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 CRC-32 of a data stream.
  33  *
  34  * <p> Passing a {@code null} argument to a method in this class will cause
  35  * a {@link NullPointerException} to be thrown.
  36  *
  37  * @see         Checksum
  38  * @author      David Connelly
  39  */
  40 public
  41 class CRC32 implements Checksum {
  42     private int crc;
  43 
  44     /**
  45      * Creates a new CRC32 object.
  46      */
  47     public CRC32() {
  48     }
  49 
  50 
  51     /**
  52      * Updates the CRC-32 checksum with the specified byte (the low
  53      * eight bits of the argument b).
  54      *
  55      * @param b the byte to update the checksum with
  56      */
  57     public void update(int b) {
  58         crc = update(crc, b);
  59     }
  60 
  61     /**
  62      * Updates the CRC-32 checksum with the specified array of bytes.





  63      */
  64     public void update(byte[] b, int off, int len) {
  65         if (b == null) {
  66             throw new NullPointerException();
  67         }
  68         if (off < 0 || len < 0 || off > b.length - len) {
  69             throw new ArrayIndexOutOfBoundsException();
  70         }
  71         crc = updateBytes(crc, b, off, len);
  72     }
  73 
  74     /**
  75      * Updates the CRC-32 checksum with the specified array of bytes.
  76      *
  77      * @param b the array of bytes to update the checksum with
  78      */
  79     public void update(byte[] b) {
  80         crc = updateBytes(crc, b, 0, b.length);
  81     }
  82 
  83     /**
  84      * Updates the checksum with the bytes from the specified buffer.
  85      *
  86      * The checksum is updated using
  87      * buffer.{@link java.nio.Buffer#remaining() remaining()}
  88      * bytes starting at
  89      * buffer.{@link java.nio.Buffer#position() position()}
  90      * Upon return, the buffer's position will
  91      * be updated to its limit; its limit will not have been changed.
  92      *
  93      * @param buffer the ByteBuffer to update the checksum with
  94      * @since 1.8
  95      */
  96     public void update(ByteBuffer buffer) {
  97         int pos = buffer.position();
  98         int limit = buffer.limit();
  99         assert (pos <= limit);
 100         int rem = limit - pos;
 101         if (rem <= 0)
 102             return;
 103         if (buffer instanceof DirectBuffer) {
 104             crc = updateByteBuffer(crc, ((DirectBuffer)buffer).address(), pos, rem);
 105         } else if (buffer.hasArray()) {
 106             crc = updateBytes(crc, buffer.array(), pos + buffer.arrayOffset(), rem);
 107         } else {
 108             byte[] b = new byte[rem];
 109             buffer.get(b);
 110             crc = updateBytes(crc, b, 0, b.length);
 111         }
 112         buffer.position(limit);
 113     }
 114 
 115     /**
 116      * Resets CRC-32 to initial value.
 117      */
 118     public void reset() {
 119         crc = 0;
 120     }
 121 
 122     /**
 123      * Returns CRC-32 value.
 124      */
 125     public long getValue() {
 126         return (long)crc & 0xffffffffL;
 127     }
 128 
 129     private native static int update(int crc, int b);
 130     private native static int updateBytes(int crc, byte[] b, int off, int len);
 131 
 132     private native static int updateByteBuffer(int adler, long addr,
 133                                                int off, int len);
 134 }
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