Re: About the F-22 software bug

[Phil Clayton <phil.clayton@lineone.net>]

On Feb 5, 9:02 am, Martin <martin.do...@btopenworld.com> wrote:
> On Feb 5, 8:52 am, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
>
>
>
> > Martin wrote on comp.lang.ada:
>
> > > On Feb 5, 6:42 am, Dennis Lee Bieber <wlfr...@ix.netcom.com> wrote:
> > > > On Thu, 04 Feb 2010 19:46:15 +0100, Pascal Obry <pas...@obry.net>
> > > > declaimed the following in comp.lang.ada:
> > > > > I know that the F-22 is 90% of Ada. Is there some public information
> > > > > about this bug? Is that a design bug?
>
> > > >         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 longitude.
>
> > > >         I didn't hear that they had to follow the tankers back -- was under
> > > > the impression once they managed to cross back heading east a reboot of
> > > > the navigation system started working again...
>
> > > > --
> > > >         Wulfraed         Dennis Lee Bieber               KD6MOG
> > > >         wlfr...@ix.netcom.com HTTP://wlfraed.home.netcom.com/
>
> > > For some reason (that I don't get at all) lots of systems define long
> > > as -180 <= x <= +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 <= 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 <= x <(=) +180...always - check any map / globe!!
>
> Lat is always -90 <= x <= +90 deg - no doubt about that one :-)
>
> Adding "shifts" would make understanding any problem very hard...
>
> "So the position coming in is (+40, -100) but what's that inside the
> code again????"

Interesting to see that 'cyclic fixed point types' are under
discussion:

http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ai05s/ai05-0175-1.txt?rev=1.2

http://www.ada-auth.org/ai-files/minutes/min-0911.html#AI175

Phil