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      * @throws  ArrayIndexOutOfBoundsException
  65      *          if {@code off} is negative, or {@code len} is negative,
  66      *          or {@code off+len} is greater than the length of the
  67      *          array {@code b}
  68      */
  69     public void update(byte[] b, int off, int len) {
  70         if (b == null) {
  71             throw new NullPointerException();
  72         }
  73         if (off < 0 || len < 0 || off > b.length - len) {
  74             throw new ArrayIndexOutOfBoundsException();
  75         }
  76         crc = updateBytes(crc, b, off, len);
  77     }
  78 
  79     /**
  80      * Updates the CRC-32 checksum with the specified array of bytes.
  81      *
  82      * @param b the array of bytes to update the checksum with
  83      */
  84     public void update(byte[] b) {
  85         crc = updateBytes(crc, b, 0, b.length);
  86     }
  87 
  88     /**
  89      * Updates the checksum with the bytes from the specified buffer.
  90      *
  91      * The checksum is updated using
  92      * buffer.{@link java.nio.Buffer#remaining() remaining()}
  93      * bytes starting at
  94      * buffer.{@link java.nio.Buffer#position() position()}
  95      * Upon return, the buffer's position will
  96      * be updated to its limit; its limit will not have been changed.
  97      *
  98      * @param buffer the ByteBuffer to update the checksum with
  99      * @since 1.8
 100      */
 101     public void update(ByteBuffer buffer) {
 102         int pos = buffer.position();
 103         int limit = buffer.limit();
 104         assert (pos <= limit);
 105         int rem = limit - pos;
 106         if (rem <= 0)
 107             return;
 108         if (buffer instanceof DirectBuffer) {
 109             crc = updateByteBuffer(crc, ((DirectBuffer)buffer).address(), pos, rem);
 110         } else if (buffer.hasArray()) {
 111             crc = updateBytes(crc, buffer.array(), pos + buffer.arrayOffset(), rem);
 112         } else {
 113             byte[] b = new byte[rem];
 114             buffer.get(b);
 115             crc = updateBytes(crc, b, 0, b.length);
 116         }
 117         buffer.position(limit);
 118     }
 119 
 120     /**
 121      * Resets CRC-32 to initial value.
 122      */
 123     public void reset() {
 124         crc = 0;
 125     }
 126 
 127     /**
 128      * Returns CRC-32 value.
 129      */
 130     public long getValue() {
 131         return (long)crc & 0xffffffffL;
 132     }
 133 
 134     private native static int update(int crc, int b);
 135     private native static int updateBytes(int crc, byte[] b, int off, int len);
 136 
 137     private native static int updateByteBuffer(int adler, long addr,
 138                                                int off, int len);
 139 }