Mercurial > hg > sv-dependency-builds

annotate src/fftw-3.3.5/doc/html/SIMD-alignment-and-fftw_005fmalloc.html @ 127:7867fa7e1b6b

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Current fftw source
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 18 Oct 2016 13:40:26 +0100
parents
children
rev   line source
cannam@127 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
cannam@127 2 <html>
cannam@127 3 <!-- This manual is for FFTW
cannam@127 4 (version 3.3.5, 30 July 2016).
cannam@127 5
cannam@127 6 Copyright (C) 2003 Matteo Frigo.
cannam@127 7
cannam@127 8 Copyright (C) 2003 Massachusetts Institute of Technology.
cannam@127 9
cannam@127 10 Permission is granted to make and distribute verbatim copies of this
cannam@127 11 manual provided the copyright notice and this permission notice are
cannam@127 12 preserved on all copies.
cannam@127 13
cannam@127 14 Permission is granted to copy and distribute modified versions of this
cannam@127 15 manual under the conditions for verbatim copying, provided that the
cannam@127 16 entire resulting derived work is distributed under the terms of a
cannam@127 17 permission notice identical to this one.
cannam@127 18
cannam@127 19 Permission is granted to copy and distribute translations of this manual
cannam@127 20 into another language, under the above conditions for modified versions,
cannam@127 21 except that this permission notice may be stated in a translation
cannam@127 22 approved by the Free Software Foundation. -->
cannam@127 23 <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
cannam@127 24 <head>
cannam@127 25 <title>FFTW 3.3.5: SIMD alignment and fftw_malloc</title>
cannam@127 26
cannam@127 27 <meta name="description" content="FFTW 3.3.5: SIMD alignment and fftw_malloc">
cannam@127 28 <meta name="keywords" content="FFTW 3.3.5: SIMD alignment and fftw_malloc">
cannam@127 29 <meta name="resource-type" content="document">
cannam@127 30 <meta name="distribution" content="global">
cannam@127 31 <meta name="Generator" content="makeinfo">
cannam@127 32 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
cannam@127 33 <link href="index.html#Top" rel="start" title="Top">
cannam@127 34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
cannam@127 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
cannam@127 36 <link href="Other-Important-Topics.html#Other-Important-Topics" rel="up" title="Other Important Topics">
cannam@127 37 <link href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="next" title="Multi-dimensional Array Format">
cannam@127 38 <link href="Other-Important-Topics.html#Other-Important-Topics" rel="prev" title="Other Important Topics">
cannam@127 39 <style type="text/css">
cannam@127 40 <!--
cannam@127 41 a.summary-letter {text-decoration: none}
cannam@127 42 blockquote.smallquotation {font-size: smaller}
cannam@127 43 div.display {margin-left: 3.2em}
cannam@127 44 div.example {margin-left: 3.2em}
cannam@127 45 div.indentedblock {margin-left: 3.2em}
cannam@127 46 div.lisp {margin-left: 3.2em}
cannam@127 47 div.smalldisplay {margin-left: 3.2em}
cannam@127 48 div.smallexample {margin-left: 3.2em}
cannam@127 49 div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
cannam@127 50 div.smalllisp {margin-left: 3.2em}
cannam@127 51 kbd {font-style:oblique}
cannam@127 52 pre.display {font-family: inherit}
cannam@127 53 pre.format {font-family: inherit}
cannam@127 54 pre.menu-comment {font-family: serif}
cannam@127 55 pre.menu-preformatted {font-family: serif}
cannam@127 56 pre.smalldisplay {font-family: inherit; font-size: smaller}
cannam@127 57 pre.smallexample {font-size: smaller}
cannam@127 58 pre.smallformat {font-family: inherit; font-size: smaller}
cannam@127 59 pre.smalllisp {font-size: smaller}
cannam@127 60 span.nocodebreak {white-space:nowrap}
cannam@127 61 span.nolinebreak {white-space:nowrap}
cannam@127 62 span.roman {font-family:serif; font-weight:normal}
cannam@127 63 span.sansserif {font-family:sans-serif; font-weight:normal}
cannam@127 64 ul.no-bullet {list-style: none}
cannam@127 65 -->
cannam@127 66 </style>
cannam@127 67
cannam@127 68
cannam@127 69 </head>
cannam@127 70
cannam@127 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
cannam@127 72 <a name="SIMD-alignment-and-fftw_005fmalloc"></a>
cannam@127 73 <div class="header">
cannam@127 74 <p>
cannam@127 75 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@127 76 </div>
cannam@127 77 <hr>
cannam@127 78 <a name="SIMD-alignment-and-fftw_005fmalloc-1"></a>
cannam@127 79 <h3 class="section">3.1 SIMD alignment and fftw_malloc</h3>
cannam@127 80
cannam@127 81 <p>SIMD, which stands for &ldquo;Single Instruction Multiple Data,&rdquo; is a set of
cannam@127 82 special operations supported by some processors to perform a single
cannam@127 83 operation on several numbers (usually 2 or 4) simultaneously. SIMD
cannam@127 84 floating-point instructions are available on several popular CPUs:
cannam@127 85 SSE/SSE2/AVX/AVX2/AVX512/KCVI on some x86/x86-64 processors, AltiVec and
cannam@127 86 VSX on some POWER/PowerPCs, NEON on some ARM models. FFTW can be
cannam@127 87 compiled to support the SIMD instructions on any of these systems.
