Merge pull request #5964 from bunnei/timing-fix

common: wall_clock: Fix integer overflow with StandardWallClock.
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bunnei 2021-02-19 19:11:05 -08:00 committed by GitHub
commit def03d4075
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2 changed files with 28 additions and 7 deletions

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@ -98,4 +98,24 @@ namespace Common {
#endif #endif
} }
// This function divides a u128 by a u32 value and produces two u64 values:
// the result of division and the remainder
[[nodiscard]] static inline std::pair<u64, u64> Divide128On32(u128 dividend, u32 divisor) {
u64 remainder = dividend[0] % divisor;
u64 accum = dividend[0] / divisor;
if (dividend[1] == 0)
return {accum, remainder};
// We ignore dividend[1] / divisor as that overflows
const u64 first_segment = (dividend[1] % divisor) << 32;
accum += (first_segment / divisor) << 32;
const u64 second_segment = (first_segment % divisor) << 32;
accum += (second_segment / divisor);
remainder += second_segment % divisor;
if (remainder >= divisor) {
accum++;
remainder -= divisor;
}
return {accum, remainder};
}
} // namespace Common } // namespace Common

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@ -20,9 +20,7 @@ using base_time_point = std::chrono::time_point<base_timer>;
class StandardWallClock final : public WallClock { class StandardWallClock final : public WallClock {
public: public:
explicit StandardWallClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequency_) explicit StandardWallClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequency_)
: WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, false), : WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, false) {
emulated_clock_factor{GetFixedPoint64Factor(emulated_clock_frequency, 1000000000)},
emulated_cpu_factor{GetFixedPoint64Factor(emulated_cpu_frequency, 1000000000)} {
start_time = base_timer::now(); start_time = base_timer::now();
} }
@ -45,11 +43,16 @@ public:
} }
u64 GetClockCycles() override { u64 GetClockCycles() override {
return MultiplyHigh(GetTimeNS().count(), emulated_clock_factor); std::chrono::nanoseconds time_now = GetTimeNS();
const u128 temporary =
Common::Multiply64Into128(time_now.count(), emulated_clock_frequency);
return Common::Divide128On32(temporary, 1000000000).first;
} }
u64 GetCPUCycles() override { u64 GetCPUCycles() override {
return MultiplyHigh(GetTimeNS().count(), emulated_cpu_factor); std::chrono::nanoseconds time_now = GetTimeNS();
const u128 temporary = Common::Multiply64Into128(time_now.count(), emulated_cpu_frequency);
return Common::Divide128On32(temporary, 1000000000).first;
} }
void Pause([[maybe_unused]] bool is_paused) override { void Pause([[maybe_unused]] bool is_paused) override {
@ -58,8 +61,6 @@ public:
private: private:
base_time_point start_time; base_time_point start_time;
const u64 emulated_clock_factor;
const u64 emulated_cpu_factor;
}; };
#ifdef ARCHITECTURE_x86_64 #ifdef ARCHITECTURE_x86_64