crc.c

/******************************************************************************
 *
 * Author      : Mario Korand, Mario.Konrad@gmx.net
 * Creation    : August 04, 2001
 * Last Change : August 04, 2001 / Mario Konrad
 *
 * Copyright (C) Mario Konrad
 *
 ******************************************************************************
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 ******************************************************************************/

#include "crc.h"

struct CRC
{
	int bits;
	unsigned long mask;
	unsigned long r_mask;
};

static const struct CRC CRC_TYPES[] =
{
	{  8, 0x00000007, 0x000000ff }, /* CRC_8     */
	{ 10, 0x00000233, 0x000003ff }, /* CRC_10    */
	{ 12, 0x0000080f, 0x00000fff }, /* CRC_12    */
	{ 16, 0x00008005, 0x0000ffff }, /* CRC_16    */
	{ 16, 0x00001021, 0x0000ffff }, /* CRC_CCITT */
	{ 32, 0x04c11db7, 0xffffffff }, /* CRC_32    */
};

void crc(int type, unsigned long* crc, const char* data, int len)
{
	unsigned long tmpcrc;
	int i;
	int j;
	unsigned long c;

	if (!data)
		return;
	if (!crc)
		return;
	tmpcrc = *crc;
	for (j = 0; j < len; j++) {
		c = data[j] << (CRC_TYPES[type].bits - 8);
		for (i = 0; i < 8; ++i) {
			if ((tmpcrc ^ c) & (1 << (CRC_TYPES[type].bits-1))) {
				tmpcrc = (tmpcrc << 1) ^ CRC_TYPES[type].mask;
			} else {
				tmpcrc <<= 1;
			}
			c <<= 1;
		}
	}
	*crc = tmpcrc & CRC_TYPES[type].r_mask;
}

unsigned long crc_block(int type, const char* data, int len)
{
	unsigned long crc_value = CRC_INIT;
	crc(type, &crc_value, data, len);
	return crc_value;
}