J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1996-2005 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package java.util.zip; |
| 27 | |
| 28 | /** |
| 29 | * A class that can be used to compute the Adler-32 checksum of a data |
| 30 | * stream. An Adler-32 checksum is almost as reliable as a CRC-32 but |
| 31 | * can be computed much faster. |
| 32 | * |
| 33 | * @see Checksum |
| 34 | * @author David Connelly |
| 35 | */ |
| 36 | public |
| 37 | class Adler32 implements Checksum { |
| 38 | private int adler = 1; |
| 39 | |
| 40 | /** |
| 41 | * Creates a new Adler32 object. |
| 42 | */ |
| 43 | public Adler32() { |
| 44 | } |
| 45 | |
| 46 | |
| 47 | /** |
| 48 | * Updates checksum with specified byte. |
| 49 | * |
| 50 | * @param b an array of bytes |
| 51 | */ |
| 52 | public void update(int b) { |
| 53 | adler = update(adler, b); |
| 54 | } |
| 55 | |
| 56 | /** |
| 57 | * Updates checksum with specified array of bytes. |
| 58 | */ |
| 59 | public void update(byte[] b, int off, int len) { |
| 60 | if (b == null) { |
| 61 | throw new NullPointerException(); |
| 62 | } |
| 63 | if (off < 0 || len < 0 || off > b.length - len) { |
| 64 | throw new ArrayIndexOutOfBoundsException(); |
| 65 | } |
| 66 | adler = updateBytes(adler, b, off, len); |
| 67 | } |
| 68 | |
| 69 | /** |
| 70 | * Updates checksum with specified array of bytes. |
| 71 | */ |
| 72 | public void update(byte[] b) { |
| 73 | adler = updateBytes(adler, b, 0, b.length); |
| 74 | } |
| 75 | |
| 76 | /** |
| 77 | * Resets checksum to initial value. |
| 78 | */ |
| 79 | public void reset() { |
| 80 | adler = 1; |
| 81 | } |
| 82 | |
| 83 | /** |
| 84 | * Returns checksum value. |
| 85 | */ |
| 86 | public long getValue() { |
| 87 | return (long)adler & 0xffffffffL; |
| 88 | } |
| 89 | |
| 90 | private native static int update(int adler, int b); |
| 91 | private native static int updateBytes(int adler, byte[] b, int off, |
| 92 | int len); |
| 93 | } |