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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam
date Tue, 19 Nov 2019 14:52:55 +0000
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Chris@82 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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Chris@82 3 <!-- This manual is for FFTW
Chris@82 4 (version 3.3.8, 24 May 2018).
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Chris@82 6 Copyright (C) 2003 Matteo Frigo.
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Chris@82 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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Chris@82 24 <head>
Chris@82 25 <title>FFTW 3.3.8: Planner Flags</title>
Chris@82 26
Chris@82 27 <meta name="description" content="FFTW 3.3.8: Planner Flags">
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Chris@82 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
Chris@82 36 <link href="Basic-Interface.html#Basic-Interface" rel="up" title="Basic Interface">
Chris@82 37 <link href="Real_002ddata-DFTs.html#Real_002ddata-DFTs" rel="next" title="Real-data DFTs">
Chris@82 38 <link href="Complex-DFTs.html#Complex-DFTs" rel="prev" title="Complex DFTs">
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Chris@82 66
Chris@82 67
Chris@82 68 </head>
Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="Planner-Flags"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 74 Next: <a href="Real_002ddata-DFTs.html#Real_002ddata-DFTs" accesskey="n" rel="next">Real-data DFTs</a>, Previous: <a href="Complex-DFTs.html#Complex-DFTs" accesskey="p" rel="prev">Complex DFTs</a>, Up: <a href="Basic-Interface.html#Basic-Interface" accesskey="u" rel="up">Basic 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>
Chris@82 75 </div>
Chris@82 76 <hr>
Chris@82 77 <a name="Planner-Flags-1"></a>
Chris@82 78 <h4 class="subsection">4.3.2 Planner Flags</h4>
Chris@82 79
Chris@82 80 <p>All of the planner routines in FFTW accept an integer <code>flags</code>
Chris@82 81 argument, which is a bitwise OR (&lsquo;<samp>|</samp>&rsquo;) of zero or more of the flag
Chris@82 82 constants defined below. These flags control the rigor (and time) of
Chris@82 83 the planning process, and can also impose (or lift) restrictions on the
Chris@82 84 type of transform algorithm that is employed.
Chris@82 85 </p>
Chris@82 86 <p><em>Important:</em> the planner overwrites the input array during
Chris@82 87 planning unless a saved plan (see <a href="Wisdom.html#Wisdom">Wisdom</a>) is available for that
Chris@82 88 problem, so you should initialize your input data after creating the
Chris@82 89 plan. The only exceptions to this are the <code>FFTW_ESTIMATE</code> and
Chris@82 90 <code>FFTW_WISDOM_ONLY</code> flags, as mentioned below.
Chris@82 91 </p>
Chris@82 92 <p>In all cases, if wisdom is available for the given problem that was
Chris@82 93 created with equal-or-greater planning rigor, then the more rigorous
Chris@82 94 wisdom is used. For example, in <code>FFTW_ESTIMATE</code> mode any available
Chris@82 95 wisdom is used, whereas in <code>FFTW_PATIENT</code> mode only wisdom created
Chris@82 96 in patient or exhaustive mode can be used. See <a href="Words-of-Wisdom_002dSaving-Plans.html#Words-of-Wisdom_002dSaving-Plans">Words of Wisdom-Saving Plans</a>.
Chris@82 97 </p>
Chris@82 98 <a name="Planning_002drigor-flags"></a>
Chris@82 99 <h4 class="subsubheading">Planning-rigor flags</h4>
Chris@82 100 <ul>
Chris@82 101 <li> <a name="index-FFTW_005fESTIMATE-2"></a>
Chris@82 102 <code>FFTW_ESTIMATE</code> specifies that, instead of actual measurements of
Chris@82 103 different algorithms, a simple heuristic is used to pick a (probably
Chris@82 104 sub-optimal) plan quickly. With this flag, the input/output arrays are
Chris@82 105 not overwritten during planning.
