bootloader/crc.c

   1 /*
   2     e07 bootloader suite
   3     Copyright (c) 2008 Daniel Mack <daniel@caiaq.de>
   4
   5     This program is free software: you can redistribute it and/or modify
   6     it under the terms of the GNU General Public License as published by
   7     the Free Software Foundation, either version 3 of the License, or
   8     (at your option) any later version.
   9
  10     This program is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13     GNU General Public License for more details.
  14
  15     You should have received a copy of the GNU General Public License
  16     along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17 */
  18
  19 #include "types.h"
  20 #include "crc.h"
  21
  22 u8 crc_byte(unsigned int crc, u8 byte, u8 nbits)
  23 {
  24         s8 bit;
  25
  26         for (bit = nbits - 1; bit >= 0; bit--) {
  27                 crc <<= 1;
  28                 crc |= (byte >> bit) & 1;
  29                 if ((crc & 0x80) ^ (byte & 0x80))
  30                         crc ^= 0x09;
  31
  32         }
  33
  34         return crc & 0xff;
  35 }
  36
  37 u8 crc7(const u8 *buffer, int len)
  38 {
  39         u8 crc = 0;
  40
  41         while (len--)
  42                 crc = crc_byte(crc, *buffer++, 8);
  43
  44         return crc_byte(crc, 0, 7);
  45 }
  46