1 files changed, 61 insertions, 0 deletions
diff --git a/src/org/xbill/DNS/Serial.java b/src/org/xbill/DNS/Serial.java
new file mode 100644
index 0000000..3a146c6
--- /dev/null
+++ b/src/org/xbill/DNS/Serial.java
@@ -0,0 +1,61 @@
+// 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;
+}
+
+}