code: func GetIndexedIP(subnet *net.IPNet, index int) (net.IP, error) {
  	ip := addIPOffset(bigForIP(subnet.IP), index)
  	if !subnet.Contains(ip) {
  		return nil, fmt.Errorf("can't generate IP with index %d from subnet. subnet too small. subnet: %q", index, subnet)
  	}
  	return ip, nil
  }
docs: // GetIndexedIP returns a net.IP that is subnet.IP + index in the contiguous IP space.