Re: How would Ariane 5 have behaved if overflow checking were not turned off?

[KK6GM <mjsilva@scriptoriumdesigns.com>]

On Mar 14, 8:49 am, Elias Salomão Helou Neto <eshn...@gmail.com>
wrote:
> I have followed the (quite lenghty) on a topic, IIRC, about bitwise
> operators, which eventually lead to people mentioning the Ariane 5
> case.
>
> Since then I have been wondering. If compiler checking where actually
> turned on, what would have happened? How could it avoid the disaster?
>
> Right now I think of three possibilities, the two former seem very
> unlikely to me.
>
> a) It would, even if the problem went undetected during testing, have
> made the developers actually develop code handling this exceptional
> possibility.
>
> b) The compiler default action for unhandled overflows have saved the
> day;
>
> c) Developers would probably ignore the exceptional flow path and the
> disaster would happen anyway.
>
> Which one, if any, is close to reality?

To be clear, "overflow checking" was not turned off.  It was, rather,
left to the default handling for the conversion in question.  The
default handling was designed based on the assumption that anything
that triggered it was due to a hardware problem.  So the two other
options would have been (a) have the default handling ignore ALL range
errors (really?!!), or add custom exception handling to the conversion
in question.  In that case, what would the exception handling have
done differently, and by what justification?

It really all comes back to the essential question, if variable X is
known, PROVEN, to never exceed the range A..B, and suddenly it does
exceed that range, what is the correct action?  You can't just throw
it away and read it again, since in the Ariane 5 case it would have
continued to exceed its proven valid range.  So what do you do?