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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 mozilla_StickyTimeDuration_h
+#define mozilla_StickyTimeDuration_h
+
+#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 || (!IsInfinite(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 || IsInfinite(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(IsInfinite(aB) == IsInfinite(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 */
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