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// Copyright (c) 2003-2004 Brian Wellington (bwelling@xbill.org)
package org.xbill.DNS;
/**
* Helper functions for doing serial arithmetic. These should be used when
* setting/checking SOA serial numbers. SOA serial number arithmetic is
* defined in RFC 1982.
*
* @author Brian Wellington
*/
public final class Serial {
private static final long MAX32 = 0xFFFFFFFFL;
private
Serial() {
}
/**
* Compares two numbers using serial arithmetic. The numbers are assumed
* to be 32 bit unsigned integers stored in longs.
* @param serial1 The first integer
* @param serial2 The second integer
* @return 0 if the 2 numbers are equal, a positive number if serial1 is greater
* than serial2, and a negative number if serial2 is greater than serial1.
* @throws IllegalArgumentException serial1 or serial2 is out of range
*/
public static int
compare(long serial1, long serial2) {
if (serial1 < 0 || serial1 > MAX32)
throw new IllegalArgumentException(serial1 + " out of range");
if (serial2 < 0 || serial2 > MAX32)
throw new IllegalArgumentException(serial2 + " out of range");
long diff = serial1 - serial2;
if (diff >= MAX32)
diff -= (MAX32 + 1);
else if (diff < -MAX32)
diff += (MAX32 + 1);
return (int)diff;
}
/**
* Increments a serial number. The number is assumed to be a 32 bit unsigned
* integer stored in a long. This basically adds 1 and resets the value to
* 0 if it is 2^32.
* @param serial The serial number
* @return The incremented serial number
* @throws IllegalArgumentException serial is out of range
*/
public static long
increment(long serial) {
if (serial < 0 || serial > MAX32)
throw new IllegalArgumentException(serial + " out of range");
if (serial == MAX32)
return 0;
return serial + 1;
}
}
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