1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>gmp_float</title> 5<link rel="stylesheet" href="../../../multiprecision.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../index.html" title="Chapter 1. Boost.Multiprecision"> 8<link rel="up" href="../floats.html" title="Floating-point Types"> 9<link rel="prev" href="cpp_dec_float.html" title="cpp_dec_float"> 10<link rel="next" href="mpfr_float.html" title="mpfr_float"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="cpp_dec_float.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../floats.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="mpfr_float.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="boost_multiprecision.tut.floats.gmp_float"></a><a class="link" href="gmp_float.html" title="gmp_float">gmp_float</a> 28</h4></div></div></div> 29<p> 30 <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> 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">template</span> <span class="special"><</span><span class="keyword">unsigned</span> <span class="identifier">Digits10</span><span class="special">></span> 35<span class="keyword">class</span> <span class="identifier">gmp_float</span><span class="special">;</span> 36 37<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> 38<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> 39<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> 40<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> 41<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> 42 43<span class="special">}}</span> <span class="comment">// namespaces</span> 44</pre> 45<p> 46 The <code class="computeroutput"><span class="identifier">gmp_float</span></code> back-end 47 is used in conjunction with <code class="computeroutput"><span class="identifier">number</span></code> 48 : it acts as a thin wrapper around the <a href="http://gmplib.org" target="_top">GMP</a> 49 <code class="computeroutput"><span class="identifier">mpf_t</span></code> to provide an real-number 50 type that is a drop-in replacement for the native C++ floating-point types, 51 but with much greater precision. 52 </p> 53<p> 54 Type <code class="computeroutput"><span class="identifier">gmp_float</span></code> can be used 55 at fixed precision by specifying a non-zero <code class="computeroutput"><span class="identifier">Digits10</span></code> 56 template parameter, or at variable precision by setting the template argument 57 to zero. The typedefs mpf_float_50, mpf_float_100, mpf_float_500, mpf_float_1000 58 provide arithmetic types at 50, 100, 500 and 1000 decimal digits precision 59 respectively. The typedef mpf_float provides a variable precision type 60 whose precision can be controlled via the <code class="computeroutput"><span class="identifier">number</span></code>s 61 member functions. 62 </p> 63<div class="note"><table border="0" summary="Note"> 64<tr> 65<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td> 66<th align="left">Note</th> 67</tr> 68<tr><td align="left" valign="top"><p> 69 This type only provides standard library and <code class="computeroutput"><span class="identifier">numeric_limits</span></code> 70 support when the precision is fixed at compile time. 71 </p></td></tr> 72</table></div> 73<p> 74 As well as the usual conversions from arithmetic and string types, instances 75 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 76 from: 77 </p> 78<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 79<li class="listitem"> 80 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>, 81 <code class="computeroutput"><span class="identifier">mpq_t</span></code>. 82 </li> 83<li class="listitem"> 84 The <code class="computeroutput"><span class="identifier">number</span></code> wrappers 85 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>, 86 <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_int</span><span class="special">></span></code>, 87 <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_rational</span><span class="special">></span></code>. 88 </li> 89</ul></div> 90<p> 91 It's also possible to access the underlying <code class="computeroutput"><span class="identifier">mpf_t</span></code> 92 via the <code class="computeroutput"><span class="identifier">data</span><span class="special">()</span></code> 93 member function of <code class="computeroutput"><span class="identifier">gmp_float</span></code>. 94 </p> 95<p> 96 Things you should know when using this type: 97 </p> 98<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 99<li class="listitem"> 100 Default constructed <code class="computeroutput"><span class="identifier">gmp_float</span></code>s 101 have the value zero (this is the <a href="http://gmplib.org" target="_top">GMP</a> 102 library's default behavior). 103 </li> 104<li class="listitem"> 105 No changes are made to the <a href="http://gmplib.org" target="_top">GMP</a> 106 library's global settings, so this type can be safely mixed with existing 107 <a href="http://gmplib.org" target="_top">GMP</a> code. 108 </li> 109<li class="listitem"> 110 This backend supports rvalue-references and is move-aware, making instantiations 111 of <code class="computeroutput"><span class="identifier">number</span></code> on this backend 112 move aware. 113 </li> 114<li class="listitem"> 115 It is not possible to round-trip objects of this type to and from a 116 string and get back exactly the same value. This appears to be a limitation 117 of <a href="http://gmplib.org" target="_top">GMP</a>. 118 </li> 119<li class="listitem"> 120 Since the underlying <a href="http://gmplib.org" target="_top">GMP</a> types 121 have no notion of infinities or NaNs, care should be taken to avoid 122 numeric overflow or division by zero. That latter will result in a 123 std::overflow_error being thrown, while generating excessively large 124 exponents may result in instability of the underlying <a href="http://gmplib.org" target="_top">GMP</a> 125 library (in testing, converting a number with an excessively large 126 or small exponent to a string caused <a href="http://gmplib.org" target="_top">GMP</a> 127 to segfault). 128 </li> 129<li class="listitem"> 130 This type can equally be used with <a href="http://mpir.org/" target="_top">MPIR</a> 131 as the underlying implementation - indeed that is the recommended option 132 on Win32. 133 </li> 134<li class="listitem"> 135 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> 136 being thrown if the string can not be interpreted as a valid floating-point 137 number. 138 </li> 139<li class="listitem"> 140 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> 141 being thrown. 142 </li> 143</ul></div> 144<h6> 145<a name="boost_multiprecision.tut.floats.gmp_float.h0"></a> 146 <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> 147 </h6> 148<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> 149<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> 150<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 151 152<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 153<span class="special">{</span> 154 <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> 155 156 <span class="comment">// Operations at variable precision and limited standard library support:</span> 157 <span class="identifier">mpf_float</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span> 158 <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> 159 <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> 160 <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> 161 162 <span class="comment">// Operations at fixed precision and full standard library support:</span> 163 <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> 164 <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> 165 <span class="comment">// We can use any C++ std lib function:</span> 166 <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> 167 <span class="comment">// We can also use any function from Boost.Math:</span> 168 <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> 169 <span class="comment">// These even work when the argument is an expression template:</span> 170 <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> 171 172 <span class="comment">// Access the underlying representation:</span> 173 <span class="identifier">mpf_t</span> <span class="identifier">f</span><span class="special">;</span> 174 <span class="identifier">mpf_init</span><span class="special">(</span><span class="identifier">f</span><span class="special">);</span> 175 <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> 176 <span class="identifier">mpf_clear</span><span class="special">(</span><span class="identifier">f</span><span class="special">);</span> 177 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 178<span class="special">}</span> 179</pre> 180</div> 181<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 182<td align="left"></td> 183<td align="right"><div class="copyright-footer">Copyright © 2002-2020 John 184 Maddock and Christopher Kormanyos<p> 185 Distributed under the Boost Software License, Version 1.0. (See accompanying 186 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>) 187 </p> 188</div></td> 189</tr></table> 190<hr> 191<div class="spirit-nav"> 192<a accesskey="p" href="cpp_dec_float.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../floats.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="mpfr_float.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 193</div> 194</body> 195</html> 196
