Mercurial > hg > sv-dependency-builds

annotate src/fftw-3.3.8/doc/html/SIMD-alignment-and-fftw_005fmalloc.html @ 167:bd3cc4d1df30

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
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
parents
children
rev   line source
cannam@167 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
cannam@167 2 <html>
cannam@167 3 <!-- This manual is for FFTW
cannam@167 4 (version 3.3.8, 24 May 2018).
cannam@167 5
cannam@167 6 Copyright (C) 2003 Matteo Frigo.
cannam@167 7
cannam@167 8 Copyright (C) 2003 Massachusetts Institute of Technology.
cannam@167 9
cannam@167 10 Permission is granted to make and distribute verbatim copies of this
cannam@167 11 manual provided the copyright notice and this permission notice are
cannam@167 12 preserved on all copies.
cannam@167 13
cannam@167 14 Permission is granted to copy and distribute modified versions of this
cannam@167 15 manual under the conditions for verbatim copying, provided that the
cannam@167 16 entire resulting derived work is distributed under the terms of a
cannam@167 17 permission notice identical to this one.
cannam@167 18
cannam@167 19 Permission is granted to copy and distribute translations of this manual
cannam@167 20 into another language, under the above conditions for modified versions,
cannam@167 21 except that this permission notice may be stated in a translation
cannam@167 22 approved by the Free Software Foundation. -->
cannam@167 23 <!-- Created by GNU Texinfo 6.3, http://www.gnu.org/software/texinfo/ -->
cannam@167 24 <head>
cannam@167 25 <title>FFTW 3.3.8: SIMD alignment and fftw_malloc</title>
cannam@167 26
cannam@167 27 <meta name="description" content="FFTW 3.3.8: SIMD alignment and fftw_malloc">
cannam@167 28 <meta name="keywords" content="FFTW 3.3.8: SIMD alignment and fftw_malloc">
cannam@167 29 <meta name="resource-type" content="document">
cannam@167 30 <meta name="distribution" content="global">
cannam@167 31 <meta name="Generator" content="makeinfo">
cannam@167 32 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
cannam@167 33 <link href="index.html#Top" rel="start" title="Top">
cannam@167 34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
cannam@167 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
cannam@167 36 <link href="Other-Important-Topics.html#Other-Important-Topics" rel="up" title="Other Important Topics">
cannam@167 37 <link href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="next" title="Multi-dimensional Array Format">
cannam@167 38 <link href="Other-Important-Topics.html#Other-Important-Topics" rel="prev" title="Other Important Topics">
cannam@167 39 <style type="text/css">
cannam@167 40 <!--
cannam@167 41 a.summary-letter {text-decoration: none}
cannam@167 42 blockquote.indentedblock {margin-right: 0em}
cannam@167 43 blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
cannam@167 44 blockquote.smallquotation {font-size: smaller}
cannam@167 45 div.display {margin-left: 3.2em}
cannam@167 46 div.example {margin-left: 3.2em}
cannam@167 47 div.lisp {margin-left: 3.2em}
cannam@167 48 div.smalldisplay {margin-left: 3.2em}
cannam@167 49 div.smallexample {margin-left: 3.2em}
cannam@167 50 div.smalllisp {margin-left: 3.2em}
cannam@167 51 kbd {font-style: oblique}
cannam@167 52 pre.display {font-family: inherit}
cannam@167 53 pre.format {font-family: inherit}
cannam@167 54 pre.menu-comment {font-family: serif}
cannam@167 55 pre.menu-preformatted {font-family: serif}
cannam@167 56 pre.smalldisplay {font-family: inherit; font-size: smaller}
cannam@167 57 pre.smallexample {font-size: smaller}
cannam@167 58 pre.smallformat {font-family: inherit; font-size: smaller}
cannam@167 59 pre.smalllisp {font-size: smaller}
cannam@167 60 span.nolinebreak {white-space: nowrap}
cannam@167 61 span.roman {font-family: initial; font-weight: normal}
cannam@167 62 span.sansserif {font-family: sans-serif; font-weight: normal}
cannam@167 63 ul.no-bullet {list-style: none}
cannam@167 64 -->
cannam@167 65 </style>
cannam@167 66
cannam@167 67
cannam@167 68 </head>
cannam@167 69
cannam@167 70 <body lang="en">
cannam@167 71 <a name="SIMD-alignment-and-fftw_005fmalloc"></a>
cannam@167 72 <div class="header">
cannam@167 73 <p>
cannam@167 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>
cannam@167 75 </div>
cannam@167 76 <hr>
cannam@167 77 <a name="SIMD-alignment-and-fftw_005fmalloc-1"></a>
cannam@167 78 <h3 class="section">3.1 SIMD alignment and fftw_malloc</h3>
cannam@167 79
cannam@167 80 <p>SIMD, which stands for &ldquo;Single Instruction Multiple Data,&rdquo; is a set of
cannam@167 81 special operations supported by some processors to perform a single
cannam@167 82 operation on several numbers (usually 2 or 4) simultaneously. SIMD
cannam@167 83 floating-point instructions are available on several popular CPUs:
cannam@167 84 SSE/SSE2/AVX/AVX2/AVX512/KCVI on some x86/x86-64 processors, AltiVec and
cannam@167 85 VSX on some POWER/PowerPCs, NEON on some ARM models. FFTW can be
cannam@167 86 compiled to support the SIMD instructions on any of these systems.