Chris@82 106
Chris@82 107 </li><li> <a name="index-FFTW_005fMEASURE-2"></a>
Chris@82 108 <code>FFTW_MEASURE</code> tells FFTW to find an optimized plan by actually
Chris@82 109 <em>computing</em> several FFTs and measuring their execution time.
Chris@82 110 Depending on your machine, this can take some time (often a few
Chris@82 111 seconds). <code>FFTW_MEASURE</code> is the default planning option.
Chris@82 112
Chris@82 113 </li><li> <a name="index-FFTW_005fPATIENT-2"></a>
Chris@82 114 <code>FFTW_PATIENT</code> is like <code>FFTW_MEASURE</code>, but considers a wider
Chris@82 115 range of algorithms and often produces a &ldquo;more optimal&rdquo; plan
Chris@82 116 (especially for large transforms), but at the expense of several times
Chris@82 117 longer planning time (especially for large transforms).
Chris@82 118
Chris@82 119 </li><li> <a name="index-FFTW_005fEXHAUSTIVE-1"></a>
Chris@82 120 <code>FFTW_EXHAUSTIVE</code> is like <code>FFTW_PATIENT</code>, but considers an
Chris@82 121 even wider range of algorithms, including many that we think are
Chris@82 122 unlikely to be fast, to produce the most optimal plan but with a
Chris@82 123 substantially increased planning time.
Chris@82 124
Chris@82 125 </li><li> <a name="index-FFTW_005fWISDOM_005fONLY"></a>
Chris@82 126 <code>FFTW_WISDOM_ONLY</code> is a special planning mode in which the plan
Chris@82 127 is only created if wisdom is available for the given problem, and
Chris@82 128 otherwise a <code>NULL</code> plan is returned. This can be combined with
Chris@82 129 other flags, e.g. &lsquo;<samp>FFTW_WISDOM_ONLY | FFTW_PATIENT</samp>&rsquo; creates a
Chris@82 130 plan only if wisdom is available that was created in
Chris@82 131 <code>FFTW_PATIENT</code> or <code>FFTW_EXHAUSTIVE</code> mode. The
Chris@82 132 <code>FFTW_WISDOM_ONLY</code> flag is intended for users who need to detect
Chris@82 133 whether wisdom is available; for example, if wisdom is not available
Chris@82 134 one may wish to allocate new arrays for planning so that user data is
Chris@82 135 not overwritten.
Chris@82 136
Chris@82 137 </li></ul>
Chris@82 138
Chris@82 139 <a name="Algorithm_002drestriction-flags"></a>
Chris@82 140 <h4 class="subsubheading">Algorithm-restriction flags</h4>
Chris@82 141 <ul>
Chris@82 142 <li> <a name="index-FFTW_005fDESTROY_005fINPUT"></a>
Chris@82 143 <code>FFTW_DESTROY_INPUT</code> specifies that an out-of-place transform is
Chris@82 144 allowed to <em>overwrite its input</em> array with arbitrary data; this
Chris@82 145 can sometimes allow more efficient algorithms to be employed.
Chris@82 146 <a name="index-out_002dof_002dplace"></a>
Chris@82 147
Chris@82 148 </li><li> <a name="index-FFTW_005fPRESERVE_005fINPUT-1"></a>
Chris@82 149 <code>FFTW_PRESERVE_INPUT</code> specifies that an out-of-place transform must
Chris@82 150 <em>not change its input</em> array. This is ordinarily the
Chris@82 151 <em>default</em>, except for c2r and hc2r (i.e. complex-to-real)
Chris@82 152 transforms for which <code>FFTW_DESTROY_INPUT</code> is the default. In the
Chris@82 153 latter cases, passing <code>FFTW_PRESERVE_INPUT</code> will attempt to use
Chris@82 154 algorithms that do not destroy the input, at the expense of worse
Chris@82 155 performance; for multi-dimensional c2r transforms, however, no
Chris@82 156 input-preserving algorithms are implemented and the planner will return
Chris@82 157 <code>NULL</code> if one is requested.
