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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 19 Nov 2019 14:52:55 +0000
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cannam@167 3 <!-- This manual is for FFTW
cannam@167 4 (version 3.3.8, 24 May 2018).
cannam@167 5
cannam@167 6 Copyright (C) 2003 Matteo Frigo.
cannam@167 7
cannam@167 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@167 24 <head>
cannam@167 25 <title>FFTW 3.3.8: New-array Execute Functions</title>
cannam@167 26
cannam@167 27 <meta name="description" content="FFTW 3.3.8: New-array Execute Functions">
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cannam@167 68 </head>
cannam@167 69
cannam@167 70 <body lang="en">
cannam@167 71 <a name="New_002darray-Execute-Functions"></a>
cannam@167 72 <div class="header">
cannam@167 73 <p>
cannam@167 74 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>
cannam@167 75 </div>
cannam@167 76 <hr>
cannam@167 77 <a name="New_002darray-Execute-Functions-1"></a>
cannam@167 78 <h3 class="section">4.6 New-array Execute Functions</h3>
cannam@167 79 <a name="index-execute-2"></a>
cannam@167 80 <a name="index-new_002darray-execution"></a>
cannam@167 81
cannam@167 82 <p>Normally, one executes a plan for the arrays with which the plan was
cannam@167 83 created, by calling <code>fftw_execute(plan)</code> as described in <a href="Using-Plans.html#Using-Plans">Using Plans</a>.
cannam@167 84 <a name="index-fftw_005fexecute-2"></a>
cannam@167 85 However, it is possible for sophisticated users to apply a given plan
cannam@167 86 to a <em>different</em> array using the &ldquo;new-array execute&rdquo; functions
cannam@167 87 detailed below, provided that the following conditions are met:
cannam@167 88 </p>
cannam@167 89 <ul>
cannam@167 90 <li> The array size, strides, etcetera are the same (since those are set by
cannam@167 91 the plan).
cannam@167 92
cannam@167 93 </li><li> The input and output arrays are the same (in-place) or different
cannam@167 94 (out-of-place) if the plan was originally created to be in-place or
cannam@167 95 out-of-place, respectively.
cannam@167 96
cannam@167 97 </li><li> For split arrays, the separations between the real and imaginary
cannam@167 98 parts, <code>ii-ri</code> and <code>io-ro</code>, are the same as they were for
cannam@167 99 the input and output arrays when the plan was created. (This
cannam@167 100 condition is automatically satisfied for interleaved arrays.)
cannam@167 101
cannam@167 102 </li><li> The <em>alignment</em> of the new input/output arrays is the same as that
cannam@167 103 of the input/output arrays when the plan was created, unless the plan
cannam@167 104 was created with the <code>FFTW_UNALIGNED</code> flag.
cannam@167 105 <a name="index-FFTW_005fUNALIGNED-1"></a>
cannam@167 106 Here, the alignment is a platform-dependent quantity (for example, it is
cannam@167 107 the address modulo 16 if SSE SIMD instructions are used, but the address
cannam@167 108 modulo 4 for non-SIMD single-precision FFTW on the same machine). In
cannam@167 109 general, only arrays allocated with <code>fftw_malloc</code> are guaranteed to
cannam@167 110 be equally aligned (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>).
cannam@167 111
cannam@167 112 </li></ul>
cannam@167 113
cannam@167 114 <a name="index-alignment-2"></a>
cannam@167 115 <p>The alignment issue is especially critical, because if you don&rsquo;t use
cannam@167 116 <code>fftw_malloc</code> then you may have little control over the alignment
cannam@167 117 of arrays in memory. For example, neither the C++ <code>new</code> function
cannam@167 118 nor the Fortran <code>allocate</code> statement provide strong enough
cannam@167 119 guarantees about data alignment. If you don&rsquo;t use <code>fftw_malloc</code>,
cannam@167 120 therefore, you probably have to use <code>FFTW_UNALIGNED</code> (which
cannam@167 121 disables most SIMD support). If possible, it is probably better for
cannam@167 122 you to simply create multiple plans (creating a new plan is quick once
cannam@167 123 one exists for a given size), or better yet re-use the same array for
cannam@167 124 your transforms.
