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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> |
| </div> |
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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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