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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam
date Tue, 19 Nov 2019 14:52:55 +0000
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3 <!-- This manual is for FFTW
4 (version 3.3.8, 24 May 2018).
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6 Copyright (C) 2003 Matteo Frigo.
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8 Copyright (C) 2003 Massachusetts Institute of Technology.
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25 <title>FFTW 3.3.8: Fortran-interface routines</title>
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71 <a name="Fortran_002dinterface-routines"></a>
72 <div class="header">
73 <p>
74 Next: <a href="FFTW-Constants-in-Fortran.html#FFTW-Constants-in-Fortran" accesskey="n" rel="next">FFTW Constants in Fortran</a>, Previous: <a href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" accesskey="p" rel="prev">Calling FFTW from Legacy Fortran</a>, Up: <a href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" accesskey="u" rel="up">Calling FFTW from Legacy Fortran</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
75 </div>
76 <hr>
77 <a name="Fortran_002dinterface-routines-1"></a>
78 <h3 class="section">8.1 Fortran-interface routines</h3>
79
80 <p>Nearly all of the FFTW functions have Fortran-callable equivalents.
81 The name of the legacy Fortran routine is the same as that of the
82 corresponding C routine, but with the &lsquo;<samp>fftw_</samp>&rsquo; prefix replaced by
83 &lsquo;<samp>dfftw_</samp>&rsquo;.<a name="DOCF9" href="#FOOT9"><sup>9</sup></a> The single and long-double precision
84 versions use &lsquo;<samp>sfftw_</samp>&rsquo; and &lsquo;<samp>lfftw_</samp>&rsquo;, respectively, instead of
85 &lsquo;<samp>fftwf_</samp>&rsquo; and &lsquo;<samp>fftwl_</samp>&rsquo;; quadruple precision (<code>real*16</code>)
86 is available on some systems as &lsquo;<samp>fftwq_</samp>&rsquo; (see <a href="Precision.html#Precision">Precision</a>).
87 (Note that <code>long double</code> on x86 hardware is usually at most
88 80-bit extended precision, <em>not</em> quadruple precision.)
89 </p>
90 <p>For the most part, all of the arguments to the functions are the same,
91 with the following exceptions:
92 </p>
93 <ul>
94 <li> <code>plan</code> variables (what would be of type <code>fftw_plan</code> in C),
95 must be declared as a type that is at least as big as a pointer
96 (address) on your machine. We recommend using <code>integer*8</code> everywhere,
97 since this should always be big enough.
98 <a name="index-portability-6"></a>
99
100 </li><li> Any function that returns a value (e.g. <code>fftw_plan_dft</code>) is
101 converted into a <em>subroutine</em>. The return value is converted into
102 an additional <em>first</em> parameter of this subroutine.<a name="DOCF10" href="#FOOT10"><sup>10</sup></a>
103
104 </li><li> <a name="index-column_002dmajor-2"></a>
105 The Fortran routines expect multi-dimensional arrays to be in
106 <em>column-major</em> order, which is the ordinary format of Fortran
107 arrays (see <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format">Multi-dimensional Array Format</a>). They do this
108 transparently and costlessly simply by reversing the order of the
109 dimensions passed to FFTW, but this has one important consequence for
110 multi-dimensional real-complex transforms, discussed below.
111
112 </li><li> Wisdom import and export is somewhat more tricky because one cannot
113 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>.
114
115 </li><li> Legacy Fortran cannot use the <code>fftw_malloc</code> dynamic-allocation routine.
116 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&rsquo;ll
117 need to figure out some other way to ensure that your arrays are at
118 least 16-byte aligned.
119
120 </li><li> <a name="index-fftw_005fiodim-2"></a>
121 <a name="index-guru-interface-4"></a>
122 Since Fortran 77 does not have data structures, the <code>fftw_iodim</code>
123 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
124 <code>fftw_iodim</code> array arguments in the C guru interface become three
125 integer array arguments (<code>n</code>, <code>is</code>, and <code>os</code>) in the
126 Fortran guru interface, all of whose lengths should be equal to the
127 corresponding <code>rank</code> argument.
128
129 </li><li> The guru planner interface in Fortran does <em>not</em> do any automatic
130 translation between column-major and row-major; you are responsible
131 for setting the strides etcetera to correspond to your Fortran arrays.
132 However, as a slight bug that we are preserving for backwards
133 compatibility, the &lsquo;<samp>plan_guru_r2r</samp>&rsquo; in Fortran <em>does</em> reverse the
134 order of its <code>kind</code> array parameter, so the <code>kind</code> array
135 of that routine should be in the reverse of the order of the iodim
136 arrays (see above).
137
138 </li></ul>
139
140 <p>In general, you should take care to use Fortran data types that
141 correspond to (i.e. are the same size as) the C types used by FFTW.
142 In practice, this correspondence is usually straightforward
143 (i.e. <code>integer</code> corresponds to <code>int</code>, <code>real</code>
144 corresponds to <code>float</code>, etcetera). The native Fortran
145 double/single-precision complex type should be compatible with
146 <code>fftw_complex</code>/<code>fftwf_complex</code>. Such simple correspondences
147 are assumed in the examples below.
148 <a name="index-portability-7"></a>
149 </p>
150 <div class="footnote">
151 <hr>
152 <h4 class="footnotes-heading">Footnotes</h4>
153
154 <h3><a name="FOOT9" href="#DOCF9">(9)</a></h3>
155 <p>Technically, Fortran 77 identifiers are not
156 allowed to have more than 6 characters, nor may they contain
157 underscores. Any compiler that enforces this limitation doesn&rsquo;t
158 deserve to link to FFTW.</p>
159 <h3><a name="FOOT10" href="#DOCF10">(10)</a></h3>
160 <p>The
161 reason for this is that some Fortran implementations seem to have
162 trouble with C function return values, and vice versa.</p>
163 </div>
164 <hr>
165 <div class="header">
166 <p>
167 Next: <a href="FFTW-Constants-in-Fortran.html#FFTW-Constants-in-Fortran" accesskey="n" rel="next">FFTW Constants in Fortran</a>, Previous: <a href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" accesskey="p" rel="prev">Calling FFTW from Legacy Fortran</a>, Up: <a href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" accesskey="u" rel="up">Calling FFTW from Legacy Fortran</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
168 </div>
169
170
171
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173 </html>