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From: Samuel Tardieu <sam@ada.eu.org>
Subject: Re: Interfacing Ada to C
Date: 1997/05/29
Message-ID: <m3afle72cl.fsf@zaphod.enst.fr>#1/1
X-Deja-AN: 244738364
Sender: sam@zaphod.enst.fr
References: <5mjvk9$sm7$1@luna.ffi.no>
To: ruw@ffi.no (Rune Wemberg)
Organization: Sam's machine
Newsgroups: comp.lang.ada
Date: 1997-05-29T00:00:00+00:00
List-Id: <comp.lang.ada>


>>>>> "Rune" == Rune Wemberg <ruw@ffi.no> writes:

Rune> Does anyone know what a packed Ada record is?

It's a record on which you apply a pragma Pack. For example, the
following type R is a packed record:

  type My_Natural is range 0 .. 15;
  for My_Natural'Size use 4;

  type R is record
    A, B : My_Natural;
  end record;
  pragma Pack (R);
  for R'Size use 8;

If you do:

  My_R : aliased constant R := (1, 2);

then My_R will be represented in memory by a single byte containing
00010010 (or 00100001, depending on the endianness).

Here is the code generated by GNAT for the m68k:

.data
_t__my_r:
        .byte 0x12

Hope this helps.

  Sam
-- 
Samuel Tardieu -- sam@ada.eu.org