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Thread: CRC-16 calculation

  1. #1

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    Question CRC-16 calculation

    Hello,
    This is my first post - hopefully a correct forum

    I am trying to figure out how to calculate CRC16 based on the following information. The device I am working with sends the following hex values:
    Code:
    00,00,00,00,00,00,00,39,0C,01,08,00,00,00,31,10,A1,2B,26,00,C3,FA,0A,2A,DE,12,F8,1C,5F,50,9F,CB,14,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,54,65,73,74,00,4C,10,03,01,00,00,1F,E2,1F
    According to the very limited documentation the last 4 bytes (00,1F,E2,1F) are a CRC-16 value. For the past 2 days I was trying to calculate that value. I am assuming this CRC value is a for all of the bytes from 0 to n-4.

    I need to be able to send the ACK to the device and that requires also a CRC to be attached in the last 4 bytes.

    The manual asks to use the following code which I think is in C...
    Code:
            public static int getCrc16(byte[] buffer) {
                 return getCrc16(buffer, 0, buffer.length,  0xA001, 0);
             }
    public synchronized static int getCrc16(byte[] buffer, int offset, int bufLen, int polynom, int preset) {
                 preset &= 0xFFFF;
                 polynom &= 0xFFFF;
                 int crc = preset;
                 for (int i = 0; i < bufLen; i++) {
                     int data = buffer[i + offset] & 0xFF;
                     crc ^= data;
                     for (int j = 0; j < 8; j++) {
                         if ((crc & 0x0001) != 0) {
                             crc = (crc >> 1) ^ polynom;
    					 } else {
                             crc = crc >> 1;
                         }
    			} }
                 return crc & 0xFFFF;
             }
    Which I unfortunately cannot convert successfully to vb.net...
    Any pointers to where I can find a good resource for CRC calculation would be appreciated.
    Thanks!!

  2. #2
    Angel of Code Niya's Avatar
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    Re: CRC-16 calculation

    Is that C function provided for the device is question in its documentation or did you find that separately on the internet ? If you found it separately, it may not work as I've seen here that CRC algorithms have slight variations. I don't want to spend the time to convert it and its not the variation the device expects to be used.
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  3. #3

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    Re: CRC-16 calculation

    Quote Originally Posted by Niya View Post
    Is that C function provided for the device is question in its documentation or did you find that separately on the internet ? If you found it separately, it may not work as I've seen here that CRC algorithms have slight variations. I don't want to spend the time to convert it and its not the variation the device expects to be used.
    Hello,
    Yes. This sample is in the documentation attached to the device. So it should work if converted correctly. Thanks!

  4. #4

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    Re: CRC-16 calculation

    Anyone?

  5. #5
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    Re: CRC-16 calculation

    Here is the conversion that I have published in my book. Give it a try (I think it is equivalent to the one that you want, though CRCs can get tricky):

    Code:
    'Copyright Richard L. Grier, 2009
    Public Class CRC
        Public Function CRC(ByVal Data() As Byte) As Array
            '#define POLY 0xA001
            'unsigned int crc16( unsigned char *p, unsigned char n )
            '{
            '    unsigned char  i;
            '    unsigned short crc = 0xFFFF;
            '    while (n--)
            '    {
            '        crc ^= *p++;
            '        for (i = 8; i != 0; i--)
            '        {
            '                If (crc & 1) Then
            '                crc = (crc >> 1) ^ POLY;
            '                Else
            '                crc >>= 1;
            '        }
            '    }
            '    return (crc);
            '}
            Dim CSRet(1) As Byte
            Dim CS As UShort = &HFFFF
            Dim Poly As UShort = &HA001
            For I As Byte = 0 To Data.Length - 1
                CS = CS Xor Data(I)
                For K As Byte = 0 To 7
                    If CS And 1 Then
                        CS = (CS >> 1) Xor Poly
                    Else
                        CS >>= 1
                    End If
                Next
            Next
            CSRet(0) = CByte(CS \ &HFF)
            CSRet(1) = CByte(CS And &HFF)
            Debug.Print(CS.ToString("X2"))
            Return CSRet
        End Function
    End Class
    Dick
    Richard Grier, Consultant, Hard & Software
    Microsoft MVP (Visual Basic)

  6. #6
    Angel of Code Niya's Avatar
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    Re: CRC-16 calculation

    That looks wrong. That function is returning the type Array. It would be better to return a Byte() or best, a Short.
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  7. #7
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    Re: CRC-16 calculation

    It returns an array of type Byte (which is OK, I think). If you want, you can modifiy the code -- that is fairly simple.


    Dick
    Richard Grier, Consultant, Hard & Software
    Microsoft MVP (Visual Basic)

  8. #8

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    Re: CRC-16 calculation

    Hello,
    Can someone verify where I am making a mistake? I tried to convert the C code from the original post in this thread...
    Code:
        Public Function CRCcalc(ByVal incomingList As List(Of Byte))
            Dim Preset As Integer = &HFFFF
            Dim Polynom As Integer = &HFFFF
            Dim CRC As Integer = Preset
            For i = 0 To incomingList.Count - 1
                Dim data As Integer = incomingList.Item(i) And &HFF
                CRC ^= data
                For j = 0 To 7
                    If (data And 1) <> 0 Then
                        CRC = (CRC >> 1) ^ Polynom
                    Else
                        CRC = CRC >> 1
                    End If
                Next
            Next
            Return CRC And &HFFFF
        End Function
    Any help appreciated!
    Thanks!

