Re: Ada 95 Numerics questions for the experts

[bobduff@world.std.com (Robert A Duff)]

I said:

><<It depends what you're trying to do.  If you really care about the exact
>size of the components (e.g. because you're interfacing to external
>hardware or software), then use a Component_Size clause.  If you just
>want to squeeze the thing down to a reasonably small size, because you
>know that will be more efficient, then pragma Pack is more appropriate.

In article <dewar.873592294@merv>, Robert Dewar <dewar@merv.cs.nyu.edu> wrote:

>This is surpringly wrong. Bob, you must go read the RM, it was written
>by this clever fellow Bob Duff, and will tell you the TRUTH :-) :-)

Sorry, I should have clarified that my advice was stylistic.  It doesn't
matter what the RM says -- stylistically, Pack means "minimize space,
more or less", and "for T'Component_Size use N" means, "I want exactly
N-bit components".  Surely Pack had that feeling in Ada 83, and the
addition of requirements in Ada 95 was merely a response to
implementations that failed to do *anything* to minimize space, so we
had to specify *how much* (as a minimum) space has to be minimized.

Besides, the allegedly "clever" Bob Duff who wrote that portion of the
RM is no more.  I no longer spend 24-hours a day thinking about language
issues.  ;-)

>First, in the absence of implementation of annex C, neither declaration
>will guarantee close packing.

Yeah, yeah, I know that all bets are off if the impl doesn't support
Annex C.

- Bob