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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 Adler-32 checksum of a data
33  * stream. An Adler-32 checksum is almost as reliable as a CRC-32 but
34  * can be computed much faster.
35  *
36  * <p> Passing a {@code null} argument to a method in this class will cause
37  * a {@link NullPointerException} to be thrown.
38  *
39  * @see         Checksum
40  * @author      David Connelly
41  */
42 public
43 class Adler32 implements Checksum {
44 
45     private int adler = 1;
46 
47     /**
48      * Creates a new Adler32 object.
49      */
Adler32()50     public Adler32() {
51     }
52 
53     /**
54      * Updates the checksum with the specified byte (the low eight
55      * bits of the argument b).
56      *
57      * @param b the byte to update the checksum with
58      */
update(int b)59     public void update(int b) {
60         adler = update(adler, b);
61     }
62 
63     /**
64      * Updates the checksum with the specified array of bytes.
65      *
66      * @throws  ArrayIndexOutOfBoundsException
67      *          if {@code off} is negative, or {@code len} is negative,
68      *          or {@code off+len} is greater than the length of the
69      *          array {@code b}
70      */
update(byte[] b, int off, int len)71     public void update(byte[] b, int off, int len) {
72         if (b == null) {
73             throw new NullPointerException();
74         }
75         if (off < 0 || len < 0 || off > b.length - len) {
76             throw new ArrayIndexOutOfBoundsException();
77         }
78         adler = updateBytes(adler, b, off, len);
79     }
80 
81     /**
82      * Updates the checksum with the specified array of bytes.
83      *
84      * @param b the byte array to update the checksum with
85      */
update(byte[] b)86     public void update(byte[] b) {
87         adler = updateBytes(adler, b, 0, b.length);
88     }
89 
90 
91     /**
92      * Updates the checksum with the bytes from the specified buffer.
93      *
94      * The checksum is updated using
95      * buffer.{@link java.nio.Buffer#remaining() remaining()}
96      * bytes starting at
97      * buffer.{@link java.nio.Buffer#position() position()}
98      * Upon return, the buffer's position will be updated to its
99      * limit; its limit will not have been changed.
100      *
101      * @param buffer the ByteBuffer to update the checksum with
102      * @since 1.8
103      */
update(ByteBuffer buffer)104     public void update(ByteBuffer buffer) {
105         int pos = buffer.position();
106         int limit = buffer.limit();
107         assert (pos <= limit);
108         int rem = limit - pos;
109         if (rem <= 0)
110             return;
111         if (buffer instanceof DirectBuffer) {
112             adler = updateByteBuffer(adler, ((DirectBuffer)buffer).address(), pos, rem);
113         } else if (buffer.hasArray()) {
114             adler = updateBytes(adler, buffer.array(), pos + buffer.arrayOffset(), rem);
115         } else {
116             byte[] b = new byte[rem];
117             buffer.get(b);
118             adler = updateBytes(adler, b, 0, b.length);
119         }
120         buffer.position(limit);
121     }
122 
123     /**
124      * Resets the checksum to initial value.
125      */
reset()126     public void reset() {
127         adler = 1;
128     }
129 
130     /**
131      * Returns the checksum value.
132      */
getValue()133     public long getValue() {
134         return (long)adler & 0xffffffffL;
135     }
136 
update(int adler, int b)137     private native static int update(int adler, int b);
updateBytes(int adler, byte[] b, int off, int len)138     private native static int updateBytes(int adler, byte[] b, int off,
139                                           int len);
updateByteBuffer(int adler, long addr, int off, int len)140     private native static int updateByteBuffer(int adler, long addr,
141                                                int off, int len);
142 }
143