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cannam@167:Nearly all of the FFTW functions have Fortran-callable equivalents.
cannam@167: The name of the legacy Fortran routine is the same as that of the
cannam@167: corresponding C routine, but with the ‘fftw_’ prefix replaced by
cannam@167: ‘dfftw_’.9 The single and long-double precision
cannam@167: versions use ‘sfftw_’ and ‘lfftw_’, respectively, instead of
cannam@167: ‘fftwf_’ and ‘fftwl_’; quadruple precision (real*16)
cannam@167: is available on some systems as ‘fftwq_’ (see Precision).
cannam@167: (Note that long double on x86 hardware is usually at most
cannam@167: 80-bit extended precision, not quadruple precision.)
cannam@167:
For the most part, all of the arguments to the functions are the same, cannam@167: with the following exceptions: cannam@167:
cannam@167:plan variables (what would be of type fftw_plan in C),
cannam@167: must be declared as a type that is at least as big as a pointer
cannam@167: (address) on your machine. We recommend using integer*8 everywhere,
cannam@167: since this should always be big enough.
cannam@167:
cannam@167:
cannam@167: fftw_plan_dft) is
cannam@167: converted into a subroutine. The return value is converted into
cannam@167: an additional first parameter of this subroutine.10
cannam@167:
cannam@167: fftw_malloc dynamic-allocation routine.
cannam@167: If you want to exploit the SIMD FFTW (see SIMD alignment and fftw_malloc), you’ll
cannam@167: need to figure out some other way to ensure that your arrays are at
cannam@167: least 16-byte aligned.
cannam@167:
cannam@167: fftw_iodim
cannam@167: structure from the guru interface (see Guru vector and transform sizes) must be split into separate arguments. In particular, any
cannam@167: fftw_iodim array arguments in the C guru interface become three
cannam@167: integer array arguments (n, is, and os) in the
cannam@167: Fortran guru interface, all of whose lengths should be equal to the
cannam@167: corresponding rank argument.
cannam@167:
cannam@167: kind array parameter, so the kind array
cannam@167: of that routine should be in the reverse of the order of the iodim
cannam@167: arrays (see above).
cannam@167:
cannam@167: In general, you should take care to use Fortran data types that
cannam@167: correspond to (i.e. are the same size as) the C types used by FFTW.
cannam@167: In practice, this correspondence is usually straightforward
cannam@167: (i.e. integer corresponds to int, real
cannam@167: corresponds to float, etcetera). The native Fortran
cannam@167: double/single-precision complex type should be compatible with
cannam@167: fftw_complex/fftwf_complex. Such simple correspondences
cannam@167: are assumed in the examples below.
cannam@167:
cannam@167:
Technically, Fortran 77 identifiers are not cannam@167: allowed to have more than 6 characters, nor may they contain cannam@167: underscores. Any compiler that enforces this limitation doesn’t cannam@167: deserve to link to FFTW.
cannam@167:The cannam@167: reason for this is that some Fortran implementations seem to have cannam@167: trouble with C function return values, and vice versa.
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