114 lines
4.8 KiB
HTML
114 lines
4.8 KiB
HTML
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<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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preserved on all copies.
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided that the
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entire resulting derived work is distributed under the terms of a
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permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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except that this permission notice may be stated in a translation
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approved by the Free Software Foundation. -->
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<title>Precision (FFTW 3.3.10)</title>
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<link href="index.html" rel="start" title="Top">
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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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<link href="Data-Types-and-Files.html" rel="up" title="Data Types and Files">
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<link href="Memory-Allocation.html" rel="next" title="Memory Allocation">
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<span id="Precision"></span><div class="header">
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<p>
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Next: <a href="Memory-Allocation.html" accesskey="n" rel="next">Memory Allocation</a>, Previous: <a href="Complex-numbers.html" accesskey="p" rel="prev">Complex numbers</a>, Up: <a href="Data-Types-and-Files.html" accesskey="u" rel="up">Data Types and Files</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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</div>
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<hr>
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<span id="Precision-1"></span><h4 class="subsection">4.1.2 Precision</h4>
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<span id="index-precision-3"></span>
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<p>You can install single and long-double precision versions of FFTW,
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which replace <code>double</code> with <code>float</code> and <code>long double</code>,
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respectively (see <a href="Installation-and-Customization.html">Installation and Customization</a>). To use these
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interfaces, you:
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</p>
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<ul>
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<li> Link to the single/long-double libraries; on Unix, <code>-lfftw3f</code> or
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<code>-lfftw3l</code> instead of (or in addition to) <code>-lfftw3</code>. (You
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can link to the different-precision libraries simultaneously.)
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</li><li> Include the <em>same</em> <code><fftw3.h></code> header file.
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</li><li> Replace all lowercase instances of ‘<samp>fftw_</samp>’ with ‘<samp>fftwf_</samp>’ or
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‘<samp>fftwl_</samp>’ for single or long-double precision, respectively.
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(<code>fftw_complex</code> becomes <code>fftwf_complex</code>, <code>fftw_execute</code>
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becomes <code>fftwf_execute</code>, etcetera.)
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</li><li> Uppercase names, i.e. names beginning with ‘<samp>FFTW_</samp>’, remain the
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same.
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</li><li> Replace <code>double</code> with <code>float</code> or <code>long double</code> for
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subroutine parameters.
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</li></ul>
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<p>Depending upon your compiler and/or hardware, <code>long double</code> may not
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be any more precise than <code>double</code> (or may not be supported at all,
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although it is standard in C99).
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<span id="index-C99-2"></span>
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</p>
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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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To use this type, link with <code>-lfftw3q -lquadmath -lm</code> (the
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<code>libquadmath</code> library provided by <code>gcc</code> is needed for
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quadruple-precision trigonometric functions) and use ‘<samp>fftwq_</samp>’
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identifiers.
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</p>
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</body>
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</html>
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