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[Bug math/12786] cacosh sometimes returning wrong result for real values between -1 and 1
- From: "kreckel at ginac dot de" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: Wed, 23 Nov 2011 09:04:57 +0000
- Subject: [Bug math/12786] cacosh sometimes returning wrong result for real values between -1 and 1
- Auto-submitted: auto-generated
- References: <bug-12786-131@http.sourceware.org/bugzilla/>
http://sourceware.org/bugzilla/show_bug.cgi?id=12786
Richard B. Kreckel <kreckel at ginac dot de> changed:
What |Removed |Added
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CC| |kreckel at ginac dot de
--- Comment #3 from Richard B. Kreckel <kreckel at ginac dot de> 2011-11-23 09:04:57 UTC ---
(In reply to comment #1)
> Created attachment 5740 [details]
> proposed patch for 2.13 release
That patch only fixes a symptom and not the cause. A better patch has been
attached to BZ 13305.
The rounding errors in cacosh[fl] are a completely different problem and should
be analyzed and fixed separately. They are due to the argument of the final
clog(y) being close to 1. The instability of log(1+x) for small x are
well-known and have lead to the log1p function. I believe the rounding errors
in cacosh[fl] would go away if the clog(y) would be replaced by clog1p(y), if
that would exist.
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