[Bug math/13932] x86_64 pow unexpectedly slow for some inputs

["manu at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=13932

--- Comment #7 from Manuel LÃpez-IbÃÃez <manu at gcc dot gnu.org> 2013-03-11 09:07:17 UTC ---
(In reply to comment #5)
> Nevertheless, I've added patches to master that ought to improve performance by
> at least 4x in the worst case, bringing it close to mpfr performance (still
> about 2x slower though).  There's still scope to make it faster, which is why I
> haven't closed this bug yet.


Hi, thanks for your work. Personally, I would be interested to have a pow
version that is perhaps less precise but that does not have  such nasty
corner-cases. A 4x improvement is nice, but given that the worst-case may be
12,000x slower, it is not a definitive solution.

There are some implementations on the net that perhaps could be used when
-ffast-math is given?

http://jrfonseca.blogspot.be/2008/09/fast-sse2-pow-tables-or-polynomials.html

http://www.dctsystems.co.uk/Software/power.html

http://martin.ankerl.com/2012/01/25/optimized-approximative-pow-in-c-and-cpp/

I am no expert in IEEE floating-point arithmetic, so it may well be that those
implementations produce extremely bad approximations for some inputs. Is that
the case?

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.