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First commit. VS2013, Codeblocks and Mac OSX configuration
author Geogaddi\David <d.m.ronan@qmul.ac.uk>
date Thu, 09 Jul 2015 01:12:16 +0100
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1 <html lang="en">
2 <head>
3 <title>FFTW Accuracy on Cell - FFTW 3.2.1</title>
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5 <meta name="description" content="FFTW 3.2.1">
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8 <link rel="up" href="FFTW-on-the-Cell-Processor.html#FFTW-on-the-Cell-Processor" title="FFTW on the Cell Processor">
9 <link rel="prev" href="Cell-Caveats.html#Cell-Caveats" title="Cell Caveats">
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47 <div class="node">
48 <p>
49 <a name="FFTW-Accuracy-on-Cell"></a>
50 Previous:&nbsp;<a rel="previous" accesskey="p" href="Cell-Caveats.html#Cell-Caveats">Cell Caveats</a>,
51 Up:&nbsp;<a rel="up" accesskey="u" href="FFTW-on-the-Cell-Processor.html#FFTW-on-the-Cell-Processor">FFTW on the Cell Processor</a>
52 <hr>
53 </div>
54
55 <h3 class="section">6.3 FFTW Accuracy on Cell</h3>
56
57 <p>The SPEs are fully IEEE-754 compliant in double precision. In single
58 precision, they only implement round-towards-zero as opposed to the
59 standard round-to-even mode. (The PPE is fully IEEE-754 compliant
60 like all other PowerPC implementations.) Because of the rounding
61 mode, FFTW is less accurate when running on the SPEs than on the PPE.
62 The accuracy loss is hard to quantify in general, but as a rough
63 guideline, the L2 norm of the relative roundoff error for random
64 inputs is 4 to 8 times larger than the corresponding calculation in
65 round-to-even arithmetic. In other words, expect to lose 2 to 3 bits
66 of accuracy.
67
68 <p>FFTW currently does not use any algorithm that degrades accuracy to
69 gain performance on the SPE. One implication of this choice is that
70 large 1D transforms run slower than they would if we were willing to
71 sacrifice another bit or so of accuracy.
72
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