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8.1 Fortran-interface routines

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Nearly all of the FFTW functions have Fortran-callable equivalents. Chris@19: The name of the legacy Fortran routine is the same as that of the Chris@19: corresponding C routine, but with the ‘fftw_’ prefix replaced by Chris@19: ‘dfftw_’.1 The single and long-double precision Chris@19: versions use ‘sfftw_’ and ‘lfftw_’, respectively, instead of Chris@19: ‘fftwf_’ and ‘fftwl_’; quadruple precision (real*16) Chris@19: is available on some systems as ‘fftwq_’ (see Precision). Chris@19: (Note that long double on x86 hardware is usually at most Chris@19: 80-bit extended precision, not quadruple precision.) Chris@19: Chris@19:

For the most part, all of the arguments to the functions are the same, Chris@19: with the following exceptions: Chris@19: Chris@19:

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In general, you should take care to use Fortran data types that Chris@19: correspond to (i.e. are the same size as) the C types used by FFTW. Chris@19: In practice, this correspondence is usually straightforward Chris@19: (i.e. integer corresponds to int, real Chris@19: corresponds to float, etcetera). The native Fortran Chris@19: double/single-precision complex type should be compatible with Chris@19: fftw_complex/fftwf_complex. Such simple correspondences Chris@19: are assumed in the examples below. Chris@19: Chris@19: Chris@19: Chris@19:

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Footnotes

[1] Technically, Fortran 77 identifiers are not Chris@19: allowed to have more than 6 characters, nor may they contain Chris@19: underscores. Any compiler that enforces this limitation doesn't Chris@19: deserve to link to FFTW.

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[2] The Chris@19: reason for this is that some Fortran implementations seem to have Chris@19: trouble with C function return values, and vice versa.

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