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From: Robert Dewar <robert_dewar@my-dejanews.com>
Subject: Re: Question for the folks who designed Ada95
Date: 1999/04/27
Message-ID: <7g3b5g$p92$1@nnrp1.dejanews.com>#1/1
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References: <7g2qu4$ca4$1@usenet.rational.com>
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Date: 1999-04-27T00:00:00+00:00
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In article <7g2qu4$ca4$1@usenet.rational.com>,
  "Corey Ashford" <yeroca@rocketmail.com> wrote:
>
> The problem with the interfaces package shift
> operators is that they have fixed types.  So it's
> difficult to write code for types whose size can vary.

What we do in GNAT to address this problem is to make the
shift operators intrinsics. Here is a typical declaration
from the Interfaces spec:

   pragma Import (Intrinsic, Shift_Left);

The nice thing about this approach is that indeed you
*can* apply this intrinsic to a user defined type. For
example you can put the following in your code.


  type My_Modular is mod 2**Integer'Size;
  function Shift_Left
     (Value  : My_Modular;
      Amount : Natural)
      return   My_Modular;
  pragma Import (Intrinsic, Shift_Left);

and this will work fine. Of course this is not guaranteed
to be portable (perhaps the ARG should look at this one,
since it is a perfectly legitimate implementation
decision).



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