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[Bug math/15235] Spurious underflow exception for expl ldbl128-ibm
- From: "joseph at codesourcery dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Wed, 06 Mar 2013 15:03:16 +0000
- Subject: [Bug math/15235] Spurious underflow exception for expl ldbl128-ibm
- Auto-submitted: auto-generated
- References: <bug-15235-131@http.sourceware.org/bugzilla/>
http://sourceware.org/bugzilla/show_bug.cgi?id=15235
--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2013-03-06 15:03:16 UTC ---
On Wed, 6 Mar 2013, azanella at linux dot vnet.ibm.com wrote:
> I followed your idea on 28afd92dbdb4fef4358051aad5cb944a9527a4b5 where
> you added a libc_feholdexcept_setround (&env, FE_TONEAREST) (later
> replaced to SET_RESTORE_ROUND (FE_TONEAREST)).
The point of that patch was that precision-extension techniques
(a) generally only work in round-to-nearest mode;
(b) are liable to create spurious underflows from internal calculations
that do not reflect underflow in the final result.
> The exception holding on dbl-64 prevent this implementation to also
> create an underflow exception with same argument (-744.44...) . More
Then that's a bug in the double code; the exception should be present when
the final result underflows. Please file a separate bug report in
Bugzilla (making sure of course that the argument you give is exactly
representable in double).
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