From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Thread: a07f3367d7,16f1030bd366bf59 X-Google-Attributes: gida07f3367d7,public,usenet X-Google-NewGroupId: yes X-Google-Language: ENGLISH,ASCII Path: g2news1.google.com!postnews.google.com!m16g2000yqc.googlegroups.com!not-for-mail From: Martin Newsgroups: comp.lang.ada Subject: Re: About the F-22 software bug Date: Fri, 5 Feb 2010 03:18:35 -0800 (PST) Organization: http://groups.google.com Message-ID: References: <4b6b15d2$0$929$ba4acef3@news.orange.fr> <4YKdnVFQX_suIPbWnZ2dnUVZ_rednZ2d@earthlink.com> <3050ef55-5dde-40ed-8a8f-a2daf245bf86@k19g2000yqc.googlegroups.com> NNTP-Posting-Host: 20.133.0.8 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: posting.google.com 1265368715 24065 127.0.0.1 (5 Feb 2010 11:18:35 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Fri, 5 Feb 2010 11:18:35 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: m16g2000yqc.googlegroups.com; posting-host=20.133.0.8; posting-account=g4n69woAAACHKbpceNrvOhHWViIbdQ9G User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7,gzip(gfe),gzip(gfe) Xref: g2news1.google.com comp.lang.ada:8906 Date: 2010-02-05T03:18:35-08:00 List-Id: On Feb 5, 10:31=A0am, "Dmitry A. Kazakov" wrote: > On Fri, 5 Feb 2010 01:02:40 -0800 (PST), Martin wrote: > > On Feb 5, 8:52=A0am, Ludovic Brenta wrote: > >> Martin wrote on comp.lang.ada: > > >>> On Feb 5, 6:42=A0am, Dennis Lee Bieber wrote: > >>> > On Thu, 04 Feb 2010 19:46:15 +0100, Pascal Obry > >>> > declaimed the following in comp.lang.ada: > >>> > > I know that the F-22 is 90% of Ada. Is there some public informat= ion > >>> > > about this bug? Is that a design bug? > > >>> > =A0 =A0 =A0 =A0 So far as I recall -- from some years ago -- it was= an algorithm > >>> > problem handling position information wrap-around from crossing, as > >>> > mentioned, the International Dateline... -180.0 to +180.0 deg longi= tude. > > >>> > =A0 =A0 =A0 =A0 I didn't hear that they had to follow the tankers b= ack -- was under > >>> > the impression once they managed to cross back heading east a reboo= t of > >>> > the navigation system started working again... > > >>> > -- > >>> > =A0 =A0 =A0 =A0 Wulfraed =A0 =A0 =A0 =A0 Dennis Lee Bieber =A0 =A0 = =A0 =A0 =A0 =A0 =A0 KD6MOG > >>> > =A0 =A0 =A0 =A0 wlfr...@ix.netcom.com HTTP://wlfraed.home.netcom.co= m/ > > >>> For some reason (that I don't get at all) lots of systems define long > >>> as -180 <=3D x <=3D +180 degrees. > > >>> Having the potential to alias a position seems like a bad idea for a > >>> start, so when I've been coding such systems up, I've always spent a > >>> bit of time making it convert positions into the range -180 <=3D x < > >>> +180 degrees and using a proper ADT. > > >>> I wonder if it was anything to do with that?... > > >> I would have thought a longitude was really a mod 360, shifted by -180 > >> for display purposes? For fractional degrees (i.e. minutes and > >> seconds), make that mod (360 * 60 * 60), shift by -180 * 60 * 60 and > >> split in degrees, minutes and seconds when displaying. > > >> -- > >> Ludovic Brenta. > > > No...it's -180 <=3D x <(=3D) +180...always - check any map / globe!! > > > Lat is always -90 <=3D x <=3D +90 deg - no doubt about that one :-) > > > Adding "shifts" would make understanding any problem very hard... > > And shift does not solve the problem anyway, if that existed. The potenti= al > problem is that the angle is not a real number. It could be represented b= y > one, but then the operations like +, -, *, /, =3D, /=3D must be replaced = and > ones like <, >, <=3D, >=3D disallowed. With that done the value +180 woul= d do > no harm, because -180 =3D +180 in terms of proper ADT operations. You sim= ply > would not be able to distinguish them (without tricks like > Unchecked_Conversion). > > -- > Regards, > Dmitry A. Kazakovhttp://www.dmitry-kazakov.de Yup, instead you end up with functions like "Is_Between (Anlge, First, Last : Longitude) return Boolean" Although because have 'clever' construct functions "Longitude (From : Float)" that always put things in the 'correct' range (-180 <=3D x < 180), we could allow "=3D" (and "/=3D"). Cheers -- Martin