rfc1982_serial_number

Implementation of RFC 1982 Serial Number Arithmetic.

Run as a program, this takes start and finish serial values and tells you what intermediate steps (if any) are needed to make the specified change.

Used as a module, this implements the Serial class and an iterator which returns the intermediate steps (if any) needed between two Serial values.

Per the RFC, only two operations are defined on Serial objects: addition and comparision, both within a restricted range specified by the RFC.

The default modulus is 2**32, you can change this by subclassing the Serial and overriding the class's modulus variable. The modulus must be a power of two.

See RFC 1982 for discussion of the ways in which serial numbers do not work like normal integers. In particular, note that there's a corner case in which one can have a pair of serial numbers I1 and I2 where I1 is neither equal to, less than, nor greater than I2. This is deliberate and is not a bug in the code. See the RFC.

The find_intermediate() iterator takes two Serial values start and finish and yields the sequence of intermediate values (if any) needed to step from start to finish.

There are also a couple of test programs that use random.randint() to generate test values. Maybe someday I'll recode with unittest.