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| From | Richard Heathfield <rjh@cpax.org.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Mars lander crash |
| Date | 2016-12-09 14:55 +0000 |
| Organization | Fix this later |
| Message-ID | <o2eghr$d3o$1@dont-email.me> (permalink) |
| References | <o2e7s1$ea6$1@dont-email.me> <o2e8sg$hp7$1@dont-email.me> <o2ecu8$v73$1@dont-email.me> <o2eel2$614$1@dont-email.me> <o2eg20$b90$1@dont-email.me> |
On 09/12/16 14:46, David Brown wrote:
> On 09/12/16 15:22, Richard Heathfield wrote:
>> On 09/12/16 13:53, David Brown wrote:
>>> On 09/12/16 13:44, Richard Heathfield wrote:
>
> <snip the bits we are clear on>
>
>>>> If that's what went wrong (and it's not entirely clear whether an
>>>> overflow was responsible, but let's assume it was), then that is clear
>>>> evidence of inadequate testing of the software. In such circumstances,
>>>> an implementation that tests every operation for overflow would have
>>>> been an invaluable testing tool.
>>>
>>> I agree about inadequate testing of the software. I don't agree that
>>> testing all operations for overflow is helpful. That merely introduces
>>> a vast number of code paths that cannot be taken, cannot be tested, and
>>> cannot be verified.
>>
>> I don't see how you derive that conclusion from what I wrote. Let us
>> assume that, /without/ overflow checking, we have a battery of, say, a
>> million tests. (This is rocket science, after all. But it's just a
>> number. Don't get hung up on it.) And these million tests can be run in,
>> say, a week. I see no harm, and some gain, in adding overflow checking
>> during these existing tests. Cost? Maybe it runs in 169 hours instead of
>> 168. No big deal. Potential value in terms of discovering an otherwise
>> hidden overflow? Possibly considerable. It's not something I would turn
>> down unless there were a very good reason to turn it down.
>
> In the tests without overflow checking, you have code like this:
>
> if (a) {
> x = y + z;
> }
>
> This gives you two paths to check, one of which involves a calculation.
>
> If you add overflow checking, you have this:
>
> if (a) {
> x = y + z;
> if (overflow) {
> doSomethingAboutTheOverflow();
> }
> }
No no no no no no no!
No.
No, we're talking about the *implementation* inserting code. Your source
code does not change *at all*. And you can switch it off. If you're
concerned that the introduction of the implementation's overflow check
creates hidden code paths within the object code (and that's a perfectly
reasonable concern), then here's what you do:
1) run the tests /without/ overflow checking. 168 hours. Fine,
everything passed --- keep going as if all is well (because, as far as
you know, it is), BUT...
2) find an old computer that's propping open a door, and set it to
running the same tests, this time with overflow checking enabled. 169
hours of electricity, but it's not holding you up. In fact, it *only*
holds you up if, 169 hours later, it says "BEEP! I found an overflow!"
in which case you surely do want to know about it.
<snip> - and, in the bit I snipped, you cover some of the above, so I
think we may be in violent agreement.
--
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within
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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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