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26 <div class=
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27 <a name=
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28 expression templates for Boost.Test and others
</a>
29 </h3></div></div></div>
31 As noted in the
<a href=
"../../../../../../libs/multiprecision/doc/html/index.html" target=
"_top">Boost.Multiprecision
</a>
32 documentation, certain program constructs will not compile when using expression
33 templates. One example that many users may encounter is Boost.Test (
1.54
34 and earlier) when using macro BOOST_CHECK_CLOSE and BOOST_CHECK_CLOSE_FRACTION.
37 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
38 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>
39 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>.
41 <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>
44 To define a
50 decimal digit type using
<code class=
"computeroutput"><span class=
"identifier">cpp_dec_float
</span></code>,
45 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>.
48 It may be more legible to use a two-staged type definition such as this:
50 <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>
51 <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>
54 Here, we first define
<code class=
"computeroutput"><span class=
"identifier">mp_backend
</span></code>
55 as
<code class=
"computeroutput"><span class=
"identifier">cpp_dec_float
</span></code> with
50
56 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>
57 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.
59 <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>
60 <span class=
"identifier">cpp_dec_float_50_noet
</span><span class=
"special">;
</span>
63 You can reduce typing with a
<code class=
"computeroutput"><span class=
"keyword">using
</span></code>
64 directive
<code class=
"computeroutput"><span class=
"keyword">using
</span> <span class=
"keyword">namespace
</span>
65 <span class=
"identifier">boost
</span><span class=
"special">::
</span><span class=
"identifier">multiprecision
</span><span class=
"special">;
</span></code>
66 if desired, as shown below.
68 <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>
71 Now
<code class=
"computeroutput"><span class=
"identifier">cpp_dec_float_50_noet
</span></code>
72 or
<code class=
"computeroutput"><span class=
"identifier">cpp_dec_float_50_et
</span></code> can
73 be used as a direct replacement for built-in types like
<code class=
"computeroutput"><span class=
"keyword">double
</span></code>
76 <pre class=
"programlisting"><span class=
"identifier">BOOST_AUTO_TEST_CASE
</span><span class=
"special">(
</span><span class=
"identifier">cpp_float_test_check_close_noet
</span><span class=
"special">)
</span>
77 <span class=
"special">{
</span> <span class=
"comment">// No expression templates/
</span>
78 <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>
80 <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>
81 <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>
83 <span class=
"identifier">cpp_dec_float_50_noet
</span> <span class=
"identifier">a
</span> <span class=
"special">(
</span><span class=
"string">"1.0"</span><span class=
"special">);
</span>
84 <span class=
"identifier">cpp_dec_float_50_noet
</span> <span class=
"identifier">b
</span> <span class=
"special">(
</span><span class=
"string">"1.0"</span><span class=
"special">);
</span>
85 <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>
87 <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>
89 <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>
91 <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>
92 <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>
96 <span class=
"special">}
</span> <span class=
"comment">// BOOST_AUTO_TEST_CASE(cpp_float_test_check_close)
</span>
98 <span class=
"identifier">BOOST_AUTO_TEST_CASE
</span><span class=
"special">(
</span><span class=
"identifier">cpp_float_test_check_close_et
</span><span class=
"special">)
</span>
99 <span class=
"special">{
</span> <span class=
"comment">// Using expression templates.
</span>
100 <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_on
</span><span class=
"special">></span> <span class=
"identifier">cpp_dec_float_50_et
</span><span class=
"special">;
</span>
102 <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_et
</span><span class=
"special">>::
</span><span class=
"identifier">digits10
</span><span class=
"special">);
</span> <span class=
"comment">// All significant digits.
</span>
103 <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>
105 <span class=
"identifier">cpp_dec_float_50_et
</span> <span class=
"identifier">a
</span><span class=
"special">(
</span><span class=
"string">"1.0"</span><span class=
"special">);
</span>
106 <span class=
"identifier">cpp_dec_float_50_et
</span> <span class=
"identifier">b
</span><span class=
"special">(
</span><span class=
"string">"1.0"</span><span class=
"special">);
</span>
107 <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_et
</span><span class=
"special">>::
</span><span class=
"identifier">epsilon
</span><span class=
"special">();
</span> <span class=
"comment">// Increment least significant decimal digit.
</span>
109 <span class=
"identifier">cpp_dec_float_50_et
</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_et
</span><span class=
"special">>::
</span><span class=
"identifier">epsilon
</span><span class=
"special">();
</span>
111 <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>
113 <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>
114 <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>
117 Using
<code class=
"computeroutput"><span class=
"identifier">cpp_dec_float_50
</span></code> with
118 the default expression template use switched on, the compiler error message
119 for `BOOST_CHECK_CLOSE_FRACTION(a, b, eps); would be:
121 <pre class=
"programlisting"><span class=
"comment">// failure floating_point_comparison.hpp(
59): error C2440: 'static_cast' :
</span>
122 <span class=
"comment">// cannot convert from 'int' to 'boost::multiprecision::detail::expression
<tag,Arg1,Arg2,Arg3,Arg4
>'
</span>
125 A full example code is at
<a href=
"../../../../example/test_cpp_float_close_fraction.cpp" target=
"_top">test_cpp_float_close_fraction.cpp
</a>
128 <table xmlns:
rev=
"http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width=
"100%"><tr>
129 <td align=
"left"></td>
130 <td align=
"right"><div class=
"copyright-footer">Copyright
© 2006-
2010,
2012-
2014 Nikhar Agrawal,
131 Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert
132 Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan R
åde, Gautam Sewani,
133 Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang
<p>
134 Distributed under the Boost Software License, Version
1.0. (See accompanying
135 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>)
140 <div class=
"spirit-nav">
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"Prev"></a><a accesskey=
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