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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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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.3/doc/html/Fortran_002dinterface-routines.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,141 @@ +<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> +