From: Stephen Leake <stephen_leake@stephe-leake.org>
Subject: Re: GNAT 4.4.5 Record Bit_Order Endian issues
Date: Mon, 21 Jan 2013 22:21:32 -0500 (2 minutes, 25 seconds ago)
Date: 2013-01-21T22:21:32-05:00 [thread overview]
Message-ID: <854ni9c319.fsf@stephe-leake.org> (raw)
"Randy Brukardt" <randy@rrsoftware.com> writes:
> "AdaMagica" <christ-usch.grein@t-online.de> wrote in message
> news:9dc6d5fe-3382-44dd-8460-e042bd6b808e@googlegroups.com...
> On Saturday, January 19, 2013 2:43:03 AM UTC+1, Stephen Leake wrote:
> ...
>>> Then 13.5.2 talks about the Position attribute.
>>> Which just retreives the mysterious "position" number, it doesn't say
>>> what it _means_.
>
> Huh? 13.5.2(2/2) says in part:
> "denotes Denotes the same value as R.C'Address – R'Address". That makes it
> pretty clear what it represents (for the Default_Bit_Order).
The full paragraph is:
2/2
R.C'Position
{AI95-00133-01AI95-00133-01} If the nondefault bit
ordering applies to the composite type, and if a
component_clause specifies the placement of C, denotes
the value given for the position of the
component_clause; otherwise, denotes the same value as
R.C'Address - R'Address. The value of this attribute is
of the type universal_integer.
Note the 'otherwise'; that's means the value is R.C'Address - R'Address
only if position is _not_ specified in a rep clause.
> For the non-default bit order, it just is whatever you specify (and
> that's all we can say, because it *doesn't* have a clear physical
> meaning - it defines the machine scalars to use, which makes it a
> totally confusing mess if you try to work the other way).
Cohen's paper (http://www.ada-auth.org/ai-files/grab_bag/bitorder.pdf)
gives it a clear meaning in that case.
>>> > 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 :)
>
> I don't think there is anything that would help. We surely tried when we
> created the non-default bit order stuff.
Do you think Cohen's paper makes it clear? I gather not. Why not?
If that's too complex to put in the RM, maybe the implementation advice
could include a reference to a copy of Cohen's paper on the adaic
website (somehow I doubt ISO standards allow web references).
--
-- Stephe
next reply other threads:[~2013-01-22 3:21 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-22 3:21 Stephen Leake [this message]
2013-01-22 5:14 ` GNAT 4.4.5 Record Bit_Order Endian issues Jeffrey Carter
2013-01-23 1:29 ` Stephen Leake
2013-01-22 22:40 ` Randy Brukardt
2013-01-23 1:38 ` Stephen Leake
2013-01-23 10:58 ` Simon Wright
-- strict thread matches above, loose matches on Subject: below --
2013-01-14 17:43 awdorrin
2013-01-15 0:38 ` Randy Brukardt
2013-01-15 1:57 ` Adam Beneschan
2013-01-15 16:57 ` AdaMagica
2013-01-15 22:24 ` Stephen Leake
2013-01-16 10:44 ` Simon Wright
2013-01-16 19:00 ` AdaMagica
2013-01-16 21:34 ` Simon Wright
2013-01-16 23:14 ` Randy Brukardt
2013-01-17 3:49 ` Stephen Leake
2013-01-17 15:32 ` awdorrin
2013-01-18 9:49 ` Stephen Leake
2013-01-18 13:04 ` Robert A Duff
2013-01-19 1:43 ` Stephen Leake
2013-01-19 12:48 ` AdaMagica
2013-01-22 0:14 ` Randy Brukardt
2013-01-17 17:28 ` Simon Wright
2013-01-18 9:56 ` Stephen Leake
2013-01-17 18:04 ` awdorrin
2013-01-17 19:50 ` awdorrin
2013-01-18 9:58 ` Stephen Leake
2013-01-17 20:58 ` Simon Wright
2013-01-17 21:29 ` awdorrin
2013-01-17 22:16 ` awdorrin
2013-01-18 6:15 ` J-P. Rosen
2013-01-18 15:28 ` Niklas Holsti
2013-01-18 9:37 ` Stephen Leake
2013-01-18 12:24 ` awdorrin
2013-01-18 15:11 ` awdorrin
2013-01-19 1:48 ` Stephen Leake
2013-01-18 17:19 ` Simon Wright
2013-01-22 9:49 ` quinot
2013-01-28 13:39 ` quinot
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