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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      */
CRC32()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      */
update(int b)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      */
update(byte[] b, int off, int len)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      */
update(byte[] b)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      */
update(ByteBuffer buffer)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      */
reset()123     public void reset() {
124         crc = 0;
125     }
126 
127     /**
128      * Returns CRC-32 value.
129      */
getValue()130     public long getValue() {
131         return (long)crc & 0xffffffffL;
132     }
133 
update(int crc, int b)134     private native static int update(int crc, int b);
updateBytes(int crc, byte[] b, int off, int len)135     private native static int updateBytes(int crc, byte[] b, int off, int len);
136 
updateByteBuffer(int adler, long addr, int off, int len)137     private native static int updateByteBuffer(int adler, long addr,
138                                                int off, int len);
139 }
140