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Current fftw source
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 18 Oct 2016 13:40:26 +0100
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cannam@127 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
cannam@127 2 <html>
cannam@127 3 <!-- This manual is for FFTW
cannam@127 4 (version 3.3.5, 30 July 2016).
cannam@127 5
cannam@127 6 Copyright (C) 2003 Matteo Frigo.
cannam@127 7
cannam@127 8 Copyright (C) 2003 Massachusetts Institute of Technology.
cannam@127 9
cannam@127 10 Permission is granted to make and distribute verbatim copies of this
cannam@127 11 manual provided the copyright notice and this permission notice are
cannam@127 12 preserved on all copies.
cannam@127 13
cannam@127 14 Permission is granted to copy and distribute modified versions of this
cannam@127 15 manual under the conditions for verbatim copying, provided that the
cannam@127 16 entire resulting derived work is distributed under the terms of a
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cannam@127 24 <head>
cannam@127 25 <title>FFTW 3.3.5: Precision</title>
cannam@127 26
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cannam@127 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
cannam@127 72 <a name="Precision"></a>
cannam@127 73 <div class="header">
cannam@127 74 <p>
cannam@127 75 Next: <a href="Memory-Allocation.html#Memory-Allocation" accesskey="n" rel="next">Memory Allocation</a>, Previous: <a href="Complex-numbers.html#Complex-numbers" accesskey="p" rel="prev">Complex numbers</a>, Up: <a href="Data-Types-and-Files.html#Data-Types-and-Files" accesskey="u" rel="up">Data Types and Files</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>
cannam@127 76 </div>
cannam@127 77 <hr>
cannam@127 78 <a name="Precision-1"></a>
cannam@127 79 <h4 class="subsection">4.1.2 Precision</h4>
cannam@127 80 <a name="index-precision-3"></a>
cannam@127 81
cannam@127 82 <p>You can install single and long-double precision versions of FFTW,
cannam@127 83 which replace <code>double</code> with <code>float</code> and <code>long double</code>,
cannam@127 84 respectively (see <a href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a>). To use these
cannam@127 85 interfaces, you:
cannam@127 86 </p>
cannam@127 87 <ul>
cannam@127 88 <li> Link to the single/long-double libraries; on Unix, <code>-lfftw3f</code> or
cannam@127 89 <code>-lfftw3l</code> instead of (or in addition to) <code>-lfftw3</code>. (You
cannam@127 90 can link to the different-precision libraries simultaneously.)
cannam@127 91
cannam@127 92 </li><li> Include the <em>same</em> <code>&lt;fftw3.h&gt;</code> header file.
cannam@127 93
cannam@127 94 </li><li> Replace all lowercase instances of &lsquo;<samp>fftw_</samp>&rsquo; with &lsquo;<samp>fftwf_</samp>&rsquo; or
cannam@127 95 &lsquo;<samp>fftwl_</samp>&rsquo; for single or long-double precision, respectively.
cannam@127 96 (<code>fftw_complex</code> becomes <code>fftwf_complex</code>, <code>fftw_execute</code>
cannam@127 97 becomes <code>fftwf_execute</code>, etcetera.)
cannam@127 98
cannam@127 99 </li><li> Uppercase names, i.e. names beginning with &lsquo;<samp>FFTW_</samp>&rsquo;, remain the
cannam@127 100 same.
cannam@127 101
cannam@127 102 </li><li> Replace <code>double</code> with <code>float</code> or <code>long double</code> for
cannam@127 103 subroutine parameters.
cannam@127 104
cannam@127 105 </li></ul>
cannam@127 106
cannam@127 107 <p>Depending upon your compiler and/or hardware, <code>long double</code> may not
cannam@127 108 be any more precise than <code>double</code> (or may not be supported at all,
cannam@127 109 although it is standard in C99).
cannam@127 110 <a name="index-C99-2"></a>
cannam@127 111 </p>
cannam@127 112
cannam@127 113 <p>We also support using the nonstandard <code>__float128</code>
cannam@127 114 quadruple-precision type provided by recent versions of <code>gcc</code> on
cannam@127 115 32- and 64-bit x86 hardware (see <a href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a>).
cannam@127 116 To use this type, link with <code>-lfftw3q -lquadmath -lm</code> (the
cannam@127 117 <code>libquadmath</code> library provided by <code>gcc</code> is needed for
cannam@127 118 quadruple-precision trigonometric functions) and use &lsquo;<samp>fftwq_</samp>&rsquo;
cannam@127 119 identifiers.
cannam@127 120 </p>
cannam@127 121
cannam@127 122
cannam@127 123
cannam@127 124 </body>
cannam@127 125 </html>