IP range iteration utility for golang

iprange.go

// IterateIPRange calculates the sequence of IP address from beginAddr to endAddr
// then calls the callback cb for each address of the sequence.
// beginAddr value must be smaller than endAddr.
func IterateIPRange(beginAddr, endAddr net.IP, cb func(addr net.IP)) error {
	incIP := func(ip net.IP) net.IP {
		for j := len(ip) - 1; j >= 0; j-- {
			ip[j]++
			if ip[j] > 0 {
				break
			}
		}
		return ip
	}

	gtIP := func(a, b net.IP) bool {
		for i := len(a) - 1; i >= 0; i-- {
			if a[i] > b[i] {
				return false
			}
		}
		return true
	}

	if !gtIP(beginAddr, endAddr) {
		return fmt.Errorf("beginIP must be smaller than endIP: begin=%s, end=%s", beginAddr, endAddr)
	}

	var addr = make(net.IP, len(beginAddr))
	for copy(addr, beginAddr); gtIP(addr, endAddr); addr = incIP(addr) {
		cb(addr)
	}
	return nil
}


// IterateIPSubnet walks through all the IP addresses in the subnet range.
func IterateIPSubnet(subnet *net.IPNet, cb func(addr net.IP)) {
	startAddr := subnet.IP.Mask(subnet.Mask)
	endAddr := make(net.IP, len(startAddr))
	for i := 0; i <= len(startAddr)-1; i++ {
		endAddr[i] = byte(startAddr[i]) | byte(subnet.Mask[i]^0xFF)
	}

	if err := IterateIPRange(startAddr, endAddr, cb); err != nil {
		panic(err)
	}
}

endAddr[i] = byte(startAddr[i]) | byte(subnet.Mask[i]^0xFF)
can be simplified to
endAddr[i] = startAddr[i] | ^subnet.Mask[i]

Also it seems unneccessary to return and assign the address passed to incIP since the passed instance itself is modified.