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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="boost_multiprecision.tut.floats.gmp_float"></a><a class="link" href="gmp_float.html" title="gmp_float">gmp_float</a> |
| </h4></div></div></div> |
| <p> |
| <code class="computeroutput"><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">gmp</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> |
| </p> |
| <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> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">unsigned</span> <span class="identifier">Digits10</span><span class="special">></span> |
| <span class="keyword">class</span> <span class="identifier">gmp_float</span><span class="special">;</span> |
| |
| <span class="keyword">typedef</span> <span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_float</span><span class="special"><</span><span class="number">50</span><span class="special">></span> <span class="special">></span> <span class="identifier">mpf_float_50</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_float</span><span class="special"><</span><span class="number">100</span><span class="special">></span> <span class="special">></span> <span class="identifier">mpf_float_100</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_float</span><span class="special"><</span><span class="number">500</span><span class="special">></span> <span class="special">></span> <span class="identifier">mpf_float_500</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_float</span><span class="special"><</span><span class="number">1000</span><span class="special">></span> <span class="special">></span> <span class="identifier">mpf_float_1000</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_float</span><span class="special"><</span><span class="number">0</span><span class="special">></span> <span class="special">></span> <span class="identifier">mpf_float</span><span class="special">;</span> |
| |
| <span class="special">}}</span> <span class="comment">// namespaces</span> |
| </pre> |
| <p> |
| The <code class="computeroutput"><span class="identifier">gmp_float</span></code> back-end |
| is used in conjunction with <code class="computeroutput"><span class="identifier">number</span></code> |
| : it acts as a thin wrapper around the <a href="http://gmplib.org" target="_top">GMP</a> |
| <code class="computeroutput"><span class="identifier">mpf_t</span></code> to provide an real-number |
| type that is a drop-in replacement for the native C++ floating-point types, |
| but with much greater precision. |
| </p> |
| <p> |
| Type <code class="computeroutput"><span class="identifier">gmp_float</span></code> can be used |
| at fixed precision by specifying a non-zero <code class="computeroutput"><span class="identifier">Digits10</span></code> |
| template parameter, or at variable precision by setting the template argument |
| to zero. The typedefs mpf_float_50, mpf_float_100, mpf_float_500, mpf_float_1000 |
| provide arithmetic types at 50, 100, 500 and 1000 decimal digits precision |
| respectively. The typedef mpf_float provides a variable precision type |
| whose precision can be controlled via the <code class="computeroutput"><span class="identifier">number</span></code>s |
| member functions. |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| This type only provides standard library and <code class="computeroutput"><span class="identifier">numeric_limits</span></code> |
| support when the precision is fixed at compile time. |
| </p></td></tr> |
| </table></div> |
| <p> |
| As well as the usual conversions from arithmetic and string types, instances |
| of <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">mpf_float</span><span class="special"><</span><span class="identifier">N</span><span class="special">></span> <span class="special">></span></code> are copy constructible and assignable |
| from: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| The <a href="http://gmplib.org" target="_top">GMP</a> native types <code class="computeroutput"><span class="identifier">mpf_t</span></code>, <code class="computeroutput"><span class="identifier">mpz_t</span></code>, |
| <code class="computeroutput"><span class="identifier">mpq_t</span></code>. |
| </li> |
| <li class="listitem"> |
| The <code class="computeroutput"><span class="identifier">number</span></code> wrappers |
| around those types: <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">mpf_float</span><span class="special"><</span><span class="identifier">M</span><span class="special">></span> <span class="special">></span></code>, |
| <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_int</span><span class="special">></span></code>, |
| <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_rational</span><span class="special">></span></code>. |
| </li> |
| </ul></div> |
| <p> |
| It's also possible to access the underlying <code class="computeroutput"><span class="identifier">mpf_t</span></code> |
| via the <code class="computeroutput"><span class="identifier">data</span><span class="special">()</span></code> |
| member function of <code class="computeroutput"><span class="identifier">gmp_float</span></code>. |
| </p> |
| <p> |
| Things you should know when using this type: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| Default constructed <code class="computeroutput"><span class="identifier">gmp_float</span></code>s |
| have the value zero (this is the <a href="http://gmplib.org" target="_top">GMP</a> |
