CRC Maxim/Dallas 1Wire Generation: translate Visual Basic to PHP

Question

i Need a function that generates the Maxim/Dallas 1-Wire CRC 8bit-Code like this page: http://www.datastat.com/sysadminjournal/maximcrc.cgi

For that problem I found an little Excel Calculator for solution. It works correctly, but I got the Problem to translate it into PHP language.

Original VB Code:

Private Sub ROMCRC_Click()

    Dim InHex, OutBinStr As String
    Dim OutBinArr(1 To 56) As Integer
    Dim OutDec, i, CRC(1 To 8), CRCTemp As Integer

    InHex = Range("ROMByte1").Value & Range("ROMByte2").Value & Range("ROMByte3").Value & Range("ROMByte4").Value & Range("ROMByte5").Value & Range("ROMByte6").Value & Range("ROMByte7").Value
    OutBinStr = HexToBin(InHex)

    ' Convert string to array, LSB = OutBinArr(1)
    For i = 1 To 56
    OutBinArr(57 - i) = Mid$(OutBinStr, i, 1) ' Split(OutBinStr)
    Next i

    'Initialize CRC
    For i = 1 To 8
        CRC(i) = 0
    Next i

    'Calculate CRC
    For i = 1 To 56
        CRCTemp = CRC(1) Xor OutBinArr(i)
        CRC(1) = CRC(2)
        CRC(2) = CRC(3)
        CRC(3) = CRC(4) Xor CRCTemp
        CRC(4) = CRC(5) Xor CRCTemp
        CRC(5) = CRC(6)
        CRC(6) = CRC(7)
        CRC(7) = CRC(8)
        CRC(8) = CRCTemp
    Next i

    DecCRC = BinToDec(CRC)

    Range("ROMCRCValue").Value = DecCRC

End Sub


Private Function HexToBin(hstr)
'convert hex string to binary string
    cnvarr = Array("0000", "0001", "0010", "0011", _
             "0100", "0101", "0110", "0111", "1000", _
             "1001", "1010", "1011", "1100", "1101", _
             "1110", "1111")
    bstr = ""
    For i = 1 To Len(hstr)
        hdgt = Mid(hstr, i, 1)
        cix = CInt("&H" & hdgt)
        bstr = bstr & cnvarr(cix)
    Next
    HexToBin = bstr
End Function

Function BinToDec(bstr)
'convert 8 bit Binary number to Decimal
    Dim j, Out As Integer

    Out = 0
    For j = 1 To 8
        Out = Out + bstr(j) * 2 ^ (j - 1)
    Next j

    BinToDec = Out
End Function

My PHP test code:

protected function HexToBin($hstr) {
    //convert hex string to binary string
    $cnvarr = array(
        '0000',
        '0001',
        '0010',
        '0011',
        '0100',
        '0101',
        '0110',
        '0111',
        '1000',
        '1001',
        '1010',
        '1011',
        '1100',
        '1101',
        '1110',
        '1111'
    );
    $bstr = "";
    for ($i = 1; $i <= strlen($hstr); $i++) {
        $hdgt = substr($hstr, $i, 1);
        $cix = intval($hdgt);
        echo $cix.'|';
        $bstr .= $cnvarr[$cix];
    }
    return $bstr;
}

protected function createHash($data) {
    //$OutBinStr = $this->HexToBin($data);
    $OutBinStr = hex2bin($data);

    $OutBinArr = array();
    $crc = array();

    //Convert string to array, LSB = OutBinArr(1)
    for ($i = 1; $i <= 56; $i++) {
        $OutBinArr[57 - $i] = substr($OutBinStr, $i - 1, 1);
    }

    //initialize crc
    for ($i = 1; $i <= 8; $i++) {
        $crc[$i] = 0;
    }

    // calculate
    for ($i = 1; $i <= 56; $i++) {

        $CRCTemp = $crc[1] ^ $OutBinArr[$i];
        $crc[1] = $crc[2];
        $crc[2] = $crc[3];
        $crc[3] = $crc[4] ^ $CRCTemp;
        $crc[4] = $crc[5] ^ $CRCTemp;
        $crc[5] = $crc[6];
        $crc[6] = $crc[7];
        $crc[7] = $crc[8];
        $crc[8] = $CRCTemp;
    }

    return implode('', $crc);
}

Example call:

$buttonId = '0000145D6E0F01';
echo $this->createHash($buttonId);

I thank you if you have any Ideas why the Script does not generate the correct crc.

Thank you, nice regards Michael

Answer 1

Your HexToBin() was generating wrong string. The for loop for substr() started with 1 instead of 0. See substr manual.

Imploding $crc resulted an reverse bit order value.

<?PHP    
function HexToBin($hstr){
    $hstr = str_replace(' ','',$hstr);
    $hArr = str_split($hstr);
    $bstr = "";
    foreach($hArr AS $c){
        $cix = sprintf("0x0{$c}");
        // echo sprintf("%04b|",hexdec($cix));
        $bstr .= sprintf("%04b",hexdec($cix));
    }

    return $bstr;
}

function createHash($data){
    $OutBinStr = HexToBin($data);
    $crc = array_fill(0,8,0);
    $OutBinArr = array_reverse(str_split($OutBinStr));

    // calculate
    foreach($OutBinArr AS $i){
        $CRCTemp = $crc[0] ^ $i;
        $crc[0] = $crc[1];
        $crc[1] = $crc[2];
        $crc[2] = $crc[3] ^ $CRCTemp;
        $crc[3] = $crc[4] ^ $CRCTemp;
        $crc[4] = $crc[5];
        $crc[5] = $crc[6];
        $crc[6] = $crc[7];
        $crc[7] = $CRCTemp;
    }
    $crc = array_reverse($crc);
    return implode('', $crc);
}

$buttonId = '00 00 14 5D 6E 0F 01';     // 59 => 3B
// $buttonId = '12 AA 12 5F 14 A2 12 12';   // 109 => 6D
$crc = bindec(createHash($buttonId));
printf("\n%d => %X",$crc,$crc);
?>