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1 // Copyright (c) 1999-2004 Brian Wellington (bwelling@xbill.org)
2 
3 package org.xbill.DNS;
4 
5 /**
6  * DNS Name Compression object.
7  * @see Message
8  * @see Name
9  *
10  * @author Brian Wellington
11  */
12 
13 public class Compression {
14 
15 private static class Entry {
16 	Name name;
17 	int pos;
18 	Entry next;
19 }
20 
21 private static final int TABLE_SIZE = 17;
22 private static final int MAX_POINTER = 0x3FFF;
23 private Entry [] table;
24 private boolean verbose = Options.check("verbosecompression");
25 
26 /**
27  * Creates a new Compression object.
28  */
29 public
Compression()30 Compression() {
31 	table = new Entry[TABLE_SIZE];
32 }
33 
34 /**
35  * Adds a compression entry mapping a name to a position in a message.
36  * @param pos The position at which the name is added.
37  * @param name The name being added to the message.
38  */
39 public void
add(int pos, Name name)40 add(int pos, Name name) {
41 	if (pos > MAX_POINTER)
42 		return;
43 	int row = (name.hashCode() & 0x7FFFFFFF) % TABLE_SIZE;
44 	Entry entry = new Entry();
45 	entry.name = name;
46 	entry.pos = pos;
47 	entry.next = table[row];
48 	table[row] = entry;
49 	if (verbose)
50 		System.err.println("Adding " + name + " at " + pos);
51 }
52 
53 /**
54  * Retrieves the position of the given name, if it has been previously
55  * included in the message.
56  * @param name The name to find in the compression table.
57  * @return The position of the name, or -1 if not found.
58  */
59 public int
get(Name name)60 get(Name name) {
61 	int row = (name.hashCode() & 0x7FFFFFFF) % TABLE_SIZE;
62 	int pos = -1;
63 	for (Entry entry = table[row]; entry != null; entry = entry.next) {
64 		if (entry.name.equals(name))
65 			pos = entry.pos;
66 	}
67 	if (verbose)
68 		System.err.println("Looking for " + name + ", found " + pos);
69 	return pos;
70 }
71 
72 }
73