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;
}
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
src/main/java/core/org/xbill/DNS/Serial.java