[This message was posted by Dale Wilson of Object Computing, Inc
<[email protected]> to the "FAST Protocol" discussion forum at
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Hi Shashank,
You asked:
> In template, we have decimal instruction with single field operator:
> [Please read “(“ as “<” and “)” as “>”]
>
> (decimal id="1" presence="optional" name="Price") (copy/) (/decimal)
> <SNIP>
> Whether my understanding about "Decimal having single field operator" is
> correct? Please feedback.
You are correct. Only one PMAP bit is used in this case.
If pmap == 0 then the previous values of both the exponent and mantissa are
used.
if pmap == 1 and the exponent is null then the optional field does not exist in
the decoded message.
if pmap == 1 and the exponent is not null, then the mantissa should be present
-- mantissa is NOT a nullable value.
------------------------
One case where two presence bits are used is:
(decimal presence="mandatory")
(exponent)
(default/)
(/exponent)
(mantissa)
(copy/)
(/mantissa)
(decimal)
If I changed the above example to have presence="optional" then the number of
PMAP bits would change dynamically depending on whether the exponent was
nullable.
Dale Wilson
--
Principal Software Engineer
Author of the QuickFAST open source implementation of FAST
http://www.quickfast.org
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