c# - Calculate CRC 15 for CAN BUS -

i need calculate crc checksum can bus.

scenario:

my input looks following (where x either 1 or 0, * marks multiple times x, | marks section , - change of input method, lbis label, tb textbox, cb combobox):

• lb: 0
• tb: 11x
• cb: x
• cb: x
• lb: 1
• tb: 4x => convert.tostring(8-64 / 8, 2).padleft(4, '0');
• tb: 8-64x, => 8-64 % 8 == 0
• tb: 15x => crc of above
• lb: 1
• lb: 11
• lb: 1111111
• lb: 111

which returns layout:

0|11*x-x|x-1-4*x|64*x|15*x-1|11|1111111|111 

example:

00101010101000100100101010100101010(missing 15*x crc sum)1111111111111 

this string processed following string extension, maximal 5 equal digits follow each other:

public static string correct4crc(this string s) {     return s.replace("00000", "000001").replace("11111", "111110"); } 

after following method returns divisor:

public static biginteger createdivisor(string s) {     var = biginteger.parse(s);     var d = biginteger.pow(i, 15) + biginteger.pow(i, 14) + biginteger.pow(i, 10) + biginteger.pow(i, 8) + biginteger.pow(i, 7) + biginteger.pow(i, 4) + biginteger.pow(i, 3) + 1;     return d; } 

the problem i've got part ^:

public static string crc(this string s) {     var dd = s.correct4crc();     var dr = dd.createdivisor().tostring();     int drl = dr.length;     var d = dd.substring(0, drl).createdivisor();     var f = d ^ dr.createdivisor();     var p = true;     while (p)     {         d = dd.substring(0, drl).createdivisor();         f = d ^ dr.createdivisor();         p = d > dd.createdivisor();     }     return f.tostring(); } 

i know might closed asking code, please bear me don't it. problem is, there no real documentation helped me figuring out.

anyway, if know 1 doc, solves problem please add comment. i'll check out , close answer myself if it.

i think bitstuffing wrong (the replacement of 00000 000001 , of 11111 111110), because doesn't handle avalanche replacements... 0000011110000 becomes 0000011111000001.

here http://blog.qartis.com/can-bus/ there seems example. page linked http://ghsi.de/crc/index.php?polynom=1100010110011001&message=2aa80 generates c code calculating crc-15.

// 0000011110000 becomes 0000011111000001 public static string bitstuff(string bits) {     stringbuilder sb = null;      char last = ' ';     int count = 0;      (int = 0; < bits.length; i++)     {         char ch = bits[i];          if (ch == last)         {             count++;              if (count == 5)             {                 if (sb == null)                 {                     // maximum length equal length of bits                     // plus 1 length 5, 2 length 9, 3 length 13...                     // because maximum expanion                     // 00000111100001111... or 11111000011110000...                     sb = new stringbuilder(bits.length + (bits.length - 1) / 4);                     sb.append(bits, 0, i);                 }                  sb.append(ch);                 last = ch == '0' ? '1' : '0';                 sb.append(last);                 count = 1;                  continue;             }         }         else         {             last = ch;             count = 1;         }          if (sb != null)         {             sb.append(ch);         }     }      return sb != null ? sb.tostring() : bits; }  // taken http://ghsi.de/crc/index.php?polynom=1100010110011001&message=2aa80 public static string crc15(string bits) {     var res = new char[15]; // crc result     var crc = new bool[15];      (int = 0; < bits.length; i++)     {         bool doinvert = (bits[i] == '1') ^ crc[14];         // xor required?          crc[14] = crc[13] ^ doinvert;         crc[13] = crc[12];         crc[12] = crc[11];         crc[11] = crc[10];         crc[10] = crc[9] ^ doinvert;         crc[9] = crc[8];         crc[8] = crc[7] ^ doinvert;         crc[7] = crc[6] ^ doinvert;         crc[6] = crc[5];         crc[5] = crc[4];         crc[4] = crc[3] ^ doinvert;         crc[3] = crc[2] ^ doinvert;         crc[2] = crc[1];         crc[1] = crc[0];         crc[0] = doinvert;     }      // convert binary ascii     (int = 0; < 15; i++)     {         res[14 - i] = crc[i] ? '1' : '0';     }      return new string(res); } 

and then:

string bits = "0101010101010000000"; // example data string crc = crc15(bits);  bits = bits + crc; bits = bitstuff(bits);  bits += '1'; // crc delimiter  bits += 'x'; // ack slot todo  bits += '1'; // ack delimiter bits += "1111111"; // eof 

note have put value ack slot