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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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2 <html>
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3 <head><title>
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4 FFTW FAQ - Section 4
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5 </title>
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6 <link rev="made" href="mailto:fftw@fftw.org">
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7 <link rel="Contents" href="index.html">
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8 <link rel="Start" href="index.html">
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9 <link rel="Next" href="section5.html"><link rel="Previous" href="section3.html"><link rel="Bookmark" title="FFTW FAQ" href="index.html">
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10 </head><body text="#000000" bgcolor="#FFFFFF"><h1>
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11 FFTW FAQ - Section 4 <br>
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12 Internals of FFTW
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13 </h1>
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14
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15 <ul>
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16 <li><a href="#howworks" rel=subdocument>Q4.1. How does FFTW work?</a>
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17 <li><a href="#whyfast" rel=subdocument>Q4.2. Why is FFTW so fast?</a>
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18 </ul><hr>
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19
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20 <h2><A name="howworks">
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21 Question 4.1. How does FFTW work?
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22 </A></h2>
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23
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24 The innovation (if it can be so called) in FFTW consists in having a
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25 variety of composable <i>solvers</i>, representing different FFT algorithms and implementation strategies, whose combination into a
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26 particular <i>plan</i> for a given size can be determined at runtime according to the characteristics of your machine/compiler.
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27 This peculiar software architecture allows FFTW to adapt itself to
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28 almost any machine.
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29 <p>
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30 For more details (albeit somewhat outdated), see the paper "FFTW:
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31 An Adaptive Software Architecture for the FFT", by M. Frigo and
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32 S. G. Johnson, <i>Proc. ICASSP</i> 3, 1381 (1998), also available at <A href="http://www.fftw.org">the FFTW web page</A>.
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33 <h2><A name="whyfast">
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34 Question 4.2. Why is FFTW so fast?
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35 </A></h2>
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36
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37 This is a complex question, and there is no simple answer. In fact,
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38 the authors do not fully know the answer, either. In addition to many
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39 small performance hacks throughout FFTW, there are three general
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40 reasons for FFTW's speed.
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41 <ul>
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42 <li> FFTW uses a variety of FFT algorithms and implementation styles
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43 that can be arbitrarily composed to adapt itself to
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44 a machine. See <A href="#howworks">Q4.1 `How does FFTW work?'</A>.
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45 <li> FFTW uses a code generator to produce highly-optimized
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46 routines for computing small transforms.
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47
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48 <li> FFTW uses explicit divide-and-conquer to take advantage
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49 of the memory hierarchy.
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50 </ul>
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51 For more details (albeit somewhat outdated), see the paper "FFTW:
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52 An Adaptive Software Architecture for the FFT", by M. Frigo and
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53 S. G. Johnson, <i>Proc. ICASSP</i> 3, 1381 (1998), available along with other references at
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54 <A href="http://www.fftw.org">the FFTW web page</A>. <hr>
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55 Next: <a href="section5.html" rel=precedes>Known bugs</a>.<br>
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56 Back: <a href="section3.html" rev=precedes>Using FFTW</a>.<br>
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57 <a href="index.html" rev=subdocument>Return to contents</a>.<p>
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58 <address>
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59 <A href="http://www.fftw.org">Matteo Frigo and Steven G. Johnson</A> / <A href="mailto:fftw@fftw.org">fftw@fftw.org</A>
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60 - 04 March 2014
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61 </address><br>
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62 Extracted from FFTW Frequently Asked Questions with Answers,
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63 Copyright © 2014 Matteo Frigo and Massachusetts Institute of Technology.
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64 </body></html>
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