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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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3 <!-- This manual is for FFTW
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6 Copyright (C) 2003 Matteo Frigo.
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25 <title>FFTW 3.3.5: Extended and quadruple precision in Fortran</title>
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72 <a name="Extended-and-quadruple-precision-in-Fortran"></a>
73 <div class="header">
74 <p>
75 Previous: <a href="Overview-of-Fortran-interface.html#Overview-of-Fortran-interface" accesskey="p" rel="prev">Overview of Fortran interface</a>, Up: <a href="Overview-of-Fortran-interface.html#Overview-of-Fortran-interface" accesskey="u" rel="up">Overview of Fortran interface</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="Extended-and-quadruple-precision-in-Fortran-1"></a>
79 <h4 class="subsection">7.1.1 Extended and quadruple precision in Fortran</h4>
80 <a name="index-precision-7"></a>
81
82 <p>If FFTW is compiled in <code>long double</code> (extended) precision
83 (see <a href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a>), you may be able to call the
84 resulting <code>fftwl_</code> routines (see <a href="Precision.html#Precision">Precision</a>) from Fortran if
85 your compiler supports the <code>C_LONG_DOUBLE_COMPLEX</code> type code.
86 </p>
87 <p>Because some Fortran compilers do not support
88 <code>C_LONG_DOUBLE_COMPLEX</code>, the <code>fftwl_</code> declarations are
89 segregated into a separate interface file <code>fftw3l.f03</code>, which you
90 should include <em>in addition</em> to <code>fftw3.f03</code> (which declares
91 precision-independent &lsquo;<samp>FFTW_</samp>&rsquo; constants):
92 </p>
93 <a name="index-iso_005fc_005fbinding-2"></a>
94 <div class="example">
95 <pre class="example"> use, intrinsic :: iso_c_binding
96 include 'fftw3.f03'
97 include 'fftw3l.f03'
98 </pre></div>
99
100 <p>We also support using the nonstandard <code>__float128</code>
101 quadruple-precision type provided by recent versions of <code>gcc</code> on
102 32- and 64-bit x86 hardware (see <a href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a>),
103 using the corresponding <code>real(16)</code> and <code>complex(16)</code> types
104 supported by <code>gfortran</code>. The quadruple-precision &lsquo;<samp>fftwq_</samp>&rsquo;
105 functions (see <a href="Precision.html#Precision">Precision</a>) are declared in a <code>fftw3q.f03</code>
106 interface file, which should be included in addition to
107 <code>fftw3l.f03</code>, as above. You should also link with
108 <code>-lfftw3q -lquadmath -lm</code> as in C.
109 </p>
110
111
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