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Add FFTW3
author Chris Cannam <cannam@all-day-breakfast.com>
date Wed, 20 Mar 2013 15:35:50 +0000
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+<html lang="en">
+<head>
+<title>Fixed-size Arrays in C - FFTW 3.3.3</title>
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+<link rel="up" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" title="Multi-dimensional Array Format">
+<link rel="prev" href="Column_002dmajor-Format.html#Column_002dmajor-Format" title="Column-major Format">
+<link rel="next" href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C" title="Dynamic Arrays in C">
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+<!--
+This manual is for FFTW
+(version 3.3.3, 25 November 2012).
+
+Copyright (C) 2003 Matteo Frigo.
+
+Copyright (C) 2003 Massachusetts Institute of Technology.
+
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+     this manual provided the copyright notice and this permission
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+
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+     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.
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+<div class="node">
+<a name="Fixed-size-Arrays-in-C"></a>
+<a name="Fixed_002dsize-Arrays-in-C"></a>
+<p>
+Next:&nbsp;<a rel="next" accesskey="n" href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C">Dynamic Arrays in C</a>,
+Previous:&nbsp;<a rel="previous" accesskey="p" href="Column_002dmajor-Format.html#Column_002dmajor-Format">Column-major Format</a>,
+Up:&nbsp;<a rel="up" accesskey="u" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format">Multi-dimensional Array Format</a>
+<hr>
+</div>
+
+<h4 class="subsection">3.2.3 Fixed-size Arrays in C</h4>
+
+<p><a name="index-C-multi_002ddimensional-arrays-120"></a>
+A multi-dimensional array whose size is declared at compile time in C
+is <em>already</em> in row-major order.  You don't have to do anything
+special to transform it.  For example:
+
+<pre class="example">     {
+          fftw_complex data[N0][N1][N2];
+          fftw_plan plan;
+          ...
+          plan = fftw_plan_dft_3d(N0, N1, N2, &amp;data[0][0][0], &amp;data[0][0][0],
+                                  FFTW_FORWARD, FFTW_ESTIMATE);
+          ...
+     }
+</pre>
+   <p>This will plan a 3d in-place transform of size <code>N0 x N1 x N2</code>. 
+Notice how we took the address of the zero-th element to pass to the
+planner (we could also have used a typecast).
+
+   <p>However, we tend to <em>discourage</em> users from declaring their
+arrays in this way, for two reasons.  First, this allocates the array
+on the stack (&ldquo;automatic&rdquo; storage), which has a very limited size on
+most operating systems (declaring an array with more than a few
+thousand elements will often cause a crash).  (You can get around this
+limitation on many systems by declaring the array as
+<code>static</code> and/or global, but that has its own drawbacks.) 
+Second, it may not optimally align the array for use with a SIMD
+FFTW (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>).  Instead, we recommend
+using <code>fftw_malloc</code>, as described below.
+
+<!-- =========> -->
+   </body></html>
+