|
FAST Protocol
< Previous Next >
Re: Proposal For New FAST Operator Default-Delta
David Rosenborg / Pantor Engineering AB
1 May 2006 10:43AM ETThe delta operator propsed in TD is more generic than the FE one and can handle the case
AAAA
AA
The generalized delta operator has a signed length preamble indicating how many characters to remove from the back (or front if negative). The preamble is followed by the string to append (or prepend). So the above case would be encoded as
AAAA (transmit 0AAAA)
AA (transmit 2e, where e is the empty string)
In addition, the delta operator of TD lets you specify an initial value
so that even the first occurence of the field can be delta coded. This is obviously only beneficial if the first value is predictable.
The operator would render the following sequence
AAAA (transmit 0e)
AAAAB (transmit 0B)
AAAABC (transmit 0C)
AA (transmit 4e)
And the initial value works for numbers too, assuming :
227 (transmit 2)
229 (transmit 2)
226 (transmit -3)
230 (transmit 4)
/David
>
> AAAA (transmit AAAA) AAAAB (transmit B) AAAABC (transmit C)
> AAAABC (transmit nothing) AAAABCD (transmit D)
>
> Above does work fine for string delta operator
>
> But…
>
> AAAA AAAAB AAAABC AA
>
> Does not work as there is currently no way to “reset” to a new starting
> delta value.
>
> What might be useful is a Default-Delta operator – e.g. just pass the
> difference from a default value …
>
> Default = AAAA
>
> AAAA (transmit nothing) AAAAB (transmit B)
> AAAABB (transmit BB) AAAAC (transmit C)
>
> This might also be useful for numerics, e.g. default = 225
>
> 227 (transmit 2) 229 (transmit 4) 226 (transmit
> 1) 230 (transmit 5)
>
> Is it worth investigating this for the next FAST release?
>
> Clive Browning Rapid Addition Ltd
Re: Proposal For New FAST Operator Default-Delta
David Rosenborg / Pantor Engineering AB 1 May 2006 10:43AM ET
|
