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author Chris Cannam
date Wed, 20 Mar 2013 15:35:50 +0000
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3 <title>Extended and quadruple precision in Fortran - FFTW 3.3.3</title>
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48 <a name="Extended-and-quadruple-precision-in-Fortran"></a>
49 <p>
50 Previous:&nbsp;<a rel="previous" accesskey="p" href="Overview-of-Fortran-interface.html#Overview-of-Fortran-interface">Overview of Fortran interface</a>,
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54
55 <h4 class="subsection">7.1.1 Extended and quadruple precision in Fortran</h4>
56
57 <p><a name="index-precision-515"></a>
58 If FFTW is compiled in <code>long double</code> (extended) precision
59 (see <a href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a>), you may be able to call the
60 resulting <code>fftwl_</code> routines (see <a href="Precision.html#Precision">Precision</a>) from Fortran if
61 your compiler supports the <code>C_LONG_DOUBLE_COMPLEX</code> type code.
62
63 <p>Because some Fortran compilers do not support
64 <code>C_LONG_DOUBLE_COMPLEX</code>, the <code>fftwl_</code> declarations are
65 segregated into a separate interface file <code>fftw3l.f03</code>, which you
66 should include <em>in addition</em> to <code>fftw3.f03</code> (which declares
67 precision-independent &lsquo;<samp><span class="samp">FFTW_</span></samp>&rsquo; constants):
68
69 <p><a name="index-iso_005fc_005fbinding-516"></a>
70 <pre class="example"> use, intrinsic :: iso_c_binding
71 include 'fftw3.f03'
72 include 'fftw3l.f03'
73 </pre>
74 <p>We also support using the nonstandard <code>__float128</code>
75 quadruple-precision type provided by recent versions of <code>gcc</code> on
76 32- and 64-bit x86 hardware (see <a href="Installation-and-Customization.html#Installation-and-Customization">Installation and Customization</a>),
77 using the corresponding <code>real(16)</code> and <code>complex(16)</code> types
78 supported by <code>gfortran</code>. The quadruple-precision &lsquo;<samp><span class="samp">fftwq_</span></samp>&rsquo;
79 functions (see <a href="Precision.html#Precision">Precision</a>) are declared in a <code>fftw3q.f03</code>
80 interface file, which should be included in addition to
81 <code>fftw3l.f03</code>, as above. You should also link with
82 <code>-lfftw3q -lquadmath -lm</code> as in C.
83
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86