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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: 3-bit array ...
Date: 1999/12/07
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Date: 1999-12-07T00:00:00+00:00
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In article <wccg0xgm5n4.fsf@world.std.com>,
  Robert A Duff <bobduff@world.std.com> wrote:
> GNAT has always
> supported packing to the 3-bit level.  AverStar's front end,
and the
> Green Hills compiler that uses AverStar's FE, used to use 4,
but now
> uses 3, due to customer demand for it.  That's what this whole
> discussion has been about.
>
> There's also the issue of whether you can say:
>
>     for T2'Component_Size use 3;
>
> instead of the pragma Pack above.


I must say I wonder if the GNAT (and now Averstar) decision is
the right one. It would have been cleaner to say Pack always
means 4, and you use a component size clause if you want 3.

But the gods of legacy Ada 83 code definitely demand significant
sacrifices, so this is one of them.

Bob, how far did Averstar go, did you just do 3 bits? In GNAt
we close pack all sizes up to 64. (e.g. an array of Natural
gets packed to 31, which can be quite a surprise, although the
pragma Pack in this case is junk!)


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