[This message was posted by Shashank Bhatt of Faculties India
<[email protected]> to the "FAST Protocol" discussion forum at
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Hi Dale,
Thanks for reply.
I want some clarification, still I am not clear.
According to spec ~
"6.2.2 Decimal Field Instructions: If the decimal field has optional presence
and has INDIVIDUAL OPERATORS,
the presence of the mantissa is dependent on the presence of the exponent."
and
"10.5.1 Presence Map and NULL Utilization:
Decimal fields with individual operators have the following utilization:
• If the decimal has mandatory presence, the exponent and mantissa fields are
treated as two separate
mandatory integer fields as described above.
• If the decimal has optional presence, the exponent field is treated as an
optional integer
field and the mantissa field is treated as a mandatory integer field. The
presence of the mantissa field and
any related bits in the presence map are dependent on the presence of the
exponent.
The mantissa field appears in the stream iff the exponent value is considered
present.
If the mantissa has an operator that requires a bit in the presence map, this
bit is
present iff the exponent value is considered present."
I am some what clear with "Decimal fields with individual operators"
According to my given example:
(decimal id="1" presence="optional" name="Price")
(copy/)
(/decimal)
I have a single field operator for decimal field instruction.
For "Decimal field with single field operator", my understanding is:
1. Both Exponent and mantissa will be treated as "optional" field.
(Am I right? Or always Mantissa will be treated as Mandatory.
According to spec, mantissa field is treated as a mandatory integer field,
if Decimal
is having individual operators and presence of decimal is optional)
2. The presence of the mantissa does not depend on the presence of the
exponent. (As there is no
individual field operator). Am I right here?
So, in case of "Decimal with single field operator",
Sequence 1: (Sender want to send 9427.55)
PMAP Bit will be '1'
Encoded value will be in form of exponent and mantissa:
Sender will send Exponent as "-2" and Mantissa as "942755".
Receiver will expect two fields (Exponent and Mantissa) in FAST Format.
Here presence of Mantissa does not depend on presence of exponent (as
single field operator)
Wire representation for complete decimal field will be:
0xFE 0x39 0x45 0xA3
Sequence 2: (Sender want to send NULL)
PMAP Bit will be '1'
The combined decoded decimal value should be "NULL".
Here presence of Mantissa does not depend on presence of exponent (as
single field operator)
Receiver will expect two fields (Exponent and Mantissa) in FAST Format.
whether Sender will send only one NULL (0x80) for exponent;
or two NULL (0x80 0x80) for exponent and mantissa???
Thanks & regards
Shashank
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