[DFDL-WG] proposed clarification/narrowing - no twos-complement decimal, integer or nonNegativeInteger
Steve Hanson
smh at uk.ibm.com
Wed Aug 15 08:15:57 EDT 2012
Mike
Having thought about this since our call yesterday, I am uncomfortable
with the proposed narrowing. It means DFDL can not be guaranteed to handle
the two's complement result of Java BigInteger.toByteArray(). I don't
have a concrete use case of two's complement data > 8 bytes but I am sure
that someone in the scientific community will need it at some point. Hence
why it is allowed in the spec today.
If we do allow it, then we have to decide what happens during unparsing
and lengthKind is 'prefixed'. The equivalent of Table 16 for lengthKind
'pattern' is needed for lengthKind 'prefixed', as we discussed. That
would imply that the unparsing behaviour would be 'Minimum number of bytes
to represent significant digits and sign'. In other words, a two's
complement binary integer is created that is just long enough to represent
the infoset value.
Regards
Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: dfdl-wg at ogf.org
Date: 14/08/2012 19:33
Subject: [DFDL-WG] proposed clarification/narrowing - no
twos-complement decimal, integer or nonNegativeInteger
Sent by: dfdl-wg-bounces at ogf.org
The spec is not clear on whether decimal, integer, and nonNegativeInteger
support representation='binary' with binaryNumberRep='binary' (aka
twos-complement). Since these types do not have any size limit, such a
capability allows arbitrarily large twos-complement integers, or perhaps
it would be an implementation defined limit.
I believe the right choice is that it should be disallowed. That is, only
binaryNumberRep of 'bcd' or 'packed' should be allowed for these types.
These types have always been about decimal-style representations to me.
This keeps twos-complement only for the types long, int, short, byte and
their unsigned counterparts.
--
Mike Beckerle | OGF DFDL WG Co-Chair
Tel: 781-330-0412
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