Re: g77 issues

[Sven LUTHER <luther@dpt-info.u-strasbg.fr>]

On Thu, Apr 19, 2001 at 10:50:34AM +0100, Nick Bailey wrote:
> Ionut Georgescu wrote:
> 
> > PS command line: g77 -g -pg -o programm *.f
> > PPS gcc -v:
> >     Reading specs from /usr/lib/gcc-lib/alpha-linux/2.95.3/specs
> >     gcc version 2.95.3 20010315 (Debian release)
> 
> I'm interested... I don't know enough FORTRAN to test this out, but I have been
> seeing Scilab (which has a lot of FORTRAN inside) doing some strange things
> recently.  If you were to send me a short program to compile and run on this
> debian PowerPC (Mac G4) I can let you see the results.
> 
> >
> > PPS I made another test. In the big programm I have defined a function
> > fermi2:
> >
> > ...
> >
> > and computed the following expression:
> >
> >           aux22= 1.0d0-fermi2(enpct)
> >
> > The output was:
> >
> > on x86:
> >  tmp_fermi2( -2.20214243)=  1.
> >  aux22=  1.11022302E-16  !! should have been 0. !!
> >
> 
> This is an engineering department: 1.11022302E-16 == 0  ;-)  Can you print out
> the first expression more accuately?  I bet it isn't really 1 (actually
> 1.000000000000000111022302 ;-)  Maybe there's no bug: it's just truncation
> error?  Maybe the maths unit on the alpha is better than the one on the ia32 on
> this test (no suprise there!)

Also, note that alpha is a 64bit plateform, and that as thus it could be that
it handles some things better than ia32 or ppc. Not sure if this influences
floating point values, i guess not.

Friendly,

Sven Luther