Before we continue with the Verify Method, this is a good time to introduce Custom Methods. All the methods we have encountered previously have been what we call "standard methods". A standard method is one supplied with the protocol analyzer. The method used here to verify the checksum, FPChecksum, as its name suggests, is a method specific to Fictitious Protocol. We call this a "custom method" since it is created by the decoder writer.
The protocol analyzer supplies standard methods, including standard checksum methods, to do just about everything that is commonly needed in decoders and most decoders can be written with those alone. However, should the need arise for a method unique to your protocol's particular requirements, then that is easily met by writing a custom method.
Now let's get back to Verify Methods. Other very useful Verify Methods compares the field value with a constant as in these examples:
(FieldIs LessThan 10)
(FieldIs LessThanOrEqualTo 17)
(FieldIs EqualTo 0)
(FieldIs NotEqualTo ‐1)
(FieldIs GreaterThan 4)
(FieldIs GreaterThanOrEqualTo 0)