Path: csiph.com!x330-a1.tempe.blueboxinc.net!newsfeed.hal-mli.net!feeder3.hal-mli.net!nx02.iad01.newshosting.com!newshosting.com!news-out.readnews.com!transit3.readnews.com!postnews.google.com!z15g2000pre.googlegroups.com!not-for-mail From: lewbloch Newsgroups: comp.lang.java.programmer,comp.lang.c Subject: Re: Arithmetic overflow checking Date: Tue, 12 Jul 2011 14:48:47 -0700 (PDT) Organization: http://groups.google.com Lines: 37 Message-ID: <693db00d-83be-4830-a1fc-262d9d34d672@z15g2000pre.googlegroups.com> References: <9LWdnZH2hdfmyYvTnZ2dnUVZ_vidnZ2d@posted.palinacquisition> <3797038f-22d1-40b2-8c12-60db5a0976b8@t5g2000yqj.googlegroups.com> <4e1bf1bc$0$15671$4fafbaef@reader2.news.tin.it> <36bp17tf79bhbd6hovf9srhmcs1jh1c040@4ax.com> NNTP-Posting-Host: 172.19.13.20 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: posting.google.com 1310507328 9459 127.0.0.1 (12 Jul 2011 21:48:48 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Tue, 12 Jul 2011 21:48:48 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: z15g2000pre.googlegroups.com; posting-host=172.19.13.20; posting-account=CP-lKQoAAAAGtB5diOuGlDQk0jIwmH0T User-Agent: G2/1.0 X-Google-Web-Client: true X-Google-Header-Order: ASELCHRU X-HTTP-UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.41 Safari/535.1,gzip(gfe) Xref: x330-a1.tempe.blueboxinc.net comp.lang.java.programmer:6135 comp.lang.c:8197 Martin Gregorie wrote: > Gene Wirchenko wrote: >> =A0 =A0 =A0I also suggest that they build a time machine and go for a ri= de >> on a certain Ariane 5 launch. > > An out-of-range signal might have been the initial clause[1] but the real > problem was that this exception caused an diagnostic bit pattern to be > written to the SRI's (Inertial Reference System's) normal output channel, > where the OBC (On Board Computer) interpreted it as flight data by > failing to recognise it as an exception message. Unfortunately, by > treating it as flight data, the OBC interpreted it as requiring full > engine deflection, causing the Ariane 5 to yaw violently. Unsurprisingly, > being side-on at high airspeed caused it to break up. > > There real cause of the crash was using a poorly documented A4 SRI > without fully understanding its designed-in operating parameters or > ensuring that they were reset to interpret standard A5 operating > conditions as normal and within limits and then compounding the problem > by not designing the OBC to recognise SRI exception messages. > > IOW, this crash was more a case of poor documentation and design rather > than arithmetic overflow. > > The full report is here:http://www.di.unito.it/~damiani/ariane5rep.html > > [1] The instrument causing the problem was an unmodified Ariane 4 SRI > which raised an out-of-limits exception when the normal Ariane 5 > trajectory exceeded a permitted Ariane 4 horizontal velocity limit. =A0 > In other words, this was a case where there *was* an out-of-range exception, thus it makes the exact opposite point to the one Gene presumably wanted to support. -- Lew