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Replace these with versions built using an older toolset (so as to avoid ABI compatibilities when linking on Ubuntu 14.04 for packaging purposes)
author Chris Cannam
date Fri, 07 Feb 2020 11:51:13 +0000
parents 2cd0e3b3e1fd
children
rev   line source
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Chris@42 4 (version 3.3.5, 30 July 2016).
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Chris@42 6 Copyright (C) 2003 Matteo Frigo.
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Chris@42 24 <head>
Chris@42 25 <title>FFTW 3.3.5: New-array Execute Functions</title>
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Chris@42 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
Chris@42 72 <a name="New_002darray-Execute-Functions"></a>
Chris@42 73 <div class="header">
Chris@42 74 <p>
Chris@42 75 Next: <a href="Wisdom.html#Wisdom" accesskey="n" rel="next">Wisdom</a>, Previous: <a href="Guru-Interface.html#Guru-Interface" accesskey="p" rel="prev">Guru Interface</a>, Up: <a href="FFTW-Reference.html#FFTW-Reference" accesskey="u" rel="up">FFTW Reference</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>
Chris@42 76 </div>
Chris@42 77 <hr>
Chris@42 78 <a name="New_002darray-Execute-Functions-1"></a>
Chris@42 79 <h3 class="section">4.6 New-array Execute Functions</h3>
Chris@42 80 <a name="index-execute-2"></a>
Chris@42 81 <a name="index-new_002darray-execution"></a>
Chris@42 82
Chris@42 83 <p>Normally, one executes a plan for the arrays with which the plan was
Chris@42 84 created, by calling <code>fftw_execute(plan)</code> as described in <a href="Using-Plans.html#Using-Plans">Using Plans</a>.
Chris@42 85 <a name="index-fftw_005fexecute-2"></a>
Chris@42 86 However, it is possible for sophisticated users to apply a given plan
Chris@42 87 to a <em>different</em> array using the &ldquo;new-array execute&rdquo; functions
Chris@42 88 detailed below, provided that the following conditions are met:
Chris@42 89 </p>
Chris@42 90 <ul>
Chris@42 91 <li> The array size, strides, etcetera are the same (since those are set by
Chris@42 92 the plan).
Chris@42 93
Chris@42 94 </li><li> The input and output arrays are the same (in-place) or different
Chris@42 95 (out-of-place) if the plan was originally created to be in-place or
Chris@42 96 out-of-place, respectively.
Chris@42 97
Chris@42 98 </li><li> For split arrays, the separations between the real and imaginary
Chris@42 99 parts, <code>ii-ri</code> and <code>io-ro</code>, are the same as they were for
Chris@42 100 the input and output arrays when the plan was created. (This
Chris@42 101 condition is automatically satisfied for interleaved arrays.)
Chris@42 102
Chris@42 103 </li><li> The <em>alignment</em> of the new input/output arrays is the same as that
Chris@42 104 of the input/output arrays when the plan was created, unless the plan
Chris@42 105 was created with the <code>FFTW_UNALIGNED</code> flag.
Chris@42 106 <a name="index-FFTW_005fUNALIGNED-1"></a>
Chris@42 107 Here, the alignment is a platform-dependent quantity (for example, it is
Chris@42 108 the address modulo 16 if SSE SIMD instructions are used, but the address
Chris@42 109 modulo 4 for non-SIMD single-precision FFTW on the same machine). In
Chris@42 110 general, only arrays allocated with <code>fftw_malloc</code> are guaranteed to
Chris@42 111 be equally aligned (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>).
Chris@42 112
Chris@42 113 </li></ul>
Chris@42 114
Chris@42 115 <a name="index-alignment-2"></a>
Chris@42 116 <p>The alignment issue is especially critical, because if you don&rsquo;t use
Chris@42 117 <code>fftw_malloc</code> then you may have little control over the alignment
Chris@42 118 of arrays in memory. For example, neither the C++ <code>new</code> function
Chris@42 119 nor the Fortran <code>allocate</code> statement provide strong enough
Chris@42 120 guarantees about data alignment. If you don&rsquo;t use <code>fftw_malloc</code>,
Chris@42 121 therefore, you probably have to use <code>FFTW_UNALIGNED</code> (which
Chris@42 122 disables most SIMD support). If possible, it is probably better for
Chris@42 123 you to simply create multiple plans (creating a new plan is quick once
Chris@42 124 one exists for a given size), or better yet re-use the same array for
Chris@42 125 your transforms.
