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From: Mario Amado Alves <maa@di.fct.unl.pt>
Subject: Re: S'Write and How To Count Bytes
Date: 2000/10/03
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Date: 2000-10-03T11:03:03+00:00

The "bottom line" was very simple: you may define the representation in
primary storage but not in secondary. This is what the ARM prescribes. I
also would like to see this changed in Ada20XX.

On Mon, 2 Oct 2000 tmoran@bix.com wrote:

> >... I will get out what I expect.
>   type Temperature is new Integer range 60 .. 80;
>   for Temperature'size use 8; -- or 7
> Is a Temperature'Write going to produce one byte, because that's how
> big Temperature is, or 4 bytes, because that's how big Integer is?
>   type R is record
>     Speed : Long_Integer;
>   end record;
>   for R use record
>     S at 0 range 0 .. 7;
>   end record;
> Will an R'Write produce one byte for S, or 8 or what?
> 
> >A perfect solution would be controlled representation of the (tagged)
> >record types and a fast overlay of a Stream_Element_Array.
>   I remember this discussion, but not the bottom line.  What's wrong
> with
>   TAG_SIZE : constant := 4;
>   ...
>   type This_Buffer is new Buffer with record
>     Speed : Integer;
>     T : Temperature;
>   end record;
>   for This_Buffer use record
>     Speed at TAG_SIZE range 0 .. 7;
>     T at Tag_Size+1 range 0 .. 7;
>   end record;
> and then overlay a Stream_Element_Array?  (Or a
> System.Storage_Elements.Storage_Array?)
>   I'd rather trust to TAG_SIZE being 4, or at least a single thing to
> change, as I move between compilers, rather than trusting Stream stuff.
> 

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