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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>Stack alignment on x86 - 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="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc" title="SIMD alignment and fftw_malloc">
+<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
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+</head>
+<body>
+<div class="node">
+<p>
+<a name="Stack-alignment-on-x86"></a>
+Previous:&nbsp;<a rel="previous" accesskey="p" href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>,
+Up:&nbsp;<a rel="up" accesskey="u" href="Data-Alignment.html#Data-Alignment">Data Alignment</a>
+<hr>
+</div>
+
+<h4 class="subsection">3.1.2 Stack alignment on x86</h4>
+
+<p>On the Pentium and subsequent x86 processors, there is a substantial
+performance penalty if double-precision variables are not stored
+8-byte aligned; a factor of two or more is not unusual. 
+Unfortunately, the stack (the place that local variables and
+subroutine arguments live) is not guaranteed by the Intel ABI to be
+8-byte aligned.
+
+   <p>Recent versions of <code>gcc</code> (as well as most other compilers, we are
+told, such as Intel's, Metrowerks', and Microsoft's) are able to keep
+the stack 8-byte aligned; <code>gcc</code> does this by default (see
+<code>-mpreferred-stack-boundary</code> in the <code>gcc</code> documentation). 
+If you are not certain whether your compiler maintains stack alignment
+by default, it is a good idea to make sure.
+
+   <p>Unfortunately, <code>gcc</code> only <em>preserves</em> the stack
+alignment&mdash;as a result, if the stack starts off misaligned, it will
+always be misaligned, with a disastrous effect on performance (in
+double precision).  To prevent this, FFTW includes hacks to align its
+own stack if necessary, so it should perform well even if you call it
+from a program with a misaligned stack.  Currently, our hacks support
+<code>gcc</code> and the Intel C compiler; if you use another compiler you
+are on your own.  Fortunately, recent versions of glibc (on GNU/Linux)
+provide a properly-aligned starting stack, but this was not the case
+with a number of older versions, and we are not certain of the
+situation on other operating systems.  Hopefully, as time goes by this
+will become less of a concern.
+
+<!--  -->
+</body></html>
+