mirror of
https://github.com/tildearrow/furnace.git
synced 2024-11-01 18:42:40 +00:00
109 lines
5.4 KiB
HTML
109 lines
5.4 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>Cycle Counters (FFTW 3.3.10)</title>
|
|
|
|
<meta name="description" content="Cycle Counters (FFTW 3.3.10)">
|
|
<meta name="keywords" content="Cycle Counters (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="Installation-and-Customization.html" rel="up" title="Installation and Customization">
|
|
<link href="Generating-your-own-code.html" rel="next" title="Generating your own code">
|
|
<link href="Installation-on-non_002dUnix-systems.html" rel="prev" title="Installation on non-Unix systems">
|
|
<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="Cycle-Counters"></span><div class="header">
|
|
<p>
|
|
Next: <a href="Generating-your-own-code.html" accesskey="n" rel="next">Generating your own code</a>, Previous: <a href="Installation-on-non_002dUnix-systems.html" accesskey="p" rel="prev">Installation on non-Unix systems</a>, Up: <a href="Installation-and-Customization.html" accesskey="u" rel="up">Installation and Customization</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="Cycle-Counters-1"></span><h3 class="section">10.3 Cycle Counters</h3>
|
|
<span id="index-cycle-counter-1"></span>
|
|
|
|
<p>FFTW’s planner actually executes and times different possible FFT
|
|
algorithms in order to pick the fastest plan for a given <em>n</em>. In
|
|
order to do this in as short a time as possible, however, the timer must
|
|
have a very high resolution, and to accomplish this we employ the
|
|
hardware <em>cycle counters</em> that are available on most CPUs.
|
|
Currently, FFTW supports the cycle counters on x86, PowerPC/POWER, Alpha,
|
|
UltraSPARC (SPARC v9), IA64, PA-RISC, and MIPS processors.
|
|
</p>
|
|
<span id="index-compiler-3"></span>
|
|
<p>Access to the cycle counters, unfortunately, is a compiler and/or
|
|
operating-system dependent task, often requiring inline assembly
|
|
language, and it may be that your compiler is not supported. If you are
|
|
<em>not</em> supported, FFTW will by default fall back on its estimator
|
|
(effectively using <code>FFTW_ESTIMATE</code> for all plans).
|
|
<span id="index-FFTW_005fESTIMATE-3"></span>
|
|
</p>
|
|
<p>You can add support by editing the file <code>kernel/cycle.h</code>; normally,
|
|
this will involve adapting one of the examples already present in order
|
|
to use the inline-assembler syntax for your C compiler, and will only
|
|
require a couple of lines of code. Anyone adding support for a new
|
|
system to <code>cycle.h</code> is encouraged to email us at <a href="mailto:fftw@fftw.org">fftw@fftw.org</a>.
|
|
</p>
|
|
<p>If a cycle counter is not available on your system (e.g. some embedded
|
|
processor), and you don’t want to use estimated plans, as a last resort
|
|
you can use the <code>--with-slow-timer</code> option to <code>configure</code> (on
|
|
Unix) or <code>#define WITH_SLOW_TIMER</code> in <code>config.h</code> (elsewhere).
|
|
This will use the much lower-resolution <code>gettimeofday</code> function, or even
|
|
<code>clock</code> if the former is unavailable, and planning will be
|
|
extremely slow.
|
|
</p>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Generating-your-own-code.html" accesskey="n" rel="next">Generating your own code</a>, Previous: <a href="Installation-on-non_002dUnix-systems.html" accesskey="p" rel="prev">Installation on non-Unix systems</a>, Up: <a href="Installation-and-Customization.html" accesskey="u" rel="up">Installation and Customization</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>
|