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Add FFTW3
author Chris Cannam
date Wed, 20 Mar 2013 15:35:50 +0000
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1 <html lang="en">
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3 <title>64-bit Guru Interface - FFTW 3.3.3</title>
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11 <!--
12 This manual is for FFTW
13 (version 3.3.3, 25 November 2012).
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15 Copyright (C) 2003 Matteo Frigo.
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17 Copyright (C) 2003 Massachusetts Institute of Technology.
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48 <a name="64-bit-Guru-Interface"></a>
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50 <p>
51 Previous:&nbsp;<a rel="previous" accesskey="p" href="Guru-Real_002dto_002dreal-Transforms.html#Guru-Real_002dto_002dreal-Transforms">Guru Real-to-real Transforms</a>,
52 Up:&nbsp;<a rel="up" accesskey="u" href="Guru-Interface.html#Guru-Interface">Guru Interface</a>
53 <hr>
54 </div>
55
56 <h4 class="subsection">4.5.6 64-bit Guru Interface</h4>
57
58 <p><a name="index-g_t64_002dbit-architecture-260"></a>
59 When compiled in 64-bit mode on a 64-bit architecture (where addresses
60 are 64 bits wide), FFTW uses 64-bit quantities internally for all
61 transform sizes, strides, and so on&mdash;you don't have to do anything
62 special to exploit this. However, in the ordinary FFTW interfaces,
63 you specify the transform size by an <code>int</code> quantity, which is
64 normally only 32 bits wide. This means that, even though FFTW is
65 using 64-bit sizes internally, you cannot specify a single transform
66 dimension larger than
67 2<sup><small>31</small></sup>&minus;1numbers.
68
69 <p>We expect that few users will require transforms larger than this, but,
70 for those who do, we provide a 64-bit version of the guru interface in
71 which all sizes are specified as integers of type <code>ptrdiff_t</code>
72 instead of <code>int</code>. (<code>ptrdiff_t</code> is a signed integer type
73 defined by the C standard to be wide enough to represent address
74 differences, and thus must be at least 64 bits wide on a 64-bit
75 machine.) We stress that there is <em>no performance advantage</em> to
76 using this interface&mdash;the same internal FFTW code is employed
77 regardless&mdash;and it is only necessary if you want to specify very
78 large transform sizes.
79 <a name="index-ptrdiff_005ft-261"></a>
80
81 <p>In particular, the 64-bit guru interface is a set of planner routines
82 that are exactly the same as the guru planner routines, except that
83 they are named with &lsquo;<samp><span class="samp">guru64</span></samp>&rsquo; instead of &lsquo;<samp><span class="samp">guru</span></samp>&rsquo; and they take
84 arguments of type <code>fftw_iodim64</code> instead of <code>fftw_iodim</code>.
85 For example, instead of <code>fftw_plan_guru_dft</code>, we have
86 <code>fftw_plan_guru64_dft</code>.
87
88 <pre class="example"> fftw_plan fftw_plan_guru64_dft(
89 int rank, const fftw_iodim64 *dims,
90 int howmany_rank, const fftw_iodim64 *howmany_dims,
91 fftw_complex *in, fftw_complex *out,
92 int sign, unsigned flags);
93 </pre>
94 <p><a name="index-fftw_005fplan_005fguru64_005fdft-262"></a>
95 The <code>fftw_iodim64</code> type is similar to <code>fftw_iodim</code>, with the
96 same interpretation, except that it uses type <code>ptrdiff_t</code> instead
97 of type <code>int</code>.
98
99 <pre class="example"> typedef struct {
100 ptrdiff_t n;
101 ptrdiff_t is;
102 ptrdiff_t os;
103 } fftw_iodim64;
104 </pre>
105 <p><a name="index-fftw_005fiodim64-263"></a>
106 Every other &lsquo;<samp><span class="samp">fftw_plan_guru</span></samp>&rsquo; function also has a
107 &lsquo;<samp><span class="samp">fftw_plan_guru64</span></samp>&rsquo; equivalent, but we do not repeat their
108 documentation here since they are identical to the 32-bit versions
109 except as noted above.
110
111 <!-- -->
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113