1 /*****************************************************************************

     2  *

     3  * $Id$

     4  *

     5  ****************************************************************************/

     6 

     7 #include "sii_crc.h"

     8 

     9 /*****************************************************************************/

    10 

    11 /** Calculates the SII checksum field.

    12  *

    13  * The checksum is generated with the polynom x^8+x^2+x+1 (0x07) and an

    14  * initial value of 0xff (see IEC 61158-6-12 ch. 5.4).

    15  *

    16  * The below code was originally generated with PYCRC

    17  * http://www.tty1.net/pycrc

    18  *

    19  * ./pycrc.py --width=8 --poly=0x07 --reflect-in=0 --xor-in=0xff

    20  *   --reflect-out=0 --xor-out=0 --generate c --algorithm=bit-by-bit

    21  *

    22  * \return CRC8

    23  */

    24 uint8_t calcSiiCrc(

    25         const uint8_t *data, /**< pointer to data */

    26         size_t length /**< number of bytes in \a data */

    27         )

    28 {

    29     unsigned int i;

    30     uint8_t bit, byte, crc = 0x48;

    31 

    32     while (length--) {

    33         byte = *data++;

    34         for (i = 0; i < 8; i++) {

    35             bit = crc & 0x80;

    36             crc = (crc << 1) | ((byte >> (7 - i)) & 0x01);

    37             if (bit) crc ^= 0x07;

    38         }

    39     }

    40 

    41     for (i = 0; i < 8; i++) {

    42         bit = crc & 0x80;

    43         crc <<= 1;

    44         if (bit) crc ^= 0x07;

    45     }

    46 

    47     return crc;

    48 }

    49 

    50 /*****************************************************************************/