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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam <cannam@all-day-breakfast.com>
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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25 <title>FFTW 3.3.8: Fixed-size Arrays in C</title>
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35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
36 <link href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="up" title="Multi-dimensional Array Format">
37 <link href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C" rel="next" title="Dynamic Arrays in C">
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71 <a name="Fixed_002dsize-Arrays-in-C"></a>
72 <div class="header">
73 <p>
74 Next: <a href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C" accesskey="n" rel="next">Dynamic Arrays in C</a>, Previous: <a href="Column_002dmajor-Format.html#Column_002dmajor-Format" accesskey="p" rel="prev">Column-major Format</a>, Up: <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" accesskey="u" rel="up">Multi-dimensional Array Format</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="Fixed_002dsize-Arrays-in-C-1"></a>
78 <h4 class="subsection">3.2.3 Fixed-size Arrays in C</h4>
79 <a name="index-C-multi_002ddimensional-arrays"></a>
80
81 <p>A multi-dimensional array whose size is declared at compile time in C
82 is <em>already</em> in row-major order. You don&rsquo;t have to do anything
83 special to transform it. For example:
84 </p>
85 <div class="example">
86 <pre class="example">{
87 fftw_complex data[N0][N1][N2];
88 fftw_plan plan;
89 ...
90 plan = fftw_plan_dft_3d(N0, N1, N2, &amp;data[0][0][0], &amp;data[0][0][0],
91 FFTW_FORWARD, FFTW_ESTIMATE);
92 ...
93 }
94 </pre></div>
95
96 <p>This will plan a 3d in-place transform of size <code>N0 x N1 x N2</code>.
97 Notice how we took the address of the zero-th element to pass to the
98 planner (we could also have used a typecast).
99 </p>
100 <p>However, we tend to <em>discourage</em> users from declaring their
101 arrays in this way, for two reasons. First, this allocates the array
102 on the stack (&ldquo;automatic&rdquo; storage), which has a very limited size on
103 most operating systems (declaring an array with more than a few
104 thousand elements will often cause a crash). (You can get around this
105 limitation on many systems by declaring the array as
106 <code>static</code> and/or global, but that has its own drawbacks.)
107 Second, it may not optimally align the array for use with a SIMD
108 FFTW (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>). Instead, we recommend
109 using <code>fftw_malloc</code>, as described below.
110 </p>
111
112
113
114 </body>
115 </html>