Adler32.java revision 6c877179523385568cb4752a5825bf76f46769e2 
1/*
2 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. 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.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26package java.util.zip;
27
28import java.nio.ByteBuffer;
29import sun.nio.ch.DirectBuffer;
30
31/**
32 * A class that can be used to compute the Adler-32 checksum of a data
33 * stream. An Adler-32 checksum is almost as reliable as a CRC-32 but
34 * can be computed much faster.
35 *
36 * <p> Passing a {@code null} argument to a method in this class will cause
37 * a {@link NullPointerException} to be thrown.
38 *
39 * @see         Checksum
40 * @author      David Connelly
41 */
42public
43class Adler32 implements Checksum {
44
45    private int adler = 1;
46
47    /**
48     * Creates a new Adler32 object.
49     */
50    public Adler32() {
51    }
52
53    /**
54     * Updates the checksum with the specified byte (the low eight
55     * bits of the argument b).
56     *
57     * @param b the byte to update the checksum with
58     */
59    public void update(int b) {
60        adler = update(adler, b);
61    }
62
63    /**
64     * Updates the checksum with the specified array of bytes.
65     *
66     * @throws  ArrayIndexOutOfBoundsException
67     *          if {@code off} is negative, or {@code len} is negative,
68     *          or {@code off+len} is greater than the length of the
69     *          array {@code b}
70     */
71    public void update(byte[] b, int off, int len) {
72        if (b == null) {
73            throw new NullPointerException();
74        }
75        if (off < 0 || len < 0 || off > b.length - len) {
76            throw new ArrayIndexOutOfBoundsException();
77        }
78        adler = updateBytes(adler, b, off, len);
79    }
80
81    /**
82     * Updates the checksum with the specified array of bytes.
83     *
84     * @param b the byte array to update the checksum with
85     */
86    public void update(byte[] b) {
87        adler = updateBytes(adler, b, 0, b.length);
88    }
89
90
91    /**
92     * Updates the checksum with the bytes from the specified buffer.
93     *
94     * The checksum is updated using
95     * buffer.{@link java.nio.Buffer#remaining() remaining()}
96     * bytes starting at
97     * buffer.{@link java.nio.Buffer#position() position()}
98     * Upon return, the buffer's position will be updated to its
99     * limit; its limit will not have been changed.
100     *
101     * @param buffer the ByteBuffer to update the checksum with
102     * @since 1.8
103     */
104    public void update(ByteBuffer buffer) {
105        int pos = buffer.position();
106        int limit = buffer.limit();
107        assert (pos <= limit);
108        int rem = limit - pos;
109        if (rem <= 0)
110            return;
111        if (buffer instanceof DirectBuffer) {
112            adler = updateByteBuffer(adler, ((DirectBuffer)buffer).address(), pos, rem);
113        } else if (buffer.hasArray()) {
114            adler = updateBytes(adler, buffer.array(), pos + buffer.arrayOffset(), rem);
115        } else {
116            byte[] b = new byte[rem];
117            buffer.get(b);
118            adler = updateBytes(adler, b, 0, b.length);
119        }
120        buffer.position(limit);
121    }
122
123    /**
124     * Resets the checksum to initial value.
125     */
126    public void reset() {
127        adler = 1;
128    }
129
130    /**
131     * Returns the checksum value.
132     */
133    public long getValue() {
134        return (long)adler & 0xffffffffL;
135    }
136
137    private native static int update(int adler, int b);
138    private native static int updateBytes(int adler, byte[] b, int off,
139                                          int len);
140    private native static int updateByteBuffer(int adler, long addr,
141                                               int off, int len);
142}
143