    Below is the original C code:
    Code:
            public static int getCrc16(byte[] buffer) {
                 return getCrc16(buffer, 0, buffer.length,  0xA001, 0);
             }
    public synchronized static int getCrc16(byte[] buffer, int offset, int bufLen, int polynom, int preset) {
                 preset &= 0xFFFF;
                 polynom &= 0xFFFF;
                 int crc = preset;
                 for (int i = 0; i < bufLen; i++) {
                     int data = buffer[i + offset] & 0xFF;
                     crc ^= data;
                     for (int j = 0; j < 8; j++) {
                         if ((crc & 0x0001) != 0) {
                             crc = (crc >> 1) ^ polynom;
    					 } else {
                             crc = crc >> 1;
                         }
    			} }
                 return crc & 0xFFFF;
             }

  9. #9
    Fanatic Member namrekka's Avatar
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    Re: CRC-16 calculation

    Are you sure that:

    in C: polynom &= 0xFFFF;

    in VB: Dim Polynom As Integer = &HFFFF

    is equal?

  10. #10
    Angel of Code Niya's Avatar
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    Re: CRC-16 calculation

    c++ Code:
    1. polynom &= 0xFFFF
    Should be:-
    vbnet Code:
    1. Dim Polynom As Integer = Polynom And &hFFFF
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  11. #11
    Fanatic Member namrekka's Avatar
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    Re: CRC-16 calculation

    Quote Originally Posted by Niya View Post
    c++ Code:
    1. polynom &= 0xFFFF
    Should be:-
    vbnet Code:
    1. Dim Polynom As Integer = Polynom And &hFFFF
    Right!

    @marcellus
    In your code no poly is passed into the function. It is just set to hffff which is no valid poly.

  12. #12

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    Re: CRC-16 calculation

    Quote Originally Posted by Niya View Post
    c++ Code:
    1. polynom &= 0xFFFF
    Should be:-
    vbnet Code:
    1. Dim Polynom As Integer = Polynom And &hFFFF
    Thanks!
    I don't know what I was thinking... below is the revised code.

    Code:
        Public Function CRCcalc(ByVal incomingList As List(Of Byte), ByVal preset As Integer, ByVal polynom As Integer)
            preset &= &HFFFF
            polynom &= &HFFFF
            Dim CRC As Integer = Preset
            For i = 0 To incomingList.Count - 1
                Dim data As Integer = incomingList.Item(i) And &HFF
                CRC ^= data
                For j = 0 To 7
                    If (CRC And 1) <> 0 Then
                        CRC = (CRC >> 1) ^ polynom
                    Else
                        CRC = CRC >> 1
                    End If
                Next
            Next
            Return CRC And &HFFFF
        End Function

  13. #13
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    Re: CRC-16 calculation

    Quote Originally Posted by marcellus View Post
    Thanks!
    I don't know what I was thinking... below is the revised code.

    Code:
        Public Function CRCcalc(ByVal incomingList As List(Of Byte), ByVal preset As Integer, ByVal polynom As Integer)
            preset &= &HFFFF
            polynom &= &HFFFF
            Dim CRC As Integer = Preset
            For i = 0 To incomingList.Count - 1
                Dim data As Integer = incomingList.Item(i) And &HFF
                CRC ^= data
                For j = 0 To 7
                    If (CRC And 1) <> 0 Then
                        CRC = (CRC >> 1) ^ polynom
                    Else
                        CRC = CRC >> 1
                    End If
                Next
            Next
            Return CRC And &HFFFF
        End Function

    Thanks, for help me.

    Have this code for calculation of CRC 16 in C language, I need convert to vb.

    function crc16str(str) {

    return crc16(str);
    }

    function crc16(data) {
    alert(data);
    /* CRC table for the CRC-16. The poly is 0x8005 (x^16 + x^15 + x^2 + 1) */
    const crctab16 = new Uint16Array([
    0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
    0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
    0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
    0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
    0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
    0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
    0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
    0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
    0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
    0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
    0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
    0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
    0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
    0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
    0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
    0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
    0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
    0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
    0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
    0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
    0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
    0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
    0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
    0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
    0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
    0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
    0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
    0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
    0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
    0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
    0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
    0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
    ]);
    var len = data.length;
    var buffer = 0;
    var crc;
    while (len--) {

    crc = ((crc >>> 8) ^ (crctab16[(crc ^ (data[buffer++])) & 0xff]));

    }
    return crc;
    // return [(crc >>> 8 & 0xff), (crc & 0xff)];
    }

  14. #14
    Angel of Code Niya's Avatar
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    Re: CRC-16 calculation

    You should probably make a new thread for this instead of resurrecting this 9 year old thread.
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    There's just no reason to use garbage like InputBox. - jmcilhinney

    The threads I start are Niya and Olaf free zones. No arguing about the benefits of VB6 over .NET here please. Happiness must reign. - yereverluvinuncleber

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