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From: "G.B." <bauhaus@futureapps.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Addressing in Object Ada v/s GNAT (2013) showing Vast Differences
Date: Thu, 10 Sep 2015 14:34:16 +0200
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Date: 2015-09-10T14:34:16+02:00
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On 10.09.15 12:47, Lucas Redding wrote:
> I need to change the alignment of each underlying type mapped into memory. I am hoping the combination of explicit alignments and precise rep clauses (size etc.) should make the code portable between compilers.

You are certainly aware of mappings that can be effected
by just using a type conversion? This way, some of the less
portable representations can be stashed away.

package P is

    type T1 is range 1 .. 10;
    type T2 is range -1_000 .. +1_000;

    type Internal is record
       A : T1;
       B : T2;
    end record;

    type Mapped is new Internal;

    for Mapped'Size use 32;
    for Mapped'Alignment use 1;
    for Mapped use record
       A at 0 range 0 .. 7;
       B at 0 range 11 .. 30;
    end record;

end P;

with P;
procedure Test_P is
    Z : P.Mapped;
    pragma Volatile (Z);

    procedure Place (Value : P.Internal) is
    begin
       Z := P.Mapped (Value);
       pragma Inspection_Point (Z);
    end Place;

begin
    Place( P.Internal'(A => 3, B => 42) );
end Test_P;