[DFDL-WG] needed: signed bit fields

[Steve Hanson]

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 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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