Chris@82 158 <a name="index-c2r-1"></a>
Chris@82 159 <a name="index-hc2r-1"></a>
Chris@82 160
Chris@82 161 </li><li> <a name="index-FFTW_005fUNALIGNED"></a>
Chris@82 162 <a name="index-alignment-1"></a>
Chris@82 163 <a name="index-fftw_005fmalloc-4"></a>
Chris@82 164 <a name="index-fftw_005falignment_005fof"></a>
Chris@82 165 <code>FFTW_UNALIGNED</code> specifies that the algorithm may not impose any
Chris@82 166 unusual alignment requirements on the input/output arrays (i.e. no
Chris@82 167 SIMD may be used). This flag is normally <em>not necessary</em>, since
Chris@82 168 the planner automatically detects misaligned arrays. The only use for
Chris@82 169 this flag is if you want to use the new-array execute interface to
Chris@82 170 execute a given plan on a different array that may not be aligned like
Chris@82 171 the original. (Using <code>fftw_malloc</code> makes this flag unnecessary
Chris@82 172 even then. You can also use <code>fftw_alignment_of</code> to detect
Chris@82 173 whether two arrays are equivalently aligned.)
Chris@82 174
Chris@82 175 </li></ul>
Chris@82 176
Chris@82 177 <a name="Limiting-planning-time"></a>
Chris@82 178 <h4 class="subsubheading">Limiting planning time</h4>
Chris@82 179
Chris@82 180 <div class="example">
Chris@82 181 <pre class="example">extern void fftw_set_timelimit(double seconds);
Chris@82 182 </pre></div>
Chris@82 183 <a name="index-fftw_005fset_005ftimelimit"></a>
Chris@82 184
Chris@82 185 <p>This function instructs FFTW to spend at most <code>seconds</code> seconds
Chris@82 186 (approximately) in the planner. If <code>seconds ==
Chris@82 187 FFTW_NO_TIMELIMIT</code> (the default value, which is negative), then
Chris@82 188 planning time is unbounded. Otherwise, FFTW plans with a
Chris@82 189 progressively wider range of algorithms until the the given time limit
Chris@82 190 is reached or the given range of algorithms is explored, returning the
Chris@82 191 best available plan.
Chris@82 192 <a name="index-FFTW_005fNO_005fTIMELIMIT"></a>
Chris@82 193 </p>
Chris@82 194
Chris@82 195 <p>For example, specifying <code>FFTW_PATIENT</code> first plans in
Chris@82 196 <code>FFTW_ESTIMATE</code> mode, then in <code>FFTW_MEASURE</code> mode, then
Chris@82 197 finally (time permitting) in <code>FFTW_PATIENT</code>. If
Chris@82 198 <code>FFTW_EXHAUSTIVE</code> is specified instead, the planner will further
Chris@82 199 progress to <code>FFTW_EXHAUSTIVE</code> mode.
Chris@82 200 </p>
Chris@82 201 <p>Note that the <code>seconds</code> argument specifies only a rough limit; in
Chris@82 202 practice, the planner may use somewhat more time if the time limit is
Chris@82 203 reached when the planner is in the middle of an operation that cannot
Chris@82 204 be interrupted. At the very least, the planner will complete planning
Chris@82 205 in <code>FFTW_ESTIMATE</code> mode (which is thus equivalent to a time limit
Chris@82 206 of 0).
Chris@82 207 </p>
Chris@82 208
Chris@82 209 <hr>
Chris@82 210 <div class="header">
Chris@82 211 <p>
Chris@82 212 Next: <a href="Real_002ddata-DFTs.html#Real_002ddata-DFTs" accesskey="n" rel="next">Real-data DFTs</a>, Previous: <a href="Complex-DFTs.html#Complex-DFTs" accesskey="p" rel="prev">Complex DFTs</a>, Up: <a href="Basic-Interface.html#Basic-Interface" accesskey="u" rel="up">Basic 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>
Chris@82 213 </div>
Chris@82 214
Chris@82 215
Chris@82 216
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Chris@82 218 </html>