mirror of
https://github.com/tildearrow/furnace.git
synced 2024-11-14 16:55:06 +00:00
108 lines
4.7 KiB
HTML
108 lines
4.7 KiB
HTML
<!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 3.3.10, 10 December 2020).
|
|
|
|
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 6.7, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<title>Dynamic Arrays in C-The Wrong Way (FFTW 3.3.10)</title>
|
|
|
|
<meta name="description" content="Dynamic Arrays in C-The Wrong Way (FFTW 3.3.10)">
|
|
<meta name="keywords" content="Dynamic Arrays in C-The Wrong Way (FFTW 3.3.10)">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<link href="index.html" rel="start" title="Top">
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Multi_002ddimensional-Array-Format.html" rel="up" title="Multi-dimensional Array Format">
|
|
<link href="Words-of-Wisdom_002dSaving-Plans.html" rel="next" title="Words of Wisdom-Saving Plans">
|
|
<link href="Dynamic-Arrays-in-C.html" rel="prev" title="Dynamic Arrays in C">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
kbd {font-style: oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
span.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<span id="Dynamic-Arrays-in-C_002dThe-Wrong-Way"></span><div class="header">
|
|
<p>
|
|
Previous: <a href="Dynamic-Arrays-in-C.html" accesskey="p" rel="prev">Dynamic Arrays in C</a>, Up: <a href="Multi_002ddimensional-Array-Format.html" accesskey="u" rel="up">Multi-dimensional Array Format</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<span id="Dynamic-Arrays-in-C_002d_002d_002dThe-Wrong-Way"></span><h4 class="subsection">3.2.5 Dynamic Arrays in C—The Wrong Way</h4>
|
|
|
|
<p>A different method for allocating multi-dimensional arrays in C is
|
|
often suggested that is incompatible with FFTW: <em>using it will
|
|
cause FFTW to die a painful death</em>. We discuss the technique here,
|
|
however, because it is so commonly known and used. This method is to
|
|
create arrays of pointers of arrays of pointers of …etcetera.
|
|
For example, the analogue in this method to the example above is:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example">int i,j;
|
|
fftw_complex ***a_bad_array; /* <span class="roman">another way to make a 5x12x27 array</span> */
|
|
|
|
a_bad_array = (fftw_complex ***) malloc(5 * sizeof(fftw_complex **));
|
|
for (i = 0; i < 5; ++i) {
|
|
a_bad_array[i] =
|
|
(fftw_complex **) malloc(12 * sizeof(fftw_complex *));
|
|
for (j = 0; j < 12; ++j)
|
|
a_bad_array[i][j] =
|
|
(fftw_complex *) malloc(27 * sizeof(fftw_complex));
|
|
}
|
|
</pre></div>
|
|
|
|
<p>As you can see, this sort of array is inconvenient to allocate (and
|
|
deallocate). On the other hand, it has the advantage that the
|
|
<em>(i,j,k)</em>-th element can be referenced simply by
|
|
<code>a_bad_array[i][j][k]</code>.
|
|
</p>
|
|
<p>If you like this technique and want to maximize convenience in accessing
|
|
the array, but still want to pass the array to FFTW, you can use a
|
|
hybrid method. Allocate the array as one contiguous block, but also
|
|
declare an array of arrays of pointers that point to appropriate places
|
|
in the block. That sort of trick is beyond the scope of this
|
|
documentation; for more information on multi-dimensional arrays in C,
|
|
see the <code>comp.lang.c</code>
|
|
<a href="http://c-faq.com/aryptr/dynmuldimary.html">FAQ</a>.
|
|
</p>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|