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[Bug math/16339] log1p missing underflows
- From: "zimmerma+gcc at loria dot fr" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Wed, 29 Jan 2014 12:00:45 +0000
- Subject: [Bug math/16339] log1p missing underflows
- Auto-submitted: auto-generated
- References: <bug-16339-131 at http dot sourceware dot org/bugzilla/>
https://sourceware.org/bugzilla/show_bug.cgi?id=16339
Paul Zimmermann <zimmerma+gcc at loria dot fr> changed:
What |Removed |Added
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CC| |zimmerma+gcc at loria dot fr
--- Comment #1 from Paul Zimmermann <zimmerma+gcc at loria dot fr> ---
on the other hand we get some spurious underflow exceptions, for example for
long double on x86_64:
Testing function log1p for exponent 16383 [seed=8473].
rounding mode MPFR_RNDD:
wrong underflow flag: mpfr gives 0, library 16
x=-3.36210314311209350626e-4932
library gives -3.36210314311209350626e-4932
mpfr gives -3.36210314311209350663e-4932
The glibc result is incorrect since log(1+x) = x - x^2/2 + o(x^2), thus it is
smaller than x for tiny x, and rounding down should give nextbelow(x).
Since |x| is the smallest normal number, no underflow exception should be
raised.
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