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

[Mike Beckerle]

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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