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2 <head>
3 <title>New-array Execute Functions - FFTW 3.3.4</title>
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16 Copyright (C) 2003 Matteo Frigo.
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49 <a name="New-array-Execute-Functions"></a>
50 <a name="New_002darray-Execute-Functions"></a>
51 <p>
52 Next:&nbsp;<a rel="next" accesskey="n" href="Wisdom.html#Wisdom">Wisdom</a>,
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56 </div>
57
58 <h3 class="section">4.6 New-array Execute Functions</h3>
59
60 <p><a name="index-execute-266"></a><a name="index-new_002darray-execution-267"></a>
61 Normally, one executes a plan for the arrays with which the plan was
62 created, by calling <code>fftw_execute(plan)</code> as described in <a href="Using-Plans.html#Using-Plans">Using Plans</a>.
63 <a name="index-fftw_005fexecute-268"></a>However, it is possible for sophisticated users to apply a given plan
64 to a <em>different</em> array using the &ldquo;new-array execute&rdquo; functions
65 detailed below, provided that the following conditions are met:
66
67 <ul>
68 <li>The array size, strides, etcetera are the same (since those are set by
69 the plan).
70
71 <li>The input and output arrays are the same (in-place) or different
72 (out-of-place) if the plan was originally created to be in-place or
73 out-of-place, respectively.
74
75 <li>For split arrays, the separations between the real and imaginary
76 parts, <code>ii-ri</code> and <code>io-ro</code>, are the same as they were for
77 the input and output arrays when the plan was created. (This
78 condition is automatically satisfied for interleaved arrays.)
79
80 <li>The <dfn>alignment</dfn> of the new input/output arrays is the same as that
81 of the input/output arrays when the plan was created, unless the plan
82 was created with the <code>FFTW_UNALIGNED</code> flag.
83 <a name="index-FFTW_005fUNALIGNED-269"></a>Here, the alignment is a platform-dependent quantity (for example, it is
84 the address modulo 16 if SSE SIMD instructions are used, but the address
85 modulo 4 for non-SIMD single-precision FFTW on the same machine). In
86 general, only arrays allocated with <code>fftw_malloc</code> are guaranteed to
87 be equally aligned (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>).
88
89 </ul>
90
91 <p><a name="index-alignment-270"></a>The alignment issue is especially critical, because if you don't use
92 <code>fftw_malloc</code> then you may have little control over the alignment
93 of arrays in memory. For example, neither the C++ <code>new</code> function
94 nor the Fortran <code>allocate</code> statement provide strong enough
95 guarantees about data alignment. If you don't use <code>fftw_malloc</code>,
96 therefore, you probably have to use <code>FFTW_UNALIGNED</code> (which
97 disables most SIMD support). If possible, it is probably better for
98 you to simply create multiple plans (creating a new plan is quick once
99 one exists for a given size), or better yet re-use the same array for
100 your transforms.
101
102 <p><a name="index-fftw_005falignment_005fof-271"></a>For rare circumstances in which you cannot control the alignment of
103 allocated memory, but wish to determine where a given array is
104 aligned like the original array for which a plan was created, you can
105 use the <code>fftw_alignment_of</code> function:
106 <pre class="example"> int fftw_alignment_of(double *p);
107 </pre>
108 <p>Two arrays have equivalent alignment (for the purposes of applying a
109 plan) if and only if <code>fftw_alignment_of</code> returns the same value
110 for the corresponding pointers to their data (typecast to <code>double*</code>
111 if necessary).
112
113 <p>If you are tempted to use the new-array execute interface because you
114 want to transform a known bunch of arrays of the same size, you should
115 probably go use the advanced interface instead (see <a href="Advanced-Interface.html#Advanced-Interface">Advanced Interface</a>)).
116
117 <p>The new-array execute functions are:
118
119 <pre class="example"> void fftw_execute_dft(
120 const fftw_plan p,
121 fftw_complex *in, fftw_complex *out);
122
123 void fftw_execute_split_dft(
124 const fftw_plan p,
125 double *ri, double *ii, double *ro, double *io);
126
127 void fftw_execute_dft_r2c(
128 const fftw_plan p,
129 double *in, fftw_complex *out);
130
131 void fftw_execute_split_dft_r2c(
132 const fftw_plan p,
133 double *in, double *ro, double *io);
134
135 void fftw_execute_dft_c2r(
136 const fftw_plan p,
137 fftw_complex *in, double *out);
138
139 void fftw_execute_split_dft_c2r(
140 const fftw_plan p,
141 double *ri, double *ii, double *out);
142
143 void fftw_execute_r2r(
144 const fftw_plan p,
145 double *in, double *out);
146 </pre>
147 <p><a name="index-fftw_005fexecute_005fdft-272"></a><a name="index-fftw_005fexecute_005fsplit_005fdft-273"></a><a name="index-fftw_005fexecute_005fdft_005fr2c-274"></a><a name="index-fftw_005fexecute_005fsplit_005fdft_005fr2c-275"></a><a name="index-fftw_005fexecute_005fdft_005fc2r-276"></a><a name="index-fftw_005fexecute_005fsplit_005fdft_005fc2r-277"></a><a name="index-fftw_005fexecute_005fr2r-278"></a>
148 These execute the <code>plan</code> to compute the corresponding transform on
149 the input/output arrays specified by the subsequent arguments. The
150 input/output array arguments have the same meanings as the ones passed
151 to the guru planner routines in the preceding sections. The <code>plan</code>
152 is not modified, and these routines can be called as many times as
153 desired, or intermixed with calls to the ordinary <code>fftw_execute</code>.
154
155 <p>The <code>plan</code> <em>must</em> have been created for the transform type
156 corresponding to the execute function, e.g. it must be a complex-DFT
157 plan for <code>fftw_execute_dft</code>. Any of the planner routines for that
158 transform type, from the basic to the guru interface, could have been
159 used to create the plan, however.
160
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163