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64 lines
2.8 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<head><title>
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FFTW FAQ - Section 4
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</title>
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<link rev="made" href="mailto:fftw@fftw.org">
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<link rel="Contents" href="index.html">
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<link rel="Start" href="index.html">
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<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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</head><body text="#000000" bgcolor="#FFFFFF"><h1>
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FFTW FAQ - Section 4 <br>
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Internals of FFTW
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</h1>
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<ul>
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<li><a href="#howworks" rel=subdocument>Q4.1. How does FFTW work?</a>
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<li><a href="#whyfast" rel=subdocument>Q4.2. Why is FFTW so fast?</a>
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</ul><hr>
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<h2><A name="howworks">
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Question 4.1. How does FFTW work?
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</A></h2>
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The innovation (if it can be so called) in FFTW consists in having a
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variety of composable <i>solvers</i>, representing different FFT algorithms and implementation strategies, whose combination into a
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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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This peculiar software architecture allows FFTW to adapt itself to
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almost any machine.
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<p>
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For more details (albeit somewhat outdated), see the paper "FFTW:
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An Adaptive Software Architecture for the FFT", by M. Frigo and
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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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<h2><A name="whyfast">
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Question 4.2. Why is FFTW so fast?
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</A></h2>
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This is a complex question, and there is no simple answer. In fact,
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the authors do not fully know the answer, either. In addition to many
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small performance hacks throughout FFTW, there are three general
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reasons for FFTW's speed.
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<ul>
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<li> FFTW uses a variety of FFT algorithms and implementation styles
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that can be arbitrarily composed to adapt itself to
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a machine. See <A href="#howworks">Q4.1 `How does FFTW work?'</A>.
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<li> FFTW uses a code generator to produce highly-optimized
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routines for computing small transforms.
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<li> FFTW uses explicit divide-and-conquer to take advantage
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of the memory hierarchy.
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</ul>
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For more details (albeit somewhat outdated), see the paper "FFTW:
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An Adaptive Software Architecture for the FFT", by M. Frigo and
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S. G. Johnson, <i>Proc. ICASSP</i> 3, 1381 (1998), available along with other references at
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<A href="http://www.fftw.org">the FFTW web page</A>. <hr>
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Next: <a href="section5.html" rel=precedes>Known bugs</a>.<br>
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Back: <a href="section3.html" rev=precedes>Using FFTW</a>.<br>
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<a href="index.html" rev=subdocument>Return to contents</a>.<p>
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<address>
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<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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- 14 September 2021
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</address><br>
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Extracted from FFTW Frequently Asked Questions with Answers,
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Copyright © 2021 Matteo Frigo and Massachusetts Institute of Technology.
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</body></html>
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