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Add null config files
author Chris Cannam <cannam@all-day-breakfast.com>
date Mon, 02 Mar 2020 14:03:47 +0000
parents bd3cc4d1df30
children
rev   line source
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cannam@167 3 <!-- This manual is for FFTW
cannam@167 4 (version 3.3.8, 24 May 2018).
cannam@167 5
cannam@167 6 Copyright (C) 2003 Matteo Frigo.
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cannam@167 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@167 24 <head>
cannam@167 25 <title>FFTW 3.3.8: Fixed-size Arrays in C</title>
cannam@167 26
cannam@167 27 <meta name="description" content="FFTW 3.3.8: Fixed-size Arrays in C">
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cannam@167 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
cannam@167 36 <link href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="up" title="Multi-dimensional Array Format">
cannam@167 37 <link href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C" rel="next" title="Dynamic Arrays in C">
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cannam@167 68 </head>
cannam@167 69
cannam@167 70 <body lang="en">
cannam@167 71 <a name="Fixed_002dsize-Arrays-in-C"></a>
cannam@167 72 <div class="header">
cannam@167 73 <p>
cannam@167 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>
cannam@167 75 </div>
cannam@167 76 <hr>
cannam@167 77 <a name="Fixed_002dsize-Arrays-in-C-1"></a>
cannam@167 78 <h4 class="subsection">3.2.3 Fixed-size Arrays in C</h4>
cannam@167 79 <a name="index-C-multi_002ddimensional-arrays"></a>
cannam@167 80
cannam@167 81 <p>A multi-dimensional array whose size is declared at compile time in C
cannam@167 82 is <em>already</em> in row-major order. You don&rsquo;t have to do anything
cannam@167 83 special to transform it. For example:
cannam@167 84 </p>
cannam@167 85 <div class="example">
cannam@167 86 <pre class="example">{
cannam@167 87 fftw_complex data[N0][N1][N2];
cannam@167 88 fftw_plan plan;
cannam@167 89 ...
cannam@167 90 plan = fftw_plan_dft_3d(N0, N1, N2, &amp;data[0][0][0], &amp;data[0][0][0],
cannam@167 91 FFTW_FORWARD, FFTW_ESTIMATE);
cannam@167 92 ...
cannam@167 93 }
cannam@167 94 </pre></div>
cannam@167 95
cannam@167 96 <p>This will plan a 3d in-place transform of size <code>N0 x N1 x N2</code>.
cannam@167 97 Notice how we took the address of the zero-th element to pass to the
cannam@167 98 planner (we could also have used a typecast).
cannam@167 99 </p>
cannam@167 100 <p>However, we tend to <em>discourage</em> users from declaring their
cannam@167 101 arrays in this way, for two reasons. First, this allocates the array
cannam@167 102 on the stack (&ldquo;automatic&rdquo; storage), which has a very limited size on
cannam@167 103 most operating systems (declaring an array with more than a few
cannam@167 104 thousand elements will often cause a crash). (You can get around this
cannam@167 105 limitation on many systems by declaring the array as
cannam@167 106 <code>static</code> and/or global, but that has its own drawbacks.)
cannam@167 107 Second, it may not optimally align the array for use with a SIMD
cannam@167 108 FFTW (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>). Instead, we recommend
cannam@167 109 using <code>fftw_malloc</code>, as described below.
cannam@167 110 </p>
cannam@167 111
cannam@167 112
cannam@167 113
cannam@167 114 </body>
cannam@167 115 </html>