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 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.</p>
  36  *
  37  * @author      David Connelly
  38  */
  39 public
  40 class CRC32 implements Checksum {
  41     private int crc;
  42 
  43     /**
  44      * Creates a new CRC32 object.
  45      */
  46     public CRC32() {
  47     }
  48 
  49 
  50     /**
  51      * Updates the CRC-32 checksum with the specified byte (the low
  52      * eight bits of the argument b).
  53      */
  54     @Override
  55     public void update(int b) {
  56         crc = update(crc, b);
  57     }
  58 
  59     /**
  60      * Updates the CRC-32 checksum with the specified array of bytes.
  61      *
  62      * @throws ArrayIndexOutOfBoundsException
  63      *         if {@code off} is negative, or {@code len} is negative, or
  64      *         {@code off+len} is negative or greater than the length of
  65      *         the array {@code b}.
  66      */
  67     @Override
  68     public void update(byte[] b, int off, int len) {
  69         if (b == null) {
  70             throw new NullPointerException();
  71         }
  72         if (off < 0 || len < 0 || off > b.length - len) {
  73             throw new ArrayIndexOutOfBoundsException();
  74         }
  75         crc = updateBytes(crc, b, off, len);
  76     }
  77 
  78     /**
  79      * Updates the CRC-32 checksum with the bytes from the specified buffer.
  80      *
  81      * The checksum is updated with the remaining bytes in the buffer, starting
  82      * at the buffer's position. Upon return, the buffer's position will be
  83      * updated to its limit; its limit will not have been changed.
  84      *
  85      * @since 1.8
  86      */
  87     @Override
  88     public void update(ByteBuffer buffer) {
  89         int pos = buffer.position();
  90         int limit = buffer.limit();
  91         assert (pos <= limit);
  92         int rem = limit - pos;
  93         if (rem <= 0)
  94             return;
  95         if (buffer instanceof DirectBuffer) {
  96             crc = updateByteBuffer(crc, ((DirectBuffer)buffer).address(), pos, rem);
  97         } else if (buffer.hasArray()) {
  98             crc = updateBytes(crc, buffer.array(), pos + buffer.arrayOffset(), rem);
  99         } else {
 100             byte[] b = new byte[Math.min(buffer.remaining(), 4096)];
 101             while (buffer.hasRemaining()) {
 102                 int length = Math.min(buffer.remaining(), b.length);
 103                 buffer.get(b, 0, length);
 104                 update(b, 0, length);
 105             }
 106         }
 107         buffer.position(limit);
 108     }
 109 
 110     /**
 111      * Resets CRC-32 to initial value.
 112      */
 113     @Override
 114     public void reset() {
 115         crc = 0;
 116     }
 117 
 118     /**
 119      * Returns CRC-32 value.
 120      */
 121     @Override
 122     public long getValue() {
 123         return (long)crc & 0xffffffffL;
 124     }
 125 
 126     private native static int update(int crc, int b);
 127     private native static int updateBytes(int crc, byte[] b, int off, int len);
 128 
 129     private native static int updateByteBuffer(int adler, long addr,
 130                                                int off, int len);
 131 }