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cannam@127:Nearly all of the FFTW functions have Fortran-callable equivalents.
cannam@127: The name of the legacy Fortran routine is the same as that of the
cannam@127: corresponding C routine, but with the ‘fftw_’ prefix replaced by
cannam@127: ‘dfftw_’.9 The single and long-double precision
cannam@127: versions use ‘sfftw_’ and ‘lfftw_’, respectively, instead of
cannam@127: ‘fftwf_’ and ‘fftwl_’; quadruple precision (real*16)
cannam@127: is available on some systems as ‘fftwq_’ (see Precision).
cannam@127: (Note that long double on x86 hardware is usually at most
cannam@127: 80-bit extended precision, not quadruple precision.)
cannam@127:
For the most part, all of the arguments to the functions are the same, cannam@127: with the following exceptions: cannam@127:
cannam@127:plan variables (what would be of type fftw_plan in C),
cannam@127: must be declared as a type that is at least as big as a pointer
cannam@127: (address) on your machine. We recommend using integer*8 everywhere,
cannam@127: since this should always be big enough.
cannam@127:
cannam@127:
cannam@127: fftw_plan_dft) is
cannam@127: converted into a subroutine. The return value is converted into
cannam@127: an additional first parameter of this subroutine.10
cannam@127:
cannam@127: fftw_malloc dynamic-allocation routine.
cannam@127: If you want to exploit the SIMD FFTW (see SIMD alignment and fftw_malloc), you’ll
cannam@127: need to figure out some other way to ensure that your arrays are at
cannam@127: least 16-byte aligned.
cannam@127:
cannam@127: fftw_iodim
cannam@127: structure from the guru interface (see Guru vector and transform sizes) must be split into separate arguments. In particular, any
cannam@127: fftw_iodim array arguments in the C guru interface become three
cannam@127: integer array arguments (n, is, and os) in the
cannam@127: Fortran guru interface, all of whose lengths should be equal to the
cannam@127: corresponding rank argument.
cannam@127:
cannam@127: kind array parameter, so the kind array
cannam@127: of that routine should be in the reverse of the order of the iodim
cannam@127: arrays (see above).
cannam@127:
cannam@127: In general, you should take care to use Fortran data types that
cannam@127: correspond to (i.e. are the same size as) the C types used by FFTW.
cannam@127: In practice, this correspondence is usually straightforward
cannam@127: (i.e. integer corresponds to int, real
cannam@127: corresponds to float, etcetera). The native Fortran
cannam@127: double/single-precision complex type should be compatible with
cannam@127: fftw_complex/fftwf_complex. Such simple correspondences
cannam@127: are assumed in the examples below.
cannam@127:
cannam@127:
Technically, Fortran 77 identifiers are not cannam@127: allowed to have more than 6 characters, nor may they contain cannam@127: underscores. Any compiler that enforces this limitation doesn’t cannam@127: deserve to link to FFTW.
cannam@127:The cannam@127: reason for this is that some Fortran implementations seem to have cannam@127: trouble with C function return values, and vice versa.
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