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A port of the Free Lossless Audio Codec (FLAC) decoder to Java and a FLAC encoder implemented in Java.

There is a newer version: 1.4.1

/*
 * Copyright (C) 2010  Preston Lacey http://javaflacencoder.sourceforge.net/
 * All Rights Reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

package net.sourceforge.javaflacencoder;

/**
 * Class to calculate a CRC16 checksum.
 * @author Preston Lacey
 */
public class CRC16 {
  /** For Debugging: Higher level equals more debug statements */
  public static int DEBUG_LEV = 0;

  /** CRC Divisor: 0x8005(implicit 1 at MSB for 0x18005) */
  static final int divisorCRC16 = 0x8005;

  /** working checksum stored between calls to update(..) */
  protected int workingCRC;

  private static final short xorTable[] = generateTable();

  /**
   * Constructor. Creates a CRC16 object that is ready to be used. Next step
   * would be to call update(...) with appropriate data.
   */
  public CRC16() {
    reset();
  }

  /**
   * Resets stored data, preparing object for a new checksum.
   */
  public void reset() {
    workingCRC = 0;
  }

  public short checksum() {
    return (short)(workingCRC & 0xFFFF);
  }

  public int update(byte input) {
    workingCRC = (workingCRC << 8)^xorTable[((workingCRC >>> 8)^input) & 0xFF];
    return workingCRC;
  }

  public int update(byte[] input, int start, int stop) {
    for(int i = start; i < stop; i++) {
      byte b = input[i];
      workingCRC = (workingCRC << 8) ^ xorTable[((workingCRC >>> 8)^b) & 0xFF];
    }
    return workingCRC;
  }

  private static short[] generateTable() {
    short[] table = new short[256];
    for(int i = 0; i < table.length; i++) {
      int polynomial = divisorCRC16;
      int xorVal = i << 8;
      int topmask = 1 << 16;
      for(int x = 0; x < 8; x++ ) {
        xorVal = xorVal << 1;
        if( (xorVal & topmask) > 0) xorVal = (xorVal) ^ polynomial;
      }
      table[i] = (short)(xorVal & 0xFFFF);
    }
    return table;
  }
}