---------- Forwarded message ----------
From:
Mike Beckerle <mbeckerle.dfdl@gmail.com>
Date: Thu, Jun 20, 2013 at 12:39 PM
Subject: Re: [DFDL-WG] proposal: functions to allow reasonable syntax for hex constants in DFDL expression language
To:
dfdl-wg@ogf.org
Revised proposal (version 2) based on feedback:
Rationale: in writing DFDL schemas for binary data formats, there is a
strong need to express binary data constants in hexadecimal.
Proposed new functions:
dfdl:byte
dfdl:unsignedByte
dfdl:short
dfdl:unsignedShort
dfdl:int
dfdl:unsignedInt
dfdl:long
dfdl:unsignedLong
These functions behave identically to the XPath standard functions of the same names in the 'fn:' namespace, with one exception. When the argument is a string beginning with the letter 'x', then then argument must contain in addition one or more hexadecimal digits.
Besides the initial 'x', the argument string must contain only hexadecimal digits, that is, the characters
0-9a-zA-Z. It is a schema definition error otherwise.
The hex digits represent a big endian twos complement representation of
a binary number.
Each function has a limit on the number of hex digits, with no more digits
than 2, 4, 8, or 16 for the byte, short, int, and long versions. That is
to say for dfdl:byte and dfdl:unsignedByte, there can be at most 2 hex digits.
For dfdl:short and dfdl:unsignedShort, there can be at most 4 hex digits, and
so on. It is a schema definition error if more digits are encountered than
are suitable for the type being created.
Examples:
dfdl:unsignedInt("0xa1b2c3d4") is the value 2712847316. Note that in
the first byte 'a1' the most significant bit is set, but since this is
an unsigned type, this is not interpreted as a sign bit.
dfdl:int("0xFFFFFFFF") is the int value -1. The sign bit indicates
that the number is negative, and this twos complement value represents
-1.
dfdl:unsignedByte("0xFF") is the unsigned byte value 255
dfdl:byte("0xff") is the byte value -1.
dfdl:byte("0x7F") is the byte value 127
dfdl:byte("0x80") is the byte value -128
dfdl:unsignedByte("0x80") is the unsigned byte value 128
dfdl:byte("0x0A3") is a schema definition error as the leading
zero is not allowed because at most 2 digits are allowed for byte types.
dfdl:short("0x0A3") is short value 208. Leading zero causes
no issue here because up to 4 digits are allowed.
Example of usage in expressions:
<xs:element name="magic_number" type="ex:uint32"
dfdl:byteOrder="bigEndian">
<xs:annotation>
<xs:appinfo source="http://www.ogf.org/dfdl/dfdl-1.0/">
<dfdl:setVariable ref="ex:bOrd">
{
if (xs:unsignedInt(.) eq dfdl:unsignedInt('0xa1b2c3d4'))
then 'bigEndian'
else if (xs:unsignedInt(.) eq dfdl:unsignedInt('0xd4c3b2a1')) then 'littleEndian'
else fn:error(ex:magic_number, "Magic
number was not 0xA1B2C3D4 (for bigEndian) or 0xD4C3B2A1 (for littleEndian).")
}
</dfdl:setVariable>
</xs:appinfo>
</xs:annotation>
</xs:element>
On Thu, Jun 20, 2013 at 12:04 PM, Steve Hanson
<smh@uk.ibm.com> wrote:
Tim I think you are right - it should just
be 'x'.
Regards
Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF
DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
From:
Tim Kimber/UK/IBM@IBMGB
To:
dfdl-wg@ogf.org,
Date:
20/06/2013 14:19
Subject:
Re: [DFDL-WG]
proposal: functions to allow reasonable syntax for hex constants in DFDL
expression language
Sent by:
dfdl-wg-bounces@ogf.org
Interesting...that never occurred to
me. I have always considered the # to be a qualifier on the XML character
reference entity.
In XML, the carriage-return character can be specified in any of the following
ways:
&cr; -
A named entity
-
A numeric entity ( starts with '#' )

 -
A numeric entity in base 16 ( the numeric part starts
with 'x' )
So the '#' character is signalling that the entity is a numeric entity.
But there's no need for that to be signalled in this case - the parameter
for these integer constructors will always be a number.
On that basis, the prefix should be 'x'. I would prefer that to '#x' on
the grounds of readability.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert@uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Steve
Hanson/UK/IBM
To: Tim
Kimber/UK/IBM@IBMGB,
Cc: dfdl-wg@ogf.org,
dfdl-wg-bounces@ogf.org
Date: 20/06/2013
14:01
Subject: Re:
[DFDL-WG] proposal: functions to allow reasonable syntax for hex constants
in DFDL expression language
I was thinking along the same lines as Tim.
