yuzu/src/common/x64/native_clock.cpp

// Copyright 2020 yuzu Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

#include <array>
#include <chrono>
#include <limits>
#include <mutex>
#include <thread>

#ifdef _MSC_VER
#include <intrin.h>

#pragma intrinsic(__umulh)
#pragma intrinsic(_udiv128)
#else
#include <x86intrin.h>
#endif

#include "common/uint128.h"
#include "common/x64/native_clock.h"

namespace {

[[nodiscard]] u64 GetFixedPoint64Factor(u64 numerator, u64 divisor) {
#ifdef __SIZEOF_INT128__
    const auto base = static_cast<unsigned __int128>(numerator) << 64ULL;
    return static_cast<u64>(base / divisor);
#elif defined(_M_X64) || defined(_M_ARM64)
    std::array<u64, 2> r = {0, numerator};
    u64 remainder;
#if _MSC_VER < 1923
    return udiv128(r[1], r[0], divisor, &remainder);
#else
    return _udiv128(r[1], r[0], divisor, &remainder);
#endif
#else
    // This one is bit more inaccurate.
    return MultiplyAndDivide64(std::numeric_limits<u64>::max(), numerator, divisor);
#endif
}

[[nodiscard]] u64 MultiplyHigh(u64 a, u64 b) {
#ifdef __SIZEOF_INT128__
    return (static_cast<unsigned __int128>(a) * static_cast<unsigned __int128>(b)) >> 64;
#elif defined(_M_X64) || defined(_M_ARM64)
    return __umulh(a, b); // MSVC
#else
    // Generic fallback
    const u64 a_lo = u32(a);
    const u64 a_hi = a >> 32;
    const u64 b_lo = u32(b);
    const u64 b_hi = b >> 32;

    const u64 a_x_b_hi = a_hi * b_hi;
    const u64 a_x_b_mid = a_hi * b_lo;
    const u64 b_x_a_mid = b_hi * a_lo;
    const u64 a_x_b_lo = a_lo * b_lo;

    const u64 carry_bit = (static_cast<u64>(static_cast<u32>(a_x_b_mid)) +
                           static_cast<u64>(static_cast<u32>(b_x_a_mid)) + (a_x_b_lo >> 32)) >>
                          32;

    const u64 multhi = a_x_b_hi + (a_x_b_mid >> 32) + (b_x_a_mid >> 32) + carry_bit;

    return multhi;
#endif
}

} // namespace

namespace Common {

u64 EstimateRDTSCFrequency() {
    const auto milli_10 = std::chrono::milliseconds{10};
    // get current time
    _mm_mfence();
    const u64 tscStart = __rdtsc();
    const auto startTime = std::chrono::high_resolution_clock::now();
    // wait roughly 3 seconds
    while (true) {
        auto milli = std::chrono::duration_cast<std::chrono::milliseconds>(
            std::chrono::high_resolution_clock::now() - startTime);
        if (milli.count() >= 3000)
            break;
        std::this_thread::sleep_for(milli_10);
    }
    const auto endTime = std::chrono::high_resolution_clock::now();
    _mm_mfence();
    const u64 tscEnd = __rdtsc();
    // calculate difference
    const u64 timer_diff =
        std::chrono::duration_cast<std::chrono::nanoseconds>(endTime - startTime).count();
    const u64 tsc_diff = tscEnd - tscStart;
    const u64 tsc_freq = MultiplyAndDivide64(tsc_diff, 1000000000ULL, timer_diff);
    return tsc_freq;
}

namespace X64 {
NativeClock::NativeClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequency_,
                         u64 rtsc_frequency_)
    : WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, true), rtsc_frequency{
                                                                               rtsc_frequency_} {
    _mm_mfence();
    last_measure = __rdtsc();
    accumulated_ticks = 0U;
    ns_rtsc_factor = GetFixedPoint64Factor(1000000000, rtsc_frequency);
    us_rtsc_factor = GetFixedPoint64Factor(1000000, rtsc_frequency);
    ms_rtsc_factor = GetFixedPoint64Factor(1000, rtsc_frequency);
    clock_rtsc_factor = GetFixedPoint64Factor(emulated_clock_frequency, rtsc_frequency);
    cpu_rtsc_factor = GetFixedPoint64Factor(emulated_cpu_frequency, rtsc_frequency);
}

u64 NativeClock::GetRTSC() {
    std::scoped_lock scope{rtsc_serialize};
    _mm_mfence();
    const u64 current_measure = __rdtsc();
    u64 diff = current_measure - last_measure;
    diff = diff & ~static_cast<u64>(static_cast<s64>(diff) >> 63); // max(diff, 0)
    if (current_measure > last_measure) {
        last_measure = current_measure;
    }
    accumulated_ticks += diff;
    /// The clock cannot be more precise than the guest timer, remove the lower bits
    return accumulated_ticks & inaccuracy_mask;
}

void NativeClock::Pause(bool is_paused) {
    if (!is_paused) {
        _mm_mfence();
        last_measure = __rdtsc();
    }
}

std::chrono::nanoseconds NativeClock::GetTimeNS() {
    const u64 rtsc_value = GetRTSC();
    return std::chrono::nanoseconds{MultiplyHigh(rtsc_value, ns_rtsc_factor)};
}

std::chrono::microseconds NativeClock::GetTimeUS() {
    const u64 rtsc_value = GetRTSC();
    return std::chrono::microseconds{MultiplyHigh(rtsc_value, us_rtsc_factor)};
}

std::chrono::milliseconds NativeClock::GetTimeMS() {
    const u64 rtsc_value = GetRTSC();
    return std::chrono::milliseconds{MultiplyHigh(rtsc_value, ms_rtsc_factor)};
}

u64 NativeClock::GetClockCycles() {
    const u64 rtsc_value = GetRTSC();
    return MultiplyHigh(rtsc_value, clock_rtsc_factor);
}

u64 NativeClock::GetCPUCycles() {
    const u64 rtsc_value = GetRTSC();
    return MultiplyHigh(rtsc_value, cpu_rtsc_factor);
}

} // namespace X64

} // namespace Common