121 lines
4.9 KiB
HTML
121 lines
4.9 KiB
HTML
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<!-- This manual is for FFTW
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(version 3.3.10, 10 December 2020).
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Copyright (C) 2003 Matteo Frigo.
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Copyright (C) 2003 Massachusetts Institute of Technology.
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<title>Memory Allocation (FFTW 3.3.10)</title>
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<span id="Memory-Allocation"></span><div class="header">
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<p>
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Previous: <a href="Precision.html" accesskey="p" rel="prev">Precision</a>, Up: <a href="Data-Types-and-Files.html" accesskey="u" rel="up">Data Types and Files</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<hr>
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<span id="Memory-Allocation-1"></span><h4 class="subsection">4.1.3 Memory Allocation</h4>
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<div class="example">
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<pre class="example">void *fftw_malloc(size_t n);
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void fftw_free(void *p);
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</pre></div>
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<span id="index-fftw_005fmalloc-3"></span>
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<span id="index-fftw_005ffree-2"></span>
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<p>These are functions that behave identically to <code>malloc</code> and
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<code>free</code>, except that they guarantee that the returned pointer obeys
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any special alignment restrictions imposed by any algorithm in FFTW
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(e.g. for SIMD acceleration). See <a href="SIMD-alignment-and-fftw_005fmalloc.html">SIMD alignment and fftw_malloc</a>.
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<span id="index-alignment"></span>
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</p>
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<p>Data allocated by <code>fftw_malloc</code> <em>must</em> be deallocated by
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<code>fftw_free</code> and not by the ordinary <code>free</code>.
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</p>
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<p>These routines simply call through to your operating system’s
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<code>malloc</code> or, if necessary, its aligned equivalent
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(e.g. <code>memalign</code>), so you normally need not worry about any
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significant time or space overhead. You are <em>not required</em> to use
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them to allocate your data, but we strongly recommend it.
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</p>
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<p>Note: in C++, just as with ordinary <code>malloc</code>, you must typecast
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the output of <code>fftw_malloc</code> to whatever pointer type you are
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allocating.
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<span id="index-C_002b_002b-4"></span>
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</p>
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<p>We also provide the following two convenience functions to allocate
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real and complex arrays with <code>n</code> elements, which are equivalent
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to <code>(double *) fftw_malloc(sizeof(double) * n)</code> and
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<code>(fftw_complex *) fftw_malloc(sizeof(fftw_complex) * n)</code>,
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respectively:
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</p>
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<div class="example">
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<pre class="example">double *fftw_alloc_real(size_t n);
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fftw_complex *fftw_alloc_complex(size_t n);
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</pre></div>
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<span id="index-fftw_005falloc_005freal-1"></span>
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<span id="index-fftw_005falloc_005fcomplex-2"></span>
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<p>The equivalent functions in other precisions allocate arrays of <code>n</code>
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elements in that precision. e.g. <code>fftwf_alloc_real(n)</code> is
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equivalent to <code>(float *) fftwf_malloc(sizeof(float) * n)</code>.
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<span id="index-precision-4"></span>
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</p>
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