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From: Vinzent Hoefler <ada.rocks@jlfencey.com>
Newsgroups: comp.lang.ada
Subject: Re: Q re pack & aliased
Date: Wed, 23 Apr 2003 10:07:55 +0200
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Date: 2003-04-23T10:07:55+02:00
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tmoran@acm.org wrote:

>  The case at hand is a DIBitmap in Windows.  It needs to be in packed, =
24
>bit, format so I can pass it to Windows (not to mention size
>considerations).  I also need sometimes to make pointers to individual
>elements, so the components need to be aliased.

Well, why don't you do this, then?

|with Ada.Text_IO;
|
|procedure t is
|   type color is range 0 .. 2**8 - 1;
|   for color'Size use 8;
|
|   type triples is record
|      red,
|      green,
|      blue : color;
|   end record;
|   for triples'Size use 24;
|
|   type bunches is array (Integer range <>) of aliased triples;
|   x : bunches (1 .. 10);
|   for x'Size use 240;
|begin
|   x :=3D (1 =3D> (red =3D> 0, green =3D> 1, blue =3D> 1), others =3D> =
(0, 0, 0));
|   Ada.Text_IO.Put_Line (Integer'Image (x'Size / 80)
|                         & " should =3D 3, not 4");
|end t;

Probably some of the 'Size-attributes are not needed here (especially
the "x'Size use 240"-one), but I put them in to see if the compiler
warns about any of them. It doesn't and the generated code for the
assignment looks correct to me, too.

I don't know how this would fit into your existing code, but I guess,
a conversion between a 24-bit-type like you used before and the
triples-record is quite easy without breaking too much...


Vinzent.

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