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List:       freebsd-hackers
Subject:    Re: [tobi@caida.org: Re: [MRTG-DEV] CDEF's with LT and IF in .42]
From:       Dan Nelson <dnelson () emsphone ! com>
Date:       1999-06-30 15:39:10
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In the last episode (Jun 30), Jos Backus said:
> ----- Forwarded message from Tobi Oetiker <tobi@caida.org> -----
> > OK found your problem .... it is that old FreeBSD does no proper
> > IEEE math ...
> > 
> > for some comparison operations it raises an sigfpe if an NaN is
> > involved ...
> >
> > the next release of rrdtool will come with a proper test to find
> > the problem and a proper fix in the software to ignore sigfpe
>
> Saw this on the MRTG-DEV list.
> NaN handling is perceived to be problematic, it seems.

The last time this came up (and it comes up every 6 months or so), the
consensus was that we would rather trap FP errors than blindly pass
them on to the user application.  If a program wants to ignore NaN,
divide-by-zero, underflow, and overflow conditions, let it wrap the
offending line of code with two fpsetmask() calls; one to mask the
condition, and one to restore the previous mask.  If you want to
completely ignore floating point errors, call fpsetmask(0) at the top
of main().

I scanned the mailinglists and the thread that covers this issue most
completely is

http://www.freebsd.org/cgi/mid.cgi?id=199710101907.OAA09470@millenia.srrc.usda.gov
 
	-Dan Nelson
	dnelson@emsphone.com


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