Re: Ariane 5 failure

[Ken Garlington <garlingtonke@lmtas.lmco.com>]

Marin David Condic, 561.796.8997, M/S 731-93 wrote:
> 
> robin <rav@GOANNA.CS.RMIT.EDU.AU> writes:
> >---The issue was not the addition of a new exception handler.
> >The issue was that a magnitude check should have been
> >performed on a conversion from double precision floating
> >point to 16-bit integer, but it wasn't.
> >Of course, having an exceptin handler for this specific purpose
> >would have helped, and should have been included as a fallback.
> >
> >        >Assuming that a new exception _handler_ had been added, then it _might
> >made
> >        >a difference.
> >
> >You can be absolutely certain that it would have helped.
> >
>     procedure ARIANE_FIVE_OPERATION is
>         X   : FLOAT range -65536.0..65535.0 := 65535.0 ;
>         Y   : INTEGER range -32768..32767 := 0 ;
>     begin
>         if (X not in -32768.0..32767.0) then
>             SHUT_DOWN_THE_CHANNEL_AND_PASS_CONTROL_TO_THE_OTHER_SIDE ; --Boom!
>         else
>             Y := INTEGER (X) ;
>         end if ;
>     end ARIANE_FIVE_OPERATION ;
> 
>     *Absolutely* certain?

Well, in PL/I, it won't permit an exception handler to shut down the channel. :)

(I wasn't going to answer the silly assertion posted above, but I'm glad someone
did.)

> 
>     Seems that the above algorithm *DOES* have runtime checks to
>     constrain the assignment of a float to an integer, yet the
>     accommodation is still a *BAD* engineering decision. We can polish
>     and polish and polish the software all we want and perform all
>     sorts of runtime checks, but if the accommodation remains wrong,
>     we're polishing a turd.
> 
>     MDC
> 
> Marin David Condic, Senior Computer Engineer    ATT:        561.796.8997
> M/S 731-96                                      Technet:    796.8997
> Pratt & Whitney, GESP                           Fax:        561.796.4669
> P.O. Box 109600                                 Internet:   CONDICMA@PWFL.COM
> West Palm Beach, FL 33410-9600                  Internet:   CONDIC@FLINET.COM
> ===============================================================================
>     "If you don't say anything, you won't be called on to repeat it."
> 
>         --  Calvin Coolidge
> ===============================================================================

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