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
  11
  12 unsigned short update_crc16( unsigned short crc, unsigned char c )
  13 {
  14         unsigned short i, v, tcrc = 0;
  15
  16         v = (crc ^ c) & 0xff;
  17         for (i = 0; i < 8; i++) {
  18                 tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ 0x8408 : tcrc >> 1;
  19                 v >>= 1;
  20         }
  21
  22         return ((crc >> 8) ^ tcrc)&0xffff;
  23 }
  24
  25 uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t polynomial) {
  26
  27         if (length == 0) return (~remainder);
  28
  29         for (int byte = 0; byte < length; ++byte) {
  30                 remainder ^= (message[byte] << 8);
  31                 for (uint8_t bit = 8; bit > 0; --bit) {
  32                         if (remainder & 0x8000) {
  33                                 remainder = (remainder << 1) ^ polynomial;
  34                         } else {
  35                                 remainder = (remainder << 1);
  36                         }
  37                 }
  38         }
  39         return remainder;
  40 }
  41
  42 uint16_t crc16_ccitt(uint8_t const *message, int length) {
  43         return crc16(message, length, 0xffff, 0x1021);
  44 }
  45
  46 uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) {
  47         if (length == 0) return 0;
  48         uint32_t crc = 0, q = 0;
  49         uint8_t c;
  50
  51         for (int i = 0; i < length; i++){
  52                 c = message[i];
  53                 q = (crc ^ c ) & 0xF;
  54                 crc = (crc >> 4) ^ (q * 0x1081);
  55                 q = (crc ^ (c >> 4)) & 0xF;
  56                 crc = (crc >> 4) ^ (q * 0x1081);
  57         }
  58         return crc;
  59 }