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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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1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
2 <html>
3 <!-- This manual is for FFTW
4 (version 3.3.5, 30 July 2016).
5
6 Copyright (C) 2003 Matteo Frigo.
7
8 Copyright (C) 2003 Massachusetts Institute of Technology.
9
10 Permission is granted to make and distribute verbatim copies of this
11 manual provided the copyright notice and this permission notice are
12 preserved on all copies.
13
14 Permission is granted to copy and distribute modified versions of this
15 manual under the conditions for verbatim copying, provided that the
16 entire resulting derived work is distributed under the terms of a
17 permission notice identical to this one.
18
19 Permission is granted to copy and distribute translations of this manual
20 into another language, under the above conditions for modified versions,
21 except that this permission notice may be stated in a translation
22 approved by the Free Software Foundation. -->
23 <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
24 <head>
25 <title>FFTW 3.3.5: Precision</title>
26
27 <meta name="description" content="FFTW 3.3.5: Precision">
28 <meta name="keywords" content="FFTW 3.3.5: Precision">
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33 <link href="index.html#Top" rel="start" title="Top">
34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
36 <link href="Data-Types-and-Files.html#Data-Types-and-Files" rel="up" title="Data Types and Files">
37 <link href="Memory-Allocation.html#Memory-Allocation" rel="next" title="Memory Allocation">
38 <link href="Complex-numbers.html#Complex-numbers" rel="prev" title="Complex numbers">
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69 </head>
70
71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
72 <a name="Precision"></a>
73 <div class="header">
74 <p>
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>
76 </div>
77 <hr>
78 <a name="Precision-1"></a>
79 <h4 class="subsection">4.1.2 Precision</h4>
80 <a name="index-precision-3"></a>
81
82 <p>You can install single and long-double precision versions of FFTW,
83 which replace <code>double</code> with <code>float</code> and <code>long double</code>,
84 respectively (see <a href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a>). To use these
85 interfaces, you:
86 </p>
87 <ul>
88 <li> Link to the single/long-double libraries; on Unix, <code>-lfftw3f</code> or
89 <code>-lfftw3l</code> instead of (or in addition to) <code>-lfftw3</code>. (You
90 can link to the different-precision libraries simultaneously.)
91
92 </li><li> Include the <em>same</em> <code>&lt;fftw3.h&gt;</code> header file.
93
94 </li><li> Replace all lowercase instances of &lsquo;<samp>fftw_</samp>&rsquo; with &lsquo;<samp>fftwf_</samp>&rsquo; or
95 &lsquo;<samp>fftwl_</samp>&rsquo; for single or long-double precision, respectively.
96 (<code>fftw_complex</code> becomes <code>fftwf_complex</code>, <code>fftw_execute</code>
97 becomes <code>fftwf_execute</code>, etcetera.)
98
99 </li><li> Uppercase names, i.e. names beginning with &lsquo;<samp>FFTW_</samp>&rsquo;, remain the
100 same.
101
102 </li><li> Replace <code>double</code> with <code>float</code> or <code>long double</code> for
103 subroutine parameters.
104
105 </li></ul>
106
107 <p>Depending upon your compiler and/or hardware, <code>long double</code> may not
108 be any more precise than <code>double</code> (or may not be supported at all,
109 although it is standard in C99).
110 <a name="index-C99-2"></a>
111 </p>
112
113 <p>We also support using the nonstandard <code>__float128</code>
114 quadruple-precision type provided by recent versions of <code>gcc</code> on
115 32- and 64-bit x86 hardware (see <a href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a>).
116 To use this type, link with <code>-lfftw3q -lquadmath -lm</code> (the
117 <code>libquadmath</code> library provided by <code>gcc</code> is needed for
118 quadruple-precision trigonometric functions) and use &lsquo;<samp>fftwq_</samp>&rsquo;
119 identifiers.
120 </p>
121
122
123
124 </body>
125 </html>