Mercurial > hg > sv-dependency-builds
diff src/fftw-3.3.3/doc/html/Cycle-Counters.html @ 10:37bf6b4a2645
Add FFTW3
| author | Chris Cannam |
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| date | Wed, 20 Mar 2013 15:35:50 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.3/doc/html/Cycle-Counters.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,90 @@ +<html lang="en"> +<head> +<title>Cycle Counters - FFTW 3.3.3</title> +<meta http-equiv="Content-Type" content="text/html"> +<meta name="description" content="FFTW 3.3.3"> +<meta name="generator" content="makeinfo 4.13"> +<link title="Top" rel="start" href="index.html#Top"> +<link rel="up" href="Installation-and-Customization.html#Installation-and-Customization" title="Installation and Customization"> +<link rel="prev" href="Installation-on-non_002dUnix-systems.html#Installation-on-non_002dUnix-systems" title="Installation on non-Unix systems"> +<link rel="next" href="Generating-your-own-code.html#Generating-your-own-code" title="Generating your own code"> +<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> +<!-- +This manual is for FFTW +(version 3.3.3, 25 November 2012). + +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. + --> +<meta http-equiv="Content-Style-Type" content="text/css"> +<style type="text/css"><!-- + pre.display { font-family:inherit } + pre.format { font-family:inherit } + pre.smalldisplay { font-family:inherit; font-size:smaller } + pre.smallformat { font-family:inherit; font-size:smaller } + pre.smallexample { font-size:smaller } + pre.smalllisp { font-size:smaller } + span.sc { font-variant:small-caps } + span.roman { font-family:serif; font-weight:normal; } + span.sansserif { font-family:sans-serif; font-weight:normal; } +--></style> +</head> +<body> +<div class="node"> +<a name="Cycle-Counters"></a> +<p> +Next: <a rel="next" accesskey="n" href="Generating-your-own-code.html#Generating-your-own-code">Generating your own code</a>, +Previous: <a rel="previous" accesskey="p" href="Installation-on-non_002dUnix-systems.html#Installation-on-non_002dUnix-systems">Installation on non-Unix systems</a>, +Up: <a rel="up" accesskey="u" href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a> +<hr> +</div> + +<h3 class="section">10.3 Cycle Counters</h3> + +<p><a name="index-cycle-counter-619"></a> +FFTW's planner actually executes and times different possible FFT +algorithms in order to pick the fastest plan for a given n. 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 <dfn>cycle counters</dfn> 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><a name="index-compiler-620"></a>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). +<a name="index-FFTW_005fESTIMATE-621"></a> +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>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. + +<!-- --> + </body></html> +