wasSharpNET – Rev 5

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///////////////////////////////////////////////////////////////////////////
//  Copyright (C) Wizardry and Steamworks 2016 - License: GNU GPLv3      //
//  Please see: http://www.gnu.org/licenses/gpl.html for legal details,  //
//  rights of fair usage, the disclaimer and warranty conditions.        //
///////////////////////////////////////////////////////////////////////////

using System;
using System.Net;

namespace wasSharpNET.Network
{
    /// <summary>
    ///     Subnet Mask.
    /// </summary>
    /// <remarks>https://blogs.msdn.microsoft.com/knom/2008/12/31/ip-address-calculations-with-c-subnetmasks-networks/</remarks>
    public static class SubnetMask
    {
        public static readonly IPAddress ClassA = IPAddress.Parse("255.0.0.0");
        public static readonly IPAddress ClassB = IPAddress.Parse("255.255.0.0");
        public static readonly IPAddress ClassC = IPAddress.Parse("255.255.255.0");

        public static IPAddress CreateByHostBitLength(int hostpartLength)
        {
            var hostPartLength = hostpartLength;
            var netPartLength = 32 - hostPartLength;

            if (netPartLength < 2)
                throw new ArgumentException("Number of hosts is to large for IPv4");

            var binaryMask = new byte[4];

            for (var i = 0; i < 4; i++)
            {
                if (i*8 + 8 <= netPartLength)
                    binaryMask[i] = 255;
                else if (i*8 > netPartLength)
                    binaryMask[i] = 0;
                else
                {
                    var oneLength = netPartLength - i*8;
                    var binaryDigit =
                        string.Empty.PadLeft(oneLength, '1').PadRight(8, '0');
                    binaryMask[i] = Convert.ToByte(binaryDigit, 2);
                }
            }
            return new IPAddress(binaryMask);
        }

        public static IPAddress CreateByNetBitLength(int netpartLength)
        {
            var hostPartLength = 32 - netpartLength;
            return CreateByHostBitLength(hostPartLength);
        }

        public static IPAddress CreateByHostNumber(int numberOfHosts)
        {
            var maxNumber = numberOfHosts + 1;

            var b = Convert.ToString(maxNumber, 2);

            return CreateByHostBitLength(b.Length);
        }
    }
}

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