WebCore/platform/win/SystemTimeWin.cpp

/*
 * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "config.h"
#include "SystemTime.h"

#include <windows.h>

namespace WebCore {

double currentTime()
{
    FILETIME ft;
    GetSystemTimeAsFileTime(&ft);

    // As per Windows documentation for FILETIME, copy the resulting FILETIME structure to a
    // ULARGE_INTEGER structure using memcpy (using memcpy instead of direct assignment can
    // prevent alignment faults on 64-bit Windows).

    ULARGE_INTEGER t;
    memcpy(&t, &ft, sizeof(t));

    // Windows file times are in 100s of nanoseconds.
    // To convert to seconds, we have to divide by 10,000,000, which is more quickly
    // done by multiplying by 0.0000001.
    
    // Between January 1, 1601 and January 1, 1970, there were 369 complete years,
    // of which 89 were leap years (1700, 1800, and 1900 were not leap years).
    // That is a total of 134774 days, which is 11644473600 seconds.

    return t.QuadPart * 0.0000001 - 11644473600.0;
}

}