Exemplo n.º 1
0
double currentTime()
{
    // Use a combination of ftime and QueryPerformanceCounter.
    // ftime returns the information we want, but doesn't have sufficient resolution.
    // QueryPerformanceCounter has high resolution, but is only usable to measure time intervals.
    // To combine them, we call ftime and QueryPerformanceCounter initially. Later calls will use QueryPerformanceCounter
    // by itself, adding the delta to the saved ftime.  We periodically re-sync to correct for drift.
    static bool started;
    static double syncLowResUTCTime;
    static double syncHighResUpTime;
    static double lastUTCTime;

    double lowResTime = lowResUTCTime();

    if (!qpcAvailable())
        return lowResTime / 1000.0;

    double highResTime = highResUpTime();

    if (!syncedTime) {
        timeBeginPeriod(1); // increase time resolution around low-res time getter
        syncLowResUTCTime = lowResTime = lowResUTCTime();
        timeEndPeriod(1); // restore time resolution
        syncHighResUpTime = highResTime;
        syncedTime = true;
    }

    double highResElapsed = highResTime - syncHighResUpTime;
    double utc = syncLowResUTCTime + highResElapsed;

    // force a clock re-sync if we've drifted
    double lowResElapsed = lowResTime - syncLowResUTCTime;
    const double maximumAllowedDriftMsec = 15.625 * 2.0; // 2x the typical low-res accuracy
    if (fabs(highResElapsed - lowResElapsed) > maximumAllowedDriftMsec)
        syncedTime = false;

    // make sure time doesn't run backwards (only correct if difference is < 2 seconds, since DST or clock changes could occur)
    const double backwardTimeLimit = 2000.0;
    if (utc < lastUTCTime && (lastUTCTime - utc) < backwardTimeLimit)
        return lastUTCTime / 1000.0;
    lastUTCTime = utc;
    return utc / 1000.0;
}
double currentTime()
{
    static bool init = false;
    static double lastTime;
    static DWORD lastTickCount;
    if (!init) {
        lastTime = lowResUTCTime();
        lastTickCount = GetTickCount();
        init = true;
        return lastTime;
    }

    DWORD tickCountNow = GetTickCount();
    DWORD elapsed = tickCountNow - lastTickCount;
    double timeNow = lastTime + (double)elapsed / 1000.;
    if (elapsed >= 0x7FFFFFFF) {
        lastTime = timeNow;
        lastTickCount = tickCountNow;
    }
    return timeNow;
}