[Bug math/15235] Spurious underflow exception for expl ldbl128-ibm

["joseph at codesourcery dot com" <sourceware-bugzilla at sourceware dot org>]

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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