As one of the upstream developers, I would currently recommend against
this patch.
FFTW itself contains no Fortran code. It only uses the Fortran compiler
to detect how Fortran linking works in order to provide Fortran-callable
wrappers. This link detection should work with both g77 and gfortran, but
will produce different results.
gfortran, like many other Fortran compilers (e.g. Intel, IBM), converts
all identifiers to lower-case plus an underscore. g77, however, uses an
odd behavior inherited from f2c: it converts all identifiers to lower-case
plus an underscore, plus an extra underscore if the identifier contains an
underscore. This means that the same functions are not callable from g77
and gfortran simultaneously if they contain underscores (like all FFTW
functions).
If you configure FFTW with gfortran (e.g. if gfortran is present but not
g77), then FFTW will be callable from gfortran and most other Fortran
compilers, but not from g77.
If you configure FFTW with g77 (which is the default if g77 is present,
even if gfortran is present as well), then FFTW will be callable from
*both* g77 and gfortran. The reason is that FFTW detects g77's odd
behavior and includes two versions of the Fortran-callable wrappers: one
for g77 and one for other Fortran compilers without the extra underscore.
Because of this, FFTW libraries configured with g77 are currently more
appropriate for Debian; switching to gfortran may break the library for
some developers (and some programs?).
Regards,
Steven G. Johnson
PS. On the other hand, I can certainly see the motivation for switching to
gfortran: g77 is not available in recent gcc versions, and thus including
it in the build-depends requires the build machine to install a bunch of
legacy gcc code. In the next upstream version of FFTW, I'm planning on
adding a --with-g77-wrappers flag to force inclusion of g77-compatible
wrappers, so that you can configure with gfortran and still remain
g77-compatible.
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