cannam@167 125 </p>
cannam@167 126 <a name="index-fftw_005falignment_005fof-1"></a>
cannam@167 127 <p>For rare circumstances in which you cannot control the alignment of
cannam@167 128 allocated memory, but wish to determine where a given array is
cannam@167 129 aligned like the original array for which a plan was created, you can
cannam@167 130 use the <code>fftw_alignment_of</code> function:
cannam@167 131 </p><div class="example">
cannam@167 132 <pre class="example">int fftw_alignment_of(double *p);
cannam@167 133 </pre></div>
cannam@167 134 <p>Two arrays have equivalent alignment (for the purposes of applying a
cannam@167 135 plan) if and only if <code>fftw_alignment_of</code> returns the same value
cannam@167 136 for the corresponding pointers to their data (typecast to <code>double*</code>
cannam@167 137 if necessary).
cannam@167 138 </p>
cannam@167 139 <p>If you are tempted to use the new-array execute interface because you
cannam@167 140 want to transform a known bunch of arrays of the same size, you should
cannam@167 141 probably go use the advanced interface instead (see <a href="Advanced-Interface.html#Advanced-Interface">Advanced Interface</a>)).
cannam@167 142 </p>
cannam@167 143 <p>The new-array execute functions are:
cannam@167 144 </p>
cannam@167 145 <div class="example">
cannam@167 146 <pre class="example">void fftw_execute_dft(
cannam@167 147 const fftw_plan p,
cannam@167 148 fftw_complex *in, fftw_complex *out);
cannam@167 149
cannam@167 150 void fftw_execute_split_dft(
cannam@167 151 const fftw_plan p,
cannam@167 152 double *ri, double *ii, double *ro, double *io);
cannam@167 153
cannam@167 154 void fftw_execute_dft_r2c(
cannam@167 155 const fftw_plan p,
cannam@167 156 double *in, fftw_complex *out);
cannam@167 157
cannam@167 158 void fftw_execute_split_dft_r2c(
cannam@167 159 const fftw_plan p,
cannam@167 160 double *in, double *ro, double *io);
cannam@167 161
cannam@167 162 void fftw_execute_dft_c2r(
cannam@167 163 const fftw_plan p,
cannam@167 164 fftw_complex *in, double *out);
cannam@167 165
cannam@167 166 void fftw_execute_split_dft_c2r(
cannam@167 167 const fftw_plan p,
cannam@167 168 double *ri, double *ii, double *out);
cannam@167 169
cannam@167 170 void fftw_execute_r2r(
cannam@167 171 const fftw_plan p,
cannam@167 172 double *in, double *out);
cannam@167 173 </pre></div>
cannam@167 174 <a name="index-fftw_005fexecute_005fdft"></a>
cannam@167 175 <a name="index-fftw_005fexecute_005fsplit_005fdft"></a>
cannam@167 176 <a name="index-fftw_005fexecute_005fdft_005fr2c"></a>
cannam@167 177 <a name="index-fftw_005fexecute_005fsplit_005fdft_005fr2c"></a>
cannam@167 178 <a name="index-fftw_005fexecute_005fdft_005fc2r"></a>
cannam@167 179 <a name="index-fftw_005fexecute_005fsplit_005fdft_005fc2r"></a>
cannam@167 180 <a name="index-fftw_005fexecute_005fr2r"></a>
cannam@167 181
cannam@167 182 <p>These execute the <code>plan</code> to compute the corresponding transform on
cannam@167 183 the input/output arrays specified by the subsequent arguments. The
cannam@167 184 input/output array arguments have the same meanings as the ones passed
cannam@167 185 to the guru planner routines in the preceding sections. The <code>plan</code>
cannam@167 186 is not modified, and these routines can be called as many times as
cannam@167 187 desired, or intermixed with calls to the ordinary <code>fftw_execute</code>.
cannam@167 188 </p>
cannam@167 189 <p>The <code>plan</code> <em>must</em> have been created for the transform type
cannam@167 190 corresponding to the execute function, e.g. it must be a complex-DFT
cannam@167 191 plan for <code>fftw_execute_dft</code>. Any of the planner routines for that
cannam@167 192 transform type, from the basic to the guru interface, could have been
cannam@167 193 used to create the plan, however.
cannam@167 194 </p>
cannam@167 195 <hr>
cannam@167 196 <div class="header">
cannam@167 197 <p>
cannam@167 198 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>
cannam@167 199 </div>
cannam@167 200
cannam@167 201
cannam@167 202
cannam@167 203 </body>
cannam@167 204 </html>