Get last IP address of network at golang

lastip.go

package main

import (
	"log"
	"net"
)

func main() {
	// convert string to IPNet struct
	ip1, net1, _ := net.ParseCIDR("fd34:0135:0123::2/120")

	ip2, net2, _ := net.ParseCIDR("10.0.1.2/20")

	last1 := lastIP(net1)
	log.Printf("ip1: %s, net1: %d, last1: %s", ip1, net1.Mask, last1)

	last2 := lastIP(net2)
	log.Printf("ip2: %s, net2: %d, last2: %s", ip2, net2.Mask, last2)

}
func lastIP(n *net.IPNet) net.IP {

	lastIp, lastMask, _ := net.ParseCIDR("fd::/128")
	size := 16
	if n.IP.To4() != nil {
		lastIp, lastMask, _ = net.ParseCIDR("10.0.0.1/32")
		log.Println(len(lastIp))
		size = 4
	}

	for i := 0; i < size; i++ {
		lastIp[i] = (n.IP[i] & n.Mask[i]) | (n.Mask[i] ^ lastMask.Mask[i])
	}

	return lastIp[:size]
}