double hirestime( void )
{
    static uint32_t num =  0 ;
    static uint32_t denom =  0 ;
    uint64_t now;

    if (denom ==  0 ) {
            struct mach_timebase_info tbi;
            kern_return_t r;
            r = mach_timebase_info(&tbi);
            if (r != KERN_SUCCESS) {
                    abort();
            }
            num = tbi.numer;
            denom = tbi.denom;
    }
    now = mach_absolute_time();
    return (double)(now * (double)num / denom / NSEC_PER_SEC);
}

double hirestime (void)
{
  struct timeval tv;
  gettimeofday( &tv, NULL );
  return (double)tv.tv_sec + (double)tv.tv_usec/ 1000000 . 0 ;
}