1// Copyright (c) 1999-2004 Brian Wellington (bwelling@xbill.org)
2
3package org.xbill.DNS;
4
5/**
6 * DNS Name Compression object.
7 * @see Message
8 * @see Name
9 *
10 * @author Brian Wellington
11 */
12
13public class Compression {
14
15private static class Entry {
16	Name name;
17	int pos;
18	Entry next;
19}
20
21private static final int TABLE_SIZE = 17;
22private static final int MAX_POINTER = 0x3FFF;
23private Entry [] table;
24private boolean verbose = Options.check("verbosecompression");
25
26/**
27 * Creates a new Compression object.
28 */
29public
30Compression() {
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 */
39public void
40add(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 */
59public int
60get(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