1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>The Bigger Picture</title> 5<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Chapter 1. Boost.Convert 2.0"> 8<link rel="up" href="../performance.html" title="Performance"> 9<link rel="prev" href="boost_convert_overhead.html" title="Boost.Convert Overhead"> 10<link rel="next" href="../other_conversions.html" title="Beyond Basic Conversions"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="boost_convert_overhead.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../performance.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="../other_conversions.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="boost_convert.performance.the_bigger_picture"></a><a class="link" href="the_bigger_picture.html" title="The Bigger Picture">The Bigger 28 Picture</a> 29</h3></div></div></div> 30<p> 31 The presented conversion-related performance data (and potential performance-related 32 concerns) have to be taken in perspective. A special project with serious 33 high performance requirements is most likely to require special solutions 34 which are most likely to cast out many generic libraries. Still, the existence 35 of such projects did not kill or diminish in any way the importance of generic 36 libraries. And <span class="emphasis"><em>Boost.Convert</em></span> is one such <span class="emphasis"><em>generic</em></span> 37 library. 38 </p> 39<p> 40 More so, if performance is a concern, then, in all likelihood, for the great 41 majority of the mainstream projects <span class="emphasis"><em>Boost.Convert</em></span> will 42 be far from the top on the performance profiler's list. For example, to measure 43 conversion-related overhead relative to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>-related 44 overhead, <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> was replaced with a custom <span class="emphasis"><em>small-string</em></span> 45 type: 46 </p> 47<p> 48</p> 49<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_string</span> 50<span class="special">{</span> 51 <span class="keyword">typedef</span> <span class="identifier">my_string</span> <span class="identifier">this_type</span><span class="special">;</span> 52 <span class="keyword">typedef</span> <span class="keyword">char</span> <span class="identifier">value_type</span><span class="special">;</span> 53 <span class="keyword">typedef</span> <span class="identifier">value_type</span><span class="special">*</span> <span class="identifier">iterator</span><span class="special">;</span> 54 <span class="keyword">typedef</span> <span class="identifier">value_type</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">const_iterator</span><span class="special">;</span> 55 56 <span class="identifier">my_string</span> <span class="special">();</span> 57 <span class="identifier">my_string</span> <span class="special">(</span><span class="identifier">const_iterator</span><span class="special">,</span> <span class="identifier">const_iterator</span> <span class="special">=</span><span class="number">0</span><span class="special">);</span> 58 59 <span class="keyword">char</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">c_str</span> <span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">storage_</span><span class="special">;</span> <span class="special">}</span> 60 <span class="identifier">const_iterator</span> <span class="identifier">begin</span> <span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">storage_</span><span class="special">;</span> <span class="special">}</span> 61 <span class="identifier">const_iterator</span> <span class="identifier">end</span> <span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">storage_</span> <span class="special">+</span> <span class="identifier">strlen</span><span class="special">(</span><span class="identifier">storage_</span><span class="special">);</span> <span class="special">}</span> 62 <span class="identifier">this_type</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*);</span> 63 64 <span class="keyword">private</span><span class="special">:</span> 65 66 <span class="keyword">static</span> <span class="identifier">size_t</span> <span class="keyword">const</span> <span class="identifier">size_</span> <span class="special">=</span> <span class="number">12</span><span class="special">;</span> 67 <span class="keyword">char</span> <span class="identifier">storage_</span><span class="special">[</span><span class="identifier">size_</span><span class="special">];</span> 68<span class="special">};</span> 69</pre> 70<p> 71 </p> 72<p> 73 The class above is essentially a glorified 12-bytes character buffer sufficient 74 to accommodate string representations of 32-bit integers. Deployed with the 75 same converters and the same algorithms: 76 </p> 77<p> 78</p> 79<pre class="programlisting"><span class="identifier">printf</span><span class="special">(</span><span class="string">"strtol int-to std::string/small-string: %.2f/%.2f seconds.\n"</span><span class="special">,</span> 80 <span class="identifier">local</span><span class="special">::</span><span class="identifier">to_str</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">strtol</span><span class="special">()),</span> 81 <span class="identifier">local</span><span class="special">::</span><span class="identifier">to_str</span><span class="special"><</span> <span class="identifier">my_string</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">strtol</span><span class="special">()));</span> 82<span class="identifier">printf</span><span class="special">(</span><span class="string">"spirit int-to std::string/small-string: %.2f/%.2f seconds.\n"</span><span class="special">,</span> 83 <span class="identifier">local</span><span class="special">::</span><span class="identifier">to_str</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">()),</span> 84 <span class="identifier">local</span><span class="special">::</span><span class="identifier">to_str</span><span class="special"><</span> <span class="identifier">my_string</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">()));</span> 85<span class="identifier">printf</span><span class="special">(</span><span class="string">"stream int-to std::string/small-string: %.2f/%.2f seconds.\n"</span><span class="special">,</span> 86 <span class="identifier">local</span><span class="special">::</span><span class="identifier">to_str</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">cstream</span><span class="special">()),</span> 87 <span class="identifier">local</span><span class="special">::</span><span class="identifier">to_str</span><span class="special"><</span> <span class="identifier">my_string</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cnv</span><span class="special">::</span><span class="identifier">cstream</span><span class="special">()));</span> 88</pre> 89<p> 90 </p> 91<p> 92 It produced the following relative results (compiled with <code class="computeroutput"><span class="identifier">gcc</span> 93 <span class="special">-</span><span class="identifier">O3</span></code>): 94 </p> 95<pre class="programlisting"><span class="identifier">strtol</span> <span class="keyword">int</span><span class="special">-</span><span class="identifier">to</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">/</span><span class="identifier">small</span><span class="special">-</span><span class="identifier">string</span><span class="special">:</span> <span class="number">1.41</span><span class="special">/</span><span class="number">0.53</span> <span class="identifier">seconds</span><span class="special">.</span> 96<span class="identifier">spirit</span> <span class="keyword">int</span><span class="special">-</span><span class="identifier">to</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">/</span><span class="identifier">small</span><span class="special">-</span><span class="identifier">string</span><span class="special">:</span> <span class="number">1.98</span><span class="special">/</span><span class="number">1.04</span> <span class="identifier">seconds</span><span class="special">.</span> 97<span class="identifier">stream</span> <span class="keyword">int</span><span class="special">-</span><span class="identifier">to</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">/</span><span class="identifier">small</span><span class="special">-</span><span class="identifier">string</span><span class="special">:</span> <span class="number">2.49</span><span class="special">/</span><span class="number">1.40</span> <span class="identifier">seconds</span><span class="special">.</span> 98</pre> 99<p> 100 The results suggest that for the projects that deal with string-related conversions 101 and routinely deploy <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> 102 facilities the conversion-related overhead will be outweighed by the overhead 103 of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>-related operations. 104 </p> 105</div> 106<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 107<td align="left"></td> 108<td align="right"><div class="copyright-footer">Copyright © 2009-2016 Vladimir Batov<p> 109 Distributed under the Boost Software License, Version 1.0. See copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>. 110 </p> 111</div></td> 112</tr></table> 113<hr> 114<div class="spirit-nav"> 115<a accesskey="p" href="boost_convert_overhead.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../performance.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="../other_conversions.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 116</div> 117</body> 118</html> 119
