CRC CCITT

After failing to find the answer to VFP's SYS(2007) return value for CRC, I did a little more hunting and found there are other algorithms that produce different results. I ended up finding another page from www.sanity-free.org that actually did the trick (http://www.sanity-free.org/133/crc_16_ccitt_in_csharp.html). Using a CRC-16, CCITT Algorithm and passing 0xFFFF as an initial value, it produced the same return value as VFP.

A listing of the code is below:

public class Crc16Ccitt

{

const ushort poly = 4129;

ushort[] table = new ushort[256];

ushort initialValue = 0;

public ushort ComputeChecksum(byte[] bytes)

{

ushort crc = this.initialValue;

for (int i = 0; i <>

{

crc = (ushort)((crc <<>> 8) ^ (0xff & bytes[i]))]);

}

return crc;

}

public byte[] ComputeChecksumBytes(byte[] bytes)

{

ushort crc = ComputeChecksum(bytes);

return new byte[] { (byte)(crc >> 8), (byte)(crc & 0x00ff) };

}

public Crc16Ccitt(InitialCrcValue initialValue)

{

this.initialValue = (ushort)initialValue;

ushort temp, a;

for (int i = 0; i <>

{

temp = 0;

a = (ushort)(i <<>

for (int j = 0; j <>

{

if (((temp ^ a) & 0x8000) != 0)

{

temp = (ushort)((temp <<>

}

else

{

temp <<= 1;

}

a <<= 1;

}

table[i] = temp;

}

}

}

}

Here is the code I wrote to produce the result:

System.Text.ASCIIEncoding encoding=new System.Text.ASCIIEncoding();
byte[] byteKey = encoding.GetBytes(strKey);
Crc16Ccitt crcChecksum = new Crc16Ccitt(InitialCrcValue.NonZero1);
intCheckSumReturn = crcChecksum.ComputeChecksum(byteKey);