1 /*
   2  * Copyright (c) 1996, 2011, 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.
  38  *
  39  * @see         Checksum
  40  * @author      David Connelly
  41  */
  42 public
  43 class 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 }