| /* Adler.java - Computes Adler32 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 Adler32 algorithm is taken from RFC 1950. |
| * Status: Believed complete and correct. |
| */ |
| |
| /** |
| * Computes Adler32 data checksum of a data stream. |
| * The actual Adler32 algorithm is described in RFC 1950 |
| * (ZLIB Compressed Data Format Specification version 3.3). |
| * 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 6, 1999. |
| */ |
| public class Adler32 implements Checksum |
| { |
| |
| /** largest prime smaller than 65536 */ |
| private static int BASE = 65521; |
| |
| private int s1; |
| private int s2; |
| |
| /** |
| * Creates an Adler32 data checksum. |
| */ |
| public Adler32 () |
| { |
| reset(); |
| } |
| |
| /** |
| * Resets the Adler32 data checksum as if no update was ever called. |
| */ |
| public void reset () { s1 = 1; s2 = 0; } |
| |
| /** |
| * Adds one byte to the data checksum. |
| * |
| * @param bval the data value to add. The high byte of the int is ignored. |
| */ |
| public void update (int bval) |
| { |
| s1 = (s1 + (bval & 0xFF)) % BASE; |
| s2 = (s1 + s2) % BASE; |
| } |
| |
| /** |
| * Adds the complete byte array to the data checksum. |
| */ |
| public void update (byte[] buffer) |
| { |
| update(buffer, 0, buffer.length); |
| } |
| |
| /** |
| * 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 s1 = this.s1; |
| int s2 = this.s2; |
| while (len > 0) |
| { |
| // We can defer the modulo operation. |
| int n = 4000; |
| if (n > len) |
| n = len; |
| len -= n; |
| while (--n >= 0) |
| { |
| s1 = s1 + (buf[off++] & 0xFF); |
| s2 = s2 + s1; |
| } |
| s1 %= BASE; |
| s2 %= BASE; |
| } |
| this.s1 = s1; |
| this.s2 = s2; |
| } |
| |
| /** |
| * Returns the Adler32 data checksum computed so far. |
| */ |
| public long getValue() |
| { |
| return ((long) s2 << 16) + s1; |
| } |
| } |