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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: SIMD alignment and fftw_malloc</title>
Chris@82 26
Chris@82 27 <meta name="description" content="FFTW 3.3.8: SIMD alignment and fftw_malloc">
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Chris@82 68 </head>
Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="SIMD-alignment-and-fftw_005fmalloc"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 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>
Chris@82 75 </div>
Chris@82 76 <hr>
Chris@82 77 <a name="SIMD-alignment-and-fftw_005fmalloc-1"></a>
Chris@82 78 <h3 class="section">3.1 SIMD alignment and fftw_malloc</h3>
Chris@82 79
Chris@82 80 <p>SIMD, which stands for &ldquo;Single Instruction Multiple Data,&rdquo; is a set of
Chris@82 81 special operations supported by some processors to perform a single
Chris@82 82 operation on several numbers (usually 2 or 4) simultaneously. SIMD
Chris@82 83 floating-point instructions are available on several popular CPUs:
Chris@82 84 SSE/SSE2/AVX/AVX2/AVX512/KCVI on some x86/x86-64 processors, AltiVec and
Chris@82 85 VSX on some POWER/PowerPCs, NEON on some ARM models. FFTW can be
Chris@82 86 compiled to support the SIMD instructions on any of these systems.
Chris@82 87 <a name="index-SIMD-1"></a>
Chris@82 88 <a name="index-SSE"></a>
Chris@82 89 <a name="index-SSE2"></a>
Chris@82 90 <a name="index-AVX"></a>
Chris@82 91 <a name="index-AVX2"></a>
Chris@82 92 <a name="index-AVX512"></a>
Chris@82 93 <a name="index-AltiVec"></a>
Chris@82 94 <a name="index-VSX"></a>
Chris@82 95 <a name="index-precision-2"></a>
Chris@82 96 </p>
Chris@82 97
Chris@82 98 <p>A program linking to an FFTW library compiled with SIMD support can
Chris@82 99 obtain a nonnegligible speedup for most complex and r2c/c2r
Chris@82 100 transforms. In order to obtain this speedup, however, the arrays of
Chris@82 101 complex (or real) data passed to FFTW must be specially aligned in
Chris@82 102 memory (typically 16-byte aligned), and often this alignment is more
Chris@82 103 stringent than that provided by the usual <code>malloc</code> (etc.)
Chris@82 104 allocation routines.
Chris@82 105 </p>
Chris@82 106 <a name="index-portability"></a>
Chris@82 107 <p>In order to guarantee proper alignment for SIMD, therefore, in case
Chris@82 108 your program is ever linked against a SIMD-using FFTW, we recommend
Chris@82 109 allocating your transform data with <code>fftw_malloc</code> and
Chris@82 110 de-allocating it with <code>fftw_free</code>.
Chris@82 111 <a name="index-fftw_005fmalloc-1"></a>
Chris@82 112 <a name="index-fftw_005ffree-1"></a>
Chris@82 113 These have exactly the same interface and behavior as
Chris@82 114 <code>malloc</code>/<code>free</code>, except that for a SIMD FFTW they ensure
Chris@82 115 that the returned pointer has the necessary alignment (by calling
Chris@82 116 <code>memalign</code> or its equivalent on your OS).
Chris@82 117 </p>
Chris@82 118 <p>You are not <em>required</em> to use <code>fftw_malloc</code>. You can
Chris@82 119 allocate your data in any way that you like, from <code>malloc</code> to
Chris@82 120 <code>new</code> (in C++) to a fixed-size array declaration. If the array
Chris@82 121 happens not to be properly aligned, FFTW will not use the SIMD
Chris@82 122 extensions.
Chris@82 123 <a name="index-C_002b_002b-1"></a>
Chris@82 124 </p>
Chris@82 125 <a name="index-fftw_005falloc_005freal"></a>
Chris@82 126 <a name="index-fftw_005falloc_005fcomplex-1"></a>
Chris@82 127 <p>Since <code>fftw_malloc</code> only ever needs to be used for real and
Chris@82 128 complex arrays, we provide two convenient wrapper routines
Chris@82 129 <code>fftw_alloc_real(N)</code> and <code>fftw_alloc_complex(N)</code> that are
Chris@82 130 equivalent to <code>(double*)fftw_malloc(sizeof(double) * N)</code> and
Chris@82 131 <code>(fftw_complex*)fftw_malloc(sizeof(fftw_complex) * N)</code>,
Chris@82 132 respectively (or their equivalents in other precisions).
Chris@82 133 </p>
Chris@82 134 <hr>
Chris@82 135 <div class="header">
Chris@82 136 <p>
Chris@82 137 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>
Chris@82 138 </div>
Chris@82 139
Chris@82 140
Chris@82 141
Chris@82 142 </body>
Chris@82 143 </html>