Mercurial > hg > sv-dependency-builds

annotate src/fftw-3.3.8/doc/html/Fixed_002dsize-Arrays-in-C.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: Fixed-size Arrays in C</title>
cannam@167 26
cannam@167 27 <meta name="description" content="FFTW 3.3.8: Fixed-size Arrays in C">
cannam@167 28 <meta name="keywords" content="FFTW 3.3.8: Fixed-size Arrays in C">
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="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="up" title="Multi-dimensional Array Format">
cannam@167 37 <link href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C" rel="next" title="Dynamic Arrays in C">
cannam@167 38 <link href="Column_002dmajor-Format.html#Column_002dmajor-Format" rel="prev" title="Column-major Format">
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="Fixed_002dsize-Arrays-in-C"></a>
cannam@167 72 <div class="header">
cannam@167 73 <p>
cannam@167 74 Next: <a href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C" accesskey="n" rel="next">Dynamic Arrays in C</a>, Previous: <a href="Column_002dmajor-Format.html#Column_002dmajor-Format" accesskey="p" rel="prev">Column-major Format</a>, Up: <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" accesskey="u" rel="up">Multi-dimensional Array Format</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="Fixed_002dsize-Arrays-in-C-1"></a>
cannam@167 78 <h4 class="subsection">3.2.3 Fixed-size Arrays in C</h4>
cannam@167 79 <a name="index-C-multi_002ddimensional-arrays"></a>
cannam@167 80
cannam@167 81 <p>A multi-dimensional array whose size is declared at compile time in C
cannam@167 82 is <em>already</em> in row-major order. You don&rsquo;t have to do anything
cannam@167 83 special to transform it. For example:
cannam@167 84 </p>
cannam@167 85 <div class="example">
cannam@167 86 <pre class="example">{
cannam@167 87 fftw_complex data[N0][N1][N2];
cannam@167 88 fftw_plan plan;
cannam@167 89 ...
cannam@167 90 plan = fftw_plan_dft_3d(N0, N1, N2, &amp;data[0][0][0], &amp;data[0][0][0],
cannam@167 91 FFTW_FORWARD, FFTW_ESTIMATE);
cannam@167 92 ...
cannam@167 93 }
cannam@167 94 </pre></div>
cannam@167 95
cannam@167 96 <p>This will plan a 3d in-place transform of size <code>N0 x N1 x N2</code>.
cannam@167 97 Notice how we took the address of the zero-th element to pass to the
cannam@167 98 planner (we could also have used a typecast).
cannam@167 99 </p>
cannam@167 100 <p>However, we tend to <em>discourage</em> users from declaring their
cannam@167 101 arrays in this way, for two reasons. First, this allocates the array
cannam@167 102 on the stack (&ldquo;automatic&rdquo; storage), which has a very limited size on
cannam@167 103 most operating systems (declaring an array with more than a few
cannam@167 104 thousand elements will often cause a crash). (You can get around this
cannam@167 105 limitation on many systems by declaring the array as
cannam@167 106 <code>static</code> and/or global, but that has its own drawbacks.)
cannam@167 107 Second, it may not optimally align the array for use with a SIMD
cannam@167 108 FFTW (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>). Instead, we recommend
cannam@167 109 using <code>fftw_malloc</code>, as described below.
cannam@167 110 </p>
cannam@167 111
cannam@167 112
cannam@167 113
cannam@167 114 </body>
cannam@167 115 </html>