[DFDL-WG] Action 242 - propose simplification for length units in dfdl:valuelength and dfdl:contentLength functions

[Mike Beckerle]

These functions currently take the desired result units as the second
argument.

It is very complicated if the length units of the element are bytes, to ask
for this length to be recast in characters due to the
fragment-of-a-character on the end problem. In some sense there is
quotient/remainder here, which means there are multiple operations here,
not just one. There is the equivalent of floor (as many characters as fit,
then fillByte) ceiling (every byte filled from some character), remainder
(how many left over bytes are there). I think this is silly unless we have
use cases driving this.

I believe this restriction matches all use-cases I can think of:

Restriction: If the element (first argument) to either valueLength or
contentLength has length units of

characters -> can ask for valueLength or contentLength in any of
characters, bytes, or bits

bytes -> can ask for valueLength or contentLength in bytes or bits

bits -> can only ask for valueLength or contentLength only in bits.


and it is an SDE otherwise.


This insures that the result of these functions is always well defined.

I understand why there is a box sized in characters and I need to know its
size in bytes, but the opposite I can't see a use case for, and it isn't
crisply defined even.
Ditto for length in bits. If the box is sized in bytes I might want that in
bits (so * 8), but if the box is sized in bits, and I ask for bytes, what
do I want if there is a fragment of a byte? ceiling? floor? remainder?

Thoughts?


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