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<div class="titlepage"><div><div><h3 class="title">
<a name="math_toolkit.high_precision.using_test"></a><a class="link" href="using_test.html" title="Using without expression templates for Boost.Test and others">Using without
expression templates for Boost.Test and others</a>
</h3></div></div></div>
<p>
As noted in the <a href="http://www.boost.org/doc/libs/1_53_0_beta1/libs/multiprecision/doc/html/index.html" target="_top">Boost.Multiprecision</a>
documentation, certain program constructs will not compile when using expression
templates. One example that many users may encounter is Boost.Test (1.54
and earlier) when using macro BOOST_CHECK_CLOSE and BOOST_CHECK_CLOSE_FRACTION.
</p>
<p>
If, for example, you wish to use any multiprecision type like <code class="computeroutput"><span class="identifier">cpp_dec_float_50</span></code> in place of <code class="computeroutput"><span class="keyword">double</span></code> to give more precision, you will need
to override the default <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">et_on</span></code>
with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">et_off</span></code>.
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multiprecision</span><span class="special">/</span><span class="identifier">cpp_dec_float</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
</pre>
<p>
To define a 50 decimal digit type using <code class="computeroutput"><span class="identifier">cpp_dec_float</span></code>,
you must pass two template parameters to <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">number</span></code>.
</p>
<p>
It may be more legible to use a two-staged type definition such as this:
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">cpp_dec_float</span><span class="special"><</span><span class="number">50</span><span class="special">></span> <span class="identifier">mp_backend</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">number</span><span class="special"><</span><span class="identifier">mp_backend</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">et_off</span><span class="special">></span> <span class="identifier">cpp_dec_float_50_noet</span><span class="special">;</span>
</pre>
<p>
Here, we first define <code class="computeroutput"><span class="identifier">mp_backend</span></code>
as <code class="computeroutput"><span class="identifier">cpp_dec_float</span></code> with 50
digits. The second step passes this backend to <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">number</span></code>
with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">et_off</span></code>, an enumerated type.
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">number</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">cpp_dec_float</span><span class="special"><</span><span class="number">50</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">et_off</span><span class="special">></span>
<span class="identifier">cpp_dec_float_50_noet</span><span class="special">;</span>
</pre>
<p>
You can reduce typing with a <code class="computeroutput"><span class="keyword">using</span></code>
directive <code class="computeroutput"><span class="keyword">using</span> <span class="keyword">namespace</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">;</span></code>
if desired, as shown below.
</p>
<pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">number</span><span class="special"><</span><span class="identifier">cpp_dec_float</span><span class="special"><</span><span class="number">50</span><span class="special">>,</span> <span class="identifier">et_off</span><span class="special">></span> <span class="identifier">cpp_dec_float_50_noet</span><span class="special">;</span>
</pre>
<p>
Now <code class="computeroutput"><span class="identifier">cpp_dec_float_50_noet</span></code>
can be used as a direct replacement for built-in types like <code class="computeroutput"><span class="keyword">double</span></code> etc.
</p>
<pre class="programlisting"><span class="identifier">BOOST_AUTO_TEST_CASE</span><span class="special">(</span><span class="identifier">cpp_float_test_check_close</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">.</span><span class="identifier">precision</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">cpp_dec_float_50_noet</span><span class="special">>::</span><span class="identifier">digits10</span><span class="special">);</span> <span class="comment">// All significant digits.</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">showpoint</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="comment">// Show trailing zeros.</span>
<span class="identifier">cpp_dec_float_50_noet</span> <span class="identifier">a</span> <span class="special">(</span><span class="string">"1."</span><span class="special">);</span>
<span class="identifier">cpp_dec_float_50_noet</span> <span class="identifier">b</span> <span class="special">(</span><span class="string">"1."</span><span class="special">);</span>
<span class="identifier">b</span> <span class="special">+=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">cpp_dec_float_50_noet</span><span class="special">>::</span><span class="identifier">epsilon</span><span class="special">();</span> <span class="comment">// Increment least significant decimal digit.</span>
<span class="identifier">cpp_dec_float_50_noet</span> <span class="identifier">eps</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">cpp_dec_float_50_noet</span><span class="special">>::</span><span class="identifier">epsilon</span><span class="special">();</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span><span class="string">"a = "</span> <span class="special"><<</span> <span class="identifier">a</span> <span class="special"><<</span> <span class="string">",\nb = "</span> <span class="special"><<</span> <span class="identifier">b</span> <span class="special"><<</span> <span class="string">",\neps = "</span> <span class="special"><<</span> <span class="identifier">eps</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">BOOST_CHECK_CLOSE</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">b</span><span class="special">,</span> <span class="identifier">eps</span> <span class="special">*</span> <span class="number">100</span><span class="special">);</span> <span class="comment">// Expected to pass (because tolerance is as percent).</span>
<span class="identifier">BOOST_CHECK_CLOSE_FRACTION</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">b</span><span class="special">,</span> <span class="identifier">eps</span><span class="special">);</span> <span class="comment">// Expected to pass (because tolerance is as fraction).</span>
</pre>
<p>
Using <code class="computeroutput"><span class="identifier">cpp_dec_float_50</span></code> with
the default expression template use switched on, the compiler error message
for `BOOST_CHECK_CLOSE_FRACTION(a, b, eps); would be:
</p>
<pre class="programlisting"><span class="comment">// failure floating_point_comparison.hpp(59): error C2440: 'static_cast' :</span>
<span class="comment">// cannot convert from 'int' to 'boost::multiprecision::detail::expression<tag,Arg1,Arg2,Arg3,Arg4>'</span>
</pre>
<p>
A full example code is at <a href="../../../../example/test_cpp_float_close_fraction.cpp" target="_top">test_cpp_float_close_fraction.cpp</a>
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2006-2010, 2012-2014 Nikhar Agrawal,
Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert
Holin, Bruno Lalande, John Maddock, Johan Råde, Gautam Sewani, Benjamin Sobotta,
Thijs van den Berg, Daryle Walker and Xiaogang Zhang<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>)
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