103 lines
4.8 KiB
HTML
103 lines
4.8 KiB
HTML
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<!-- This manual is for FFTW
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(version 3.3.10, 10 December 2020).
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Copyright (C) 2003 Matteo Frigo.
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Copyright (C) 2003 Massachusetts Institute of Technology.
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Permission is granted to make and distribute verbatim copies of this
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manual provided the copyright notice and this permission notice are
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<title>Extended and quadruple precision in Fortran (FFTW 3.3.10)</title>
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<span id="Extended-and-quadruple-precision-in-Fortran"></span><div class="header">
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<p>
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Previous: <a href="Overview-of-Fortran-interface.html" accesskey="p" rel="prev">Overview of Fortran interface</a>, Up: <a href="Overview-of-Fortran-interface.html" accesskey="u" rel="up">Overview of Fortran interface</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<hr>
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<span id="Extended-and-quadruple-precision-in-Fortran-1"></span><h4 class="subsection">7.1.1 Extended and quadruple precision in Fortran</h4>
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<span id="index-precision-7"></span>
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<p>If FFTW is compiled in <code>long double</code> (extended) precision
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(see <a href="Installation-and-Customization.html">Installation and Customization</a>), you may be able to call the
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resulting <code>fftwl_</code> routines (see <a href="Precision.html">Precision</a>) from Fortran if
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your compiler supports the <code>C_LONG_DOUBLE_COMPLEX</code> type code.
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</p>
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<p>Because some Fortran compilers do not support
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<code>C_LONG_DOUBLE_COMPLEX</code>, the <code>fftwl_</code> declarations are
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segregated into a separate interface file <code>fftw3l.f03</code>, which you
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should include <em>in addition</em> to <code>fftw3.f03</code> (which declares
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precision-independent ‘<samp>FFTW_</samp>’ constants):
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</p>
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<span id="index-iso_005fc_005fbinding-2"></span>
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<div class="example">
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<pre class="example"> use, intrinsic :: iso_c_binding
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include 'fftw3.f03'
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include 'fftw3l.f03'
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</pre></div>
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<p>We also support using the nonstandard <code>__float128</code>
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quadruple-precision type provided by recent versions of <code>gcc</code> on
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32- and 64-bit x86 hardware (see <a href="Installation-and-Customization.html">Installation and Customization</a>),
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using the corresponding <code>real(16)</code> and <code>complex(16)</code> types
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supported by <code>gfortran</code>. The quadruple-precision ‘<samp>fftwq_</samp>’
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functions (see <a href="Precision.html">Precision</a>) are declared in a <code>fftw3q.f03</code>
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interface file, which should be included in addition to
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<code>fftw3.f03</code>, as above. You should also link with
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<code>-lfftw3q -lquadmath -lm</code> as in C.
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</p>
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