Re: Mars lander crash

From	jacobnavia <jacob@jacob.remcomp.fr>
Newsgroups	comp.lang.c
Subject	Re: Mars lander crash
Date	2016-12-11 20:52 +0100
Organization	A noiseless patient Spider
Message-ID	<o2kame$cvb$1@dont-email.me> (permalink)
References	(8 earlier) <o2jgbu$ih7$1@dont-email.me> <87d1gyzhsd.fsf@bsb.me.uk> <o2k3vc$ahp$1@dont-email.me> <o2k5gi$ofr$1@dont-email.me> <o2k7c2$crl$1@dont-email.me>

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Le 11/12/2016 à 19:55, David Brown a écrit :

> The signal mechanism is okay for a "integer overflow causes crash"
> mechanism during testing.

OK. But you go on...

> But it is no use for a "overflow causes
> saturation",

No, since you can act on the info and return a result if you wish.
The compiler can generate tables of associations between operations and 
program counter values, so, the handler can just unwind the interrupt 
call and go on with a result in the right register if the compiler 
generates those tables and the runtime knows about it.

You can return a default result for the operation.

  or "overflow causes predictable wraparound",

I do not have any idea what a predictable wraparound could be.

> or "overflow
> detectable by the programmer at runtime",

A signal always should generate an action, but some people here insist 
that this is too much for them since they are using old machines. They 
think that it would be impossible to tell the compiler that in this 
function you want overflow check or not, and they bring all kinds of 
contrieved examples to prove that this is not good for the general case.


> or "overflow checked in
> advance" solution.

This doesn't look like a good idea for me, after the crash of that lander.

Maybe it wasn't overflow, but a saturation (whatever that means besides 
overflow) of the system with the noisy input data from sensors means 
that data was not laundered properly somehow isn't it?

How comes that the system thought that it was underground with a 
negative height that has been mentioned in several reports? We will know 
for sure when ESA reports exactly what happened but it looks like an 
overflow, a negative height.

In general, an overflow is an interesting condition where it should not 
happen. It means wrong input. Reacting to wrong inputs depends on the 
application, and surely some stuff is more sensitive than others...

What is interesting is the total absence of interest for treating the 
typical case, and that spotlight focus in old machines and obsolete 
stuff when we speak about C, even if machines have evolved immensely 
since only 10 years.

You have a sentimental link with that old MIPS processor? OK. Do not use 
this in that processor. But why all the other people that use better 
machines than that one should be put on hold?

> And for processors that don't have a suitable
> trapping mechanism such as an "add and trap on overflow" instruction or
> at least a "trap if overflow flag set" instruction, it would be
> hopelessly inefficient.
>

Yes, poor guys. They will not be able to do any overflow processing.

And so what?

Implicitely is the idea that C is for old machines only, and some better 
language for new software isn't it Mr Brown?

> And like all overflow detection mechanisms, you either wave goodbye to
> all sorts of optimisations based on the associativity and commutativity
> of integer arithmetic, or your results and possible overflows are
> totally dependent on the arrangement of code by the optimiser.
>

That is a quality of implementation issue. If your code analysis is 
unable to move several instructions as a block you should upgrade to a 
better one, what do you want me to do. I did not write you optimizer but 
shouldn't we check for overflow Mr Brown? I mean, OK, that mips machine 
and your strange optimizer can't cope. But that means that all people 
doing C in a modern environment should be hold down waiting that those 
situations improve?

> So again, this is /one/ possible type of overflow detection that may be
> of use to some people during testing and debugging.  This might be
> enough to make it worth the effort implementing it - but it is very far
> from being a universal, useful, efficient and helpful method that could
> sensibly be standardised in C.
>

The situation is already solved anyway. The C standard specifically 
prescribes SIGFPE for overflow. So actually it is that none of the C 
compilers implement this. I think this is totally wrong. It should be 
stressed to the main compiler people that the user has the right to 
receive SIGFPE when an overflow occurs as specified in
7.14 when defining the signals available:
<quote>
SIGFPE an erroneous arithmetic operation, such as zero divide or an 
operation resulting in overflow
<end quote>

