A MOO-like ftime() function for Genesis.

ftime.c

COLDC_FUNC(ftime) {
    cData *args;
    Int num_args;

    /* Take an optional integer argument indicating whether we use monotonic time or not. */
    if (!func_init_0_or_1(&args, &num_args, INTEGER))
        return;

#ifdef __MACH__
    // macOS only provides SYSTEM_CLOCK for monotonic time, so our arguments don't matter.
    clock_id_t clock_type = (num_args == 0 ? CALENDAR_CLOCK : SYSTEM_CLOCK);
#else
    // Other OSes provide MONOTONIC_RAW and MONOTONIC, so we'll check args for 2(raw) or 1.
    clockid_t clock_type = 0;
    if (num_args == 0)
        clock_type = CLOCK_REALTIME;
    else
#if defined(__WIN32) || defined(__CYGWIN__)
    // CYGWIN doesn't give us MONOTONIC_RAW
    clock_type = CLOCK_MONOTONIC;
#else
    clock_type = args[0].u.val  == 2 ? CLOCK_MONOTONIC_RAW : CLOCK_MONOTONIC;
#endif
#endif

    struct timespec ts;

#ifdef __MACH__
    // macOS lacks clock_gettime, use clock_get_time instead
    clock_serv_t cclock;
    mach_timespec_t mts;
    host_get_clock_service(mach_host_self(), clock_type, &cclock);
    clock_get_time(cclock, &mts);
    mach_port_deallocate(mach_task_self(), cclock);
    ts.tv_sec = mts.tv_sec;
    ts.tv_nsec = mts.tv_nsec;
#else
    clock_gettime(clock_type, &ts);
#endif

    Float r = (Float)ts.tv_sec + (Float)ts.tv_nsec * 1e-9;

    push_float(r);
}