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Re: C Code "sanity checking" tools

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Rainer Weikusat <rweikusat@mssgmbh.com> writes:
> Rainer Weikusat <rweikusat@mssgmbh.com> writes:
>
> [...]
>
>>>> >>>> http://www.di.unito.it/~damiani/ariane5rep.html
>
> [...]
>
>> But that's a rather tangential point: A 16-bit
>> variable overflowed. A runtime check for this caused the CPU to be
>> halted.
>
> Nevertheless, I'd like to clarify my original statement after
> rereading (the relevant parts of) the text: Using a particular
> programming language does not protect against "cannot happen"-coding
> and the Ada-code involved here had needed explicit overflow checks,
> combined with a sensible strategy for dealing with overflows, in
> exactly the same way as code which had been written in C had also
> needed them.
[...]

Yes, adding additional explicit overflow checks to the Ariane
4 code might have prevented the Ariane 5 failure.  It would also
have cost additional CPU time, code space, and perhaps other scarce
resources, to implement those checks.  The omission of the checks
was the result of a deliberate decision, based on the fact that
that particular value physically could not exceed a certain range,
and that therefore the expense of checking it was unneeded.

Documenting the reason for omitting that particular check *might*
also have prevented the Ariane 5 failure -- but I get the impression
that the documentation would not have been read even if it had
existed.  (This could easily be a false impression.)

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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C Code "sanity checking" tools Martin Crouch <spamspamspam@spaml.com> - 2011-08-08 12:00 +0100
  Re: C Code "sanity checking" tools Richard Kettlewell <rjk@greenend.org.uk> - 2011-08-08 12:09 +0100
    Re: C Code "sanity checking" tools Fritz Wuehler <fritz@spamexpire-201108.rodent.frell.theremailer.net> - 2011-08-09 08:50 +0200
      Re: C Code "sanity checking" tools Måns Rullgård <mans@mansr.com> - 2011-08-09 10:55 +0100
        Re: C Code "sanity checking" tools Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-08-09 14:15 +0100
        Re: C Code "sanity checking" tools Nomen Nescio <nobody@dizum.com> - 2011-08-10 01:58 +0200
        Re: C Code "sanity checking" tools Nomen Nescio <nobody@dizum.com> - 2011-08-10 12:29 +0200
      Re: C Code "sanity checking" tools Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-08-09 14:17 +0100
        Re: C Code "sanity checking" tools Keith Thompson <kst-u@mib.org> - 2011-08-09 09:17 -0700
          Re: C Code "sanity checking" tools Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-08-09 17:36 +0100
            Re: C Code "sanity checking" tools Keith Thompson <kst-u@mib.org> - 2011-08-09 12:19 -0700
              Re: C Code "sanity checking" tools Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-08-09 20:36 +0100
                Re: C Code "sanity checking" tools Michael Press <rubrum@pacbell.net> - 2011-08-09 19:24 -0700
                Re: C Code "sanity checking" tools Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-08-10 10:27 +0100
                Re: C Code "sanity checking" tools Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-08-10 14:01 +0100
                Re: C Code "sanity checking" tools "io_x" <a@b.c.invalid> - 2011-08-13 09:42 +0200
                Re: C Code "sanity checking" tools Keith Thompson <kst-u@mib.org> - 2011-08-13 16:04 -0700
                Re: C Code "sanity checking" tools Rainer Weikusat <rweikusat@mssgmbh.com> - 2011-08-14 19:46 +0100
  Re: C Code "sanity checking" tools Ian Collins <ian-news@hotmail.com> - 2011-08-08 23:12 +1200
    Re: C Code "sanity checking" tools Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-08-08 15:35 +0100
      Re: C Code "sanity checking" tools Martin Crouch <spamspamspam@spaml.com> - 2011-08-08 16:05 +0100
        Re: C Code "sanity checking" tools Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-08-08 22:57 +0100
          Re: C Code "sanity checking" tools Måns Rullgård <mans@mansr.com> - 2011-08-08 23:32 +0100
      Re: C Code "sanity checking" tools Ian Collins <ian-news@hotmail.com> - 2011-08-09 08:03 +1200
        Re: C Code "sanity checking" tools Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-08-08 22:51 +0100
          Re: C Code "sanity checking" tools Ian Collins <ian-news@hotmail.com> - 2011-08-09 10:01 +1200
    Re: C Code "sanity checking" tools jt@toerring.de (Jens Thoms Toerring) - 2011-08-08 22:06 +0000
      Re: C Code "sanity checking" tools Ian Collins <ian-news@hotmail.com> - 2011-08-09 10:18 +1200
        Re: C Code "sanity checking" tools jt@toerring.de (Jens Thoms Toerring) - 2011-08-08 23:25 +0000
  Re: C Code "sanity checking" tools Nobody <nobody@nowhere.com> - 2011-08-08 14:01 +0100
    Re: C Code "sanity checking" tools Måns Rullgård <mans@mansr.com> - 2011-08-08 14:47 +0100
      Re: C Code "sanity checking" tools Martin Crouch <spamspamspam@spaml.com> - 2011-08-08 16:08 +0100
        Re: C Code "sanity checking" tools Marc <marc.glisse@gmail.com> - 2011-08-08 15:39 +0000
      Re: C Code "sanity checking" tools William Ahern <william@wilbur.25thandClement.com> - 2011-08-08 10:20 -0700
      Re: C Code "sanity checking" tools Nobody <nobody@nowhere.com> - 2011-08-09 00:59 +0100
  Re: C Code "sanity checking" tools mathog <dmathog@gmail.com> - 2011-08-08 08:48 -0700

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