cvs.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
  13 uint16_t update_crc16( uint16_t crc, unsigned char c ) {
  14   uint16_t i, v, tcrc = 0;
  15
  16   v = (crc ^ c) & 0xff;
  17   for (i = 0; i < 8; i++) {
  18       tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ CRC16_POLY : 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)
  28         return (~remainder);
  29
  30     for (uint32_t i = 0; i < length; ++i) {
  31         remainder ^= (message[i] << 8);
  32         for (uint8_t bit = 8; bit > 0; --bit) {
  33             if (remainder & 0x8000) {
  34                 remainder = (remainder << 1) ^ polynomial;
  35             } else {
  36                 remainder = (remainder << 1);
  37             }
  38         }
  39     }
  40     return remainder;
  41 }
  42
  43 uint16_t crc16_ccitt(uint8_t const *message, int length) {
  44     return crc16(message, length, 0xffff, CRC16_POLY_CCITT);
  45 }
  46
  47 uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) {
  48         uint16_t val = crc16(message, length, 0x0000, CRC16_POLY_CCITT);
  49     return SwapBits(val, 16);
  50 }