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Posted to users@daffodil.apache.org by "Costello, Roger L." <co...@mitre.org> on 2019/02/11 11:43:08 UTC
Can bits be cast to string, concatenated, and then cast to an
unsigned int?
Hello DFDL Community,
My input file contains a 32-bit field (bit 0 to bit 31). Bit 31 determines how to interpret the other bits: if bit 31 = 1 then bits 0 to 15 is an unsigned int denoting an ordinal number and the other bits must be zero. If bit 30 = 0 then bits 0 to 30 is an unsigned int denoting a hint/name table RVA. The following graphic illustrates the structure:
[cid:image002.png@01D4C1D5.0B737DA0]
How to express this in DFDL? I figured that I would create a hidden group that contains 32 1-bit elements. I would have a choice that expresses this: If hidden bit 31 = 1 then choose the ordinal_number element, otherwise (hidden bit 31 = 0) choose hint_name_table_RVA element.
The value of ordinal_number is calculated by concatenating hidden bit 0 with hidden bit 1, ..., hidden bit 15. Then, cast that to unsigned int.
The value of hint_name_table_RVA is calculated by concatenating hidden bit 0 with hidden bit 1, ..., hidden bit 30. Then, cast that to unsigned int.
You can see my schema below. Unfortunately, it fails. What is the right way to approach this problem, please? /Roger
<xs:element name="Ordinal_Number" type="unsignedint16" dfdl:inputValueCalc="{
unsignedint16(
fn:concat(./Hidden_Lookup_Table_bit0,
./Hidden_Lookup_Table_bit1,
./Hidden_Lookup_Table_bit2,
./Hidden_Lookup_Table_bit3,
./Hidden_Lookup_Table_bit4,
./Hidden_Lookup_Table_bit5,
./Hidden_Lookup_Table_bit6,
./Hidden_Lookup_Table_bit7,
./Hidden_Lookup_Table_bit8,
./Hidden_Lookup_Table_bit9,
./Hidden_Lookup_Table_bit10,
./Hidden_Lookup_Table_bit11,
./Hidden_Lookup_Table_bit12,
./Hidden_Lookup_Table_bit13,
./Hidden_Lookup_Table_bit14,
./Hidden_Lookup_Table_bit15))
}" />
<xs:element name="Hint_Name_Table_RVA" type="unsignedint31" dfdl:inputValueCalc="{
unsignedint31(
fn:concat(./Hidden_Lookup_Table_bit0,
./Hidden_Lookup_Table_bit1,
./Hidden_Lookup_Table_bit2,
./Hidden_Lookup_Table_bit3,
./Hidden_Lookup_Table_bit4,
./Hidden_Lookup_Table_bit5,
./Hidden_Lookup_Table_bit6,
./Hidden_Lookup_Table_bit7,
./Hidden_Lookup_Table_bit8,
./Hidden_Lookup_Table_bit9,
./Hidden_Lookup_Table_bit10,
./Hidden_Lookup_Table_bit11,
./Hidden_Lookup_Table_bit12,
./Hidden_Lookup_Table_bit13,
./Hidden_Lookup_Table_bit14,
./Hidden_Lookup_Table_bit15,
./Hidden_Lookup_Table_bit16,
./Hidden_Lookup_Table_bit17,
./Hidden_Lookup_Table_bit18,
./Hidden_Lookup_Table_bit19,
./Hidden_Lookup_Table_bit20,
./Hidden_Lookup_Table_bit21,
./Hidden_Lookup_Table_bit22,
./Hidden_Lookup_Table_bit23,
./Hidden_Lookup_Table_bit24,
./Hidden_Lookup_Table_bit25,
./Hidden_Lookup_Table_bit26,
./Hidden_Lookup_Table_bit27,
./Hidden_Lookup_Table_bit28,
./Hidden_Lookup_Table_bit29,
./Hidden_Lookup_Table_bit30
))
}" />
<xs:group name="hidden_Lookup_Table_Group">
<xs:sequence dfdl:alignmentUnits="bits">
<xs:element name="Hidden_Lookup_Table_bit7" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit6" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit5" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit4" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit3" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit2" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit1" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit0" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit15" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit14" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit13" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit12" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit11" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit10" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit9" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit8" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit23" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit22" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit21" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit20" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit19" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit18" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit17" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit16" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit31" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit30" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit29" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit28" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit27" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit26" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit25" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
<xs:element name="Hidden_Lookup_Table_bit24" type="unsignedint1"
dfdl:outputValueCalc='{ . }'
/>
</xs:sequence>
</xs:group>
Re: Can bits be cast to string, concatenated, and then cast to an
unsigned int?
Posted by Steve Lawrence <sl...@apache.org>.
Concating bit values will not work because there are no constructor
functions that accept a bit string. The dfdl:setBits() function can be
used, but only for only for bytes (i.e. 8 bits or less). You could
always just use math to construct an int, e.g.:
./bit1 * fn:pow(2,31) +
./bit2 * fn:pow(2,30) +
...
./bitN * fn:pow(2,0)
It would probably be more efficient to expand the fn:pow's to their
actual values, but this gives the idea.
