libjava/java/util/zip/CRC32.java

/* Copyright (C) 1999  Cygnus Solutions

   This file is part of libgcj.

This software is copyrighted work licensed under the terms of the
Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
details.  */

package java.util.zip;

/**
 * @author Per Bothner
 * @date April 1, 1999.
 */

/*
 * Written using on-line Java Platform 1.2 API Specification, as well
 * as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998).
 * The actual CRC32 algorithm is taken from RFC 1952.
 * Status:  Believed complete and correct.
 */

public class CRC32 implements Checksum
{
  int crc = 0;

  static int[] crc_table = make_crc_table();

  /* Make the table for a fast CRC. */
  static int[] make_crc_table ()
  {
    int[] crc_table = new int[256];
    for (int n = 0; n < 256; n++)
      {
	int c = n;
	for (int k = 8;  --k >= 0; )
	  {
	    if ((c & 1) != 0)
	      c = 0xedb88320 ^ (c >>> 1);
	    else
	      c = c >>> 1;
	  }
	crc_table[n] = c;
      }
    return crc_table;
  }

  public long getValue ()
  {
    return (long) crc & 0xffffffffL;
  }

  public void reset () { crc = 0; }

  public void update (int bval)
  {
    int c = ~crc;
    c = crc_table[(c ^ bval) & 0xff] ^ (c >>> 8);
    crc = ~c;
  }

  public void update (byte[] buf, int off, int len)
  {
    int c = ~crc;
    while (--len >= 0)
      c = crc_table[(c ^ buf[off++]) & 0xff] ^ (c >>> 8);
    crc = ~c;
  }
  public void update (byte[] buf) { update(buf, 0, buf.length); }
}