mirror of
https://github.com/tildearrow/furnace.git
synced 2024-11-02 02:52:40 +00:00
204 lines
9.9 KiB
HTML
204 lines
9.9 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>Planner Flags (FFTW 3.3.10)</title>
|
|
|
|
<meta name="description" content="Planner Flags (FFTW 3.3.10)">
|
|
<meta name="keywords" content="Planner Flags (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="Basic-Interface.html" rel="up" title="Basic Interface">
|
|
<link href="Real_002ddata-DFTs.html" rel="next" title="Real-data DFTs">
|
|
<link href="Complex-DFTs.html" rel="prev" title="Complex DFTs">
|
|
<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="Planner-Flags"></span><div class="header">
|
|
<p>
|
|
Next: <a href="Real_002ddata-DFTs.html" accesskey="n" rel="next">Real-data DFTs</a>, Previous: <a href="Complex-DFTs.html" accesskey="p" rel="prev">Complex DFTs</a>, Up: <a href="Basic-Interface.html" accesskey="u" rel="up">Basic Interface</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="Planner-Flags-1"></span><h4 class="subsection">4.3.2 Planner Flags</h4>
|
|
|
|
<p>All of the planner routines in FFTW accept an integer <code>flags</code>
|
|
argument, which is a bitwise OR (‘<samp>|</samp>’) of zero or more of the flag
|
|
constants defined below. These flags control the rigor (and time) of
|
|
the planning process, and can also impose (or lift) restrictions on the
|
|
type of transform algorithm that is employed.
|
|
</p>
|
|
<p><em>Important:</em> the planner overwrites the input array during
|
|
planning unless a saved plan (see <a href="Wisdom.html">Wisdom</a>) is available for that
|
|
problem, so you should initialize your input data after creating the
|
|
plan. The only exceptions to this are the <code>FFTW_ESTIMATE</code> and
|
|
<code>FFTW_WISDOM_ONLY</code> flags, as mentioned below.
|
|
</p>
|
|
<p>In all cases, if wisdom is available for the given problem that was
|
|
created with equal-or-greater planning rigor, then the more rigorous
|
|
wisdom is used. For example, in <code>FFTW_ESTIMATE</code> mode any available
|
|
wisdom is used, whereas in <code>FFTW_PATIENT</code> mode only wisdom created
|
|
in patient or exhaustive mode can be used. See <a href="Words-of-Wisdom_002dSaving-Plans.html">Words of Wisdom-Saving Plans</a>.
|
|
</p>
|
|
<span id="Planning_002drigor-flags"></span><h4 class="subsubheading">Planning-rigor flags</h4>
|
|
<ul>
|
|
<li> <span id="index-FFTW_005fESTIMATE-2"></span>
|
|
<code>FFTW_ESTIMATE</code> specifies that, instead of actual measurements of
|
|
different algorithms, a simple heuristic is used to pick a (probably
|
|
sub-optimal) plan quickly. With this flag, the input/output arrays are
|
|
not overwritten during planning.
|
|
|
|
</li><li> <span id="index-FFTW_005fMEASURE-2"></span>
|
|
<code>FFTW_MEASURE</code> tells FFTW to find an optimized plan by actually
|
|
<em>computing</em> several FFTs and measuring their execution time.
|
|
Depending on your machine, this can take some time (often a few
|
|
seconds). <code>FFTW_MEASURE</code> is the default planning option.
|
|
|
|
</li><li> <span id="index-FFTW_005fPATIENT-2"></span>
|
|
<code>FFTW_PATIENT</code> is like <code>FFTW_MEASURE</code>, but considers a wider
|
|
range of algorithms and often produces a “more optimal” plan
|
|
(especially for large transforms), but at the expense of several times
|
|
longer planning time (especially for large transforms).
|
|
|
|
</li><li> <span id="index-FFTW_005fEXHAUSTIVE-1"></span>
|
|
<code>FFTW_EXHAUSTIVE</code> is like <code>FFTW_PATIENT</code>, but considers an
|
|
even wider range of algorithms, including many that we think are
|
|
unlikely to be fast, to produce the most optimal plan but with a
|
|
substantially increased planning time.
|
|
|
|
</li><li> <span id="index-FFTW_005fWISDOM_005fONLY"></span>
|
|
<code>FFTW_WISDOM_ONLY</code> is a special planning mode in which the plan
|
|
is only created if wisdom is available for the given problem, and
|
|
otherwise a <code>NULL</code> plan is returned. This can be combined with
|
|
other flags, e.g. ‘<samp>FFTW_WISDOM_ONLY | FFTW_PATIENT</samp>’ creates a
|
|
plan only if wisdom is available that was created in
|
|
<code>FFTW_PATIENT</code> or <code>FFTW_EXHAUSTIVE</code> mode. The
|
|
<code>FFTW_WISDOM_ONLY</code> flag is intended for users who need to detect
|
|
whether wisdom is available; for example, if wisdom is not available
|
|
one may wish to allocate new arrays for planning so that user data is
|
|
not overwritten.