| library's default behavior). |
| </li> |
| <li class="listitem"> |
| No changes are made to the <a href="http://gmplib.org" target="_top">GMP</a> |
| library's global settings, so this type can be safely mixed with existing |
| <a href="http://gmplib.org" target="_top">GMP</a> code. |
| </li> |
| <li class="listitem"> |
| This backend supports rvalue-references and is move-aware, making instantiations |
| of <code class="computeroutput"><span class="identifier">number</span></code> on this backend |
| move aware. |
| </li> |
| <li class="listitem"> |
| It is not possible to round-trip objects of this type to and from a |
| string and get back exactly the same value. This appears to be a limitation |
| of <a href="http://gmplib.org" target="_top">GMP</a>. |
| </li> |
| <li class="listitem"> |
| Since the underlying <a href="http://gmplib.org" target="_top">GMP</a> types |
| have no notion of infinities or NaN's, care should be taken to avoid |
| numeric overflow or division by zero. That latter will result in a |
| std::overflow_error being thrown, while generating excessively large |
| exponents may result in instability of the underlying <a href="http://gmplib.org" target="_top">GMP</a> |
| library (in testing, converting a number with an excessively large |
| or small exponent to a string caused <a href="http://gmplib.org" target="_top">GMP</a> |
| to segfault). |
| </li> |
| <li class="listitem"> |
| This type can equally be used with <a href="http://mpir.org/" target="_top">MPIR</a> |
| as the underlying implementation - indeed that is the recommended option |
| on Win32. |
| </li> |
| <li class="listitem"> |
| 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> |
| being thrown if the string can not be interpreted as a valid floating |
| point number. |
| </li> |
| <li class="listitem"> |
| 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> |
| being thrown. |
| </li> |
| </ul></div> |
| <h6> |
| <a name="boost_multiprecision.tut.floats.gmp_float.h0"></a> |
| <span class="phrase"><a name="boost_multiprecision.tut.floats.gmp_float.gmp_example"></a></span><a class="link" href="gmp_float.html#boost_multiprecision.tut.floats.gmp_float.gmp_example"> GMP example:</a> |
| </h6> |
| <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">gmp</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">special_functions</span><span class="special">/</span><span class="identifier">gamma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <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="comment">// Operations at variable precision and limited standard library support:</span> |
| <span class="identifier">mpf_float</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span> |
| <span class="identifier">mpf_float</span><span class="special">::</span><span class="identifier">default_precision</span><span class="special">(</span><span class="number">1000</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">mpf_float</span><span class="special">::</span><span class="identifier">default_precision</span><span class="special">()</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">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">sqrt</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</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">// print root-2</span> |
| |
| <span class="comment">// Operations at fixed precision and full standard library support:</span> |
| <span class="identifier">mpf_float_100</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</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">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">mpf_float_100</span><span class="special">>::</span><span class="identifier">digits</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">// We can use any C++ std lib function:</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">log</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</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">// print log(2)</span> |
| <span class="comment">// We can also use any function from Boost.Math:</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</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">// These even work when the argument is an expression template:</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">b</span> <span class="special">*</span> <span class="identifier">b</span><span class="special">)</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">// Access the underlying representation:</span> |
| <span class="identifier">mpf_t</span> <span class="identifier">f</span><span class="special">;</span> |
| <span class="identifier">mpf_init</span><span class="special">(</span><span class="identifier">f</span><span class="special">);</span> |
| <span class="identifier">mpf_set</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">backend</span><span class="special">().</span><span class="identifier">data</span><span class="special">());</span> |
| <span class="identifier">mpf_clear</span><span class="special">(</span><span class="identifier">f</span><span class="special">);</span> |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| </div> |
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| <td align="right"><div class="copyright-footer">Copyright © 2002-2013 John Maddock and Christopher Kormanyos<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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