[DFDL-WG] needed: signed bit fields

[Mike Beckerle]

Doesn't seem to say what happens if type is signed, but length in bits is 1.

Can we make this an SDE please, since it can't be interpreted as a
twos-complement integer? Alternatively, can we clarify that if the length
is 1, the bit is interpreted as if there was a sign bit of 0?

When people write: <element name="myBit" type="xs:int" dfdl:length="1"/>

I am pretty sure they aren't expecting values of 0 or -1. They're expecting
0 or 1.

...mikeb

On Tue, Dec 11, 2012 at 3:46 AM, Steve Hanson <smh at uk.ibm.com> wrote:

> *Errata 2.90*. *Sections 12.3, 12.3.7.2*. Additionally allow lengthUnits
> 'bits' to apply to binary signed integer types, to support the modeling of
> signed integer bit fields in the C language. The physical bits are
> interpreted as a two's complement integer.
>
> Regards
>
> Steve Hanson
> Architect, Data Format Description Language (DFDL)
> Co-Chair, *OGF DFDL Working Group* <http://www.ogf.org/dfdl/>
> IBM SWG, Hursley, UK*
> **smh at uk.ibm.com* <smh at uk.ibm.com>
> tel:+44-1962-815848
>
>
>
> From:        Mike Beckerle <mbeckerle.dfdl at gmail.com>
> To:        dfdl-wg at ogf.org,
> Date:        10/12/2012 21:42
> Subject:        [DFDL-WG] needed: signed bit fields
> Sent by:        dfdl-wg-bounces at ogf.org
> ------------------------------
>
>
>
>
> current DFDL v1.0 spec says bit fields are all unsigned integers up to
> length 64.
>
> I am modeling data that uses lots of twos-complement 24-bit long and other
> length signed integers on various bit-boundaries.
>
> Was there a reason to leave signed twos-complement out for bit fields
> (other than perhaps just we thought we might get away with it?)
>
> The only corner case I can think of is if you make a 1-bit wide signed bit
> field. This should be a Schema Defintion Error I believe, because
> twos-complement isn't defined unless you have at  one sign bit, and at
> least 1 mantissa bit.
>
> ...mikeb
>
>
> --
> Mike Beckerle | OGF DFDL WG Co-Chair | Tresys Technologies
> Tel:  781-330-0412
>
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-- 
Mike Beckerle | OGF DFDL WG Co-Chair | Tresys Technologies
Tel:  781-330-0412
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