Process.clock_gettime

static VALUE
rb_clock_gettime(int argc, VALUE *argv, VALUE _)
{
    int ret;

    struct timetick tt;
    timetick_int_t numerators[2];
    timetick_int_t denominators[2];
    int num_numerators = 0;
    int num_denominators = 0;

    VALUE unit = (rb_check_arity(argc, 1, 2) == 2) ? argv[1] : Qnil;
    VALUE clk_id = argv[0];
    clockid_t c;

    if (SYMBOL_P(clk_id)) {
#ifdef CLOCK_REALTIME
        if (clk_id == RUBY_CLOCK_REALTIME) {
            c = CLOCK_REALTIME;
            goto gettime;
        }
#endif

#ifdef CLOCK_MONOTONIC
        if (clk_id == RUBY_CLOCK_MONOTONIC) {
            c = CLOCK_MONOTONIC;
            goto gettime;
        }
#endif

#ifdef CLOCK_PROCESS_CPUTIME_ID
        if (clk_id == RUBY_CLOCK_PROCESS_CPUTIME_ID) {
            c = CLOCK_PROCESS_CPUTIME_ID;
            goto gettime;
        }
#endif

#ifdef CLOCK_THREAD_CPUTIME_ID
        if (clk_id == RUBY_CLOCK_THREAD_CPUTIME_ID) {
            c = CLOCK_THREAD_CPUTIME_ID;
            goto gettime;
        }
#endif

        /*
         * Non-clock_gettime clocks are provided by symbol clk_id.
         */
#ifdef HAVE_GETTIMEOFDAY
        /*
         * GETTIMEOFDAY_BASED_CLOCK_REALTIME is used for
         * CLOCK_REALTIME if clock_gettime is not available.
         */
#define RUBY_GETTIMEOFDAY_BASED_CLOCK_REALTIME ID2SYM(id_GETTIMEOFDAY_BASED_CLOCK_REALTIME)
        if (clk_id == RUBY_GETTIMEOFDAY_BASED_CLOCK_REALTIME) {
            struct timeval tv;
            ret = gettimeofday(&tv, 0);
            if (ret != 0)
                rb_sys_fail("gettimeofday");
            tt.giga_count = tv.tv_sec;
            tt.count = (int32_t)tv.tv_usec * 1000;
            denominators[num_denominators++] = 1000000000;
            goto success;
        }
#endif

#define RUBY_TIME_BASED_CLOCK_REALTIME ID2SYM(id_TIME_BASED_CLOCK_REALTIME)
        if (clk_id == RUBY_TIME_BASED_CLOCK_REALTIME) {
            time_t t;
            t = time(NULL);
            if (t == (time_t)-1)
                rb_sys_fail("time");
            tt.giga_count = t;
            tt.count = 0;
            denominators[num_denominators++] = 1000000000;
            goto success;
        }

#ifdef HAVE_TIMES
#define RUBY_TIMES_BASED_CLOCK_MONOTONIC \
        ID2SYM(id_TIMES_BASED_CLOCK_MONOTONIC)
        if (clk_id == RUBY_TIMES_BASED_CLOCK_MONOTONIC) {
            struct tms buf;
            clock_t c;
            unsigned_clock_t uc;
            c = times(&buf);
            if (c ==  (clock_t)-1)
                rb_sys_fail("times");
            uc = (unsigned_clock_t)c;
            tt.count = (int32_t)(uc % 1000000000);
            tt.giga_count = (uc / 1000000000);
            denominators[num_denominators++] = get_clk_tck();
            goto success;
        }
#endif

#ifdef RUSAGE_SELF
#define RUBY_GETRUSAGE_BASED_CLOCK_PROCESS_CPUTIME_ID \
        ID2SYM(id_GETRUSAGE_BASED_CLOCK_PROCESS_CPUTIME_ID)
        if (clk_id == RUBY_GETRUSAGE_BASED_CLOCK_PROCESS_CPUTIME_ID) {
            struct rusage usage;
            int32_t usec;
            ret = getrusage(RUSAGE_SELF, &usage);
            if (ret != 0)
                rb_sys_fail("getrusage");
            tt.giga_count = usage.ru_utime.tv_sec + usage.ru_stime.tv_sec;
            usec = (int32_t)(usage.ru_utime.tv_usec + usage.ru_stime.tv_usec);
            if (1000000 <= usec) {
                tt.giga_count++;
                usec -= 1000000;
            }
            tt.count = usec * 1000;
            denominators[num_denominators++] = 1000000000;
            goto success;
        }
#endif

#ifdef HAVE_TIMES
#define RUBY_TIMES_BASED_CLOCK_PROCESS_CPUTIME_ID \
        ID2SYM(id_TIMES_BASED_CLOCK_PROCESS_CPUTIME_ID)
        if (clk_id == RUBY_TIMES_BASED_CLOCK_PROCESS_CPUTIME_ID) {
            struct tms buf;
            unsigned_clock_t utime, stime;
            if (times(&buf) ==  (clock_t)-1)
                rb_sys_fail("times");
            utime = (unsigned_clock_t)buf.tms_utime;
            stime = (unsigned_clock_t)buf.tms_stime;
            tt.count = (int32_t)((utime % 1000000000) + (stime % 1000000000));
            tt.giga_count = (utime / 1000000000) + (stime / 1000000000);
            if (1000000000 <= tt.count) {
                tt.count -= 1000000000;
                tt.giga_count++;
            }
            denominators[num_denominators++] = get_clk_tck();
            goto success;
        }
#endif

#define RUBY_CLOCK_BASED_CLOCK_PROCESS_CPUTIME_ID \
        ID2SYM(id_CLOCK_BASED_CLOCK_PROCESS_CPUTIME_ID)
        if (clk_id == RUBY_CLOCK_BASED_CLOCK_PROCESS_CPUTIME_ID) {
            clock_t c;
            unsigned_clock_t uc;
            errno = 0;
            c = clock();
            if (c == (clock_t)-1)
                rb_sys_fail("clock");
            uc = (unsigned_clock_t)c;
            tt.count = (int32_t)(uc % 1000000000);
            tt.giga_count = uc / 1000000000;
            denominators[num_denominators++] = CLOCKS_PER_SEC;
            goto success;
        }

#ifdef __APPLE__
        if (clk_id == RUBY_MACH_ABSOLUTE_TIME_BASED_CLOCK_MONOTONIC) {
            const mach_timebase_info_data_t *info = get_mach_timebase_info();
            uint64_t t = mach_absolute_time();
            tt.count = (int32_t)(t % 1000000000);
            tt.giga_count = t / 1000000000;
            numerators[num_numerators++] = info->numer;
            denominators[num_denominators++] = info->denom;
            denominators[num_denominators++] = 1000000000;
            goto success;
        }
#endif
    }
    else if (NUMERIC_CLOCKID) {
#if defined(HAVE_CLOCK_GETTIME)
        struct timespec ts;
        c = NUM2CLOCKID(clk_id);
      gettime:
        ret = clock_gettime(c, &ts);
        if (ret == -1)
            rb_sys_fail("clock_gettime");
        tt.count = (int32_t)ts.tv_nsec;
        tt.giga_count = ts.tv_sec;
        denominators[num_denominators++] = 1000000000;
        goto success;
#endif
    }
    /* EINVAL emulates clock_gettime behavior when clock_id is invalid. */
    rb_syserr_fail(EINVAL, 0);

  success:
    return make_clock_result(&tt, numerators, num_numerators, denominators, num_denominators, unit);
}