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From: "J-P. Rosen" <rosen@adalog.fr>
Newsgroups: comp.lang.ada
Subject: Re: Question about package Interfaces.
Date: Tue, 14 Sep 2010 08:33:14 +0200
Organization: Adalog
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Date: 2010-09-14T08:33:14+02:00
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Le 13/09/2010 15:47, Peter C. Chapin a �crit :
> On 2010-09-12 23:54, Robert A Duff wrote:
> 
>> Unsigned_8'Size = 8.  But that does not mean that all objects
>> of subtype Unsigned_8 are 8 bits, nor that X'Size = 8
>> (where "X: Unsigned_8;").  For example, an object could
>> be stored in a 64-bit register.
>>
>> A packed array A of Unsigned_8 will have A'Component_Size = 8,
>> and A(I)'Size = 8 for all I.
> 
> So I have to explicitly ask for a packed array in order to get this
> guarantee? 
I don't know exactly what you want to achieve, but bear in mind that
talking about the size of a single variable is meaningless.

Imagine that you declared:
X : Unsigned_8;
and you discover that the declaration advances the data counter by 4
bytes. You can interpret that as X occupying 32 bits, or as X occupying
only 8 bits with 3 unused padding bytes ahead of it.

There is positively no way to tell the difference.
-- 
---------------------------------------------------------
           J-P. Rosen (rosen@adalog.fr)
Visit Adalog's web site at http://www.adalog.fr