mirror of
https://github.com/tildearrow/furnace.git
synced 2024-11-16 09:45:06 +00:00
181 lines
8.2 KiB
HTML
181 lines
8.2 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>Using Plans (FFTW 3.3.10)</title>
|
|
|
|
<meta name="description" content="Using Plans (FFTW 3.3.10)">
|
|
<meta name="keywords" content="Using Plans (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="FFTW-Reference.html" rel="up" title="FFTW Reference">
|
|
<link href="Basic-Interface.html" rel="next" title="Basic Interface">
|
|
<link href="Memory-Allocation.html" rel="prev" title="Memory Allocation">
|
|
<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="Using-Plans"></span><div class="header">
|
|
<p>
|
|
Next: <a href="Basic-Interface.html" accesskey="n" rel="next">Basic Interface</a>, Previous: <a href="Data-Types-and-Files.html" accesskey="p" rel="prev">Data Types and Files</a>, Up: <a href="FFTW-Reference.html" accesskey="u" rel="up">FFTW Reference</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="Using-Plans-1"></span><h3 class="section">4.2 Using Plans</h3>
|
|
|
|
<p>Plans for all transform types in FFTW are stored as type
|
|
<code>fftw_plan</code> (an opaque pointer type), and are created by one of the
|
|
various planning routines described in the following sections.
|
|
<span id="index-fftw_005fplan-1"></span>
|
|
An <code>fftw_plan</code> contains all information necessary to compute the
|
|
transform, including the pointers to the input and output arrays.
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example">void fftw_execute(const fftw_plan plan);
|
|
</pre></div>
|
|
<span id="index-fftw_005fexecute-1"></span>
|
|
|
|
<p>This executes the <code>plan</code>, to compute the corresponding transform on
|
|
the arrays for which it was planned (which must still exist). The plan
|
|
is not modified, and <code>fftw_execute</code> can be called as many times as
|
|
desired.
|
|
</p>
|
|
<p>To apply a given plan to a different array, you can use the new-array execute
|
|
interface. See <a href="New_002darray-Execute-Functions.html">New-array Execute Functions</a>.
|
|
</p>
|
|
<p><code>fftw_execute</code> (and equivalents) is the only function in FFTW
|
|
guaranteed to be thread-safe; see <a href="Thread-safety.html">Thread safety</a>.
|
|
</p>
|
|
<p>This function:
|
|
</p><div class="example">
|
|
<pre class="example">void fftw_destroy_plan(fftw_plan plan);
|
|
</pre></div>
|
|
<span id="index-fftw_005fdestroy_005fplan-1"></span>
|
|
<p>deallocates the <code>plan</code> and all its associated data.
|
|
</p>
|
|
<p>FFTW’s planner saves some other persistent data, such as the
|
|
accumulated wisdom and a list of algorithms available in the current
|
|
configuration. If you want to deallocate all of that and reset FFTW
|
|
to the pristine state it was in when you started your program, you can
|
|
call:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example">void fftw_cleanup(void);
|
|
</pre></div>
|
|
<span id="index-fftw_005fcleanup"></span>
|
|
|
|
<p>After calling <code>fftw_cleanup</code>, all existing plans become undefined,
|
|
and you should not attempt to execute them nor to destroy them. You can
|
|
however create and execute/destroy new plans, in which case FFTW starts
|
|
accumulating wisdom information again.
|
|
</p>
|
|
<p><code>fftw_cleanup</code> does not deallocate your plans, however. To prevent
|
|
memory leaks, you must still call <code>fftw_destroy_plan</code> before
|
|
executing <code>fftw_cleanup</code>.
|
|
</p>
|
|
<p>Occasionally, it may useful to know FFTW’s internal “cost” metric
|
|
that it uses to compare plans to one another; this cost is
|
|
proportional to an execution time of the plan, in undocumented units,
|
|
if the plan was created with the <code>FFTW_MEASURE</code> or other
|
|
timing-based options, or alternatively is a heuristic cost function
|
|
for <code>FFTW_ESTIMATE</code> plans. (The cost values of measured and
|
|
estimated plans are not comparable, being in different units. Also,
|
|
costs from different FFTW versions or the same version compiled
|
|
differently may not be in the same units. Plans created from wisdom
|
|
have a cost of 0 since no timing measurement is performed for them.
|
|
Finally, certain problems for which only one top-level algorithm was
|
|
possible may have required no measurements of the cost of the whole
|
|
plan, in which case <code>fftw_cost</code> will also return 0.) The cost
|
|
metric for a given plan is returned by:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example">double fftw_cost(const fftw_plan plan);
|
|
</pre></div>
|
|
<span id="index-fftw_005fcost"></span>
|
|
|
|
<p>The following two routines are provided purely for academic purposes
|
|
(that is, for entertainment).
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example">void fftw_flops(const fftw_plan plan,
|
|
double *add, double *mul, double *fma);
|
|
</pre></div>
|
|
<span id="index-fftw_005fflops"></span>
|
|
|
|
<p>Given a <code>plan</code>, set <code>add</code>, <code>mul</code>, and <code>fma</code> to an
|
|
exact count of the number of floating-point additions, multiplications,
|
|
and fused multiply-add operations involved in the plan’s execution. The
|
|
total number of floating-point operations (flops) is <code>add + mul +
|
|
2*fma</code>, or <code>add + mul + fma</code> if the hardware supports fused
|
|
multiply-add instructions (although the number of FMA operations is only
|
|
approximate because of compiler voodoo). (The number of operations
|
|
should be an integer, but we use <code>double</code> to avoid overflowing
|
|
<code>int</code> for large transforms; the arguments are of type <code>double</code>
|
|
even for single and long-double precision versions of FFTW.)
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example">void fftw_fprint_plan(const fftw_plan plan, FILE *output_file);
|
|
void fftw_print_plan(const fftw_plan plan);
|
|
char *fftw_sprint_plan(const fftw_plan plan);
|
|
</pre></div>
|
|
<span id="index-fftw_005ffprint_005fplan"></span>
|
|
<span id="index-fftw_005fprint_005fplan"></span>
|
|
|
|
<p>This outputs a “nerd-readable” representation of the <code>plan</code> to
|
|
the given file, to <code>stdout</code>, or two a newly allocated
|
|
NUL-terminated string (which the caller is responsible for deallocating
|
|
with <code>free</code>), respectively.
|
|
</p>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Basic-Interface.html" accesskey="n" rel="next">Basic Interface</a>, Previous: <a href="Data-Types-and-Files.html" accesskey="p" rel="prev">Data Types and Files</a>, Up: <a href="FFTW-Reference.html" accesskey="u" rel="up">FFTW Reference</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>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|