNum) {
+ return size_t(aNum) * 1024;
+}
+
+constexpr size_t operator"" _KiB(long double aNum) {
+ return size_t(aNum * 1024);
+}
+
+constexpr size_t operator"" _MiB(unsigned long long int aNum) {
+ return size_t(aNum) * 1024_KiB;
+}
+
+constexpr size_t operator"" _MiB(long double aNum) {
+ return size_t(aNum * 1024_KiB);
+}
+
+constexpr double operator""_percent(long double aPercent) {
+ return double(aPercent) / 100;
+}
+
+// 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