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Replace these with versions built using an older toolset (so as to avoid ABI compatibilities when linking on Ubuntu 14.04 for packaging purposes)
author Chris Cannam
date Fri, 07 Feb 2020 11:51:13 +0000
parents d0c2a83c1364
children
rev   line source
Chris@82 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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Chris@82 3 <!-- This manual is for FFTW
Chris@82 4 (version 3.3.8, 24 May 2018).
Chris@82 5
Chris@82 6 Copyright (C) 2003 Matteo Frigo.
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Chris@82 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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Chris@82 24 <head>
Chris@82 25 <title>FFTW 3.3.8: Cycle Counters</title>
Chris@82 26
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Chris@82 68 </head>
Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="Cycle-Counters"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 74 Next: <a href="Generating-your-own-code.html#Generating-your-own-code" accesskey="n" rel="next">Generating your own code</a>, Previous: <a href="Installation-on-non_002dUnix-systems.html#Installation-on-non_002dUnix-systems" accesskey="p" rel="prev">Installation on non-Unix systems</a>, Up: <a href="Installation-and-Customization.html#Installation-and-Customization" accesskey="u" rel="up">Installation and Customization</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
Chris@82 75 </div>
Chris@82 76 <hr>
Chris@82 77 <a name="Cycle-Counters-1"></a>
Chris@82 78 <h3 class="section">10.3 Cycle Counters</h3>
Chris@82 79 <a name="index-cycle-counter-1"></a>
Chris@82 80
Chris@82 81 <p>FFTW&rsquo;s planner actually executes and times different possible FFT
Chris@82 82 algorithms in order to pick the fastest plan for a given <em>n</em>. In
Chris@82 83 order to do this in as short a time as possible, however, the timer must
Chris@82 84 have a very high resolution, and to accomplish this we employ the
Chris@82 85 hardware <em>cycle counters</em> that are available on most CPUs.
Chris@82 86 Currently, FFTW supports the cycle counters on x86, PowerPC/POWER, Alpha,
Chris@82 87 UltraSPARC (SPARC v9), IA64, PA-RISC, and MIPS processors.
Chris@82 88 </p>
Chris@82 89 <a name="index-compiler-3"></a>
Chris@82 90 <p>Access to the cycle counters, unfortunately, is a compiler and/or
Chris@82 91 operating-system dependent task, often requiring inline assembly
Chris@82 92 language, and it may be that your compiler is not supported. If you are
Chris@82 93 <em>not</em> supported, FFTW will by default fall back on its estimator
Chris@82 94 (effectively using <code>FFTW_ESTIMATE</code> for all plans).
Chris@82 95 <a name="index-FFTW_005fESTIMATE-3"></a>
Chris@82 96 </p>
Chris@82 97 <p>You can add support by editing the file <code>kernel/cycle.h</code>; normally,
Chris@82 98 this will involve adapting one of the examples already present in order
Chris@82 99 to use the inline-assembler syntax for your C compiler, and will only
Chris@82 100 require a couple of lines of code. Anyone adding support for a new
Chris@82 101 system to <code>cycle.h</code> is encouraged to email us at <a href="mailto:fftw@fftw.org">fftw@fftw.org</a>.
Chris@82 102 </p>
Chris@82 103 <p>If a cycle counter is not available on your system (e.g. some embedded
Chris@82 104 processor), and you don&rsquo;t want to use estimated plans, as a last resort
Chris@82 105 you can use the <code>--with-slow-timer</code> option to <code>configure</code> (on
Chris@82 106 Unix) or <code>#define WITH_SLOW_TIMER</code> in <code>config.h</code> (elsewhere).
Chris@82 107 This will use the much lower-resolution <code>gettimeofday</code> function, or even
Chris@82 108 <code>clock</code> if the former is unavailable, and planning will be
Chris@82 109 extremely slow.
Chris@82 110 </p>
Chris@82 111 <hr>
Chris@82 112 <div class="header">
Chris@82 113 <p>
Chris@82 114 Next: <a href="Generating-your-own-code.html#Generating-your-own-code" accesskey="n" rel="next">Generating your own code</a>, Previous: <a href="Installation-on-non_002dUnix-systems.html#Installation-on-non_002dUnix-systems" accesskey="p" rel="prev">Installation on non-Unix systems</a>, Up: <a href="Installation-and-Customization.html#Installation-and-Customization" accesskey="u" rel="up">Installation and Customization</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
Chris@82 115 </div>
Chris@82 116
Chris@82 117
Chris@82 118
Chris@82 119 </body>
Chris@82 120 </html>