| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
| <title>The Overhead in the Number Class Wrapper</title> |
| <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> |
| <meta name="generator" content="DocBook XSL Stylesheets V1.77.1"> |
| <link rel="home" href="../../index.html" title="Chapter 1. Boost.Multiprecision"> |
| <link rel="up" href="../perf.html" title="Performance Comparison"> |
| <link rel="prev" href="../perf.html" title="Performance Comparison"> |
| <link rel="next" href="realworld.html" title="Floating-Point Real World Tests"> |
| </head> |
| <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> |
| <table cellpadding="2" width="100%"><tr> |
| <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> |
| <td align="center"><a href="../../../../../../index.html">Home</a></td> |
| <td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> |
| <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> |
| <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> |
| <td align="center"><a href="../../../../../../more/index.htm">More</a></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="../perf.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../perf.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="realworld.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_multiprecision.perf.overhead"></a><a class="link" href="overhead.html" title="The Overhead in the Number Class Wrapper">The Overhead in the |
| Number Class Wrapper</a> |
| </h3></div></div></div> |
| <p> |
| Using a simple <a href="../../../../performance/arithmetic_backend.hpp" target="_top">backend |
| class</a> that wraps any built in arithmetic type we can measure the |
| overhead involved in wrapping a type inside the <code class="computeroutput"><span class="identifier">number</span></code> |
| frontend, and the effect that turning on expression templates has. The following |
| table compares the performance between <code class="computeroutput"><span class="keyword">double</span></code> |
| and a <code class="computeroutput"><span class="keyword">double</span></code> wrapped inside |
| class <code class="computeroutput"><span class="identifier">number</span></code>: |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Type |
| </p> |
| </th> |
| <th> |
| <p> |
| Bessel Function Evaluation |
| </p> |
| </th> |
| <th> |
| <p> |
| Non-Central T Evaluation |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">double</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <span class="bold"><strong>1.0 (0.016s)</strong></span> |
| </p> |
| </td> |
| <td> |
| <p> |
| <span class="bold"><strong>1.0</strong></span> (0.46s) |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">arithmetic_backend</span><span class="special"><</span><span class="keyword">double</span><span class="special">>,</span> |
| <span class="identifier">et_off</span><span class="special">></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| 1.2 (0.019s) |
| </p> |
| </td> |
| <td> |
| <p> |
| <span class="bold"><strong>1.0</strong></span>(0.46s) |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">arithmetic_backend</span><span class="special"><</span><span class="keyword">double</span><span class="special">>,</span> |
| <span class="identifier">et_on</span><span class="special">></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| 1.2 (0.019s) |
| </p> |
| </td> |
| <td> |
| <p> |
| 1.7 (0.79s) |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <p> |
| As you can see whether or not there is an overhead, and how large it is depends |
| on the actual situation, but the overhead is in any cases small. Expression |
| templates generally add a greater overhead the more complex the expression |
| becomes due to the logic of figuring out how to best unpack and evaluate |
| the expression, but of course this is also the situation where you save more |
| temporaries. For a "trivial" backend like this, saving temporaries |
| has no benefit, but for larger types it becomes a bigger win. |
| </p> |
| <p> |
| The following table compares arithmetic using either <code class="computeroutput"><span class="keyword">long</span> |
| <span class="keyword">long</span></code> or <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">arithmetic_backend</span><span class="special"><</span><span class="keyword">long</span> <span class="keyword">long</span><span class="special">></span> <span class="special">></span></code> for the <a href="../../../../performance/voronoi_performance.cpp" target="_top">voronoi-diagram |
| builder test</a>: |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Type |
| </p> |
| </th> |
| <th> |
| <p> |
| Relative time |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">long</span> <span class="keyword">long</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <span class="bold"><strong>1.0</strong></span>(0.0823s) |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">arithmetic_backend</span><span class="special"><</span><span class="keyword">long</span> <span class="keyword">long</span><span class="special">>,</span> <span class="identifier">et_off</span><span class="special">></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| 1.05 (0.0875s) |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <p> |
| This test involves mainly creating a lot of temporaries and performing a |
| small amount of arithmetic on them, with very little difference in performance |
| between the native and "wrapped" types. |
| </p> |
| <p> |
| The test code was compiled with Microsoft Visual Studio 2010 with all optimisations |
| turned on (/Ox), and used MPIR-2.3.0 and <a href="http://libtom.org/?page=features&newsitems=5&whatfile=ltm" target="_top">libtommath</a>-0.42.0. |
| The tests were run on 32-bit Windows Vista machine. |
| </p> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2002-2013 John Maddock and Christopher Kormanyos<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="../perf.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../perf.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="realworld.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| </body> |
| </html> |
