133 lines
3.9 KiB
Java
133 lines
3.9 KiB
Java
/* CRC32.java - Computes CRC32 data checksum of a data stream
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Copyright (C) 1999. 2000, 2001 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.util.zip;
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/*
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* Written using on-line Java Platform 1.2 API Specification, as well
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* as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998).
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* The actual CRC32 algorithm is taken from RFC 1952.
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* Status: Believed complete and correct.
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*/
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/**
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* Computes CRC32 data checksum of a data stream.
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* The actual CRC32 algorithm is described in RFC 1952
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* (GZIP file format specification version 4.3).
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* Can be used to get the CRC32 over a stream if used with checked input/output
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* streams.
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*
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* @see InflaterInputStream
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* @see DeflaterOutputStream
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*
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* @author Per Bothner
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* @date April 1, 1999.
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*/
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public class CRC32 implements Checksum
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{
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/** The crc data checksum so far. */
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private int crc = 0;
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/** The fast CRC table. Computed once when the CRC32 class is loaded. */
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private static int[] crc_table = make_crc_table();
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/** Make the table for a fast CRC. */
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private static int[] make_crc_table ()
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{
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int[] crc_table = new int[256];
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for (int n = 0; n < 256; n++)
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{
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int c = n;
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for (int k = 8; --k >= 0; )
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{
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if ((c & 1) != 0)
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c = 0xedb88320 ^ (c >>> 1);
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else
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c = c >>> 1;
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}
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crc_table[n] = c;
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}
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return crc_table;
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}
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/**
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* Returns the CRC32 data checksum computed so far.
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*/
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public long getValue ()
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{
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return (long) crc & 0xffffffffL;
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}
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/**
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* Resets the CRC32 data checksum as if no update was ever called.
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*/
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public void reset () { crc = 0; }
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/**
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* Updates the checksum with the int bval.
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*
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* @param bval (the byte is taken as the lower 8 bits of bval)
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*/
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public void update (int bval)
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{
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int c = ~crc;
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c = crc_table[(c ^ bval) & 0xff] ^ (c >>> 8);
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crc = ~c;
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}
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/**
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* Adds the byte array to the data checksum.
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*
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* @param buf the buffer which contains the data
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* @param off the offset in the buffer where the data starts
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* @param len the length of the data
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*/
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public void update (byte[] buf, int off, int len)
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{
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int c = ~crc;
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while (--len >= 0)
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c = crc_table[(c ^ buf[off++]) & 0xff] ^ (c >>> 8);
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crc = ~c;
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}
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/**
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* Adds the complete byte array to the data checksum.
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*/
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public void update (byte[] buf) { update(buf, 0, buf.length); }
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}
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