jaroslav@640: /* CRC32.java - Computes CRC32 data checksum of a data stream
jaroslav@640:    Copyright (C) 1999. 2000, 2001 Free Software Foundation, Inc.
jaroslav@640: 
jaroslav@640: This file is part of GNU Classpath.
jaroslav@640: 
jaroslav@640: GNU Classpath is free software; you can redistribute it and/or modify
jaroslav@640: it under the terms of the GNU General Public License as published by
jaroslav@640: the Free Software Foundation; either version 2, or (at your option)
jaroslav@640: any later version.
jaroslav@640: 
jaroslav@640: GNU Classpath is distributed in the hope that it will be useful, but
jaroslav@640: WITHOUT ANY WARRANTY; without even the implied warranty of
jaroslav@640: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
jaroslav@640: General Public License for more details.
jaroslav@640: 
jaroslav@640: You should have received a copy of the GNU General Public License
jaroslav@640: along with GNU Classpath; see the file COPYING.  If not, write to the
jaroslav@640: Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
jaroslav@640: 02111-1307 USA.
jaroslav@640: 
jaroslav@640: Linking this library statically or dynamically with other modules is
jaroslav@640: making a combined work based on this library.  Thus, the terms and
jaroslav@640: conditions of the GNU General Public License cover the whole
jaroslav@640: combination.
jaroslav@640: 
jaroslav@640: As a special exception, the copyright holders of this library give you
jaroslav@640: permission to link this library with independent modules to produce an
jaroslav@640: executable, regardless of the license terms of these independent
jaroslav@640: modules, and to copy and distribute the resulting executable under
jaroslav@640: terms of your choice, provided that you also meet, for each linked
jaroslav@640: independent module, the terms and conditions of the license of that
jaroslav@640: module.  An independent module is a module which is not derived from
jaroslav@640: or based on this library.  If you modify this library, you may extend
jaroslav@640: this exception to your version of the library, but you are not
jaroslav@640: obligated to do so.  If you do not wish to do so, delete this
jaroslav@640: exception statement from your version. */
jaroslav@609: 
jaroslav@609: package java.util.zip;
jaroslav@609: 
jaroslav@640: /*
jaroslav@640:  * Written using on-line Java Platform 1.2 API Specification, as well
jaroslav@640:  * as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998).
jaroslav@640:  * The actual CRC32 algorithm is taken from RFC 1952.
jaroslav@640:  * Status:  Believed complete and correct.
jaroslav@640:  */
jaroslav@640: 
jaroslav@609: /**
jaroslav@640:  * Computes CRC32 data checksum of a data stream.
jaroslav@640:  * The actual CRC32 algorithm is described in RFC 1952
jaroslav@640:  * (GZIP file format specification version 4.3).
jaroslav@640:  * Can be used to get the CRC32 over a stream if used with checked input/output
jaroslav@640:  * streams.
jaroslav@609:  *
jaroslav@640:  * @see InflaterInputStream
jaroslav@640:  * @see DeflaterOutputStream
jaroslav@640:  *
jaroslav@640:  * @author Per Bothner
jaroslav@640:  * @date April 1, 1999.
jaroslav@609:  */
jaroslav@640: public class CRC32 implements Checksum
jaroslav@640: {
jaroslav@640:   /** The crc data checksum so far. */
jaroslav@640:   private int crc = 0;
jaroslav@609: 
jaroslav@640:   /** The fast CRC table. Computed once when the CRC32 class is loaded. */
jaroslav@640:   private static int[] crc_table = make_crc_table();
jaroslav@609: 
jaroslav@640:   /** Make the table for a fast CRC. */
jaroslav@640:   private static int[] make_crc_table ()
jaroslav@640:   {
jaroslav@640:     int[] crc_table = new int[256];
jaroslav@640:     for (int n = 0; n < 256; n++)
jaroslav@640:       {
jaroslav@640: 	int c = n;
jaroslav@640: 	for (int k = 8;  --k >= 0; )
jaroslav@640: 	  {
jaroslav@640: 	    if ((c & 1) != 0)
jaroslav@640: 	      c = 0xedb88320 ^ (c >>> 1);
jaroslav@640: 	    else
jaroslav@640: 	      c = c >>> 1;
jaroslav@640: 	  }
jaroslav@640: 	crc_table[n] = c;
jaroslav@640:       }
jaroslav@640:     return crc_table;
jaroslav@640:   }
jaroslav@609: 
jaroslav@640:   /**
jaroslav@640:    * Returns the CRC32 data checksum computed so far.
jaroslav@640:    */
jaroslav@640:   public long getValue ()
jaroslav@640:   {
jaroslav@640:     return (long) crc & 0xffffffffL;
jaroslav@640:   }
jaroslav@609: 
jaroslav@640:   /**
jaroslav@640:    * Resets the CRC32 data checksum as if no update was ever called.
jaroslav@640:    */
jaroslav@640:   public void reset () { crc = 0; }
jaroslav@609: 
jaroslav@640:   /**
jaroslav@640:    * Updates the checksum with the int bval. 
jaroslav@640:    *
jaroslav@640:    * @param bval (the byte is taken as the lower 8 bits of bval)
jaroslav@640:    */
jaroslav@609: 
jaroslav@640:   public void update (int bval)
jaroslav@640:   {
jaroslav@640:     int c = ~crc;
jaroslav@640:     c = crc_table[(c ^ bval) & 0xff] ^ (c >>> 8);
jaroslav@640:     crc = ~c;
jaroslav@640:   }
jaroslav@609: 
jaroslav@640:   /**
jaroslav@640:    * Adds the byte array to the data checksum.
jaroslav@640:    *
jaroslav@640:    * @param buf the buffer which contains the data
jaroslav@640:    * @param off the offset in the buffer where the data starts
jaroslav@640:    * @param len the length of the data
jaroslav@640:    */
jaroslav@640:   public void update (byte[] buf, int off, int len)
jaroslav@640:   {
jaroslav@640:     int c = ~crc;
jaroslav@640:     while (--len >= 0)
jaroslav@640:       c = crc_table[(c ^ buf[off++]) & 0xff] ^ (c >>> 8);
jaroslav@640:     crc = ~c;
jaroslav@640:   }
jaroslav@609: 
jaroslav@640:   /**
jaroslav@640:    * Adds the complete byte array to the data checksum.
jaroslav@640:    */
jaroslav@640:   public void update (byte[] buf) { update(buf, 0, buf.length); }
jaroslav@609: }