javazoom.jl.decoder.Crc16 Maven / Gradle / Ivy

Go to download
/*
 * 11/19/04 : 1.0 moved to LGPL.
 * 
 * 02/12/99 : Java Conversion by E.B , [email protected]
 * 
 * @(#) crc.h 1.5, last edit: 6/15/94 16:55:32
 * 
 * @(#) Copyright (C) 1993, 1994 Tobias Bading ([email protected])
 * 
 * @(#) Berlin University of Technology----------------------------------------------------------------------- This program is
 * free software; you can redistribute it and/or modify it under the terms of the GNU Library 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 Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public License along with this program; if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 * ----------------------------------------------------------------------
 */

package javazoom.jl.decoder;

/**
 * 16-Bit CRC checksum
 */
public final class Crc16 {
	private static short polynomial = (short)0x8005;
	private short crc;

	/**
	 * Dummy Constructor
	 */
	public Crc16 () {
		crc = (short)0xFFFF;
	}

	/**
	 * Feed a bitstring to the crc calculation (0 < length <= 32).
	 */
	public void add_bits (int bitstring, int length) {
		int bitmask = 1 << length - 1;
		do
			if ((crc & 0x8000) == 0 ^ (bitstring & bitmask) == 0) {
				crc <<= 1;
				crc ^= polynomial;
			} else
				crc <<= 1;
		while ((bitmask >>>= 1) != 0);
	}

	/**
	 * Return the calculated checksum. Erase it for next calls to add_bits().
	 */
	public short checksum () {
		short sum = crc;
		crc = (short)0xFFFF;
		return sum;
	}
}