/*

 * 11/19/04 : 1.0 moved to LGPL.

 * 

 * 02/12/99 : Java Conversion by E.B , javalayer@javazoom.net

 *

 *  @(#) crc.h 1.5, last edit: 6/15/94 16:55:32

 *  @(#) Copyright (C) 1993, 1994 Tobias Bading (bading@cs.tu-berlin.de)

 *  @(#) 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;

  }

}