git.zerfleddert.de Git - proxmark3-svn/blob - common/crc.c

   1 //-----------------------------------------------------------------------------
   2 // This code is licensed to you under the terms of the GNU GPL, version 2 or,
   3 // at your option, any later version. See the LICENSE.txt file for the text of
   4 // the license.
   5 //-----------------------------------------------------------------------------
   6 // Generic CRC calculation code.
   7 //-----------------------------------------------------------------------------
   8 #include "crc.h"
   9 #include <stdint.h>
  10 #include <stddef.h>
  11
  12 void crc_init(crc_t *crc, int order, uint32_t polynom, uint32_t initial_value, uint32_t final_xor)
  13 {
  14         crc->order = order;
  15         crc->polynom = polynom;
  16         crc->initial_value = initial_value;
  17         crc->final_xor = final_xor;
  18         crc->mask = (1L<<order)-1;
  19         crc_clear(crc);
  20 }
  21
  22 void crc_update(crc_t *crc, uint32_t data, int data_width)
  23 {
  24         int i;
  25         for(i=0; i<data_width; i++) {
  26                 int oldstate = crc->state;
  27                 crc->state = crc->state >> 1;
  28                 if( (oldstate^data) & 1 ) {
  29                         crc->state ^= crc->polynom;
  30                 }
  31                 data >>= 1;
  32         }
  33 }
  34
  35 void crc_clear(crc_t *crc)
  36 {
  37         crc->state = crc->initial_value & crc->mask;
  38 }
  39
  40 uint32_t crc_finish(crc_t *crc)
  41 {
  42         return ( crc->state ^ crc->final_xor ) & crc->mask;
  43 }
  44
  45 //credits to iceman
  46 uint32_t CRC8Maxim(uint8_t *buff, size_t size)
  47 {
  48         crc_t crc;
  49         crc_init(&crc, 9, 0x8c, 0x00, 0x00);
  50         crc_clear(&crc);
  51
  52         for (size_t i=0; i < size; ++i){
  53                 crc_update(&crc, buff[i], 8);
  54         }
  55         return crc_finish(&crc);
  56 }