How can I achieve nanosecond precision timing on Windows without native clock_gettime support?

Porting clock_gettime to Windows

The clock_gettime function is a POSIX standard function that provides a way to obtain the current time with nanosecond precision. However, it is not natively supported on Windows.

Porting Code to Windows

To port code that uses clock_gettime to Windows, you can implement a replacement function using the Win32 API. Here is an example of how you can do this:

<code class="C++">#include <Windows.h>

// Returns the file time offset for Windows.
LARGE_INTEGER getFILETIMEoffset() {
    SYSTEMTIME s;
    FILETIME f;
    LARGE_INTEGER t;

    s.wYear = 1970;
    s.wMonth = 1;
    s.wDay = 1;
    s.wHour = 0;
    s.wMinute = 0;
    s.wSecond = 0;
    s.wMilliseconds = 0;
    SystemTimeToFileTime(&amp;s, &amp;f);
    t.QuadPart = f.dwHighDateTime;
    t.QuadPart <<= 32;
    t.QuadPart |= f.dwLowDateTime;
    return (t);
}

// Replacement for clock_gettime function.
int clock_gettime(int X, struct timeval *tv) {
    LARGE_INTEGER t;
    FILETIME f;
    double microseconds;
    static LARGE_INTEGER offset;
    static double frequencyToMicroseconds;
    static int initialized = 0;
    static BOOL usePerformanceCounter = 0;

    if (!initialized) {
        LARGE_INTEGER performanceFrequency;
        initialized = 1;
        usePerformanceCounter = QueryPerformanceFrequency(&amp;performanceFrequency);
        if (usePerformanceCounter) {
            QueryPerformanceCounter(&amp;offset);
            frequencyToMicroseconds = (double)performanceFrequency.QuadPart / 1000000.;
        } else {
            offset = getFILETIMEoffset();
            frequencyToMicroseconds = 10.;
        }
    }
    if (usePerformanceCounter) QueryPerformanceCounter(&amp;t);
    else {
        GetSystemTimeAsFileTime(&amp;f);
        t.QuadPart = f.dwHighDateTime;
        t.QuadPart <<= 32;
        t.QuadPart |= f.dwLowDateTime;
    }

    t.QuadPart -= offset.QuadPart;
    microseconds = (double)t.QuadPart / frequencyToMicroseconds;
    t.QuadPart = microseconds;
    tv->tv_sec = t.QuadPart / 1000000;
    tv->tv_usec = t.QuadPart % 1000000;
    return (0);
}</code>

Once you have implemented the replacement function, you can use it in your code to obtain the current time with nanosecond precision. Note that you may need to make additional modifications to your code to account for any differences in the behavior of clock_gettime on different platforms.

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