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