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From: Martin Krischik <krischik@users.sourceforge.net>
Subject: Re: Contracted exceptions for Ada
Newsgroups: comp.lang.ada
Date: Sun, 09 Dec 2007 20:04:44 +0100
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Date: 2007-12-09T20:04:44+01:00
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Dmitry A. Kazakov wrote:

> On Sun, 09 Dec 2007 16:11:13 +0100, Martin Krischik wrote:
> 
>> Dmitry A. Kazakov wrote:
>> 
>>> (Maybe a wild guess, but this could save Ariane V. A program assumed
>>> Constraint_Error exception free was recompiled for the hardware where
>>> that was not the case.)
>> 
>> My understanding is that the system was brought down by an unexpected
>> hardware exception - i.E. one which the CPU's floating point unit
>> generated.
> 
> Yes, and that would be detected by the compiler:
> 
>    function Integer (X : Float) return Integer;
> 
> which was contracted as exception-free on one platform will not be on
> another. So the compiler would reject either its implementation that
> raises Constraint_Error or else its use contracted as
> Constraint_Error-free. So the idea.
> 
> (Contracted exceptions would mean a damn LOT of work for the compiler
> vendors.)

I forgot to mention mentioned that they used pragma Suppress to speed thing
up (the old 'pedia article mentioned that). With pragma Suppress  in place
the HW-exception was never converted into an Ada-exception.

Even the best exception handling won't help if you switch it off :-( .

Martin

-- 
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