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128 lines
3.3 KiB
Java
128 lines
3.3 KiB
Java
/* Adler.java - Computes Adler32 data checksum of a data stream
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Copyright (C) 1999, 2000 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., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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As a special exception, if you link this library with other files to
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produce an executable, this library does not by itself cause the
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resulting executable to be covered by the GNU General Public License.
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This exception does not however invalidate any other reasons why the
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executable file might be covered by the GNU General Public License. */
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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 Adler32 algorithm is taken from RFC 1950.
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* Status: Believed complete and correct.
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*/
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/**
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* Computes Adler32 data checksum of a data stream.
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* The actual Adler32 algorithm is described in RFC 1950
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* (ZLIB Compressed Data Format Specification version 3.3).
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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 InflaterOutputStream
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*
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* @author Per Bothner
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* @date April 6, 1999.
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*/
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public class Adler32 implements Checksum
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{
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/** largest prime smaller than 65536 */
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private static int BASE = 65521;
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private int s1;
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private int s2;
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/**
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* Creates an Adler32 data checksum.
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*/
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public Adler32 ()
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{
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reset();
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}
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/**
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* Resets the Adler32 data checksum as if no update was ever called.
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*/
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public void reset () { s1 = 1; s2 = 0; }
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/**
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* Adds one byte to the data checksum.
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*
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* @param bval the data value to add. The high byte of the int is ignored.
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*/
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public void update (int bval)
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{
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s1 = (s1 + (bval & 0xFF)) % BASE;
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s2 = (s1 + s2) % BASE;
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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[] buffer)
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{
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update(buffer, 0, buffer.length);
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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 s1 = this.s1;
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int s2 = this.s2;
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while (len > 0)
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{
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// We can defer the modulo operation.
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int n = 4000;
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if (n > len)
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n = len;
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len -= n;
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while (--n >= 0)
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{
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s1 = s1 + (buf[off++] & 0xFF);
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s2 = s2 + s1;
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}
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s1 %= BASE;
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s2 %= BASE;
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}
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this.s1 = s1;
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this.s2 = s2;
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}
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/**
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* Returns the Adler32 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) s2 << 16) + s1;
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}
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}
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