cannam@167 87 <a name="index-SIMD-1"></a>
cannam@167 88 <a name="index-SSE"></a>
cannam@167 89 <a name="index-SSE2"></a>
cannam@167 90 <a name="index-AVX"></a>
cannam@167 91 <a name="index-AVX2"></a>
cannam@167 92 <a name="index-AVX512"></a>
cannam@167 93 <a name="index-AltiVec"></a>
cannam@167 94 <a name="index-VSX"></a>
cannam@167 95 <a name="index-precision-2"></a>
cannam@167 96 </p>
cannam@167 97
cannam@167 98 <p>A program linking to an FFTW library compiled with SIMD support can
cannam@167 99 obtain a nonnegligible speedup for most complex and r2c/c2r
cannam@167 100 transforms. In order to obtain this speedup, however, the arrays of
cannam@167 101 complex (or real) data passed to FFTW must be specially aligned in
cannam@167 102 memory (typically 16-byte aligned), and often this alignment is more
cannam@167 103 stringent than that provided by the usual <code>malloc</code> (etc.)
cannam@167 104 allocation routines.
cannam@167 105 </p>
cannam@167 106 <a name="index-portability"></a>
cannam@167 107 <p>In order to guarantee proper alignment for SIMD, therefore, in case
cannam@167 108 your program is ever linked against a SIMD-using FFTW, we recommend
cannam@167 109 allocating your transform data with <code>fftw_malloc</code> and
cannam@167 110 de-allocating it with <code>fftw_free</code>.
cannam@167 111 <a name="index-fftw_005fmalloc-1"></a>
cannam@167 112 <a name="index-fftw_005ffree-1"></a>
cannam@167 113 These have exactly the same interface and behavior as
cannam@167 114 <code>malloc</code>/<code>free</code>, except that for a SIMD FFTW they ensure
cannam@167 115 that the returned pointer has the necessary alignment (by calling
cannam@167 116 <code>memalign</code> or its equivalent on your OS).
cannam@167 117 </p>
cannam@167 118 <p>You are not <em>required</em> to use <code>fftw_malloc</code>. You can
cannam@167 119 allocate your data in any way that you like, from <code>malloc</code> to
cannam@167 120 <code>new</code> (in C++) to a fixed-size array declaration. If the array
cannam@167 121 happens not to be properly aligned, FFTW will not use the SIMD
cannam@167 122 extensions.
cannam@167 123 <a name="index-C_002b_002b-1"></a>
cannam@167 124 </p>
cannam@167 125 <a name="index-fftw_005falloc_005freal"></a>
cannam@167 126 <a name="index-fftw_005falloc_005fcomplex-1"></a>
cannam@167 127 <p>Since <code>fftw_malloc</code> only ever needs to be used for real and
cannam@167 128 complex arrays, we provide two convenient wrapper routines
cannam@167 129 <code>fftw_alloc_real(N)</code> and <code>fftw_alloc_complex(N)</code> that are
cannam@167 130 equivalent to <code>(double*)fftw_malloc(sizeof(double) * N)</code> and
cannam@167 131 <code>(fftw_complex*)fftw_malloc(sizeof(fftw_complex) * N)</code>,
cannam@167 132 respectively (or their equivalents in other precisions).
cannam@167 133 </p>
cannam@167 134 <hr>
cannam@167 135 <div class="header">
cannam@167 136 <p>
cannam@167 137 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>
cannam@167 138 </div>
cannam@167 139
cannam@167 140
cannam@167 141
cannam@167 142 </body>
cannam@167 143 </html>