Mercurial > hg > batch-feature-extraction-tool
view Lib/fftw-3.2.1/doc/html/SIMD-alignment-and-fftw_005fmalloc.html @ 9:262e084a15a9
Vectorised everything and made use of unique_ptr so there should be no more memory leaks. Hurrah for RAII
author | Geogaddi\David <d.m.ronan@qmul.ac.uk> |
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date | Wed, 12 Aug 2015 22:25:06 +0100 |
parents | 25bf17994ef1 |
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<html lang="en"> <head> <title>SIMD alignment and fftw_malloc - FFTW 3.2.1</title> <meta http-equiv="Content-Type" content="text/html"> <meta name="description" content="FFTW 3.2.1"> <meta name="generator" content="makeinfo 4.8"> <link title="Top" rel="start" href="index.html#Top"> <link rel="up" href="Data-Alignment.html#Data-Alignment" title="Data Alignment"> <link rel="prev" href="Data-Alignment.html#Data-Alignment" title="Data Alignment"> <link rel="next" href="Stack-alignment-on-x86.html#Stack-alignment-on-x86" title="Stack alignment on x86"> <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> <!-- This manual is for FFTW (version 3.2.1, 5 February 2009). 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"> <p> <a name="SIMD-alignment-and-fftw_malloc"></a> <a name="SIMD-alignment-and-fftw_005fmalloc"></a> Next: <a rel="next" accesskey="n" href="Stack-alignment-on-x86.html#Stack-alignment-on-x86">Stack alignment on x86</a>, Previous: <a rel="previous" accesskey="p" href="Data-Alignment.html#Data-Alignment">Data Alignment</a>, Up: <a rel="up" accesskey="u" href="Data-Alignment.html#Data-Alignment">Data Alignment</a> <hr> </div> <h4 class="subsection">3.1.1 SIMD alignment and fftw_malloc</h4> <p>SIMD, which stands for “Single Instruction Multiple Data,” is a set of special operations supported by some processors to perform a single operation on several numbers (usually 2 or 4) simultaneously. SIMD floating-point instructions are available on several popular CPUs: SSE/SSE2 (single/double precision) on Pentium III and higher and on AMD64, AltiVec (single precision) on some PowerPCs (Apple G4 and higher), and MIPS Paired Single. FFTW can be compiled to support the SIMD instructions on any of these systems. <a name="index-SIMD-102"></a><a name="index-SSE-103"></a><a name="index-SSE2-104"></a><a name="index-AltiVec-105"></a><a name="index-MIPS-PS-106"></a><a name="index-precision-107"></a> A program linking to an FFTW library compiled with SIMD support can obtain a nonnegligible speedup for most complex and r2c/c2r transforms. In order to obtain this speedup, however, the arrays of complex (or real) data passed to FFTW must be specially aligned in memory (typically 16-byte aligned), and often this alignment is more stringent than that provided by the usual <code>malloc</code> (etc.) allocation routines. <p><a name="index-portability-108"></a>In order to guarantee proper alignment for SIMD, therefore, in case your program is ever linked against a SIMD-using FFTW, we recommend allocating your transform data with <code>fftw_malloc</code> and de-allocating it with <code>fftw_free</code>. <a name="index-fftw_005fmalloc-109"></a><a name="index-fftw_005ffree-110"></a>These have exactly the same interface and behavior as <code>malloc</code>/<code>free</code>, except that for a SIMD FFTW they ensure that the returned pointer has the necessary alignment (by calling <code>memalign</code> or its equivalent on your OS). <p>You are not <em>required</em> to use <code>fftw_malloc</code>. You can allocate your data in any way that you like, from <code>malloc</code> to <code>new</code> (in C++) to a fixed-size array declaration. If the array happens not to be properly aligned, FFTW will not use the SIMD extensions. <a name="index-C_002b_002b-111"></a> <!-- =========> --> </body></html>