iperf-2.0.5/compat/gettimeofday.c

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 *
 * gettimeofday.c
 * by Mark Gates <mgates@nlanr.net>
 * -------------------------------------------------------------------
 * A (hack) implementation of gettimeofday for Windows.
 * Since I send sec/usec in UDP packets, this made the most sense.
 * ------------------------------------------------------------------- */

#ifdef HAVE_CONFIG_H
    #include "config.h"
#endif

#ifndef HAVE_GETTIMEOFDAY

    #include "headers.h"
    #include "gettimeofday.h"

    #ifdef __cplusplus
extern "C" {
#endif

int gettimeofday( struct timeval* tv, void* timezone ) {
    FILETIME time;
    double   timed;

    GetSystemTimeAsFileTime( &time );

    // Apparently Win32 has units of 1e-7 sec (tenths of microsecs)
    // 4294967296 is 2^32, to shift high word over
    // 11644473600 is the number of seconds between
    // the Win32 epoch 1601-Jan-01 and the Unix epoch 1970-Jan-01
    // Tests found floating point to be 10x faster than 64bit int math.

    timed = ((time.dwHighDateTime * 4294967296e-7) - 11644473600.0) +
            (time.dwLowDateTime  * 1e-7);

    tv->tv_sec  = (long) timed;
    tv->tv_usec = (long) ((timed - tv->tv_sec) * 1e6);

    return 0;
}

#ifdef __cplusplus
} /* end extern "C" */
    #endif

#endif /* HAVE_GETTIMEOFDAY */