Set#hash

static VALUE
set_i_hash(VALUE set)
{
    st_index_t size = RSET_SIZE(set);
    st_index_t hval = rb_st_hash_start(size);
    hval = rb_hash_uint(hval, (st_index_t)set_i_hash);
    if (size) {
        set_iter(set, set_hash_i, (VALUE)&hval);
    }
    hval = rb_st_hash_end(hval);
    return ST2FIX(hval);
}