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<a name="Memory-Allocation"></a>
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Previous: <a href="Precision.html#Precision" accesskey="p" rel="prev">Precision</a>, Up: <a href="Data-Types-and-Files.html#Data-Types-and-Files" accesskey="u" rel="up">Data Types and Files</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>
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<a name="Memory-Allocation-1"></a>
<h4 class="subsection">4.1.3 Memory Allocation</h4>

<div class="example">
<pre class="example">void *fftw_malloc(size_t n);
void fftw_free(void *p);
</pre></div>
<a name="index-fftw_005fmalloc-3"></a>
<a name="index-fftw_005ffree-2"></a>

<p>These are functions that behave identically to <code>malloc</code> and
<code>free</code>, except that they guarantee that the returned pointer obeys
any special alignment restrictions imposed by any algorithm in FFTW
(e.g. for SIMD acceleration).  See <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>.
<a name="index-alignment"></a>
</p>

<p>Data allocated by <code>fftw_malloc</code> <em>must</em> be deallocated by
<code>fftw_free</code> and not by the ordinary <code>free</code>.
</p>
<p>These routines simply call through to your operating system&rsquo;s
<code>malloc</code> or, if necessary, its aligned equivalent
(e.g. <code>memalign</code>), so you normally need not worry about any
significant time or space overhead.  You are <em>not required</em> to use
them to allocate your data, but we strongly recommend it.
</p>
<p>Note: in C++, just as with ordinary <code>malloc</code>, you must typecast
the output of <code>fftw_malloc</code> to whatever pointer type you are
allocating.
<a name="index-C_002b_002b-4"></a>
</p>

<p>We also provide the following two convenience functions to allocate
real and complex arrays with <code>n</code> elements, which are equivalent
to <code>(double *) fftw_malloc(sizeof(double) * n)</code> and
<code>(fftw_complex *) fftw_malloc(sizeof(fftw_complex) * n)</code>,
respectively:
</p>
<div class="example">
<pre class="example">double *fftw_alloc_real(size_t n);
fftw_complex *fftw_alloc_complex(size_t n);
</pre></div>
<a name="index-fftw_005falloc_005freal-1"></a>
<a name="index-fftw_005falloc_005fcomplex-2"></a>

<p>The equivalent functions in other precisions allocate arrays of <code>n</code>
elements in that precision.  e.g. <code>fftwf_alloc_real(n)</code> is
equivalent to <code>(float *) fftwf_malloc(sizeof(float) * n)</code>.
<a name="index-precision-4"></a>
</p>


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author	Chris Cannam <cannam@all-day-breakfast.com>
date	Mon, 02 Mar 2020 14:03:47 +0000
parents	7867fa7e1b6b
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