Re: GNAT 4.4.5 Record Bit_Order Endian issues

[AdaMagica <christ-usch.grein@t-online.de>]

On Saturday, January 19, 2013 2:43:03 AM UTC+1, Stephen Leake wrote:
> Robert A Duff <bobduff@shell01.TheWorld.com> writes:
> > Stephen Leake <stephen_leake@stephe-leake.org> writes:
> >>      component_clause ::=
> >>          component_local_name at position range first_bit .. last_bit;
> >> But I could find no definition of "position"!
> > The very next paragraph defines the syntax:
> >     position ::= static_expression
> That doesn't say "position is the number of storage_units from the start
> of the record" (there's probably a better definition in Cohen's paper).
> For all I can tell from the ARM, "position" could be a color number, or
> the number of angels on the head of a pin!
> Then 13.5.2 talks about the Position attribute.
> Which just retreives the mysterious "position" number, it doesn't say
> what it _means_.
> > I agree that the RM is confusing in this area.
> > It's partly my fault.  :-(
> Ok. What paragraphs do we add? (in five years; better late than never :)

The AARM helps, but this is of course not a binding standard:

13.5.2(2.a/2) Ramification: {AI95-00133-01} Thus, for the default bit order, R.C'Position is the offset of C in storage elements from the beginning of the object, where the first storage element of an object is numbered zero. R'Address + R.C'Position = R.C'Address. For record extensions, the offset is not measured from the beginning of the extension part, but from the beginning of the whole object, as usual.
(2.b) In “R.C'Address – R'Address”, the "–" operator is the one in System.Storage_Elements that takes two Addresses and
returns a Storage_Offset.

Why isn't this in the RM itself? An oversight?