Thread

Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-09 13:26 +0100
  Re: Mars lander crash Richard Heathfield <rjh@cpax.org.uk> - 2016-12-09 12:44 +0000
    Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-09 14:53 +0100
      Re: Mars lander crash already5chosen@yahoo.com - 2016-12-09 05:58 -0800
        Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-09 15:11 +0100
        Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-09 16:56 +0100
          Re: Mars lander crash supercat@casperkitty.com - 2016-12-09 08:51 -0800
          Re: Mars lander crash already5chosen@yahoo.com - 2016-12-11 02:23 -0800
            Re: Mars lander crash Gareth Owen <gwowen@gmail.com> - 2016-12-11 10:57 +0000
          Re: Mars lander crash "James R. Kuyper" <jameskuyper@verizon.net> - 2016-12-11 12:34 -0500
            Re: Mars lander crash Robert Wessel <robertwessel2@yahoo.com> - 2016-12-11 23:33 -0600
      Re: Mars lander crash Richard Heathfield <rjh@cpax.org.uk> - 2016-12-09 14:22 +0000
        Re: Mars lander crash asetofsymbols@gmail.com - 2016-12-09 06:30 -0800
          Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-09 15:48 +0100
        Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-09 15:46 +0100
          Re: Mars lander crash Richard Heathfield <rjh@cpax.org.uk> - 2016-12-09 14:55 +0000
            Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-09 16:08 +0100
              Re: Mars lander crash Richard Heathfield <rjh@cpax.org.uk> - 2016-12-09 15:52 +0000
          Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-09 17:35 +0100
            Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-09 18:35 +0100
              Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-09 19:10 +0100
                Re: Mars lander crash "James R. Kuyper" <jameskuyper@verizon.net> - 2016-12-09 19:18 -0500
                Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-09 16:49 -0800
                Re: Mars lander crash "J. Clarke" <j.clarke.873638@gmail.com> - 2016-12-20 20:03 -0500
                Re: Mars lander crash <william@wilbur.25thandClement.com> - 2016-12-09 22:04 -0800
                Re: Mars lander crash supercat@casperkitty.com - 2016-12-10 10:59 -0800
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-11 13:22 +0100
                Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 14:18 +0100
                Re: Mars lander crash already5chosen@yahoo.com - 2016-12-11 06:03 -0800
                Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 15:08 +0100
                Re: Mars lander crash already5chosen@yahoo.com - 2016-12-11 06:20 -0800
                Re: Mars lander crash luser droog <luser.droog@gmail.com> - 2016-12-11 07:08 -0800
                Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-11 11:56 -0800
                Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 21:05 +0100
                Re: Mars lander crash jameskuyper@verizon.net - 2016-12-11 12:57 -0800
                Re: Mars lander crash Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-11 21:26 +0000
                Re: Mars lander crash supercat@casperkitty.com - 2016-12-11 09:23 -0800
                Re: Mars lander crash Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-11 14:01 +0000
                Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 15:11 +0100
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-11 18:57 +0100
                Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 19:23 +0100
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-11 19:55 +0100
                Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 20:52 +0100
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-11 23:37 +0100
                Re: Mars lander crash supercat@casperkitty.com - 2016-12-11 16:10 -0800
                Re: Mars lander crash BartC <bc@freeuk.com> - 2016-12-12 01:13 +0000
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-12 09:53 +0100
                Re: Mars lander crash supercat@casperkitty.com - 2016-12-12 08:30 -0800
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-12 09:25 +0100
                Re: Mars lander crash supercat@casperkitty.com - 2016-12-11 10:36 -0800
                Re: Mars lander crash Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-11 18:46 +0000
                Re: Mars lander crash supercat@casperkitty.com - 2016-12-11 09:12 -0800
                Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 18:53 +0100
                Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-11 12:09 -0800
                Re: Mars lander crash Jean-Marc Bourguet <jm@bourguet.org> - 2016-12-11 21:30 +0100
                Re: Mars lander crash Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2016-12-11 15:50 -0500
                Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-11 23:02 +0100
                Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-11 18:29 -0800
                Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-11 12:03 -0800
                Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-11 11:55 -0800
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-11 23:42 +0100
                Re: Mars lander crash Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-11 14:53 -0800
