1 /*
   2  * Copyright (c) 1996, 2014, 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 
  26 package java.util.zip;
  27 
  28 import java.nio.ByteBuffer;
  29 import 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.</p>
  38  *
  39  * @author      David Connelly
  40  */
  41 public
  42 class Adler32 implements Checksum {
  43 
  44     private int adler = 1;
  45 
  46     /**
  47      * Creates a new Adler32 object.
  48      */
  49     public Adler32() {
  50     }
  51 
  52     /**
  53      * Updates the checksum with the specified byte (the low eight
  54      * bits of the argument b).
  55      */
  56     @Override
  57     public void update(int b) {
  58         adler = update(adler, b);
  59     }
  60 
  61     /**
  62      * Updates the checksum with the specified array of bytes.
  63      *
  64      * @throws ArrayIndexOutOfBoundsException
  65      *         if {@code off} is negative, or {@code len} is negative, or
  66      *         {@code off+len} is negative or greater than the length of
  67      *         the array {@code b}.
  68      */
  69     @Override
  70     public void update(byte[] b, int off, int len) {
  71         if (b == null) {
  72             throw new NullPointerException();
  73         }
  74         if (off < 0 || len < 0 || off > b.length - len) {
  75             throw new ArrayIndexOutOfBoundsException();
  76         }
  77         adler = updateBytes(adler, b, off, len);
  78     }
  79 
  80     /**
  81      * Updates the checksum with the bytes from the specified buffer.
  82      *
  83      * The checksum is updated with the remaining bytes in the buffer, starting
  84      * at the buffer's position. Upon return, the buffer's position will be
  85      * updated to its limit; its limit will not have been changed.
  86      *
  87      * @since 1.8
  88      */
  89     @Override
  90     public void update(ByteBuffer buffer) {
  91         int pos = buffer.position();
  92         int limit = buffer.limit();
  93         assert (pos <= limit);
  94         int rem = limit - pos;
  95         if (rem <= 0)
  96             return;
  97         if (buffer instanceof DirectBuffer) {
  98             adler = updateByteBuffer(adler, ((DirectBuffer)buffer).address(), pos, rem);
  99         } else if (buffer.hasArray()) {
 100             adler = updateBytes(adler, buffer.array(), pos + buffer.arrayOffset(), rem);
 101         } else {
 102             byte[] b = new byte[Math.min(buffer.remaining(), 4096)];
 103             while (buffer.hasRemaining()) {
 104                 int length = Math.min(buffer.remaining(), b.length);
 105                 buffer.get(b, 0, length);
 106                 update(b, 0, length);
 107             }
 108         }
 109         buffer.position(limit);
 110     }
 111 
 112     /**
 113      * Resets the checksum to initial value.
 114      */
 115     @Override
 116     public void reset() {
 117         adler = 1;
 118     }
 119 
 120     /**
 121      * Returns the checksum value.
 122      */
 123     @Override
 124     public long getValue() {
 125         return (long)adler & 0xffffffffL;
 126     }
 127 
 128     private native static int update(int adler, int b);
 129     private native static int updateBytes(int adler, byte[] b, int off,
 130                                           int len);
 131     private native static int updateByteBuffer(int adler, long addr,
 132                                                int off, int len);
 133 }