code: func IPNetLast(in *net.IPNet) (last net.IP) {
  	n := len(in.IP)
  	if n != len(in.Mask) {
  		panic("wat")
  	}
  	last = make(net.IP, n)
  	for i := 0; i < n; i++ {
  		last[i] = in.IP[i] | ^in.Mask[i]
  	}
  	return
  }
docs: // Returns the last, inclusive IP in a net.IPNet.