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Tidy up for ROLI
author Geogaddi\David <d.m.ronan@qmul.ac.uk>
date Tue, 17 May 2016 18:50:19 +0100
parents 636c989477e7
children
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--- a/Lib/fftw-3.2.1/doc/html/.svn/text-base/Stack-alignment-on-x86.html.svn-base	Wed May 04 11:02:59 2016 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
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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">
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-<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).
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-Copyright (C) 2003 Matteo Frigo.
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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>
-