Cyclic redundancy check calculation C to C# code conversion not working

Question

unsigned short CalculateCRC(char* buffer, int size)
{
    unsigned short cword = 0;
    unsigned short ch;
    int i,j;

    for (i = 0; i < size; i++) {
        ch = buffer[i] << 8;
        for (j = 0; j < 8; j++) {
            if ((ch & 0x8000) ^ (cword & 0x8000)) {
                cword = (cword <<= 1) ^ 4129;
            }
            else {
                cword <<= 1;
            }
            ch <<= 1;
        }
    }
    return cword;
}

I converted above code in to C# but it is not working could any one can figure out the problem. I converted above code as follows.

public static int CalculateCheckSum(byte[] strsResponse)
{
    short crc = 0;
    try
    {
        short ch;
        for (int i = 0; i < strsResponse.Length; i++)
        {
            ch = (short)(strsResponse[i] << 8);
            for (int j = 0; j < 8; j++)
            {
                bool xorFlag = (ch & 0x8000)==1?false:true;
                if (xorFlag)
                {
                    crc = (short)((crc <<= 1) ^ 4129);
                }
                else
                {
                    crc <<= 1;
                }
                ch <<= 1;
            }
        }
    }
    catch (Exception ex)
    {
        return crc = 0;
    }
    return crc;
}

I cant figure out the problem any one can show me the mistakes.

Rather than starting an extensive discussion about what 'doesn't work' means (any compile errors, runtime errors, unexpected behaviour, etc), maybe you should look for an existing CRC implementation for C#. I can't imagine that no-one has written this before in C#. — GolezTrol, May 05 '14 at 17:41
@GolezTrol Unless it's hiding somewhere unexpected, oddly it doesn't appear to be in .NET. — Dan Lugg, May 05 '14 at 17:45
possible duplicate of [How do I calculate CRC32 of a string](http://stackoverflow.com/questions/8128/how-do-i-calculate-crc32-of-a-string) — GolezTrol, May 05 '14 at 17:46
http://damieng.com/blog/2006/08/08/Calculating_CRC32_in_C_and_NET — GolezTrol, May 05 '14 at 17:47
for starters, `short != unsigned short` and those sign bits do make a difference. — Henk Holterman, May 05 '14 at 18:04
`bool xorFlag = (ch & 0x8000)==1?false:true;` is not a good translation of the original. That's one mistake for starters. — ClickRick, May 05 '14 at 20:20

score 0 · Answer 1 · answered May 05 '14 at 20:10

Try this:

public static int CalculateCheckSum(byte[] strsResponse)
{
    short crc = 0;
    try
    {
        ushort ch;
        for (int i = 0; i < strsResponse.Length; i++)
        {
                ch = (ushort)(strsResponse[i] << 8);
                for (int j = 0; j < 8; j++)
                {
                    bool xorFlag = ((ch & 0x8000) ^ (cword & 0x8000)) == 0 ? false : true;
                    if (xorFlag)
                    {
                        crc = (ushort)((crc <<= 1) ^ 4129);
                    }
                    else
                    {
                        crc <<= 1;
                    }
                    ch <<= 1;
                }
        }
    }
    catch (Exception ex)
    {
        return crc = 0;
    }
    return crc;
}

Cyclic redundancy check calculation C to C# code conversion not working

1 Answers1