|
|
|
|
</li></ul>
|
|
|
|
<span id="Algorithm_002drestriction-flags"></span><h4 class="subsubheading">Algorithm-restriction flags</h4>
|
|
<ul>
|
|
<li> <span id="index-FFTW_005fDESTROY_005fINPUT"></span>
|
|
<code>FFTW_DESTROY_INPUT</code> specifies that an out-of-place transform is
|
|
allowed to <em>overwrite its input</em> array with arbitrary data; this
|
|
can sometimes allow more efficient algorithms to be employed.
|
|
<span id="index-out_002dof_002dplace"></span>
|
|
|
|
</li><li> <span id="index-FFTW_005fPRESERVE_005fINPUT-1"></span>
|
|
<code>FFTW_PRESERVE_INPUT</code> specifies that an out-of-place transform must
|
|
<em>not change its input</em> array. This is ordinarily the
|
|
<em>default</em>, except for c2r and hc2r (i.e. complex-to-real)
|
|
transforms for which <code>FFTW_DESTROY_INPUT</code> is the default. In the
|
|
latter cases, passing <code>FFTW_PRESERVE_INPUT</code> will attempt to use
|
|
algorithms that do not destroy the input, at the expense of worse
|
|
performance; for multi-dimensional c2r transforms, however, no
|
|
input-preserving algorithms are implemented and the planner will return
|
|
<code>NULL</code> if one is requested.
|
|
<span id="index-c2r-1"></span>
|
|
<span id="index-hc2r-1"></span>
|
|
|
|
</li><li> <span id="index-FFTW_005fUNALIGNED"></span>
|
|
<span id="index-alignment-1"></span>
|
|
<span id="index-fftw_005fmalloc-4"></span>
|
|
<span id="index-fftw_005falignment_005fof"></span>
|
|
<code>FFTW_UNALIGNED</code> specifies that the algorithm may not impose any
|
|
unusual alignment requirements on the input/output arrays (i.e. no
|
|
SIMD may be used). This flag is normally <em>not necessary</em>, since
|
|
the planner automatically detects misaligned arrays. The only use for
|
|
this flag is if you want to use the new-array execute interface to
|
|
execute a given plan on a different array that may not be aligned like
|
|
the original. (Using <code>fftw_malloc</code> makes this flag unnecessary
|
|
even then. You can also use <code>fftw_alignment_of</code> to detect
|
|
whether two arrays are equivalently aligned.)
|
|
|
|
</li></ul>
|
|
|
|
<span id="Limiting-planning-time"></span><h4 class="subsubheading">Limiting planning time</h4>
|
|
|
|
<div class="example">
|
|
<pre class="example">extern void fftw_set_timelimit(double seconds);
|
|
</pre></div>
|
|
<span id="index-fftw_005fset_005ftimelimit"></span>
|
|
|
|
<p>This function instructs FFTW to spend at most <code>seconds</code> seconds
|
|
(approximately) in the planner. If <code>seconds ==
|
|
FFTW_NO_TIMELIMIT</code> (the default value, which is negative), then
|
|
planning time is unbounded. Otherwise, FFTW plans with a
|
|
progressively wider range of algorithms until the given time limit
|
|
is reached or the given range of algorithms is explored, returning the
|
|
best available plan.
|
|
<span id="index-FFTW_005fNO_005fTIMELIMIT"></span>
|
|
</p>
|
|
|
|
<p>For example, specifying <code>FFTW_PATIENT</code> first plans in
|
|
<code>FFTW_ESTIMATE</code> mode, then in <code>FFTW_MEASURE</code> mode, then
|
|
finally (time permitting) in <code>FFTW_PATIENT</code>. If
|
|
<code>FFTW_EXHAUSTIVE</code> is specified instead, the planner will further
|
|
progress to <code>FFTW_EXHAUSTIVE</code> mode.
|
|
</p>
|
|
<p>Note that the <code>seconds</code> argument specifies only a rough limit; in
|
|
practice, the planner may use somewhat more time if the time limit is
|
|
reached when the planner is in the middle of an operation that cannot
|
|
be interrupted. At the very least, the planner will complete planning
|
|
in <code>FFTW_ESTIMATE</code> mode (which is thus equivalent to a time limit
|
|
of 0).
|
|
</p>
|
|
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Real_002ddata-DFTs.html" accesskey="n" rel="next">Real-data DFTs</a>, Previous: <a href="Complex-DFTs.html" accesskey="p" rel="prev">Complex DFTs</a>, Up: <a href="Basic-Interface.html" accesskey="u" rel="up">Basic Interface</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>
|