[This message was posted by Ravi Ravisankar of IBM <[email protected]> to the 
"FAST Protocol" discussion forum at http://fixprotocol.org/discuss/46. You can 
reply to it on-line at http://fixprotocol.org/discuss/read/eb9ff34c - PLEASE DO 
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Rolf,
I used configuration settings to do things differently for OPRA where it 
deviates from the spec., so that the code remains same with very few cmp and 
jmp.
 
>Ravi, thank you for your comments.
> 
> How do you communicate to your common decoder about:
> - The fixed presence bit offsets
> - The added skip logic required for 'k' messages
> 
> Do you use extensions to the template spec or do you use some other
> configuration mechanism?
> 
> Best, Rolf
> 
> > Rolf, We decided to have a common decoder for all the FAST feeds.
> > Since OPRA FAST implementation is non-standard, it posed challenges in
> > the following area:
> >
> > 1. Lack of templates for messages. OPRA defines FAST fields and
> >    messages in header files. We generated templates for OPRA messages
> >    from the header files, so that the common decoder could consume it.
> >
> > 2. The presence offset for a field in the PMAP is static and based on
> >    field id. This is a deviation from FAST specification, but can be
> >    handled in the decoder logic. (Adds a cmp and jmp instructions in
> >    the presence bit lookup, not very bad!)
> 
> > 3. Messages k and Y (OPRA actually discontinued this message now)
> > needs special processing. Both include/exclude some fields
> > conditionally, based on runtime value of another field.
> >
> >> Ravi,
> >>
> >> thank you for your comments. Would it be possible for you to share
> >> some thoughts regarding the OPRA impl? What did you do to efficiently
> >> support the non-std aspects of OPRA?
> >>
> >> Best, Rolf


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