[DFDL-WG] propose new dfdl:binaryNumberRep "offsetBinary"

[Mike Beckerle]

I think you've got it. It's pretty simple really.

Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
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On Thu, Sep 14, 2017 at 9:49 PM, Steve Hanson <smh at uk.ibm.com> wrote:

> Hi Mike
>
> If I understand this correctly, it is just a way of being able to encode
> negative numbers. For a given precision the offset is always fixed, so in
> your example no of bits is 3 so offset is 4. So the lengthKind must be
> 'explicit' or 'implicit'.
>
> If so then the table in 13.7 becomes:
> *Logical Type* *Permitted Value*
> Decimal, Integer, NonNegativeInteger packed, bcd, binary, ibm4690Packed
> Long, Int, Short, Byte, packed, binary, *offsetBinary*, ibm4690Packed
> (but not bcd)
> UnsignedLong, Unsignedint, UnsignedShort, UnsignedByte packed, bcd,
> binary, ibm4690Packed
>
> Any other subtleties?
>
> Regards
>
> Steve Hanson
>
> IBM Hybrid Integration, Hursley, UK
> Architect, *IBM DFDL*
> <http://www.ibm.com/developerworks/library/se-dfdl/index.html>
> Co-Chair, *OGF DFDL Working Group* <http://www.ogf.org/dfdl/>
> *smh at uk.ibm.com* <smh at uk.ibm.com>
> tel:+44-1962-815848 <+44%201962%20815848>
> mob:+44-7717-378890 <+44%207717%20378890>
>
>
>
> From:        Mike Beckerle <mbeckerle.dfdl at gmail.com>
> To:        "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
> Date:        14/09/2017 01:35
> Subject:        [DFDL-WG] propose new dfdl:binaryNumberRep "offsetBinary"
> Sent by:        "dfdl-wg" <dfdl-wg-bounces at ogf.org>
> ------------------------------
>
>
>
> We have found a number of places that use offset-binary numeric
> representation. This is also called excess-K, or biased, but I think offset
> binary is a better description of it.
>
> In this representation you take an unsigned binary, and just subtract an
> offset. E.g., for a 3-bit number, mostSignificantBitFirst:
>
> bits    unsigned  twos-comp  offsetBinary
>
> 000       0         0          -4
> 001       1         1          -3
> 010       2         2          -2
> 011       3         3          -1
> 100       4        -4           0
> 101       5        -3           1
> 110       6        -2           2
> 111       7        -1           3
>
> At the moment, users have to work around this in Daffodil using
> inputValueCalc and outputValueCalc. This is feasible, but really awkward
> for such a simple concept.
>
> So we suggest that the next revision of DFDL include dfdl:binaryNumberRep="
> offsetBinary"
>
> Thoughts?
>
> ...mikeb
>
> Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
> *www.tresys.com*
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