That said, I think an approach that makes for a more descriptive schema
that is easier to understand is to use a choice where each branch of the
choice parses the 30 bits differently, and a discriminator is used to
ensure the correct branch is taken based on the lst bit. Something like:
<xs:choice>
<xs:sequence>
<xs:element name="OrdinalNumber" dfdl:length="16" ... />
<xs:element name="Zero" dfdl:length="15 ... />
<xs:element name="Flag" dfdl:length=1" ... >
<xs:annotation>
<xs:appinfo source="http://www.ogf.org/dfdl/">
<dfdl:discriminator test="{ . eq 1 }" />
</xs:appinfo>
</xs:annotation>
</xs:element>
</xs:sequence>
<xs:sequence>
<xs:element name="HintNameTableRVA" dfdl:length="31" ... />
<xs:element name="Flag" dfdl:length=1" ... >
<xs:annotation>
<xs:appinfo source="http://www.ogf.org/dfdl/">
<dfdl:discriminator test="{ . eq 0 }" />
</xs:appinfo>
</xs:annotation>
</xs:element>
</xs:sequence>
</xs:choice>
This is bit inefficient since it requires parsing the same 32 bits twice
if the last bit is a 0, but it's much easier to understand what data
looks like.
- Steve
On 2/11/19 6:43 AM, Costello, Roger L. wrote:
> Hello DFDL Community,
>
> My input file contains a 32-bit field (bit 0 to bit 31). Bit 31 determines how
> to interpret the other bits: if bit 31 = 1 then bits 0 to 15 is an unsigned int
> denoting an ordinal number and the other bits must be zero. If bit 30 = 0 then
> bits 0 to 30 is an unsigned int denoting a hint/name table RVA. The following
> graphic illustrates the structure:
>
> How to express this in DFDL? I figured that I would create a hidden group that
> contains 32 1-bit elements. I would have a choice that expresses this: If hidden
> bit 31 = 1 then choose the ordinal_number element, otherwise (hidden bit 31 = 0)
> choose hint_name_table_RVA element.
>
> The value of ordinal_number is calculated by concatenating hidden bit 0 with
> hidden bit 1, …, hidden bit 15. Then, cast that to unsigned int.
>
> The value of hint_name_table_RVA is calculated by concatenating hidden bit 0
> with hidden bit 1, …, hidden bit 30. Then, cast that to unsigned int.
>
> You can see my schema below. Unfortunately, it fails. What is the right way to
> approach this problem, please? /Roger
>
> <xs:elementname="Ordinal_Number"type="unsignedint16"dfdl:inputValueCalc="{
> unsignedint16(
> fn:concat(./Hidden_Lookup_Table_bit0,
> ./Hidden_Lookup_Table_bit1,
> ./Hidden_Lookup_Table_bit2,
> ./Hidden_Lookup_Table_bit3,
> ./Hidden_Lookup_Table_bit4,
> ./Hidden_Lookup_Table_bit5,
> ./Hidden_Lookup_Table_bit6,
> ./Hidden_Lookup_Table_bit7,
> ./Hidden_Lookup_Table_bit8,
> ./Hidden_Lookup_Table_bit9,
> ./Hidden_Lookup_Table_bit10,
> ./Hidden_Lookup_Table_bit11,
> ./Hidden_Lookup_Table_bit12,
> ./Hidden_Lookup_Table_bit13,
> ./Hidden_Lookup_Table_bit14,
> ./Hidden_Lookup_Table_bit15))
> }"/>
>
> <xs:elementname="Hint_Name_Table_RVA"type="unsignedint31"dfdl:inputValueCalc="{
> unsignedint31(
> fn:concat(./Hidden_Lookup_Table_bit0,
> ./Hidden_Lookup_Table_bit1,
> ./Hidden_Lookup_Table_bit2,
> ./Hidden_Lookup_Table_bit3,
> ./Hidden_Lookup_Table_bit4,
> ./Hidden_Lookup_Table_bit5,
> ./Hidden_Lookup_Table_bit6,
> ./Hidden_Lookup_Table_bit7,
> ./Hidden_Lookup_Table_bit8,
> ./Hidden_Lookup_Table_bit9,
> ./Hidden_Lookup_Table_bit10,
> ./Hidden_Lookup_Table_bit11,
> ./Hidden_Lookup_Table_bit12,
> ./Hidden_Lookup_Table_bit13,
> ./Hidden_Lookup_Table_bit14,
> ./Hidden_Lookup_Table_bit15,
> ./Hidden_Lookup_Table_bit16,
> ./Hidden_Lookup_Table_bit17,
> ./Hidden_Lookup_Table_bit18,
> ./Hidden_Lookup_Table_bit19,
> ./Hidden_Lookup_Table_bit20,
> ./Hidden_Lookup_Table_bit21,
> ./Hidden_Lookup_Table_bit22,
> ./Hidden_Lookup_Table_bit23,
> ./Hidden_Lookup_Table_bit24,
> ./Hidden_Lookup_Table_bit25,
> ./Hidden_Lookup_Table_bit26,
> ./Hidden_Lookup_Table_bit27,
> ./Hidden_Lookup_Table_bit28,
> ./Hidden_Lookup_Table_bit29,
> ./Hidden_Lookup_Table_bit30
> ))
> }"/>
>
> <xs:groupname="hidden_Lookup_Table_Group">
> <xs:sequencedfdl:alignmentUnits="bits">
> <xs:elementname="Hidden_Lookup_Table_bit7"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit6"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit5"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit4"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit3"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit2"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit1"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit0"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit15"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit14"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit13"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit12"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit11"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit10"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit9"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit8"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit23"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit22"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit21"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit20"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit19"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit18"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit17"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit16"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit31"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit30"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit29"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit28"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit27"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit26"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit25"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> <xs:elementname="Hidden_Lookup_Table_bit24"type="unsignedint1"
> dfdl:outputValueCalc='{ . }'
> />
> </xs:sequence>
> </xs:group>
>