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Re: Optional decimal fields with individual operators
David Rosenborg / Pantor Engineering AB
1 Sep 2008 7:27AM ETAle -
1. No. Whether you should process the mantissa or not is only dependent on a single thing: if the exponent is NULL or not. Whether you use a operator on the exponent doesn't change this property.
In your example you use the copy operator. If the bit is not set this means "copy the previous value". If the previous value is not NULL, then the value of the exponent is not NULL and the mantissa is present.
2. The mantissa and exponent parts are treated as two individual fields in the dictionary so there are one or two separate signed integer fields in the dictionary to manage. There is no corresponding scaled number field in the dictionary in this case. However, when you communicate the value of the field from the decoder to the application you would typically combine them into a scaled number or similar.
/David
> Actually may be I was not so clear.
>
> In the specific case:
>
> < decimal name="MDEntryPx" id="270" presence="optional" > < exponent >
> < copy value="-2" / > < / exponent > < mantissa > < delta / > < /
> mantissa > < /decimal >
>
> since the decimal is optional, then the exponent is optional. Moreover,
> since the exponent has the individual copy operator, then the exponent
> will have a bit in the pmap (no matter if it is set or not).
>
> The exponent will be considered absent in two distinct cases:
>
> a) The bit is not set.
> b) The bit is set but, since the exponent is optional, it is present in
> the stream in its NULL representation.
>
> In both these cases the mantissa will be not present in the stream as
> well and has to be considered absent.
>
> The only case in which the mantissa is present in the stream is when the
> exponent bit in pmap is set and the exponent value is not NULL.
>
> 1. Is all that right?
>
> 2. How should we set the new previous value of the decimal (the
> corresponding Scaled Number) if the exponent has to be considered
> absent?
>
>
>
> Note that even if the exponent bit in pmap was not set, the value of the
> exponent field could result assigned (for example it should be assigned
> to the copy initial value, or to the previous value stored in the
> dictionary).
>
> 3. Let suppose the mantissa is not in the stream (because of the
> exponent absence), what does it imply in term of the mantissa field
> value, and what in term of the mantissa new previous value?
>
>
> Many thanks in advance.
>
> Regards, -- Ale
>
>
>
> > Ale -
> >
> > A bit in the pmap indicates how a field operator should be executed.
> > The exact meaning of the bit is dependent on the operator type and its
> > attributes.
> >
> > The bit doesn't automatically indicate whether an optional field is
> > NULL or not. Only after exercising the operator according to the bit
> > you'll know if the value is NULL or not.
> >
> > When using a decimal field with individual operators, and the value of
> > an exponent field is NULL, the instruction for the mantissa should be
> > skipped.
> >
> > You may want to have a look a this post (and other posts in the same
> > thread):
> >
> > http://www.fixprotocol.org/discuss/read/24ed599c
> >
> > /David
> >
> >
> > > Hello, I would need a clarification.
> > >
> > > The handbook [section 10.5.1 -- Presence Map and NULL
> > > Utilization] says:
> > >
> > > [...]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.[...]
> > >
> > > Let suppose I have the following decimal field in my template
> > > definition:
> > >
> > > < decimal name="MDEntryPx" id="270" presence="optional" > < exponent
> > > > < copy value="-2" / > < / exponent > < mantissa > < delta / > < /
> > > mantissa
> > > > < /decimal >
> > >
> > > For the best of my comprehension in this case the exponent is
> > > optional, and has its own bit in pmap (due to the copy operator). If
> > > that bit is not set (the exponent is not present in the stream for
> > > sure) then the mantissa will be not present in the stream as well.
> > >
> > > 1. Does the same worth if the bit in pmap is set but the exponent
> > > value is NULL?
> > > 2. What about the new previous value of the Scaled Number if the
> > > exponent has to be considered absent?
> > >
> > > Moreover, the fact that the exponent bit in pmap is not set should
> > > not imply that the value of the exponent field will be not assigned
> > > (e.g. it should be assigned to the copy initial value, or to the
> > > previous value stored in the dictionary).
> > >
> > > 3.Let suppose the mantissa is not in the stream (because of the
> > > exponent absence), what does it imply in term of the mantissa field
> > > value, and in term of the mantissa new previous value?
> > >
> > > Many thanks in advance. Kind regards, -- Ale
Re: Optional decimal fields with individual operators
David Rosenborg / Pantor Engineering AB 1 Sep 2008 7:27AM ET
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