forked from osmocom/wireshark
51 lines
1.5 KiB
C
51 lines
1.5 KiB
C
/* crcdrm.c
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* another CRC 16
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* Copyright 2006, British Broadcasting Corporation
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*
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* $Id$
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*
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* Wireshark - Network traffic analyzer
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* By Gerald Combs <gerald@wireshark.org>
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* Copyright 1998 Gerald Combs
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*/
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#include "crcdrm.h"
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unsigned long crc_drm(const char *data, size_t bytesize,
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unsigned short num_crc_bits, unsigned long crc_gen, int invert)
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{
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unsigned long crc_holder, ones, i, msb, databit;
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signed short j;
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ones = (1 << num_crc_bits) - 1;
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crc_holder = ones;
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for (i=0; i<bytesize; i++)
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for (j=7; j>=0; j--)
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{
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crc_holder <<= 1;
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msb = crc_holder >> num_crc_bits;
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databit = (data[i] >> j) & 1;
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if ((msb ^ databit) != 0)
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crc_holder = crc_holder ^ crc_gen;
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crc_holder = crc_holder & ones;
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}
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if (invert)
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crc_holder = crc_holder ^ ones; /* invert checksum */
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return crc_holder;
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}
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