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 #define BITMASK(X) (1 << (X))
  13
  14 uint32_t reflect(uint32_t v, int b) {
  15     uint32_t t = v;
  16     for (int i = 0; i < b; ++i) {
  17         if (t & 1)
  18             v |=  BITMASK((b - 1) - i);
  19         else
  20             v &= ~BITMASK((b - 1) - i);
  21         t >>= 1;
  22     }
  23     return v;
  24 }
  25
  26 void crc_init(crc_t *crc, int order, uint32_t polynom, uint32_t initial_value, uint32_t final_xor)
  27 {
  28         crc->order = order;
  29         crc->polynom = polynom;
  30         crc->initial_value = initial_value;
  31         crc->final_xor = final_xor;
  32         crc->mask = (1L<<order)-1;
  33         crc_clear(crc);
  34 }
  35
  36 void crc_update(crc_t *crc, uint32_t data, int data_width)
  37 {
  38         int i;
  39         for(i=0; i<data_width; i++) {
  40                 int oldstate = crc->state;
  41                 crc->state = crc->state >> 1;
  42                 if( (oldstate^data) & 1 ) {
  43                         crc->state ^= crc->polynom;
  44                 }
  45                 data >>= 1;
  46         }
  47 }
  48
  49 void crc_clear(crc_t *crc)
  50 {
  51         crc->state = crc->initial_value & crc->mask;
  52 }
  53
  54 uint32_t crc_finish(crc_t *crc)
  55 {
  56         return ( crc->state ^ crc->final_xor ) & crc->mask;
  57 }
  58
  59 //credits to iceman
  60 uint32_t CRC8Maxim(uint8_t *buff, size_t size)
  61 {
  62         crc_t crc;
  63         crc_init(&crc, 9, 0x8c, 0x00, 0x00);
  64         crc_clear(&crc);
  65
  66         for (size_t i=0; i < size; ++i){
  67                 crc_update(&crc, buff[i], 8);
  68         }
  69         return crc_finish(&crc);
  70 }
  71
  72 // width=8 poly=0x1d, init=0xc7 (0xe3 - WRONG! but it mentioned in MAD datasheet) refin=false  refout=false  xorout=0x00 name="CRC-8/MIFARE-MAD"
  73 uint32_t CRC8Mad(uint8_t *buff, size_t size) {
  74     crc_t crc;
  75     crc_init(&crc, 8, reflect(0x1d, 8), reflect(0xc7, 8), 0);
  76     for (int i = 0; i < size; ++i)
  77         crc_update(&crc, reflect(buff[i], 8), 8);
  78
  79     return reflect(crc_finish(&crc), 8);
  80 }