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6 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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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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into another language, under the above conditions for modified versions,
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approved by the Free Software Foundation. -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>64-bit Guru Interface (FFTW 3.3.10)</title>
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<meta name="description" content="64-bit Guru Interface (FFTW 3.3.10)">
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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="Guru-Interface.html" rel="up" title="Guru Interface">
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<link href="New_002darray-Execute-Functions.html" rel="next" title="New-array Execute Functions">
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<link href="Guru-Real_002dto_002dreal-Transforms.html" rel="prev" title="Guru Real-to-real Transforms">
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</head>
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<body lang="en">
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<span id="g_t64_002dbit-Guru-Interface"></span><div class="header">
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<p>
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Previous: <a href="Guru-Real_002dto_002dreal-Transforms.html" accesskey="p" rel="prev">Guru Real-to-real Transforms</a>, Up: <a href="Guru-Interface.html" accesskey="u" rel="up">Guru 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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</div>
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<hr>
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<span id="g_t64_002dbit-Guru-Interface-1"></span><h4 class="subsection">4.5.6 64-bit Guru Interface</h4>
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<span id="index-64_002dbit-architecture"></span>
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<p>When compiled in 64-bit mode on a 64-bit architecture (where addresses
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are 64 bits wide), FFTW uses 64-bit quantities internally for all
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transform sizes, strides, and so on—you don’t have to do anything
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special to exploit this. However, in the ordinary FFTW interfaces,
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you specify the transform size by an <code>int</code> quantity, which is
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normally only 32 bits wide. This means that, even though FFTW is
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using 64-bit sizes internally, you cannot specify a single transform
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dimension larger than
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2<sup><small>31</small></sup>−1
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numbers.
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</p>
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<p>We expect that few users will require transforms larger than this, but,
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for those who do, we provide a 64-bit version of the guru interface in
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which all sizes are specified as integers of type <code>ptrdiff_t</code>
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instead of <code>int</code>. (<code>ptrdiff_t</code> is a signed integer type
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defined by the C standard to be wide enough to represent address
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differences, and thus must be at least 64 bits wide on a 64-bit
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machine.) We stress that there is <em>no performance advantage</em> to
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using this interface—the same internal FFTW code is employed
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regardless—and it is only necessary if you want to specify very
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large transform sizes.
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<span id="index-ptrdiff_005ft"></span>
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</p>
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<p>In particular, the 64-bit guru interface is a set of planner routines
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that are exactly the same as the guru planner routines, except that
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they are named with ‘<samp>guru64</samp>’ instead of ‘<samp>guru</samp>’ and they take
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arguments of type <code>fftw_iodim64</code> instead of <code>fftw_iodim</code>.
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For example, instead of <code>fftw_plan_guru_dft</code>, we have
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<code>fftw_plan_guru64_dft</code>.
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</p>
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<div class="example">
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<pre class="example">fftw_plan fftw_plan_guru64_dft(
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int rank, const fftw_iodim64 *dims,
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int howmany_rank, const fftw_iodim64 *howmany_dims,
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fftw_complex *in, fftw_complex *out,
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int sign, unsigned flags);
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</pre></div>
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<span id="index-fftw_005fplan_005fguru64_005fdft"></span>
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<p>The <code>fftw_iodim64</code> type is similar to <code>fftw_iodim</code>, with the
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same interpretation, except that it uses type <code>ptrdiff_t</code> instead
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of type <code>int</code>.
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</p>
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<div class="example">
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<pre class="example">typedef struct {
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ptrdiff_t n;
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ptrdiff_t is;
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ptrdiff_t os;
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} fftw_iodim64;
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</pre></div>
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<span id="index-fftw_005fiodim64"></span>
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<p>Every other ‘<samp>fftw_plan_guru</samp>’ function also has a
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‘<samp>fftw_plan_guru64</samp>’ equivalent, but we do not repeat their
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documentation here since they are identical to the 32-bit versions
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except as noted above.
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</p>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="Guru-Real_002dto_002dreal-Transforms.html" accesskey="p" rel="prev">Guru Real-to-real Transforms</a>, Up: <a href="Guru-Interface.html" accesskey="u" rel="up">Guru 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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</div>
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</body>
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</html>
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