[DFDL-WG] Action 275 - Updates to Experience 3 (Bit Order) document

[Steve Hanson]

Mike

I believe that section 13.7.1.2 1.1.1.1 Bit strings, Alignment, and 
dfdl:fillByte already addresses this:

Corresponding bits from the dfdl:fillByte value are used to fill in 
unspecified bits of the data stream. That is, if bit K (K will be 1 or 
greater, but less than or equal to 8) of a data stream byte is 
unspecified, its value will be taken from bit K of the dfdl:fillByte 
property value.

Regards
 
Steve Hanson
Architect, IBM 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" <dfdl-wg at ogf.org>
Date:   29/01/2015 23:14
Subject:        [DFDL-WG] Action 275 - Updates to Experience 3 (Bit Order) 
document
Sent by:        dfdl-wg-bounces at ogf.org




I have modified this document per the public review comment.

There are minor changes here which should be brought over to the main 
specification. These changes should be incorporated into the corresponding 
sections of the main DFDL spec such time as we respin that.

There is one stipulation which should be discussed.

When changing from one bit order to another, the document says that this 
happens on the next byte boundary, hence, there is a partial byte that is 
lost to this byte alignment. The public commentor suggested we specify 
what these bits are filled with when unparsing. The DFDL spec is clear 
about filling for whole bytes, but when parts of a byte must be filled 
there are three choices

1) partial bytes are filled with 0
2) partial bytes are filled from the fillByte in some unspecified way
3) partial bytes are filled from the fillByte in a specific way.

Consistent with the rest of the DFDL Spec, I took a shot and put 
clarifying language in that says the fillByte is used, but not specifying 
details on exactly how the fillByte's bits are used.  However, the more 
general issue is there independent of the bit-order issues. The 
description of alignmentFill regions and how they are filled does not say 
anything about partial bytes.

A clarifying sentence in the table for the dfdl:fillByte property should 
probably say "When unparsing, if a region being filled is a partial byte, 
then it is filled with bits taken from the value of the dfdl:fillByte 
property in an implementation-specific manner."

Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | 
www.tresys.com
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