cannam@127 88 <a name="index-SIMD-1"></a>
cannam@127 89 <a name="index-SSE"></a>
cannam@127 90 <a name="index-SSE2"></a>
cannam@127 91 <a name="index-AVX"></a>
cannam@127 92 <a name="index-AVX2"></a>
cannam@127 93 <a name="index-AVX512"></a>
cannam@127 94 <a name="index-AltiVec"></a>
cannam@127 95 <a name="index-VSX"></a>
cannam@127 96 <a name="index-precision-2"></a>
cannam@127 97 </p>
cannam@127 98
cannam@127 99 <p>A program linking to an FFTW library compiled with SIMD support can
cannam@127 100 obtain a nonnegligible speedup for most complex and r2c/c2r
cannam@127 101 transforms. In order to obtain this speedup, however, the arrays of
cannam@127 102 complex (or real) data passed to FFTW must be specially aligned in
cannam@127 103 memory (typically 16-byte aligned), and often this alignment is more
cannam@127 104 stringent than that provided by the usual <code>malloc</code> (etc.)
cannam@127 105 allocation routines.
cannam@127 106 </p>
cannam@127 107 <a name="index-portability"></a>
cannam@127 108 <p>In order to guarantee proper alignment for SIMD, therefore, in case
cannam@127 109 your program is ever linked against a SIMD-using FFTW, we recommend
cannam@127 110 allocating your transform data with <code>fftw_malloc</code> and
cannam@127 111 de-allocating it with <code>fftw_free</code>.
cannam@127 112 <a name="index-fftw_005fmalloc-1"></a>
cannam@127 113 <a name="index-fftw_005ffree-1"></a>
cannam@127 114 These have exactly the same interface and behavior as
cannam@127 115 <code>malloc</code>/<code>free</code>, except that for a SIMD FFTW they ensure
cannam@127 116 that the returned pointer has the necessary alignment (by calling
cannam@127 117 <code>memalign</code> or its equivalent on your OS).
cannam@127 118 </p>
cannam@127 119 <p>You are not <em>required</em> to use <code>fftw_malloc</code>. You can
cannam@127 120 allocate your data in any way that you like, from <code>malloc</code> to
cannam@127 121 <code>new</code> (in C++) to a fixed-size array declaration. If the array
cannam@127 122 happens not to be properly aligned, FFTW will not use the SIMD
cannam@127 123 extensions.
cannam@127 124 <a name="index-C_002b_002b-1"></a>
cannam@127 125 </p>
cannam@127 126 <a name="index-fftw_005falloc_005freal"></a>
cannam@127 127 <a name="index-fftw_005falloc_005fcomplex-1"></a>
cannam@127 128 <p>Since <code>fftw_malloc</code> only ever needs to be used for real and
cannam@127 129 complex arrays, we provide two convenient wrapper routines
cannam@127 130 <code>fftw_alloc_real(N)</code> and <code>fftw_alloc_complex(N)</code> that are
cannam@127 131 equivalent to <code>(double*)fftw_malloc(sizeof(double) * N)</code> and
cannam@127 132 <code>(fftw_complex*)fftw_malloc(sizeof(fftw_complex) * N)</code>,
cannam@127 133 respectively (or their equivalents in other precisions).
cannam@127 134 </p>
cannam@127 135 <hr>
cannam@127 136 <div class="header">
cannam@127 137 <p>
cannam@127 138 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@127 139 </div>
cannam@127 140
cannam@127 141
cannam@127 142
cannam@127 143 </body>
cannam@127 144 </html>