clock_gettime_monotonic.h

#include <time.h>

#ifdef _MSC_VER

/**
 * implementation of clock_gettime(CLOCK_MONOTONIC, tv) from unistd.h for Windows
 */

#define WIN32_LEAN_AND_MEAN
#include <Windows.h>
#define MS_PER_SEC 1000ULL // MS = milliseconds
#define US_PER_MS 1000ULL  // US = microseconds
#define HNS_PER_US 10ULL   // HNS = hundred-nanoseconds (e.g., 1 hns = 100 ns)
#define NS_PER_US 1000ULL

#define HNS_PER_SEC (MS_PER_SEC * US_PER_MS * HNS_PER_US)
#define NS_PER_HNS (100ULL) // NS = nanoseconds
#define NS_PER_SEC (MS_PER_SEC * US_PER_MS * NS_PER_US)

// https://stackoverflow.com/questions/5404277/porting-clock-gettime-to-windows
void clock_gettime_monotonic(struct timespec *tv)
{
    static LARGE_INTEGER ticksPerSec;
    LARGE_INTEGER ticks;

    if (!ticksPerSec.QuadPart)
    {
        QueryPerformanceFrequency(&ticksPerSec);
        if (!ticksPerSec.QuadPart)
        {
            errno = ENOTSUP;
            fprintf(stderr, "clock_gettime_monotonic: QueryPerformanceFrequency failed\n");
            exit(-1);
        }
    }

    QueryPerformanceCounter(&ticks);

    tv->tv_sec = (long)(ticks.QuadPart / ticksPerSec.QuadPart);
    tv->tv_nsec = (long)(((ticks.QuadPart % ticksPerSec.QuadPart) * NS_PER_SEC) / ticksPerSec.QuadPart);
}
#else

#include <unistd.h>

void clock_gettime_monotonic(struct timespec *tv) {
    clock_gettime(CLOCK_MONOTONIC, tv);
}

#endif