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Page.java

/* -*-mode:java; c-basic-offset:2; indent-tabs-mode:nil -*- */
/* JOrbis
 * Copyright (C) 2000 ymnk, JCraft,Inc.
 *  
 * Written by: 2000 ymnk<ymnk@jcraft.com>
 *   
 * Many thanks to 
 *   Monty <monty@xiph.org> and 
 *   The XIPHOPHORUS Company http://www.xiph.org/ .
 * JOrbis has been based on their awesome works, Vorbis codec.
 *   
 * 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 com.jcraft.jogg;

public class Page{
  private static int[] crc_lookup=new int[256];
  static{
    for(int i=0; i<crc_lookup.length; i++){
      crc_lookup[i]=crc_entry(i);
    }
  }

  private static int crc_entry(int index){
    int r=index<<24;
    for(int i=0; i<8; i++){
      if((r&0x80000000)!=0){
        r=(r<<1)^0x04c11db7; /* The same as the ethernet generator
                                  polynomial, although we use an
                                unreflected alg and an init/final
                                of 0, not 0xffffffff */
      }
      else{
        r<<=1;
      }
    }
    return (r&0xffffffff);
  }

  public byte[] header_base;
  public int header;
  public int header_len;
  public byte[] body_base;
  public int body;
  public int body_len;

  int version(){
    return header_base[header+4]&0xff;
  }

  int continued(){
    return (header_base[header+5]&0x01);
  }

  public int bos(){
    return (header_base[header+5]&0x02);
  }

  public int eos(){
    return (header_base[header+5]&0x04);
  }

  public long granulepos(){
    long foo=header_base[header+13]&0xff;
    foo=(foo<<8)|(header_base[header+12]&0xff);
    foo=(foo<<8)|(header_base[header+11]&0xff);
    foo=(foo<<8)|(header_base[header+10]&0xff);
    foo=(foo<<8)|(header_base[header+9]&0xff);
    foo=(foo<<8)|(header_base[header+8]&0xff);
    foo=(foo<<8)|(header_base[header+7]&0xff);
    foo=(foo<<8)|(header_base[header+6]&0xff);
    return (foo);
  }

  public int serialno(){
    return (header_base[header+14]&0xff)|((header_base[header+15]&0xff)<<8)
        |((header_base[header+16]&0xff)<<16)
        |((header_base[header+17]&0xff)<<24);
  }

  int pageno(){
    return (header_base[header+18]&0xff)|((header_base[header+19]&0xff)<<8)
        |((header_base[header+20]&0xff)<<16)
        |((header_base[header+21]&0xff)<<24);
  }

  void checksum(){
    int crc_reg=0;

    for(int i=0; i<header_len; i++){
      crc_reg=(crc_reg<<8)
          ^crc_lookup[((crc_reg>>>24)&0xff)^(header_base[header+i]&0xff)];
    }
    for(int i=0; i<body_len; i++){
      crc_reg=(crc_reg<<8)
          ^crc_lookup[((crc_reg>>>24)&0xff)^(body_base[body+i]&0xff)];
    }
    header_base[header+22]=(byte)crc_reg;
    header_base[header+23]=(byte)(crc_reg>>>8);
    header_base[header+24]=(byte)(crc_reg>>>16);
    header_base[header+25]=(byte)(crc_reg>>>24);
  }

  public Page copy(){
    return copy(new Page());
  }

  public Page copy(Page p){
    byte[] tmp=new byte[header_len];
    System.arraycopy(header_base, header, tmp, 0, header_len);
    p.header_len=header_len;
    p.header_base=tmp;
    p.header=0;
    tmp=new byte[body_len];
    System.arraycopy(body_base, body, tmp, 0, body_len);
    p.body_len=body_len;
    p.body_base=tmp;
    p.body=0;
    return p;
  }

}

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