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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
4 (version 3.3.5, 30 July 2016).
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6 Copyright (C) 2003 Matteo Frigo.
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8 Copyright (C) 2003 Massachusetts Institute of Technology.
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25 <title>FFTW 3.3.5: 64-bit Guru Interface</title>
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72 <a name="g_t64_002dbit-Guru-Interface"></a>
73 <div class="header">
74 <p>
75 Previous: <a href="Guru-Real_002dto_002dreal-Transforms.html#Guru-Real_002dto_002dreal-Transforms" accesskey="p" rel="prev">Guru Real-to-real Transforms</a>, Up: <a href="Guru-Interface.html#Guru-Interface" accesskey="u" rel="up">Guru 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="g_t64_002dbit-Guru-Interface-1"></a>
79 <h4 class="subsection">4.5.6 64-bit Guru Interface</h4>
80 <a name="index-64_002dbit-architecture"></a>
81
82 <p>When compiled in 64-bit mode on a 64-bit architecture (where addresses
83 are 64 bits wide), FFTW uses 64-bit quantities internally for all
84 transform sizes, strides, and so on&mdash;you don&rsquo;t have to do anything
85 special to exploit this. However, in the ordinary FFTW interfaces,
86 you specify the transform size by an <code>int</code> quantity, which is
87 normally only 32 bits wide. This means that, even though FFTW is
88 using 64-bit sizes internally, you cannot specify a single transform
89 dimension larger than
90 2<sup><small>31</small></sup>&minus;1numbers.
91 </p>
92 <p>We expect that few users will require transforms larger than this, but,
93 for those who do, we provide a 64-bit version of the guru interface in
94 which all sizes are specified as integers of type <code>ptrdiff_t</code>
95 instead of <code>int</code>. (<code>ptrdiff_t</code> is a signed integer type
96 defined by the C standard to be wide enough to represent address
97 differences, and thus must be at least 64 bits wide on a 64-bit
98 machine.) We stress that there is <em>no performance advantage</em> to
99 using this interface&mdash;the same internal FFTW code is employed
100 regardless&mdash;and it is only necessary if you want to specify very
101 large transform sizes.
102 <a name="index-ptrdiff_005ft"></a>
103 </p>
104
105 <p>In particular, the 64-bit guru interface is a set of planner routines
106 that are exactly the same as the guru planner routines, except that
107 they are named with &lsquo;<samp>guru64</samp>&rsquo; instead of &lsquo;<samp>guru</samp>&rsquo; and they take
108 arguments of type <code>fftw_iodim64</code> instead of <code>fftw_iodim</code>.
109 For example, instead of <code>fftw_plan_guru_dft</code>, we have
110 <code>fftw_plan_guru64_dft</code>.
111 </p>
112 <div class="example">
113 <pre class="example">fftw_plan fftw_plan_guru64_dft(
114 int rank, const fftw_iodim64 *dims,
115 int howmany_rank, const fftw_iodim64 *howmany_dims,
116 fftw_complex *in, fftw_complex *out,
117 int sign, unsigned flags);
118 </pre></div>
119 <a name="index-fftw_005fplan_005fguru64_005fdft"></a>
120
121 <p>The <code>fftw_iodim64</code> type is similar to <code>fftw_iodim</code>, with the
122 same interpretation, except that it uses type <code>ptrdiff_t</code> instead
123 of type <code>int</code>.
124 </p>
125 <div class="example">
126 <pre class="example">typedef struct {
127 ptrdiff_t n;
128 ptrdiff_t is;
129 ptrdiff_t os;
130 } fftw_iodim64;
131 </pre></div>
132 <a name="index-fftw_005fiodim64"></a>
133
134 <p>Every other &lsquo;<samp>fftw_plan_guru</samp>&rsquo; function also has a
135 &lsquo;<samp>fftw_plan_guru64</samp>&rsquo; equivalent, but we do not repeat their
136 documentation here since they are identical to the 32-bit versions
137 except as noted above.
138 </p>
139 <hr>
140 <div class="header">
141 <p>
142 Previous: <a href="Guru-Real_002dto_002dreal-Transforms.html#Guru-Real_002dto_002dreal-Transforms" accesskey="p" rel="prev">Guru Real-to-real Transforms</a>, Up: <a href="Guru-Interface.html#Guru-Interface" accesskey="u" rel="up">Guru 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>
143 </div>
144
145
146
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