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From: Ken Garlington <garlingtonke@lmtas.lmco.com>
Subject: Re: Rules for Representation of Subtypes
Date: 1996/10/01
Message-ID: <325155A5.2E50@lmtas.lmco.com>#1/1
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references: <mheaney-ya023080002209961353500001@news.ni.net>
 <1996Sep28.155354.1@eisner> <DyGwtp.Bs1@world.std.com>
 <1996Sep29.082143.1@eisner> <DyKCDB.IrI@world.std.com>
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organization: Lockheed Martin Tactical Aircraft Systems
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Date: 1996-10-01T00:00:00+00:00
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Robert A Duff wrote:
> 
> In article <1996Sep29.082143.1@eisner>,
> Larry Kilgallen <kilgallen@eisner.decus.org> wrote:
> >But my X'valid should still work.  And compilers are not allowed to
> >change the flow of a program.
> >
> >       X := my_unchecked_conversion(Y);
> >
> >       if X'valid
> 
> It depends on how you instantiated my_unchecked_conversion.  If you used
> a constrained integer, such that some values of Y will produce
> out-of-range results, then it's erroneous, and the 'Valid will *not*
> work.  Hence, my advice to always unchecked_convert to types that match
> the hardware.

I seem to remember some AI about using unchecked_conversion when the sizes of X and 
Y are different. Maybe it's compiler dependent, but I thought you were at least 
guaranteed that the unchecked_conversion of Y would _fit_ into the space allocated 
for X, although of course Y might be outside the range of X. In that case, X'Valid 
should work, shouldn't it?

> 
> - Bob

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