crc.c

/*
 *  Copyright © 2010-2015, Matthias Urlichs <matthias@urlichs.de>
 *
 *  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 3 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 (included; see the file LICENSE)
 *  for more details.
 */

/* Based on work published at http://www.mikrocontroller.net/topic/44100 */

#include "crc.h"

// this code is from owfs
static uint8_t parity_table[16] = { 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0 };

uint16_t
crc16(uint16_t r, uint8_t x)
{
	uint16_t c = (x ^ (r & 0xFF));
	r >>= 8;
	if (parity_table[c & 0x0F] ^ parity_table[(c >> 4) & 0x0F])
		r ^= 0xC001;
	r ^= (c <<= 6);
	r ^= (c << 1);
        return r;
}