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@uk.ibm.com
tel:+44-1962-815848



From:        Mike Beckerle <mbeckerle.dfdl@gmail.com>
To:        "dfdl-wg@ogf.org" <dfdl-wg@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@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
Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy
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