using System;

using System.Net;

using System.Linq;

public class Program

{

    static IPAddress CidrToMask(int cidr)

    {

        int shift = 32 - cidr;

        UInt32 mask;

        if (shift >= 32 || shift <= 0)

            mask = 0;

        else

            mask = (0xFFFFFFFF << shift) >> shift;

​

        return new IPAddress(mask);

    }

    static int MaskToCidr(string ipAsString) {

        int ones = 0;

        Array.ForEach(ipAsString.Split('.'), (s) => Array.ForEach(Convert.ToString(int.Parse(s), 2).Where(c => c == '1').ToArray(), (k) => ones++));

        return ones;

    }

​

    static void Main(string[] args)

    {

        for (int i = -10; i <= 64; i++) {

            var subnet = CidrToMask(i).ToString();

            Console.WriteLine("mask {0}", subnet);

            var cidr = MaskToCidr(subnet);

            Console.WriteLine("cidr {0}", cidr);

        }

    }

}