Your test cant work. Bit order doesnt work that way. Unless a partial byte is
involved bit order does nothing. The values of whole bytes don't change.
There is a bit order tutorial in the daffodil tutorials module.
Suggest you start there. If you view the bitOrder tdml.xml file with firefox it
should format it into html via an xslt stylesheet so it is readable.
We need to get tutorials like this up as part of the daffodil site materials.
________________________________
From: Sloane, Brandon <bslo...@tresys.com>
Sent: Monday, April 22, 2019 4:27:04 PM
To: dev@daffodil.apache.org
Subject: Understanding bitOrder=leastSignificantFirst
I am trying to work through a bug surrounding changing the bitOrder mid schema
and am having trouble figuring out how Daffodil handles bitOrder in general.
I see that in InputSourceData, we have code to mask for the correct bits and
shift out the gaps, but I do not see where we actually invert the bit-order
internal to a byte.
In an attempt to test this, I made the following schema:
<tdml:defineSchema name="s6">
<xs:include
schemaLocation="org/apache/daffodil/xsd/DFDLGeneralFormat.dfdl.xsd"/>
<dfdl:format ref="ex:GeneralFormat" representation="binary"
lengthUnits="bits" lengthKind='explicit'
alignmentUnits='bits' alignment='1' binaryNumberRep='binary'
bitOrder="leastSignificantBitFirst" byteOrder="littleEndian"
/>
<xs:element name="changeOnSequence" dfdl:lengthKind='implicit'>
<xs:complexType>
<xs:sequence>
<xs:sequence>
<xs:element name="A" type="xs:unsignedInt" dfdl:length="8"/>
<xs:element name="B" type="xs:unsignedInt" dfdl:length="8"/>
<xs:element name="C" type="xs:unsignedInt" dfdl:length="8"/>
<xs:element name="D" type="xs:unsignedInt" dfdl:length="8"/>
</xs:sequence>
</xs:sequence>
</xs:complexType>
</xs:element>
</tdml:defineSchema>
Combined with the following testcase:
<tdml:parserTestCase name="bitOrderChangeOnSequence"
root="changeOnSequence" model="s6" description="Tests changing bitOrder
when on a byte boundary.">
<document xmlns="http://www.ibm.com/xmlns/dfdl/testData";>
<documentPart type="bits">
0000 0001
0000 0001
1000 0000
1000 0000
</documentPart>
</document>
<tdml:infoset>
<tdml:dfdlInfoset xmlns:xs="http://www.w3.org/2001/XMLSchema";
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
xmlns="http://example.com";>
<changeOnSequence>
<A>128</A>
<B>128</B>
<C>1</C>
<D>1</D>
</changeOnSequence>
</tdml:dfdlInfoset>
</tdml:infoset>
</tdml:parserTestCase>
However, the actual output was:
<changeOnSequence>
<A>1</A>
<B>1</B>
<C>128</C>
<D>128</D>
</changeOnSequence>
As if I had never set the bitOrder at all.
Given that we have made extensive use of bitOrder in the past, I find it hard
to believe that it is a fundomentally non-implemented as my current
understanding of the code would suggest. Any ideas on what I am missing?
Brandon T. Sloane
Associate, Services
bslo...@tresys.com | tresys.com
