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
   9 #include "crc.h"
  10
  11 void crc_init(crc_t *crc, int order, uint32_t polynom, uint32_t initial_value, uint32_t final_xor)
  12 {
  13         crc->order = order;
  14         crc->polynom = polynom;
  15         crc->initial_value = initial_value;
  16         crc->final_xor = final_xor;
  17         crc->mask = (1L<<order)-1;
  18         crc_clear(crc);
  19 }
  20
  21 void crc_update(crc_t *crc, uint32_t data, int data_width)
  22 {
  23         int i;
  24         for(i=0; i<data_width; i++) {
  25                 int oldstate = crc->state;
  26                 crc->state = crc->state >> 1;
  27                 if( (oldstate^data) & 1 ) {
  28                         crc->state ^= crc->polynom;
  29                 }
  30                 data >>= 1;
  31         }
  32 }
  33
  34 void crc_clear(crc_t *crc)
  35 {
  36         crc->state = crc->initial_value & crc->mask;
  37 }
  38
  39 uint32_t crc_finish(crc_t *crc)
  40 {
  41         return ( crc->state ^ crc->final_xor ) & crc->mask;
  42 }