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      1 /*
      2  * Copyright (c) 1996, 2013, 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 }
    140