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| author | Chris Cannam <cannam@all-day-breakfast.com> |
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| date | Wed, 20 Mar 2013 15:35:50 +0000 |
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<html lang="en"> <head> <title>Fortran-interface routines - FFTW 3.3.3</title> <meta http-equiv="Content-Type" content="text/html"> <meta name="description" content="FFTW 3.3.3"> <meta name="generator" content="makeinfo 4.13"> <link title="Top" rel="start" href="index.html#Top"> <link rel="up" href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" title="Calling FFTW from Legacy Fortran"> <link rel="prev" href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" title="Calling FFTW from Legacy Fortran"> <link rel="next" href="FFTW-Constants-in-Fortran.html#FFTW-Constants-in-Fortran" title="FFTW Constants in Fortran"> <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> <!-- This manual is for FFTW (version 3.3.3, 25 November 2012). Copyright (C) 2003 Matteo Frigo. Copyright (C) 2003 Massachusetts Institute of Technology. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Free Software Foundation. --> <meta http-equiv="Content-Style-Type" content="text/css"> <style type="text/css"><!-- pre.display { font-family:inherit } pre.format { font-family:inherit } pre.smalldisplay { font-family:inherit; font-size:smaller } pre.smallformat { font-family:inherit; font-size:smaller } pre.smallexample { font-size:smaller } pre.smalllisp { font-size:smaller } span.sc { font-variant:small-caps } span.roman { font-family:serif; font-weight:normal; } span.sansserif { font-family:sans-serif; font-weight:normal; } --></style> </head> <body> <div class="node"> <a name="Fortran-interface-routines"></a> <a name="Fortran_002dinterface-routines"></a> <p> Next: <a rel="next" accesskey="n" href="FFTW-Constants-in-Fortran.html#FFTW-Constants-in-Fortran">FFTW Constants in Fortran</a>, Previous: <a rel="previous" accesskey="p" href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran">Calling FFTW from Legacy Fortran</a>, Up: <a rel="up" accesskey="u" href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran">Calling FFTW from Legacy Fortran</a> <hr> </div> <h3 class="section">8.1 Fortran-interface routines</h3> <p>Nearly all of the FFTW functions have Fortran-callable equivalents. The name of the legacy Fortran routine is the same as that of the corresponding C routine, but with the ‘<samp><span class="samp">fftw_</span></samp>’ prefix replaced by ‘<samp><span class="samp">dfftw_</span></samp>’.<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a> The single and long-double precision versions use ‘<samp><span class="samp">sfftw_</span></samp>’ and ‘<samp><span class="samp">lfftw_</span></samp>’, respectively, instead of ‘<samp><span class="samp">fftwf_</span></samp>’ and ‘<samp><span class="samp">fftwl_</span></samp>’; quadruple precision (<code>real*16</code>) is available on some systems as ‘<samp><span class="samp">fftwq_</span></samp>’ (see <a href="Precision.html#Precision">Precision</a>). (Note that <code>long double</code> on x86 hardware is usually at most 80-bit extended precision, <em>not</em> quadruple precision.) <p>For the most part, all of the arguments to the functions are the same, with the following exceptions: <ul> <li><code>plan</code> variables (what would be of type <code>fftw_plan</code> in C), must be declared as a type that is at least as big as a pointer (address) on your machine. We recommend using <code>integer*8</code> everywhere, since this should always be big enough. <a name="index-portability-578"></a> <li>Any function that returns a value (e.g. <code>fftw_plan_dft</code>) is converted into a <em>subroutine</em>. The return value is converted into an additional <em>first</em> parameter of this subroutine.<a rel="footnote" href="#fn-2" name="fnd-2"><sup>2</sup></a> <li><a name="index-column_002dmajor-579"></a>The Fortran routines expect multi-dimensional arrays to be in <em>column-major</em> order, which is the ordinary format of Fortran arrays (see <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format">Multi-dimensional Array Format</a>). They do this transparently and costlessly simply by reversing the order of the dimensions passed to FFTW, but this has one important consequence for multi-dimensional real-complex transforms, discussed below. <li>Wisdom import and export is somewhat more tricky because one cannot easily pass files or strings between C and Fortran; see <a href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f">Wisdom of Fortran?</a>. <li>Legacy Fortran cannot use the <code>fftw_malloc</code> dynamic-allocation routine. If you want to exploit the SIMD FFTW (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>), you'll need to figure out some other way to ensure that your arrays are at least 16-byte aligned. <li><a name="index-fftw_005fiodim-580"></a><a name="index-guru-interface-581"></a>Since Fortran 77 does not have data structures, the <code>fftw_iodim</code> structure from the guru interface (see <a href="Guru-vector-and-transform-sizes.html#Guru-vector-and-transform-sizes">Guru vector and transform sizes</a>) must be split into separate arguments. In particular, any <code>fftw_iodim</code> array arguments in the C guru interface become three integer array arguments (<code>n</code>, <code>is</code>, and <code>os</code>) in the Fortran guru interface, all of whose lengths should be equal to the corresponding <code>rank</code> argument. <li>The guru planner interface in Fortran does <em>not</em> do any automatic translation between column-major and row-major; you are responsible for setting the strides etcetera to correspond to your Fortran arrays. However, as a slight bug that we are preserving for backwards compatibility, the ‘<samp><span class="samp">plan_guru_r2r</span></samp>’ in Fortran <em>does</em> reverse the order of its <code>kind</code> array parameter, so the <code>kind</code> array of that routine should be in the reverse of the order of the iodim arrays (see above). </ul> <p>In general, you should take care to use Fortran data types that correspond to (i.e. are the same size as) the C types used by FFTW. In practice, this correspondence is usually straightforward (i.e. <code>integer</code> corresponds to <code>int</code>, <code>real</code> corresponds to <code>float</code>, etcetera). The native Fortran double/single-precision complex type should be compatible with <code>fftw_complex</code>/<code>fftwf_complex</code>. Such simple correspondences are assumed in the examples below. <a name="index-portability-582"></a> <!-- --> <div class="footnote"> <hr> <h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> Technically, Fortran 77 identifiers are not allowed to have more than 6 characters, nor may they contain underscores. Any compiler that enforces this limitation doesn't deserve to link to FFTW.</p> <p class="footnote"><small>[<a name="fn-2" href="#fnd-2">2</a>]</small> The reason for this is that some Fortran implementations seem to have trouble with C function return values, and vice versa.</p> <hr></div> </body></html>