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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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Chris@82 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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Chris@82 3 <!-- This manual is for FFTW
Chris@82 4 (version 3.3.8, 24 May 2018).
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Chris@82 6 Copyright (C) 2003 Matteo Frigo.
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Chris@82 24 <head>
Chris@82 25 <title>FFTW 3.3.8: Dynamic Arrays in C-The Wrong Way</title>
Chris@82 26
Chris@82 27 <meta name="description" content="FFTW 3.3.8: Dynamic Arrays in C-The Wrong Way">
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Chris@82 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
Chris@82 36 <link href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="up" title="Multi-dimensional Array Format">
Chris@82 37 <link href="Words-of-Wisdom_002dSaving-Plans.html#Words-of-Wisdom_002dSaving-Plans" rel="next" title="Words of Wisdom-Saving Plans">
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Chris@82 68 </head>
Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="Dynamic-Arrays-in-C_002dThe-Wrong-Way"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 74 Previous: <a href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C" accesskey="p" rel="prev">Dynamic Arrays in C</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>
Chris@82 75 </div>
Chris@82 76 <hr>
Chris@82 77 <a name="Dynamic-Arrays-in-C_002d_002d_002dThe-Wrong-Way"></a>
Chris@82 78 <h4 class="subsection">3.2.5 Dynamic Arrays in C&mdash;The Wrong Way</h4>
Chris@82 79
Chris@82 80 <p>A different method for allocating multi-dimensional arrays in C is
Chris@82 81 often suggested that is incompatible with FFTW: <em>using it will
Chris@82 82 cause FFTW to die a painful death</em>. We discuss the technique here,
Chris@82 83 however, because it is so commonly known and used. This method is to
Chris@82 84 create arrays of pointers of arrays of pointers of &hellip;etcetera.
Chris@82 85 For example, the analogue in this method to the example above is:
Chris@82 86 </p>
Chris@82 87 <div class="example">
Chris@82 88 <pre class="example">int i,j;
Chris@82 89 fftw_complex ***a_bad_array; /* <span class="roman">another way to make a 5x12x27 array</span> */
Chris@82 90
Chris@82 91 a_bad_array = (fftw_complex ***) malloc(5 * sizeof(fftw_complex **));
Chris@82 92 for (i = 0; i &lt; 5; ++i) {
Chris@82 93 a_bad_array[i] =
Chris@82 94 (fftw_complex **) malloc(12 * sizeof(fftw_complex *));
Chris@82 95 for (j = 0; j &lt; 12; ++j)
Chris@82 96 a_bad_array[i][j] =
Chris@82 97 (fftw_complex *) malloc(27 * sizeof(fftw_complex));
Chris@82 98 }
Chris@82 99 </pre></div>
Chris@82 100
Chris@82 101 <p>As you can see, this sort of array is inconvenient to allocate (and
Chris@82 102 deallocate). On the other hand, it has the advantage that the
Chris@82 103 <em>(i,j,k)</em>-th element can be referenced simply by
Chris@82 104 <code>a_bad_array[i][j][k]</code>.
Chris@82 105 </p>
Chris@82 106 <p>If you like this technique and want to maximize convenience in accessing
Chris@82 107 the array, but still want to pass the array to FFTW, you can use a
Chris@82 108 hybrid method. Allocate the array as one contiguous block, but also
Chris@82 109 declare an array of arrays of pointers that point to appropriate places
Chris@82 110 in the block. That sort of trick is beyond the scope of this
Chris@82 111 documentation; for more information on multi-dimensional arrays in C,
Chris@82 112 see the <code>comp.lang.c</code>
Chris@82 113 <a href="http://c-faq.com/aryptr/dynmuldimary.html">FAQ</a>.
Chris@82 114 </p>
Chris@82 115
Chris@82 116
Chris@82 117
Chris@82 118 </body>
Chris@82 119 </html>