[Bug fortran/33698] FAIL: gfortran.dg/gamma_5.f90

["burnus at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #8 from burnus at gcc dot gnu dot org  2007-10-09 22:06 -------
> We'll probably need to roll our own tgamma function:  To
> cover cases like this, where the system doesn't provide
> one, and to get numerically better answers.

g95 uses a C version of W. J. Cody and L. Stoltz' Fortran procedure available
from http://www.netlib.org/specfun/gamma

If I read GLIBC correctly, it implements gamma as exp(lgamma(x)), which
explains why the results are not optimal, cf.

http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/math/w_tgamma.c?cvsroot=glibc
http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/sysdeps/ieee754/dbl-64/e_gamma_r.c?cvsroot=glibc

Initially, I had claimed that it is better to use the C99/POSIX-2001 tgamma
function of the system C library (if available), but now I am not so sure
anymore.


-- 

burnus at gcc dot gnu dot org changed:

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33698