Re: [DebianGIS] grass and 64bit
On Thu, Mar 16, 2006 at 11:54:05AM +0100, Markus Neteler wrote:
> On Thu, Mar 16, 2006 at 11:41:34AM +0100, Francesco P. Lovergine wrote:
> > Now that amd64 arch just entered the great main world, I wonder if
> > it would be useful/needed(?) in grass enabling the '64bit support'
> > whose use is not so clear to me...
> >
> >
> > (C) COMPILATION NOTES for 64bit platforms
> >
> > To successfully compile GRASS on 64bit platforms, the required
> > FFTW2 library has to be compiled with -fPIC flag:
> >
> > #applies to FFTW2, not GRASS:
> > cd fftw-2.1.5/
> > CFLAGS="-fPIC" ./configure
> > make
> > make install
> >
> > To fully enable 64bit library usage for GRASS on 64bit platforms,
> > the following additional parameters are recommended/required:
> >
> > ./configure \
> > --enable-64bit \
> > --with-libs=/usr/lib64 \
> > ...
> >
>
> Francesco,
>
> I am using it for some months now (wrote above notes),
> but right, I don't know if I gain anything :-)
>
> Maybe it affects the data storage internally. Since
> the GRASS 6 data formats are portable across 32bit/64bit,
> I don't know any effective difference. but I am no
> expert.
>
Most details are hidden in the libc. On AMD64 at least /usr/lib64 and
/usr/lib are the same directory. It has been introduced to differentiate
/usr/lib32 which contain the 32bit edition for that multi-arch platform.
> Maybe someone could test the performance by creating
> fractal DEMs with r.surf.fractal and generate
> vector topology of the GSHHS dataset?
>
Well, AFAIK it is a non-sense. We already build on pure 64bit platforms
(alpha, ia64, sparc) without additional flags. The only true difference
for multi-arch amd64 is obtaining binary-compatibility without rebuilding,
but that's interesting only for 32bit native programs, not for 64bit
native ones, like grass and any other software in main for those
platforms.
If --enable-64 would select specific per-arch compiler flags, that would
be another question...
--
Francesco P. Lovergine
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