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 }
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