Chris@42 126 </p>
Chris@42 127 <a name="index-fftw_005falignment_005fof-1"></a>
Chris@42 128 <p>For rare circumstances in which you cannot control the alignment of
Chris@42 129 allocated memory, but wish to determine where a given array is
Chris@42 130 aligned like the original array for which a plan was created, you can
Chris@42 131 use the <code>fftw_alignment_of</code> function:
Chris@42 132 </p><div class="example">
Chris@42 133 <pre class="example">int fftw_alignment_of(double *p);
Chris@42 134 </pre></div>
Chris@42 135 <p>Two arrays have equivalent alignment (for the purposes of applying a
Chris@42 136 plan) if and only if <code>fftw_alignment_of</code> returns the same value
Chris@42 137 for the corresponding pointers to their data (typecast to <code>double*</code>
Chris@42 138 if necessary).
Chris@42 139 </p>
Chris@42 140 <p>If you are tempted to use the new-array execute interface because you
Chris@42 141 want to transform a known bunch of arrays of the same size, you should
Chris@42 142 probably go use the advanced interface instead (see <a href="Advanced-Interface.html#Advanced-Interface">Advanced Interface</a>)).
Chris@42 143 </p>
Chris@42 144 <p>The new-array execute functions are:
Chris@42 145 </p>
Chris@42 146 <div class="example">
Chris@42 147 <pre class="example">void fftw_execute_dft(
Chris@42 148 const fftw_plan p,
Chris@42 149 fftw_complex *in, fftw_complex *out);
Chris@42 150
Chris@42 151 void fftw_execute_split_dft(
Chris@42 152 const fftw_plan p,
Chris@42 153 double *ri, double *ii, double *ro, double *io);
Chris@42 154
Chris@42 155 void fftw_execute_dft_r2c(
Chris@42 156 const fftw_plan p,
Chris@42 157 double *in, fftw_complex *out);
Chris@42 158
Chris@42 159 void fftw_execute_split_dft_r2c(
Chris@42 160 const fftw_plan p,
Chris@42 161 double *in, double *ro, double *io);
Chris@42 162
Chris@42 163 void fftw_execute_dft_c2r(
Chris@42 164 const fftw_plan p,
Chris@42 165 fftw_complex *in, double *out);
Chris@42 166
Chris@42 167 void fftw_execute_split_dft_c2r(
Chris@42 168 const fftw_plan p,
Chris@42 169 double *ri, double *ii, double *out);
Chris@42 170
Chris@42 171 void fftw_execute_r2r(
Chris@42 172 const fftw_plan p,
Chris@42 173 double *in, double *out);
Chris@42 174 </pre></div>
Chris@42 175 <a name="index-fftw_005fexecute_005fdft"></a>
Chris@42 176 <a name="index-fftw_005fexecute_005fsplit_005fdft"></a>
Chris@42 177 <a name="index-fftw_005fexecute_005fdft_005fr2c"></a>
Chris@42 178 <a name="index-fftw_005fexecute_005fsplit_005fdft_005fr2c"></a>
Chris@42 179 <a name="index-fftw_005fexecute_005fdft_005fc2r"></a>
Chris@42 180 <a name="index-fftw_005fexecute_005fsplit_005fdft_005fc2r"></a>
Chris@42 181 <a name="index-fftw_005fexecute_005fr2r"></a>
Chris@42 182
Chris@42 183 <p>These execute the <code>plan</code> to compute the corresponding transform on
Chris@42 184 the input/output arrays specified by the subsequent arguments. The
Chris@42 185 input/output array arguments have the same meanings as the ones passed
Chris@42 186 to the guru planner routines in the preceding sections. The <code>plan</code>
Chris@42 187 is not modified, and these routines can be called as many times as
Chris@42 188 desired, or intermixed with calls to the ordinary <code>fftw_execute</code>.
Chris@42 189 </p>
Chris@42 190 <p>The <code>plan</code> <em>must</em> have been created for the transform type
Chris@42 191 corresponding to the execute function, e.g. it must be a complex-DFT
Chris@42 192 plan for <code>fftw_execute_dft</code>. Any of the planner routines for that
Chris@42 193 transform type, from the basic to the guru interface, could have been
Chris@42 194 used to create the plan, however.
Chris@42 195 </p>
Chris@42 196 <hr>
Chris@42 197 <div class="header">
Chris@42 198 <p>
Chris@42 199 Next: <a href="Wisdom.html#Wisdom" accesskey="n" rel="next">Wisdom</a>, Previous: <a href="Guru-Interface.html#Guru-Interface" accesskey="p" rel="prev">Guru Interface</a>, Up: <a href="FFTW-Reference.html#FFTW-Reference" accesskey="u" rel="up">FFTW Reference</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>
Chris@42 200 </div>
Chris@42 201
Chris@42 202
Chris@42 203
Chris@42 204 </body>
Chris@42 205 </html>