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author Chris Cannam
date Wed, 07 Sep 2016 10:40:32 +0100
parents 26056e866c29
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Chris@19 1 <html lang="en">
Chris@19 2 <head>
Chris@19 3 <title>64-bit Guru Interface - FFTW 3.3.4</title>
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Chris@19 5 <meta name="description" content="FFTW 3.3.4">
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Chris@19 8 <link rel="up" href="Guru-Interface.html#Guru-Interface" title="Guru Interface">
Chris@19 9 <link rel="prev" href="Guru-Real_002dto_002dreal-Transforms.html#Guru-Real_002dto_002dreal-Transforms" title="Guru Real-to-real Transforms">
Chris@19 10 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
Chris@19 11 <!--
Chris@19 12 This manual is for FFTW
Chris@19 13 (version 3.3.4, 20 September 2013).
Chris@19 14
Chris@19 15 Copyright (C) 2003 Matteo Frigo.
Chris@19 16
Chris@19 17 Copyright (C) 2003 Massachusetts Institute of Technology.
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Chris@19 19 Permission is granted to make and distribute verbatim copies of
Chris@19 20 this manual provided the copyright notice and this permission
Chris@19 21 notice are preserved on all copies.
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Chris@19 23 Permission is granted to copy and distribute modified versions of
Chris@19 24 this manual under the conditions for verbatim copying, provided
Chris@19 25 that the entire resulting derived work is distributed under the
Chris@19 26 terms of a permission notice identical to this one.
Chris@19 27
Chris@19 28 Permission is granted to copy and distribute translations of this
Chris@19 29 manual into another language, under the above conditions for
Chris@19 30 modified versions, except that this permission notice may be
Chris@19 31 stated in a translation approved by the Free Software Foundation.
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Chris@19 45 </head>
Chris@19 46 <body>
Chris@19 47 <div class="node">
Chris@19 48 <a name="64-bit-Guru-Interface"></a>
Chris@19 49 <a name="g_t64_002dbit-Guru-Interface"></a>
Chris@19 50 <p>
Chris@19 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>,
Chris@19 52 Up:&nbsp;<a rel="up" accesskey="u" href="Guru-Interface.html#Guru-Interface">Guru Interface</a>
Chris@19 53 <hr>
Chris@19 54 </div>
Chris@19 55
Chris@19 56 <h4 class="subsection">4.5.6 64-bit Guru Interface</h4>
Chris@19 57
Chris@19 58 <p><a name="index-g_t64_002dbit-architecture-262"></a>
Chris@19 59 When compiled in 64-bit mode on a 64-bit architecture (where addresses
Chris@19 60 are 64 bits wide), FFTW uses 64-bit quantities internally for all
Chris@19 61 transform sizes, strides, and so on&mdash;you don't have to do anything
Chris@19 62 special to exploit this. However, in the ordinary FFTW interfaces,
Chris@19 63 you specify the transform size by an <code>int</code> quantity, which is
Chris@19 64 normally only 32 bits wide. This means that, even though FFTW is
Chris@19 65 using 64-bit sizes internally, you cannot specify a single transform
Chris@19 66 dimension larger than
Chris@19 67 2<sup><small>31</small></sup>&minus;1numbers.
Chris@19 68
Chris@19 69 <p>We expect that few users will require transforms larger than this, but,
Chris@19 70 for those who do, we provide a 64-bit version of the guru interface in
Chris@19 71 which all sizes are specified as integers of type <code>ptrdiff_t</code>
Chris@19 72 instead of <code>int</code>. (<code>ptrdiff_t</code> is a signed integer type
Chris@19 73 defined by the C standard to be wide enough to represent address
Chris@19 74 differences, and thus must be at least 64 bits wide on a 64-bit
Chris@19 75 machine.) We stress that there is <em>no performance advantage</em> to
Chris@19 76 using this interface&mdash;the same internal FFTW code is employed
Chris@19 77 regardless&mdash;and it is only necessary if you want to specify very
Chris@19 78 large transform sizes.
Chris@19 79 <a name="index-ptrdiff_005ft-263"></a>
Chris@19 80
Chris@19 81 <p>In particular, the 64-bit guru interface is a set of planner routines
Chris@19 82 that are exactly the same as the guru planner routines, except that
Chris@19 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
Chris@19 84 arguments of type <code>fftw_iodim64</code> instead of <code>fftw_iodim</code>.
Chris@19 85 For example, instead of <code>fftw_plan_guru_dft</code>, we have
Chris@19 86 <code>fftw_plan_guru64_dft</code>.
Chris@19 87
Chris@19 88 <pre class="example"> fftw_plan fftw_plan_guru64_dft(
Chris@19 89 int rank, const fftw_iodim64 *dims,
Chris@19 90 int howmany_rank, const fftw_iodim64 *howmany_dims,
Chris@19 91 fftw_complex *in, fftw_complex *out,
Chris@19 92 int sign, unsigned flags);
Chris@19 93 </pre>
Chris@19 94 <p><a name="index-fftw_005fplan_005fguru64_005fdft-264"></a>
Chris@19 95 The <code>fftw_iodim64</code> type is similar to <code>fftw_iodim</code>, with the
Chris@19 96 same interpretation, except that it uses type <code>ptrdiff_t</code> instead
Chris@19 97 of type <code>int</code>.
Chris@19 98
Chris@19 99 <pre class="example"> typedef struct {
Chris@19 100 ptrdiff_t n;
Chris@19 101 ptrdiff_t is;
Chris@19 102 ptrdiff_t os;
Chris@19 103 } fftw_iodim64;
Chris@19 104 </pre>
Chris@19 105 <p><a name="index-fftw_005fiodim64-265"></a>
Chris@19 106 Every other &lsquo;<samp><span class="samp">fftw_plan_guru</span></samp>&rsquo; function also has a
Chris@19 107 &lsquo;<samp><span class="samp">fftw_plan_guru64</span></samp>&rsquo; equivalent, but we do not repeat their
Chris@19 108 documentation here since they are identical to the 32-bit versions
Chris@19 109 except as noted above.
Chris@19 110
Chris@19 111 <!-- -->
Chris@19 112 </body></html>
Chris@19 113