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** This file is part of the QtCore module of the Qt Toolkit.
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#include "qelapsedtimer.h"
#include <qt_windows.h>

typedef ULONGLONG (WINAPI *PtrGetTickCount64)(void);
#if defined(Q_OS_WINRT)
    static const PtrGetTickCount64 ptrGetTickCount64 = &GetTickCount64;
#else
    static PtrGetTickCount64 ptrGetTickCount64 = 0;
#endif

QT_BEGIN_NAMESPACE

// Result of QueryPerformanceFrequency, 0 indicates that the high resolution timer is unavailable
static quint64 counterFrequency = 0;

static void resolveLibs()
{
    static bool done = false;
    if (done)
        return;

#if !defined(Q_OS_WINRT)
    // try to get GetTickCount64 from the system
    HMODULE kernel32 = GetModuleHandleW(L"kernel32");
    if (!kernel32)
        return;
    ptrGetTickCount64 = (PtrGetTickCount64)GetProcAddress(kernel32, "GetTickCount64");
#endif // !Q_OS_WINRT

    // Retrieve the number of high-resolution performance counter ticks per second
    LARGE_INTEGER frequency;
    if (!QueryPerformanceFrequency(&frequency)) {
        counterFrequency = 0;
    } else {
        counterFrequency = frequency.QuadPart;
    }

    done = true;
}

static inline qint64 ticksToNanoseconds(qint64 ticks)
{
    if (counterFrequency > 0) {
        // QueryPerformanceCounter uses an arbitrary frequency
        qint64 seconds = ticks / counterFrequency;
        qint64 nanoSeconds = (ticks - seconds * counterFrequency) * 1000000000 / counterFrequency;
        return seconds * 1000000000 + nanoSeconds;
    } else {
        // GetTickCount(64) return milliseconds
        return ticks * 1000000;
    }
}

static quint64 getTickCount()
{
    resolveLibs();

    // This avoids a division by zero and disables the high performance counter if it's not available
    if (counterFrequency > 0) {
        LARGE_INTEGER counter;

        if (QueryPerformanceCounter(&counter)) {
            return counter.QuadPart;
        } else {
            qWarning("QueryPerformanceCounter failed, although QueryPerformanceFrequency succeeded.");
            return 0;
        }
    }

#ifndef Q_OS_WINRT
    if (ptrGetTickCount64)
        return ptrGetTickCount64();

    static quint32 highdword = 0;
    static quint32 lastval = 0;
    quint32 val = GetTickCount();
    if (val < lastval)
        ++highdword;
    lastval = val;
    return val | (quint64(highdword) << 32);
#else // !Q_OS_WINRT
    // ptrGetTickCount64 is always set on WinRT but GetTickCount is not available
    return ptrGetTickCount64();
#endif // Q_OS_WINRT
}

quint64 qt_msectime()
{
    return ticksToNanoseconds(getTickCount()) / 1000000;
}

QElapsedTimer::ClockType QElapsedTimer::clockType() Q_DECL_NOTHROW
{
    resolveLibs();

    if (counterFrequency > 0)
        return PerformanceCounter;
    else
        return TickCounter;
}

bool QElapsedTimer::isMonotonic() Q_DECL_NOTHROW
{
    return true;
}

void QElapsedTimer::start() Q_DECL_NOTHROW
{
    t1 = getTickCount();
    t2 = 0;
}

qint64 QElapsedTimer::restart() Q_DECL_NOTHROW
{
    qint64 oldt1 = t1;
    t1 = getTickCount();
    t2 = 0;
    return ticksToNanoseconds(t1 - oldt1) / 1000000;
}

qint64 QElapsedTimer::nsecsElapsed() const Q_DECL_NOTHROW
{
    qint64 elapsed = getTickCount() - t1;
    return ticksToNanoseconds(elapsed);
}

qint64 QElapsedTimer::elapsed() const Q_DECL_NOTHROW
{
    qint64 elapsed = getTickCount() - t1;
    return ticksToNanoseconds(elapsed) / 1000000;
}

qint64 QElapsedTimer::msecsSinceReference() const Q_DECL_NOTHROW
{
    return ticksToNanoseconds(t1) / 1000000;
}

qint64 QElapsedTimer::msecsTo(const QElapsedTimer &other) const Q_DECL_NOTHROW
{
    qint64 difference = other.t1 - t1;
    return ticksToNanoseconds(difference) / 1000000;
}

qint64 QElapsedTimer::secsTo(const QElapsedTimer &other) const Q_DECL_NOTHROW
{
    return msecsTo(other) / 1000;
}

bool operator<(const QElapsedTimer &v1, const QElapsedTimer &v2) Q_DECL_NOTHROW
{
    return (v1.t1 - v2.t1) < 0;
}

QT_END_NAMESPACE