[DFDL-WG] proposed dfdl:hexBinary function for hex constants in schemas

[Steve Hanson]

I think we should choose one of A-F or a-f as the nibbles, rather than 
leave it implementation dependent ?

Regards

Steve Hanson
Architect, IBM Data Format Description Language (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, 
Date:   16/07/2013 16:42
Subject:        Re: [DFDL-WG] proposed dfdl:hexBinary function for hex 
constants in    schemas
Sent by:        dfdl-wg-bounces at ogf.org



This proposal is phrased as if xs:hexBinary was a string constructor. 

That's not the case, the result type is xs:hexBinary.

Here is the rephrased proposal:

dfdl:hexBinary($arg as xs:anyAtomicType?) as xs:hexBinary? 

This function provides an extension to the behavior of the xs:hexBinary 
constructor. The argument can be a string, in which case the behavior is 
as the xs:hexBinary constructor. The argument can also be a long, 
unsignedLong, or any subtype thereof, and in that case a xs:hexBinary 
value containing a number of bytes is produced. The ordering of the bytes 
and number of bytes corresponds to a binary big-endian twos-complement 
implementation of the type of the argument. Hence, an argument of 
primitive type xs:unsignedLong would produce an xs:hexBinary value 
containing 8 bytes, and an argument of primitive type xs:short will 
produce an xs:hexBinary value containing 2 bytes.

So:

dfdl:short(xs:concat('x', xs:string(dfdl:hexBinary(xs:short(208))))) eq 
xs:short(208)

is true, and a corresponding tautology holds for all the other DFDL 
functions that construct integers from hexadecimal, if you replace the 208 
above with a value in range for the corresponding numeric type.

If the argument is a numeric literal, then the smallest signed integer 
type (long, int, short, byte) is selected that can contain the value, and 
the number of hexadecimal digits produced corresponds to that type. So:

dfdl:hexBinary(208) 

produces a hexBinary value containing 1 byte, which converted to a string 
will be either "D0" or "d0".

dfdl:hexBinary(-2084)

produces a hexBinary value containing 2 bytes, which converted to a string 
will be either "F7FF" or "f7ff".

On Tue, Jul 16, 2013 at 10:43 AM, Mike Beckerle <mbeckerle.dfdl at gmail.com> 
wrote:
Separated out from prior proposal where it was mixed in with another 
topic.

dfdl:hexBinary($arg as xs:anyAtomicType?) as xs:hexBinary? 

This function provides an extension to the behavior of the xs:hexBinary 
constructor. The argument can be a string, in which case the behavior is 
as the xs:hexBinary constructor. The argument can also be a long, 
unsignedLong, or any subtype thereof, and in that case a string containing 
hexadecimal digits is produced. The hexadecimal digits produced that are 
letters are always uppercase. The number of hex digits in the resulting 
string is a function of the input type. If byte or unsigned byte, exactly 
2 hex digits are produced, for short and unsignedShort, 4 hex digits, and 
so on. The hex digits correspond to a big-endian representation of a 
twos-complement binary representation of the argument value. So:

dfdl:short(xs:concat('x', dfdl:hexBinary(xs:short(208)))) eq xs:short(208)

is true, and a corresponding tautology holds for all the other DFDL 
functions that construct integers from hexadecimal, if you replace the 208 
above with a value in range for the corresponding numeric type.

If the argument is a numeric literal, then the smallest signed integer 
type (long, int, short, byte) is selected that can contain the value, and 
the number of hexadecimal digits produced corresponds to that type. So:

dfdl:hexBinary(208) eq 'D0'
dfdl:hexBinary(-2084) eq 'F7FF'


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




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