return a16
}

// As4 returns an IPv4 or IPv4-in-IPv6 address in its 4-byte representation.
// If ip is the zero [Addr] or an IPv6 address, As4 panics.
// Note that 0.0.0.0 is not the zero Addr.
func (ip Addr) As4() (a4 [4]byte) {
	if ip.z == z4 || ip.Is4In6() {
		byteorder.BePutUint32(a4[:], uint32(ip.addr.lo))
		return a4
	}
	if ip.z == z0 {
		panic("As4 called on IP zero value")
	}