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First commit. VS2013, Codeblocks and Mac OSX configuration
author Geogaddi\David <d.m.ronan@qmul.ac.uk>
date Thu, 09 Jul 2015 01:12:16 +0100
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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 }
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+--></style>
+</head>
+<body>
+<div class="node">
+<p>
+<a name="SIMD-alignment-and-fftw_malloc"></a>
+<a name="SIMD-alignment-and-fftw_005fmalloc"></a>
+Next:&nbsp;<a rel="next" accesskey="n" href="Stack-alignment-on-x86.html#Stack-alignment-on-x86">Stack alignment on x86</a>,
+Previous:&nbsp;<a rel="previous" accesskey="p" href="Data-Alignment.html#Data-Alignment">Data Alignment</a>,
+Up:&nbsp;<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 &ldquo;Single Instruction Multiple Data,&rdquo; 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>
+