Mercurial > hg > sv-dependency-builds
diff src/fftw-3.3.8/doc/html/Dynamic-Arrays-in-C.html @ 167:bd3cc4d1df30
Add FFTW 3.3.8 source, and a Linux build
| author | Chris Cannam <cannam@all-day-breakfast.com> |
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| date | Tue, 19 Nov 2019 14:52:55 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.8/doc/html/Dynamic-Arrays-in-C.html Tue Nov 19 14:52:55 2019 +0000 @@ -0,0 +1,119 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This manual is for FFTW +(version 3.3.8, 24 May 2018). + +Copyright (C) 2003 Matteo Frigo. + +Copyright (C) 2003 Massachusetts Institute of Technology. + +Permission is granted to make and distribute verbatim copies of this +manual provided the copyright notice and this permission notice are +preserved on all copies. + +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided that the +entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions, +except that this permission notice may be stated in a translation +approved by the Free Software Foundation. --> +<!-- Created by GNU Texinfo 6.3, http://www.gnu.org/software/texinfo/ --> +<head> +<title>FFTW 3.3.8: Dynamic Arrays in C</title> + +<meta name="description" content="FFTW 3.3.8: Dynamic Arrays in C"> +<meta name="keywords" content="FFTW 3.3.8: Dynamic Arrays in C"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="up" title="Multi-dimensional Array Format"> +<link href="Dynamic-Arrays-in-C_002dThe-Wrong-Way.html#Dynamic-Arrays-in-C_002dThe-Wrong-Way" rel="next" title="Dynamic Arrays in C-The Wrong Way"> +<link href="Fixed_002dsize-Arrays-in-C.html#Fixed_002dsize-Arrays-in-C" rel="prev" title="Fixed-size Arrays in C"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.indentedblock {margin-right: 0em} +blockquote.smallindentedblock {margin-right: 0em; font-size: smaller} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smalllisp {margin-left: 3.2em} +kbd {font-style: oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nolinebreak {white-space: nowrap} +span.roman {font-family: initial; font-weight: normal} +span.sansserif {font-family: sans-serif; font-weight: normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en"> +<a name="Dynamic-Arrays-in-C"></a> +<div class="header"> +<p> +Next: <a href="Dynamic-Arrays-in-C_002dThe-Wrong-Way.html#Dynamic-Arrays-in-C_002dThe-Wrong-Way" accesskey="n" rel="next">Dynamic Arrays in C-The Wrong Way</a>, Previous: <a href="Fixed_002dsize-Arrays-in-C.html#Fixed_002dsize-Arrays-in-C" accesskey="p" rel="prev">Fixed-size Arrays in C</a>, Up: <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" accesskey="u" rel="up">Multi-dimensional Array Format</a> [<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> +</div> +<hr> +<a name="Dynamic-Arrays-in-C-1"></a> +<h4 class="subsection">3.2.4 Dynamic Arrays in C</h4> + +<p>We recommend allocating most arrays dynamically, with +<code>fftw_malloc</code>. This isn’t too hard to do, although it is not as +straightforward for multi-dimensional arrays as it is for +one-dimensional arrays. +</p> +<p>Creating the array is simple: using a dynamic-allocation routine like +<code>fftw_malloc</code>, allocate an array big enough to store N +<code>fftw_complex</code> values (for a complex DFT), where N is the product +of the sizes of the array dimensions (i.e. the total number of complex +values in the array). For example, here is code to allocate a +5 × 12 × 27 + rank-3 array: +<a name="index-fftw_005fmalloc-2"></a> +</p> +<div class="example"> +<pre class="example">fftw_complex *an_array; +an_array = (fftw_complex*) fftw_malloc(5*12*27 * sizeof(fftw_complex)); +</pre></div> + +<p>Accessing the array elements, however, is more tricky—you can’t +simply use multiple applications of the ‘<samp>[]</samp>’ operator like you +could for fixed-size arrays. Instead, you have to explicitly compute +the offset into the array using the formula given earlier for +row-major arrays. For example, to reference the <em>(i,j,k)</em>-th +element of the array allocated above, you would use the expression +<code>an_array[k + 27 * (j + 12 * i)]</code>. +</p> +<p>This pain can be alleviated somewhat by defining appropriate macros, +or, in C++, creating a class and overloading the ‘<samp>()</samp>’ operator. +The recent C99 standard provides a way to reinterpret the dynamic +array as a “variable-length” multi-dimensional array amenable to +‘<samp>[]</samp>’, but this feature is not yet widely supported by compilers. +<a name="index-C99"></a> +<a name="index-C_002b_002b-2"></a> +</p> + + + +</body> +</html>