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1 <html lang="en">
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2 <head>
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3 <title>Precision - FFTW 3.3.3</title>
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4 <meta http-equiv="Content-Type" content="text/html">
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5 <meta name="description" content="FFTW 3.3.3">
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6 <meta name="generator" content="makeinfo 4.13">
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7 <link title="Top" rel="start" href="index.html#Top">
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8 <link rel="up" href="Data-Types-and-Files.html#Data-Types-and-Files" title="Data Types and Files">
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9 <link rel="prev" href="Complex-numbers.html#Complex-numbers" title="Complex numbers">
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10 <link rel="next" href="Memory-Allocation.html#Memory-Allocation" title="Memory Allocation">
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11 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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12 <!--
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13 This manual is for FFTW
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14 (version 3.3.3, 25 November 2012).
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15
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16 Copyright (C) 2003 Matteo Frigo.
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17
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18 Copyright (C) 2003 Massachusetts Institute of Technology.
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19
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20 Permission is granted to make and distribute verbatim copies of
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21 this manual provided the copyright notice and this permission
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22 notice are preserved on all copies.
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23
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24 Permission is granted to copy and distribute modified versions of
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25 this manual under the conditions for verbatim copying, provided
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26 that the entire resulting derived work is distributed under the
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27 terms of a permission notice identical to this one.
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28
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29 Permission is granted to copy and distribute translations of this
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30 manual into another language, under the above conditions for
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31 modified versions, except that this permission notice may be
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32 stated in a translation approved by the Free Software Foundation.
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33 -->
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34 <meta http-equiv="Content-Style-Type" content="text/css">
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35 <style type="text/css"><!--
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45 --></style>
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46 </head>
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47 <body>
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48 <div class="node">
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49 <a name="Precision"></a>
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50 <p>
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51 Next: <a rel="next" accesskey="n" href="Memory-Allocation.html#Memory-Allocation">Memory Allocation</a>,
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52 Previous: <a rel="previous" accesskey="p" href="Complex-numbers.html#Complex-numbers">Complex numbers</a>,
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53 Up: <a rel="up" accesskey="u" href="Data-Types-and-Files.html#Data-Types-and-Files">Data Types and Files</a>
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54 <hr>
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55 </div>
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56
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57 <h4 class="subsection">4.1.2 Precision</h4>
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58
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59 <p><a name="index-precision-143"></a>
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60 You can install single and long-double precision versions of FFTW,
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61 which replace <code>double</code> with <code>float</code> and <code>long double</code>,
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62 respectively (see <a href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a>). To use these
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63 interfaces, you:
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64
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65 <ul>
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66 <li>Link to the single/long-double libraries; on Unix, <code>-lfftw3f</code> or
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67 <code>-lfftw3l</code> instead of (or in addition to) <code>-lfftw3</code>. (You
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68 can link to the different-precision libraries simultaneously.)
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69
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70 <li>Include the <em>same</em> <code><fftw3.h></code> header file.
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71
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72 <li>Replace all lowercase instances of ‘<samp><span class="samp">fftw_</span></samp>’ with ‘<samp><span class="samp">fftwf_</span></samp>’ or
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73 ‘<samp><span class="samp">fftwl_</span></samp>’ for single or long-double precision, respectively.
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74 (<code>fftw_complex</code> becomes <code>fftwf_complex</code>, <code>fftw_execute</code>
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75 becomes <code>fftwf_execute</code>, etcetera.)
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76
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77 <li>Uppercase names, i.e. names beginning with ‘<samp><span class="samp">FFTW_</span></samp>’, remain the
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78 same.
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79
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80 <li>Replace <code>double</code> with <code>float</code> or <code>long double</code> for
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81 subroutine parameters.
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82
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83 </ul>
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84
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85 <p>Depending upon your compiler and/or hardware, <code>long double</code> may not
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86 be any more precise than <code>double</code> (or may not be supported at all,
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87 although it is standard in C99).
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88 <a name="index-C99-144"></a>
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89
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90 <p>We also support using the nonstandard <code>__float128</code>
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91 quadruple-precision type provided by recent versions of <code>gcc</code> on
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92 32- and 64-bit x86 hardware (see <a href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a>).
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93 To use this type, link with <code>-lfftw3q -lquadmath -lm</code> (the
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94 <code>libquadmath</code> library provided by <code>gcc</code> is needed for
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95 quadruple-precision trigonometric functions) and use ‘<samp><span class="samp">fftwq_</span></samp>’
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96 identifiers.
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97
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98 <!-- =========> -->
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99 </body></html>
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100
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