On 2008-01-03 21:52:31 -0500, Kaveh R. GHAZI wrote:
> On Wed, 2 Jan 2008, Vincent Lefevre wrote:
> > See the new bug fixed in r5162 (for the 2.3 branch). mpfr_gamma on
> > -1000000001.5 will give you -0 instead of +0.
>
> So I tried that, but mpfr_gamma on that value sets the global underflow
> flag. If overflow/underflow are set by mpfr, GCC will intentionally
> bypass folding. So this particular case is not something I can use.
OK, I forgot that.
> I don't know if this mpfr case should be setting the underflow flag or if
> it's a bug.
It's really an underflow, and the bug (wrong sign) can occur only if
there's an underflow.
> Calling the glibc tgamma doesn't seem to think it underflowed
> when looking at fetestexcept().
vin:~> gp
Reading GPRC: /home/vlefevre/.gprc ...Done.
GP/PARI CALCULATOR Version 2.3.2 (released)
i486 running linux (ix86/GMP-4.2.1 kernel) 32-bit version
compiled: Apr 13 2007, gcc-4.1.2 20061115 (prerelease) (Debian 4.1.1-21)
(readline v5.2 enabled, extended help available)
Copyright (C) 2000-2006 The PARI Group
PARI/GP is free software, covered by the GNU General Public License, and
comes WITHOUT ANY WARRANTY WHATSOEVER.
Type ? for help, \q to quit.
Type ?12 for how to get moral (and possibly technical) support.
parisize = 4000000, primelimit = 500000
? gamma(-1000000001.5)
*** gamma: exponent (expo) overflow
? gamma(-10000001.5)
%1 = 8.262136614106674385317743887 E-65657070
--
Vincent Lefèvre <[EMAIL PROTECTED]> - Web: <http://www.vinc17.org/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.org/blog/>
Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)
