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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_convert.performance.boost_convert_overhead"></a><a class="link" href="boost_convert_overhead.html" title="Boost.Convert Overhead">Boost.Convert
Overhead</a>
</h3></div></div></div>
<p>
<span class="emphasis"><em>Boost.Convert</em></span> framework adds an additional layer of
indirection and some <span class="emphasis"><em>Boost.Convert</em></span> converters are wrappers
around actual conversion facilities such as <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code>,
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span></code>, etc. Consequently, there might
be reasonable concerns with regard to the performance overhead introduced
by the framework as opposed to deploying conversion facilities directly.
</p>
<p>
To test that code has been borrowed and adapted from the Spirit.Qi performance/optimization
framework (see $BOOST_ROOT/libs/spirit/workbench/qi/int_parser.cpp). The
tests were
</p>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
compiled using gcc-4.6.3 and gcc-4.8.2;
</li>
<li class="listitem">
with optimization: <code class="computeroutput"><span class="identifier">g</span><span class="special">++</span> <span class="special">-</span><span class="identifier">O3</span>
<span class="identifier">test</span><span class="special">/</span><span class="identifier">performance_spirit</span><span class="special">.</span><span class="identifier">cpp</span> <span class="special">-</span><span class="identifier">Iinclude</span> <span class="special">-</span><span class="identifier">I</span><span class="special">../</span><span class="identifier">boost_1_56_0</span> <span class="special">-</span><span class="identifier">lrt</span></code>;
</li>
<li class="listitem">
on 64-bit Ubuntu 12.04 and 32-bit Ubuntu 14.04;
</li>
<li class="listitem">
run against the input of randomly generated 18 numeric strings (9 positive
and 9 negative numbers with the number of digits from 1 to 9);
</li>
<li class="listitem">
run for
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code> and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span></code>-based converter;
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span></code> and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">parse</span></code>-based
converter.
</li>
</ul></div>
</li>
</ol></div>
<p>
The purpose of the test was to deploy the same functionality directly and
as part of the <span class="emphasis"><em>Boost.Convert</em></span> framework. Results are
shown below for several consecutive runs:
</p>
<pre class="programlisting"><span class="identifier">gcc</span><span class="special">-</span><span class="number">4.6</span><span class="special">.</span><span class="number">3</span> <span class="special">(</span><span class="number">64</span><span class="special">-</span><span class="identifier">bit</span><span class="special">)</span>
<span class="identifier">raw_lxcast_str_to_int_test</span><span class="special">:</span> <span class="number">1.0504170070</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span>
<span class="identifier">cnv_lxcast_str_to_int_test</span><span class="special">:</span> <span class="number">1.0610595810</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">1</span><span class="special">%</span> <span class="identifier">slower</span> <span class="identifier">than</span> <span class="identifier">raw</span> <span class="identifier">above</span><span class="special">)</span>
<span class="identifier">raw_spirit_str_to_int_test</span><span class="special">:</span> <span class="number">0.2845369110</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span>
<span class="identifier">cnv_spirit_str_to_int_test</span><span class="special">:</span> <span class="number">0.2834834560</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">1</span><span class="special">%</span> <span class="identifier">faster</span> <span class="identifier">than</span> <span class="identifier">raw</span> <span class="identifier">above</span><span class="special">)</span>
<span class="identifier">raw_lxcast_str_to_int_test</span><span class="special">:</span> <span class="number">1.0770350390</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">2</span><span class="special">%</span> <span class="identifier">slower</span> <span class="identifier">than</span> <span class="identifier">prev</span><span class="special">.</span> <span class="identifier">run</span><span class="special">)</span>
<span class="identifier">cnv_lxcast_str_to_int_test</span><span class="special">:</span> <span class="number">1.0607665160</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">1</span><span class="special">%</span> <span class="identifier">faster</span> <span class="identifier">than</span> <span class="identifier">raw</span> <span class="identifier">above</span><span class="special">)</span>
<span class="identifier">raw_spirit_str_to_int_test</span><span class="special">:</span> <span class="number">0.2792295470</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">2</span><span class="special">%</span> <span class="identifier">faster</span> <span class="identifier">than</span> <span class="identifier">prev</span><span class="special">.</span> <span class="identifier">run</span><span class="special">)</span>
<span class="identifier">cnv_spirit_str_to_int_test</span><span class="special">:</span> <span class="number">0.2827574570</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">1</span><span class="special">%</span> <span class="identifier">slower</span> <span class="identifier">than</span> <span class="identifier">raw</span> <span class="identifier">above</span><span class="special">)</span>
<span class="identifier">gcc</span><span class="special">-</span><span class="number">4.8</span><span class="special">.</span><span class="number">2</span> <span class="special">(</span><span class="number">32</span><span class="special">-</span><span class="identifier">bit</span><span class="special">)</span>
<span class="identifier">raw_lxcast_str_to_int_test</span><span class="special">:</span> <span class="number">8.5153330600</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span>
<span class="identifier">cnv_lxcast_str_to_int_test</span><span class="special">:</span> <span class="number">8.6989499850</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">2</span><span class="special">%</span> <span class="identifier">slower</span> <span class="identifier">than</span> <span class="identifier">raw</span> <span class="identifier">above</span><span class="special">)</span>
<span class="identifier">raw_spirit_str_to_int_test</span><span class="special">:</span> <span class="number">2.4197476510</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span>
<span class="identifier">cnv_spirit_str_to_int_test</span><span class="special">:</span> <span class="number">2.4594171510</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">2</span><span class="special">%</span> <span class="identifier">slower</span> <span class="identifier">than</span> <span class="identifier">raw</span> <span class="identifier">above</span><span class="special">)</span>
<span class="identifier">raw_lxcast_str_to_int_test</span><span class="special">:</span> <span class="number">8.4136546980</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">1</span><span class="special">%</span> <span class="identifier">faster</span> <span class="identifier">than</span> <span class="identifier">prev</span><span class="special">.</span> <span class="identifier">run</span><span class="special">)</span>
<span class="identifier">cnv_lxcast_str_to_int_test</span><span class="special">:</span> <span class="number">8.5322524600</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">1</span><span class="special">%</span> <span class="identifier">slower</span> <span class="identifier">than</span> <span class="identifier">raw</span> <span class="identifier">above</span><span class="special">)</span>
<span class="identifier">raw_spirit_str_to_int_test</span><span class="special">:</span> <span class="number">2.3842388060</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">1</span><span class="special">%</span> <span class="identifier">faster</span> <span class="identifier">than</span> <span class="identifier">prev</span><span class="special">.</span> <span class="identifier">run</span><span class="special">)</span>
<span class="identifier">cnv_spirit_str_to_int_test</span><span class="special">:</span> <span class="number">2.3812094400</span> <span class="special">[</span><span class="identifier">s</span><span class="special">]</span> <span class="special">(</span><span class="number">0</span><span class="special">%</span> <span class="identifier">faster</span> <span class="identifier">than</span> <span class="identifier">raw</span> <span class="identifier">above</span><span class="special">)</span>
</pre>
<p>
The results for consecutive runs varied with deviations of around 2%. Under
2% was also the deviation of the "cnv" code compared to the "raw"
code. That indicates that the <span class="emphasis"><em>Boost.Convert</em></span> framework
had no detectable running overhead with the tested compilers, hardware and
deployment scenarios. The results might be different on other platforms.
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2009-2022 Vladimir
Batov<p>
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>.
</p>
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