Re: [Fwd: Re: gnuplot numerical errors on Intel MacBook]

[Daniel J S. <dan...@ie...>]

Hans-Bernhard Br=F6ker wrote:

>>I still haven't seen anything that specifically calls out that in C99
>>lgamma() must or should support signgam.
>=20
>=20
> That's because it's not there.  I stated this as fact from memory, but=20
> it turned out to be wrong on re-reading the document.

OK...

Well, the autoconf for running a program really wasn't too bad.  For thos=
e interested:

dnl check, if gamma is log of gamma.  if program
dnl compiles and gamma(2.0) < 0.5 is false, then
dnl simply say "gamma is gamma", otherwise define
dnl GAMMA_IS_LNGAMMA
AC_LANG(C)
AC_RUN_IFELSE(
[AC_LANG_PROGRAM([#include <math.h>],[exit(gamma(2.0) < 0.5);])],
[ echo "gamma is gamma" ],
[AC_DEFINE(GAMMA_IS_LGAMMA,1,[ Define if gamma() present and is log gamma=
 ])]
)

I mildly suggest the most recent patch be added for 4.2.  I think it is e=
asier to simply add this patch than it is to explain the gamma-was-once-n=
at-log-gamma confusion to a package or software maintainer.  There is a g=
ood chance, I think, someone will get bit by this, and we'd be saving him=
 or her a lot of time and headache.

It's a very straightforward patch now... on SourceForge.

Dan


PS:  I've verified this by slowly stripping away definition precedence, i=
.e., #undef HAVE_TGAMMA, #undef HAVE_LGAMMA_R, #undef HAVE_GAMMA, etc.