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/*
* 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;
}
}
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