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@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
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848



From:        Mike Beckerle <mbeckerle.dfdl@gmail.com>
To:        dfdl-wg@ogf.org,
Date:        10/12/2012 21:42
Subject:        [DFDL-WG] needed: signed bit fields
Sent by:        dfdl-wg-bounces@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


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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