3 * Copyright 2006, British Broadcasting Corporation
7 * Wireshark - Network traffic analyzer
8 * By Gerald Combs <gerald@wireshark.org>
9 * Copyright 1998 Gerald Combs
11 * This program is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU General Public License
13 * as published by the Free Software Foundation; either version 2
14 * of the License, or (at your option) any later version.
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU General Public License for more details.
21 * You should have received a copy of the GNU General Public License
22 * along with this program; if not, write to the Free Software
23 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
29 unsigned long crc_drm(const char *data, size_t bytesize,
30 unsigned short num_crc_bits, unsigned long crc_gen, int invert)
32 unsigned long crc_holder, ones, i, msb, databit;
35 ones = (1 << num_crc_bits) - 1;
37 for (i=0; i<bytesize; i++)
41 msb = crc_holder >> num_crc_bits;
42 databit = (data[i] >> j) & 1;
43 if ((msb ^ databit) != 0)
44 crc_holder = crc_holder ^ crc_gen;
45 crc_holder = crc_holder & ones;
48 crc_holder = crc_holder ^ ones; /* invert checksum */