random.c:175
static VALUE
rb_f_srand(argc, argv, obj)
    int argc;
    VALUE *argv;
    VALUE obj;
{
    VALUE sd;
    unsigned long seed, old;

    rb_secure(4);
    if (rb_scan_args(argc, argv, "01", &sd) == 0) {
	seed = random_seed();
    }
    else {
	seed = NUM2ULONG(sd);
    }
    old = rand_init(seed);

    return ULONG2NUM(old);
}
