git.zerfleddert.de Git - proxmark3-svn/blob - common/crc16.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 // CRC16
   7 //-----------------------------------------------------------------------------
   8
   9 #include "crc16.h"
  10 #define CRC16_POLY_CCITT 0x1021
  11 #define CRC16_POLY 0x8408
  12 #define CRC16_POLY_LEGIC 0xB400
  13
  14 unsigned short update_crc16( unsigned short crc, unsigned char c )
  15 {
  16   unsigned short i, v, tcrc = 0;
  17
  18   v = (crc ^ c) & 0xff;
  19   for (i = 0; i < 8; i++) {
  20       tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ CRC16_POLY : tcrc >> 1;
  21       v >>= 1;
  22   }
  23
  24   return ((crc >> 8) ^ tcrc) & 0xffff;
  25 }
  26
  27 uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t polynomial) {
  28
  29         if (length == 0)
  30         return (~remainder);
  31
  32     for (int byte = 0; byte < length; ++byte) {
  33         remainder ^= (message[byte] << 8);
  34         for (uint8_t bit = 8; bit > 0; --bit) {
  35             if (remainder & 0x8000) {
  36                 remainder = (remainder << 1) ^ polynomial;
  37             } else {
  38                 remainder = (remainder << 1);
  39             }
  40         }
  41     }
  42     return remainder;
  43 }
  44
  45 uint16_t crc16_ccitt(uint8_t const *message, int length) {
  46     return crc16(message, length, 0xffff, CRC16_POLY_CCITT);
  47 }
  48
  49 uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) {
  50     return bit_reverse_uint16(crc16(message, length, 0x0000, CRC16_POLY_CCITT));
  51 }
  52
  53 //ICEMAN: not working yet,
  54 // This CRC-16 is used in Legic Advant systems.
  55 uint16_t crc16_legic(uint8_t const *message, int length, uint16_t inital) {
  56         return crc16(message, length, inital, CRC16_POLY_LEGIC);
  57 }
  58
  59 uint16_t bit_reverse_uint16 (uint16_t value) {
  60         const uint16_t mask0 = 0x5555;
  61         const uint16_t mask1 = 0x3333;
  62         const uint16_t mask2 = 0x0F0F;
  63         const uint16_t mask3 = 0x00FF;
  64
  65         value = (((~mask0) & value) >> 1) | ((mask0 & value) << 1);
  66         value = (((~mask1) & value) >> 2) | ((mask1 & value) << 2);
  67         value = (((~mask2) & value) >> 4) | ((mask2 & value) << 4);
  68         value = (((~mask3) & value) >> 8) | ((mask3 & value) << 8);
  69
  70         return value;
  71 }