| /* CRC32.java - Computes CRC32 data checksum of a data stream |
| Copyright (C) 1999, 2000 Free Software Foundation, Inc. |
| |
| This file is part of GNU Classpath. |
| |
| GNU Classpath is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2, or (at your option) |
| any later version. |
| |
| GNU Classpath 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 |
| General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with GNU Classpath; see the file COPYING. If not, write to the |
| Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
| 02111-1307 USA. |
| |
| As a special exception, if you link this library with other files to |
| produce an executable, this library does not by itself cause the |
| resulting executable to be covered by the GNU General Public License. |
| This exception does not however invalidate any other reasons why the |
| executable file might be covered by the GNU General Public License. */ |
| |
| package java.util.zip; |
| |
| /* |
| * 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. |
| */ |
| |
| /** |
| * Computes CRC32 data checksum of a data stream. |
| * The actual CRC32 algorithm is described in RFC 1952 |
| * (GZIP file format specification version 4.3). |
| * Can be used to get the CRC32 over a stream if used with checked input/output |
| * streams. |
| * |
| * @see InflaterInputStream |
| * @see InflaterOutputStream |
| * |
| * @author Per Bothner |
| * @date April 1, 1999. |
| */ |
| public class CRC32 implements Checksum |
| { |
| /** The crc data checksum so far. */ |
| private int crc = 0; |
| |
| /** The fast CRC table. Computed once when the CRC32 class is loaded. */ |
| private static int[] crc_table = make_crc_table(); |
| |
| /** Make the table for a fast CRC. */ |
| private 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; |
| } |
| |
| /** |
| * Returns the CRC32 data checksum computed so far. |
| */ |
| public long getValue () |
| { |
| return (long) crc & 0xffffffffL; |
| } |
| |
| /** |
| * Resets the CRC32 data checksum as if no update was ever called. |
| */ |
| public void reset () { crc = 0; } |
| |
| public void update (int bval) |
| { |
| int c = ~crc; |
| c = crc_table[(c ^ bval) & 0xff] ^ (c >>> 8); |
| crc = ~c; |
| } |
| |
| /** |
| * Adds the byte array to the data checksum. |
| * |
| * @param buf the buffer which contains the data |
| * @param off the offset in the buffer where the data starts |
| * @param len the length of the data |
| */ |
| 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; |
| } |
| |
| /** |
| * Adds the complete byte array to the data checksum. |
| */ |
| public void update (byte[] buf) { update(buf, 0, buf.length); } |
| } |