How to generate a CRC-16 from C#

Question

I am trying to generate a CRC-16 using C#. The hardware I am using for RS232 requires the input string to be HEX. The screenshot below shows the correct conversion, For a te

Answer 1

In Addition, If you want CRC16-CCITT.

private ushort Crc16Ccitt(byte[] bytes)
{
    const ushort poly = 4129;
    ushort[] table = new ushort[256];
    ushort initialValue = 0xffff;
    ushort temp, a;
    ushort crc = initialValue;
    for (int i = 0; i < table.Length; ++i)
    {
        temp = 0;
        a = (ushort)(i << 8);
        for (int j = 0; j < 8; ++j)
        {
            if (((temp ^ a) & 0x8000) != 0)
                temp = (ushort)((temp << 1) ^ poly);
            else
                temp <<= 1;
            a <<= 1;
        }
        table[i] = temp;
    }
    for (int i = 0; i < bytes.Length; ++i)
    {
        crc = (ushort)((crc << 8) ^ table[((crc >> 8) ^ (0xff & bytes[i]))]);
    }
    return crc;
}

Answer 2

Here we go; note that this is a specific flavor of CRC-16 - it is confusing to say just "CRC-16". This borrows some implementation specifics from http://www.sanity-free.com/ - note I have made it static rather than instance-based.

using System;

static class Program
{
    static void Main()
    {
        string input = "8000";
        var bytes = HexToBytes(input);
        string hex = Crc16.ComputeChecksum(bytes).ToString("x2");
        Console.WriteLine(hex); //c061
    }
    static byte[] HexToBytes(string input)
    {
        byte[] result = new byte[input.Length / 2];
        for(int i = 0; i < result.Length; i++)
        {
            result[i] = Convert.ToByte(input.Substring(2 * i, 2), 16);
        }
        return result;
    }

    public static class Crc16
    {
        const ushort polynomial = 0xA001;
        static readonly ushort[] table = new ushort[256];

        public static ushort ComputeChecksum(byte[] bytes)
        {
            ushort crc = 0;
            for (int i = 0; i < bytes.Length; ++i)
            {
                byte index = (byte)(crc ^ bytes[i]);
                crc = (ushort)((crc >> 8) ^ table[index]);
            }
            return crc;
        }

        static Crc16()
        {
            ushort value;
            ushort temp;
            for (ushort i = 0; i < table.Length; ++i)
            {
                value = 0;
                temp = i;
                for (byte j = 0; j < 8; ++j)
                {
                    if (((value ^ temp) & 0x0001) != 0)
                    {
                        value = (ushort)((value >> 1) ^ polynomial);
                    }
                    else
                    {
                        value >>= 1;
                    }
                    temp >>= 1;
                }
                table[i] = value;
            }
        }
    }
}