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common: wall_clock: Fix integer overflow with StandardWallClock.
- Previous optimized impl. resulted in an integer overflow, so revert. - This is our slow/fallback path that should never be really be used, so the optimization in unimportant.
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@ -98,4 +98,24 @@ namespace Common {
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#endif
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#endif
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}
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}
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// This function divides a u128 by a u32 value and produces two u64 values:
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// the result of division and the remainder
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[[nodiscard]] static inline std::pair<u64, u64> Divide128On32(u128 dividend, u32 divisor) {
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u64 remainder = dividend[0] % divisor;
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u64 accum = dividend[0] / divisor;
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if (dividend[1] == 0)
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return {accum, remainder};
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// We ignore dividend[1] / divisor as that overflows
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const u64 first_segment = (dividend[1] % divisor) << 32;
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accum += (first_segment / divisor) << 32;
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const u64 second_segment = (first_segment % divisor) << 32;
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accum += (second_segment / divisor);
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remainder += second_segment % divisor;
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if (remainder >= divisor) {
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accum++;
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remainder -= divisor;
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}
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return {accum, remainder};
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}
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} // namespace Common
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} // namespace Common
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@ -20,9 +20,7 @@ using base_time_point = std::chrono::time_point<base_timer>;
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class StandardWallClock final : public WallClock {
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class StandardWallClock final : public WallClock {
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public:
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public:
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explicit StandardWallClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequency_)
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explicit StandardWallClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequency_)
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: WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, false),
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: WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, false) {
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emulated_clock_factor{GetFixedPoint64Factor(emulated_clock_frequency, 1000000000)},
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emulated_cpu_factor{GetFixedPoint64Factor(emulated_cpu_frequency, 1000000000)} {
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start_time = base_timer::now();
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start_time = base_timer::now();
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}
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}
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@ -45,11 +43,16 @@ public:
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}
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}
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u64 GetClockCycles() override {
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u64 GetClockCycles() override {
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return MultiplyHigh(GetTimeNS().count(), emulated_clock_factor);
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std::chrono::nanoseconds time_now = GetTimeNS();
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const u128 temporary =
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Common::Multiply64Into128(time_now.count(), emulated_clock_frequency);
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return Common::Divide128On32(temporary, 1000000000).first;
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}
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}
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u64 GetCPUCycles() override {
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u64 GetCPUCycles() override {
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return MultiplyHigh(GetTimeNS().count(), emulated_cpu_factor);
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std::chrono::nanoseconds time_now = GetTimeNS();
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const u128 temporary = Common::Multiply64Into128(time_now.count(), emulated_cpu_frequency);
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return Common::Divide128On32(temporary, 1000000000).first;
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}
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}
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void Pause([[maybe_unused]] bool is_paused) override {
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void Pause([[maybe_unused]] bool is_paused) override {
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@ -58,8 +61,6 @@ public:
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private:
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private:
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base_time_point start_time;
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base_time_point start_time;
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const u64 emulated_clock_factor;
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const u64 emulated_cpu_factor;
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};
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};
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#ifdef ARCHITECTURE_x86_64
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#ifdef ARCHITECTURE_x86_64
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