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Add FFTW3
| author | Chris Cannam |
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| date | Wed, 20 Mar 2013 15:35:50 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.3/doc/html/Dynamic-Arrays-in-C.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,91 @@ +<html lang="en"> +<head> +<title>Dynamic Arrays in C - FFTW 3.3.3</title> +<meta http-equiv="Content-Type" content="text/html"> +<meta name="description" content="FFTW 3.3.3"> +<meta name="generator" content="makeinfo 4.13"> +<link title="Top" rel="start" href="index.html#Top"> +<link rel="up" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" title="Multi-dimensional Array Format"> +<link rel="prev" href="Fixed_002dsize-Arrays-in-C.html#Fixed_002dsize-Arrays-in-C" title="Fixed-size Arrays in C"> +<link rel="next" href="Dynamic-Arrays-in-C_002dThe-Wrong-Way.html#Dynamic-Arrays-in-C_002dThe-Wrong-Way" title="Dynamic Arrays in C-The Wrong Way"> +<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> +<!-- +This manual is for FFTW +(version 3.3.3, 25 November 2012). + +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. + --> +<meta http-equiv="Content-Style-Type" content="text/css"> +<style type="text/css"><!-- + pre.display { font-family:inherit } + pre.format { font-family:inherit } + pre.smalldisplay { font-family:inherit; font-size:smaller } + pre.smallformat { font-family:inherit; font-size:smaller } + pre.smallexample { font-size:smaller } + pre.smalllisp { font-size:smaller } + span.sc { font-variant:small-caps } + span.roman { font-family:serif; font-weight:normal; } + span.sansserif { font-family:sans-serif; font-weight:normal; } +--></style> +</head> +<body> +<div class="node"> +<a name="Dynamic-Arrays-in-C"></a> +<p> +Next: <a rel="next" accesskey="n" href="Dynamic-Arrays-in-C_002dThe-Wrong-Way.html#Dynamic-Arrays-in-C_002dThe-Wrong-Way">Dynamic Arrays in C-The Wrong Way</a>, +Previous: <a rel="previous" accesskey="p" href="Fixed_002dsize-Arrays-in-C.html#Fixed_002dsize-Arrays-in-C">Fixed-size Arrays in C</a>, +Up: <a rel="up" accesskey="u" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format">Multi-dimensional Array Format</a> +<hr> +</div> + +<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>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-121"></a> +<pre class="example"> fftw_complex *an_array; + an_array = (fftw_complex*) fftw_malloc(5*12*27 * sizeof(fftw_complex)); +</pre> + <p>Accessing the array elements, however, is more tricky—you can't +simply use multiple applications of the ‘<samp><span class="samp">[]</span></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 (i,j,k)-th +element of the array allocated above, you would use the expression +<code>an_array[k + 27 * (j + 12 * i)]</code>. + + <p>This pain can be alleviated somewhat by defining appropriate macros, +or, in C++, creating a class and overloading the ‘<samp><span class="samp">()</span></samp>’ operator. +The recent C99 standard provides a way to reinterpret the dynamic +array as a “variable-length” multi-dimensional array amenable to +‘<samp><span class="samp">[]</span></samp>’, but this feature is not yet widely supported by compilers. +<a name="index-C99-122"></a><a name="index-C_002b_002b-123"></a> +<!-- =========> --> + + </body></html> +