ipv4_loopback?

static VALUE
addrinfo_ipv4_loopback_p(VALUE self)
{
    uint32_t a;
    if (!extract_in_addr(self, &a)) return Qfalse;
    if ((a & 0xff000000) == 0x7f000000) /* 127.0.0.0/8 */
        return Qtrue;
    return Qfalse;
}