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  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="boost_multiprecision.tut.rational.tommath_rational"></a><a class="link" href="tommath_rational.html" title="tommath_rational">tommath_rational</a>
  28 </h4></div></div></div>
  29 <p>
  30           <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multiprecision</span><span class="special">/</span><span class="identifier">tommath</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
  31         </p>
  32 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">multiprecision</span><span class="special">{</span>
  33
  34 <span class="keyword">typedef</span> <span class="identifier">rational_adpater</span><span class="special">&lt;</span><span class="identifier">tommath_int</span><span class="special">&gt;</span>        <span class="identifier">tommath_rational</span><span class="special">;</span>
  35 <span class="keyword">typedef</span> <span class="identifier">number</span><span class="special">&lt;</span><span class="identifier">tommath_rational</span> <span class="special">&gt;</span>         <span class="identifier">tom_rational</span><span class="special">;</span>
  36
  37 <span class="special">}}</span> <span class="comment">// namespaces</span>
  38 </pre>
  39 <p>
  40           The <code class="computeroutput"><span class="identifier">tommath_rational</span></code> back-end
  41           is used via the typedef <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">tom_rational</span></code>.
  42           It acts as a thin wrapper around <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rational</span><span class="special">&lt;</span><span class="identifier">tom_int</span><span class="special">&gt;</span></code> to provide a rational number type that
  43           is a drop-in replacement for the native C++ number types, but with unlimited
  44           precision.
  45         </p>
  46 <p>
  47           The advantage of using this type rather than <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rational</span><span class="special">&lt;</span><span class="identifier">tom_int</span><span class="special">&gt;</span></code> directly, is that it is expression-template
  48           enabled, greatly reducing the number of temporaries created in complex
  49           expressions.
  50         </p>
  51 <p>
  52           There are also non-member functions:
  53         </p>
  54 <pre class="programlisting"><span class="identifier">tom_int</span> <span class="identifier">numerator</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">tom_rational</span><span class="special">&amp;);</span>
  55 <span class="identifier">tom_int</span> <span class="identifier">denominator</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">tom_rational</span><span class="special">&amp;);</span>
  56 </pre>
  57 <p>
  58           which return the numerator and denominator of the number.
  59         </p>
  60 <p>
  61           Things you should know when using this type:
  62         </p>
  63 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  64 <li class="listitem">
  65               Default constructed <code class="computeroutput"><span class="identifier">tom_rational</span></code>s
  66               have the value zero (this the inherited Boost.Rational behavior).
  67             </li>
  68 <li class="listitem">
  69               Division by zero results in a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">overflow_error</span></code>
  70               being thrown.
  71             </li>
  72 <li class="listitem">
  73               Conversion from a string results in a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span></code>
  74               being thrown if the string can not be interpreted as a valid rational
  75               number.
  76             </li>
  77 <li class="listitem">
  78               No changes are made to <a href="http://libtom.net" target="_top">libtommath</a>'s
  79               global state, so this type can safely coexist with other <a href="http://libtom.net" target="_top">libtommath</a>
  80               code.
  81             </li>
  82 <li class="listitem">
  83               Performance of this type has been found to be pretty poor - this need
  84               further investigation - but it appears that Boost.Rational needs some
  85               improvement in this area.
  86             </li>
  87 </ul></div>
  88 <h6>
  89 <a name="boost_multiprecision.tut.rational.tommath_rational.h0"></a>
  90           <span class="phrase"><a name="boost_multiprecision.tut.rational.tommath_rational.example"></a></span><a class="link" href="tommath_rational.html#boost_multiprecision.tut.rational.tommath_rational.example">Example:</a>
  91         </h6>
  92 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multiprecision</span><span class="special">/</span><span class="identifier">tommath</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  93 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
  94
  95 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
  96 <span class="special">{</span>
  97    <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>
  98
  99    <span class="identifier">tom_rational</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>
 100
 101    <span class="comment">// Do some arithmetic:</span>
 102    <span class="keyword">for</span><span class="special">(</span><span class="keyword">unsigned</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;=</span> <span class="number">1000</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span>
 103       <span class="identifier">v</span> <span class="special">*=</span> <span class="identifier">i</span><span class="special">;</span>
 104    <span class="identifier">v</span> <span class="special">/=</span> <span class="number">10</span><span class="special">;</span>
 105
 106    <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">v</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="comment">// prints 1000! / 10</span>
 107    <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">numerator</span><span class="special">(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 108    <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">denominator</span><span class="special">(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 109
 110    <span class="identifier">tom_rational</span> <span class="identifier">w</span><span class="special">(</span><span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">);</span> <span class="comment">// Component wise constructor</span>
 111    <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">w</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="comment">// prints 2/3</span>
 112
 113    <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 114 <span class="special">}</span>
 115 </pre>
 116 </div>
 117 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 118 <td align="left"></td>
 119 <td align="right"><div class="copyright-footer">Copyright &#169; 2002-2019 John Maddock
 120       and Christopher Kormanyos<p>
 121         Distributed under the Boost Software License, Version 1.0. (See accompanying
 122         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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