                Re: Mars lander crash Ian Collins <ian-news@hotmail.com> - 2016-12-12 17:09 +1300
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-12 10:00 +0100
                Re: Mars lander crash Ian Collins <ian-news@hotmail.com> - 2016-12-12 22:20 +1300
                Re: Mars lander crash Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-12 01:28 -0800
                Re: Mars lander crash Ian Collins <ian-news@hotmail.com> - 2016-12-12 22:38 +1300
                Re: Mars lander crash Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-12 02:43 -0800
                Re: Mars lander crash Ian Collins <ian-news@hotmail.com> - 2016-12-13 08:20 +1300
                Re: Mars lander crash Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-12 12:57 -0800
                Re: Mars lander crash Ian Collins <ian-news@hotmail.com> - 2016-12-13 14:14 +1300
                Re: Mars lander crash Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-13 01:19 -0800
                Re: Mars lander crash Ian Collins <ian-news@hotmail.com> - 2016-12-13 22:56 +1300
                Re: Mars lander crash Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-13 05:16 -0800
                Re: Mars lander crash Ian Collins <ian-news@hotmail.com> - 2016-12-14 18:05 +1300
                Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-13 08:19 -0800
                Re: Mars lander crash Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-13 17:01 +0000
                Re: Mars lander crash Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-13 10:48 -0800
                Re: Mars lander crash Geoff <geoff@invalid.invalid> - 2016-12-13 11:56 -0800
                Re: Mars lander crash Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-13 13:37 -0800
                Re: Mars lander crash Geoff <geoff@invalid.invalid> - 2016-12-13 19:11 -0800
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-13 20:13 +0100
                Re: Mars lander crash supercat@casperkitty.com - 2016-12-13 11:45 -0800
                Re: Mars lander crash Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-13 23:10 +0000
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-14 10:18 +0100
                Re: Mars lander crash Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-14 12:37 +0000
                Re: Mars lander crash Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-14 21:31 -0800
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-15 13:26 +0100
                Re: Mars lander crash Ian Collins <ian-news@hotmail.com> - 2016-12-12 22:40 +1300
                Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-12 13:22 +0100
                Re: Mars lander crash supercat@casperkitty.com - 2016-12-12 08:35 -0800
        Re: Mars lander crash supercat@casperkitty.com - 2016-12-09 08:43 -0800
      Re: Mars lander crash Jerry Stuckle <jstucklex@attglobal.net> - 2016-12-09 09:47 -0500
        Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-09 16:11 +0100
          Re: Mars lander crash Jerry Stuckle <jstucklex@attglobal.net> - 2016-12-09 10:49 -0500
  Re: Mars lander crash already5chosen@yahoo.com - 2016-12-09 05:53 -0800
    Re: Mars lander crash asetofsymbols@gmail.com - 2016-12-09 06:04 -0800
      Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-09 15:09 +0100
        Re: Mars lander crash Jerry Stuckle <jstucklex@attglobal.net> - 2016-12-09 10:06 -0500
          Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-09 16:32 +0100
    Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-09 17:30 +0100
      Re: Mars lander crash BartC <bc@freeuk.com> - 2016-12-09 16:42 +0000
      Re: Mars lander crash Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2016-12-09 11:43 -0500
      Re: Mars lander crash Keith Thompson <kst-u@mib.org> - 2016-12-09 08:59 -0800
      Re: Mars lander crash "J. Clarke" <j.clarke.873638@gmail.com> - 2016-12-20 19:36 -0500
  Re: Mars lander crash "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-12-09 06:46 -0800
    Re: Mars lander crash Richard Heathfield <rjh@cpax.org.uk> - 2016-12-09 14:57 +0000
      Re: Mars lander crash Noob <root@127.0.0.1> - 2016-12-09 16:07 +0100
    Re: Mars lander crash David Brown <david.brown@hesbynett.no> - 2016-12-09 16:03 +0100
      Re: Mars lander crash "James R. Kuyper" <jameskuyper@verizon.net> - 2016-12-09 12:41 -0500
    Re: Mars lander crash Jerry Stuckle <jstucklex@attglobal.net> - 2016-12-09 10:52 -0500
      Re: Mars lander crash jameskuyper@verizon.net - 2016-12-09 12:13 -0800
        Re: Mars lander crash jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-09 21:56 +0100
          Re: Mars lander crash jameskuyper@verizon.net - 2016-12-09 14:11 -0800
        Re: Mars lander crash Jerry Stuckle <jstucklex@attglobal.net> - 2016-12-09 22:46 -0500
          Re: Mars lander crash <william@wilbur.25thandClement.com> - 2016-12-09 22:34 -0800
          Re: Mars lander crash James Kuyper <jameskuyper@verizon.net> - 2016-12-10 18:38 -0500
      Re: Mars lander crash Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-11 06:06 -0800
  Re: Mars lander crash "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-12-10 01:17 +0800
  Re: Mars lander crash Ken Brody <kenbrody@spamcop.net> - 2016-12-13 14:28 -0500
  Re: Mars lander crash Ken Brody <kenbrody@spamcop.net> - 2016-12-13 14:30 -0500

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