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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam
date Tue, 19 Nov 2019 14:52:55 +0000
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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 25 <title>FFTW 3.3.8: Cycle Counters</title>
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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>
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