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diff src/fftw-3.3.8/doc/html/Fixed_002dsize-Arrays-in-C.html @ 167:bd3cc4d1df30

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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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+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html>
+<!-- This manual is for FFTW
+(version 3.3.8, 24 May 2018).
+
+Copyright (C) 2003 Matteo Frigo.
+
+Copyright (C) 2003 Massachusetts Institute of Technology.
+
+Permission is granted to make and distribute verbatim copies of this
+manual provided the copyright notice and this permission notice are
+preserved on all copies.
+
+Permission is granted to copy and distribute modified versions of 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.
+
+Permission is granted to copy and distribute translations of this manual
+into another language, under the above conditions for modified versions,
+except that this permission notice may be stated in a translation
+approved by the Free Software Foundation. -->
+<!-- Created by GNU Texinfo 6.3, http://www.gnu.org/software/texinfo/ -->
+<head>
+<title>FFTW 3.3.8: Fixed-size Arrays in C</title>
+
+<meta name="description" content="FFTW 3.3.8: Fixed-size Arrays in C">
+<meta name="keywords" content="FFTW 3.3.8: Fixed-size Arrays in C">
+<meta name="resource-type" content="document">
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+<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+<link href="index.html#Top" rel="start" title="Top">
+<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
+<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
+<link href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="up" title="Multi-dimensional Array Format">
+<link href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C" rel="next" title="Dynamic Arrays in C">
+<link href="Column_002dmajor-Format.html#Column_002dmajor-Format" rel="prev" title="Column-major Format">
+<style type="text/css">
+<!--
+a.summary-letter {text-decoration: none}
+blockquote.indentedblock {margin-right: 0em}
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+span.sansserif {font-family: sans-serif; font-weight: normal}
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+-->
+</style>
+
+
+</head>
+
+<body lang="en">
+<a name="Fixed_002dsize-Arrays-in-C"></a>
+<div class="header">
+<p>
+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>
+</div>
+<hr>
+<a name="Fixed_002dsize-Arrays-in-C-1"></a>
+<h4 class="subsection">3.2.3 Fixed-size Arrays in C</h4>
+<a name="index-C-multi_002ddimensional-arrays"></a>
+
+<p>A multi-dimensional array whose size is declared at compile time in C
+is <em>already</em> in row-major order.  You don&rsquo;t have to do anything
+special to transform it.  For example:
+</p>
+<div class="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></div>
+
+<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>
+<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.
+</p>
+
+
+
+</body>
+</html>