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25 
26 package java.util.zip;
27 
28 import java.nio.ByteBuffer;
29 import sun.nio.ch.DirectBuffer;
30 
31 import jdk.internal.HotSpotIntrinsicCandidate;
32 
33 /**
34  * A class that can be used to compute the Adler-32 checksum of a data
35  * stream. An Adler-32 checksum is almost as reliable as a CRC-32 but
36  * can be computed much faster.
37  *
38  * <p> Passing a {@code null} argument to a method in this class will cause
39  * a {@link NullPointerException} to be thrown.</p>
40  *
41  * @author      David Connelly
42  * @since 1.1
43  */
44 public class Adler32 implements Checksum {
45 
46     private int adler = 1;
47 
48     /**
49      * Creates a new Adler32 object.
50      */
Adler32()51     public Adler32() {
52     }
53 
54     /**
55      * Updates the checksum with the specified byte (the low eight
56      * bits of the argument b).
57      */
58     @Override
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, or
68      *         {@code off+len} is negative or greater than the length of
69      *         the array {@code b}.
70      */
71     @Override
update(byte[] b, int off, int len)72     public void update(byte[] b, int off, int len) {
73         if (b == null) {
74             throw new NullPointerException();
75         }
76         if (off < 0 || len < 0 || off > b.length - len) {
77             throw new ArrayIndexOutOfBoundsException();
78         }
79         adler = updateBytes(adler, b, off, len);
80     }
81 
82     /**
83      * Updates the checksum with the bytes from the specified buffer.
84      *
85      * The checksum is updated with the remaining bytes in the buffer, starting
86      * at the buffer's position. Upon return, the buffer's position will be
87      * updated to its limit; its limit will not have been changed.
88      *
89      * @since 1.8
90      */
91     @Override
update(ByteBuffer buffer)92     public void update(ByteBuffer buffer) {
93         int pos = buffer.position();
94         int limit = buffer.limit();
95         assert (pos <= limit);
96         int rem = limit - pos;
97         if (rem <= 0)
98             return;
99         if (buffer instanceof DirectBuffer) {
100             adler = updateByteBuffer(adler, ((DirectBuffer)buffer).address(), pos, rem);
101         } else if (buffer.hasArray()) {
102             adler = updateBytes(adler, buffer.array(), pos + buffer.arrayOffset(), rem);
103         } else {
104             byte[] b = new byte[Math.min(buffer.remaining(), 4096)];
105             while (buffer.hasRemaining()) {
106                 int length = Math.min(buffer.remaining(), b.length);
107                 buffer.get(b, 0, length);
108                 update(b, 0, length);
109             }
110         }
111         buffer.position(limit);
112     }
113 
114     /**
115      * Resets the checksum to initial value.
116      */
117     @Override
reset()118     public void reset() {
119         adler = 1;
120     }
121 
122     /**
123      * Returns the checksum value.
124      */
125     @Override
getValue()126     public long getValue() {
127         return (long)adler & 0xffffffffL;
128     }
129 
update(int adler, int b)130     private static native int update(int adler, int b);
131 
132     @HotSpotIntrinsicCandidate
updateBytes(int adler, byte[] b, int off, int len)133     private static native int updateBytes(int adler, byte[] b, int off,
134                                           int len);
135     @HotSpotIntrinsicCandidate
updateByteBuffer(int adler, long addr, int off, int len)136     private static native int updateByteBuffer(int adler, long addr,
137                                                int off, int len);
138 
139     static {
ZipUtils.loadLibrary()140         ZipUtils.loadLibrary();
141     }
142 }
143