I'd prefer the hex string to start with '#x' for consistency with DFDL
hex entity syntax.
Regards
Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF
DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
From: Tim
Kimber/UK/IBM@IBMGB
To: dfdl-wg@ogf.org,
Date: 20/06/2013
09:44
Subject: Re:
[DFDL-WG] proposal: functions to allow reasonable syntax for hex constants
in DFDL expression language
Sent by: dfdl-wg-bounces@ogf.org
As an alternative, we could
- drop the 'h' prefix
- use the same names as the XPath integer constructors, including the use
of the full name for unsigned variants ( e.g. 'dfdl:unsignedInt' )
- behave exactly like xs:byte / xs:short etc when the string does not begin
with '0x'
The only difference would be the namespace of the function. So the modeller
would use the dfdl variant if they needed the '0x' notation, and they could
choose to use the dfdl variant always when constructing integers from string
literals.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert@uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Mike
Beckerle <mbeckerle.dfdl@gmail.com>
To: dfdl-wg@ogf.org,
Date: 19/06/2013
23:28
Subject: [DFDL-WG]
proposal: functions to allow reasonable syntax for hex constants in DFDL
expression language
Sent by: dfdl-wg-bounces@ogf.org
Rationale: in writing DFDL schemas for binary data formats, there is a
strong need to express binary data constants in hexadecimal.
Proposed new functions:
dfdl:hByte
dfdl:hUByte
dfdl:hShort
dfdl:hUShort
dfdl:hInt
dfdl:hUInt
dfdl:hLong
dfdl:hULong
The prefix 'h' is a reminder that the function converts from hexadecimal.
The prefix 'U' on the name denotes that the function creates an unsigned
type result. Normally one might like to write this out fully, but in this
case brevity is helpful given the expected usage of these functions to
construct literal constants in DFDL expressions.
All the functions take a single string argument. The string must begin
with "0x" and contain at least one hex digit after that.
The string must contain only hexadecimal digits, that is, the characters
0-9a-zA-Z. It is a schema definition error otherwise.
The hex digits represent a big endian twos complement representation of
a binary number.
Each function has a limit on the number of hex digits, with no more digits
than 2, 4, 8, or 16 for the byte, short, int, and long versions. That is
to say for dfdl:byte and dfdl:uByte, there can be at most 2 hex digits.
For dfdl:short and dfdl:uShort, there can be at most 4 hex digits, and
so on. It is a schema definition error if more digits are encountered than
are suitable for the type being created.
Examples:
dfdl:hUInt("0xa1b2c3d4") is the value 2712847316. Note that in
the first byte 'a1' the most significant bit is set, but since this is
an unsigned type, this is not interpreted as a sign bit.
dfdl:hInt("0xFFFFFFFF") is the int value -1. The sign bit indicates
that the number is negative, and this twos complement value represents
-1.
dfdl:hUByte("0xFF") is the unsigned byte value 255
dfdl:hByte("0xff") is the byte value -1.
dfdl:hByte("0x7F") is the byte value 127
dfdl:hByte("0x80") is the byte value -128
dfdl:hUByte("0x80") is the unsigned byte value 128
dfdl:hByte("0x0A3") is a schema definition error as the leading
zero is not allowed because at most 2 digits are allowed for byte types.
dfdl:hShort("0x0A3") is short value 208. Leading zero causes
no issue here because up to 4 digits are allowed.
Example of usage in expressions:
<xs:element name="magic_number" type="ex:uint32"
dfdl:byteOrder="bigEndian">
<xs:annotation>
<xs:appinfo source="http://www.ogf.org/dfdl/dfdl-1.0/">
<dfdl:setVariable ref="ex:bOrd">
{
if (xs:unsignedInt(.) eq dfdl:hUInt('0xa1b2c3d4'))
then 'bigEndian'
else if (xs:unsignedInt(.) eq dfdl:hUInt('0xd4c3b2a1'))
then 'littleEndian'
else fn:error(ex:magic_number, "Magic
number was not 0xA1B2C3D4 (for bigEndian) or 0xD4C3B2A1 (for littleEndian).")
}
</dfdl:setVariable>
</xs:appinfo>
</xs:annotation>
</xs:element>
--
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com--
dfdl-wg mailing list
dfdl-wg@ogf.org
https://www.ogf.org/mailman/listinfo/dfdl-wg
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU--
dfdl-wg mailing list
dfdl-wg@ogf.org
https://www.ogf.org/mailman/listinfo/dfdl-wg
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU--
dfdl-wg mailing list
dfdl-wg@ogf.org
https://www.ogf.org/mailman/listinfo/dfdl-wg
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU
--
dfdl-wg mailing list
dfdl-wg@ogf.org
https://www.ogf.org/mailman/listinfo/dfdl-wg
--
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com