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From: Simon Wright <simon.j.wright@mac.com>
Newsgroups: comp.lang.ada
Subject: Re: generic function and overloading
Date: Thu, 18 Oct 2007 21:20:52 +0100
Organization: Pushface
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Date: 2007-10-18T21:20:52+01:00
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Robert A Duff <bobduff@shell01.TheWorld.com> writes:

> But do you really want to do arithmetic on these types,
> as well as setting/clearing bits?  If all you want to
> do is set/clear bits, you might want to consider using
> a packed array of Boolean.  Then to set the Nth bit you
> can say:
>
>     X (N) := True;
>
> Alternatively, a packed array of type Bit, where:
>
>     type Bit is range 0..1;
>
> If the individual bit numbers have some specific meaning,
> the index type could be an enumeration type.

Will give surprising results on a big-endian machine. At least code
using shifts and masks is portable if gruesome -- and no more gruesome
than code I've written which says

   type Unrepresented is ..
   Internal : Unrepresented;
   ...

   if System.Default_Bit_Order = System.High_Order_First then
      declare
         type Represented is ..
         for Represented use ..
            -- record rep with big-endian usage
         External : constant Represented := Internal;
      begin
         Output (External);
      end;
   else
      --  equivalent for l-e