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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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1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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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.
7
8 Copyright (C) 2003 Massachusetts Institute of Technology.
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10 Permission is granted to make and distribute verbatim copies of this
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25 <title>FFTW 3.3.8: SIMD alignment and fftw_malloc</title>
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71 <a name="SIMD-alignment-and-fftw_005fmalloc"></a>
72 <div class="header">
73 <p>
74 Next: <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" accesskey="n" rel="next">Multi-dimensional Array Format</a>, Previous: <a href="Other-Important-Topics.html#Other-Important-Topics" accesskey="p" rel="prev">Other Important Topics</a>, Up: <a href="Other-Important-Topics.html#Other-Important-Topics" accesskey="u" rel="up">Other Important Topics</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="SIMD-alignment-and-fftw_005fmalloc-1"></a>
78 <h3 class="section">3.1 SIMD alignment and fftw_malloc</h3>
79
80 <p>SIMD, which stands for &ldquo;Single Instruction Multiple Data,&rdquo; is a set of
81 special operations supported by some processors to perform a single
82 operation on several numbers (usually 2 or 4) simultaneously. SIMD
83 floating-point instructions are available on several popular CPUs:
84 SSE/SSE2/AVX/AVX2/AVX512/KCVI on some x86/x86-64 processors, AltiVec and
85 VSX on some POWER/PowerPCs, NEON on some ARM models. FFTW can be
86 compiled to support the SIMD instructions on any of these systems.
87 <a name="index-SIMD-1"></a>
88 <a name="index-SSE"></a>
89 <a name="index-SSE2"></a>
90 <a name="index-AVX"></a>
91 <a name="index-AVX2"></a>
92 <a name="index-AVX512"></a>
93 <a name="index-AltiVec"></a>
94 <a name="index-VSX"></a>
95 <a name="index-precision-2"></a>
96 </p>
97
98 <p>A program linking to an FFTW library compiled with SIMD support can
99 obtain a nonnegligible speedup for most complex and r2c/c2r
100 transforms. In order to obtain this speedup, however, the arrays of
101 complex (or real) data passed to FFTW must be specially aligned in
102 memory (typically 16-byte aligned), and often this alignment is more
103 stringent than that provided by the usual <code>malloc</code> (etc.)
104 allocation routines.
105 </p>
106 <a name="index-portability"></a>
107 <p>In order to guarantee proper alignment for SIMD, therefore, in case
108 your program is ever linked against a SIMD-using FFTW, we recommend
109 allocating your transform data with <code>fftw_malloc</code> and
110 de-allocating it with <code>fftw_free</code>.
111 <a name="index-fftw_005fmalloc-1"></a>
112 <a name="index-fftw_005ffree-1"></a>
113 These have exactly the same interface and behavior as
114 <code>malloc</code>/<code>free</code>, except that for a SIMD FFTW they ensure
115 that the returned pointer has the necessary alignment (by calling
116 <code>memalign</code> or its equivalent on your OS).
117 </p>
118 <p>You are not <em>required</em> to use <code>fftw_malloc</code>. You can
119 allocate your data in any way that you like, from <code>malloc</code> to
120 <code>new</code> (in C++) to a fixed-size array declaration. If the array
121 happens not to be properly aligned, FFTW will not use the SIMD
122 extensions.
123 <a name="index-C_002b_002b-1"></a>
124 </p>
125 <a name="index-fftw_005falloc_005freal"></a>
126 <a name="index-fftw_005falloc_005fcomplex-1"></a>
127 <p>Since <code>fftw_malloc</code> only ever needs to be used for real and
128 complex arrays, we provide two convenient wrapper routines
129 <code>fftw_alloc_real(N)</code> and <code>fftw_alloc_complex(N)</code> that are
130 equivalent to <code>(double*)fftw_malloc(sizeof(double) * N)</code> and
131 <code>(fftw_complex*)fftw_malloc(sizeof(fftw_complex) * N)</code>,
132 respectively (or their equivalents in other precisions).
133 </p>
134 <hr>
135 <div class="header">
136 <p>
137 Next: <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" accesskey="n" rel="next">Multi-dimensional Array Format</a>, Previous: <a href="Other-Important-Topics.html#Other-Important-Topics" accesskey="p" rel="prev">Other Important Topics</a>, Up: <a href="Other-Important-Topics.html#Other-Important-Topics" accesskey="u" rel="up">Other Important Topics</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>
138 </div>
139
140
141
142 </body>
143 </html>