1// Copyright (c) 2003-2004 Brian Wellington (bwelling@xbill.org)
2
3package org.xbill.DNS;
4
5/**
6 * Helper functions for doing serial arithmetic.  These should be used when
7 * setting/checking SOA serial numbers.  SOA serial number arithmetic is
8 * defined in RFC 1982.
9 *
10 * @author Brian Wellington
11 */
12
13public final class Serial {
14
15private static final long MAX32 = 0xFFFFFFFFL;
16
17private
18Serial() {
19}
20
21/**
22 * Compares two numbers using serial arithmetic.  The numbers are assumed
23 * to be 32 bit unsigned integers stored in longs.
24 * @param serial1 The first integer
25 * @param serial2 The second integer
26 * @return 0 if the 2 numbers are equal, a positive number if serial1 is greater
27 * than serial2, and a negative number if serial2 is greater than serial1.
28 * @throws IllegalArgumentException serial1 or serial2 is out of range
29 */
30public static int
31compare(long serial1, long serial2) {
32	if (serial1 < 0 || serial1 > MAX32)
33		throw new IllegalArgumentException(serial1 + " out of range");
34	if (serial2 < 0 || serial2 > MAX32)
35		throw new IllegalArgumentException(serial2 + " out of range");
36	long diff = serial1 - serial2;
37	if (diff >= MAX32)
38		diff -= (MAX32 + 1);
39	else if (diff < -MAX32)
40		diff += (MAX32 + 1);
41	return (int)diff;
42}
43
44/**
45 * Increments a serial number.  The number is assumed to be a 32 bit unsigned
46 * integer stored in a long.  This basically adds 1 and resets the value to
47 * 0 if it is 2^32.
48 * @param serial The serial number
49 * @return The incremented serial number
50 * @throws IllegalArgumentException serial is out of range
51 */
52public static long
53increment(long serial) {
54	if (serial < 0 || serial > MAX32)
55		throw new IllegalArgumentException(serial + " out of range");
56	if (serial == MAX32)
57		return 0;
58	return serial + 1;
59}
60
61}
62