projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | <html> |
| 2 | <head> | |
| 3 | <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> | |
| 4 | <title>float128</title> | |
| 5 | <link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css"> | |
| 6 | <meta name="generator" content="DocBook XSL Stylesheets V1.77.1"> | |
| 7 | <link rel="home" href="../../../index.html" title="Chapter 1. Boost.Multiprecision"> | |
| 8 | <link rel="up" href="../floats.html" title="floating-point Numbers"> | |
| 9 | <link rel="prev" href="mpfr_float.html" title="mpfr_float"> | |
| 10 | <link rel="next" href="fp_eg.html" title="Examples"> | |
| 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="mpfr_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="fp_eg.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.float128"></a><a class="link" href="float128.html" title="float128">float128</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">float128</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">class</span> <span class="identifier">float128_backend</span><span class="special">;</span> | |
| 35 | ||
| 36 | <span class="keyword">typedef</span> <span class="identifier">number</span><span class="special"><</span><span class="identifier">float128_backend</span><span class="special">,</span> <span class="identifier">et_off</span><span class="special">></span> <span class="identifier">float128</span><span class="special">;</span> | |
| 37 | ||
| 38 | <span class="special">}}</span> <span class="comment">// namespaces</span> | |
| 39 | </pre> | |
| 40 | <p> | |
| 41 | The <code class="computeroutput"><span class="identifier">float128</span></code> number type | |
| 42 | is a very thin wrapper around GCC's <code class="computeroutput"><a class="link" href="float128.html" title="float128">float128</a></code> | |
| 43 | or Intel's <code class="computeroutput"><span class="identifier">_Quad</span></code> data types | |
| 44 | and provides an real-number type that is a drop-in replacement for the | |
| 45 | native C++ floating-point types, but with a 113 bit mantissa, and compatible | |
| 46 | with FORTRAN's 128-bit QUAD real. | |
| 47 | </p> | |
| 48 | <p> | |
| 49 | All the usual standard library and <code class="computeroutput"><span class="identifier">numeric_limits</span></code> | |
| 50 | support are available, performance should be equivalent to the underlying | |
| 51 | native types: for example the LINPACK benchmarks for GCC's <code class="computeroutput"><a class="link" href="float128.html" title="float128">float128</a></code> | |
| 52 | and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">float128</span></code> both achieved 5.6 MFLOPS<a href="#ftn.boost_multiprecision.tut.floats.float128.f0" class="footnote"><sup class="footnote"><a name="boost_multiprecision.tut.floats.float128.f0"></a>[3]</sup></a>. | |
| 53 | </p> | |
| 54 | <p> | |
| 55 | As well as the usual conversions from arithmetic and string types, instances | |
| 56 | of <code class="computeroutput"><span class="identifier">float128</span></code> are copy constructible | |
| 57 | and assignable from GCC's <code class="computeroutput"><a class="link" href="float128.html" title="float128">float128</a></code> | |
| 58 | and Intel's <code class="computeroutput"><span class="identifier">_Quad</span></code> data | |
| 59 | types. | |
| 60 | </p> | |
| 61 | <p> | |
| 62 | It's also possible to access the underlying <code class="computeroutput"><a class="link" href="float128.html" title="float128">float128</a></code> | |
| 63 | or <code class="computeroutput"><span class="identifier">_Quad</span></code> type via the | |
| 64 | <code class="computeroutput"><span class="identifier">data</span><span class="special">()</span></code> | |
| 65 | member function of <code class="computeroutput"><span class="identifier">float128_backend</span></code>. | |
| 66 | </p> | |
| 67 | <p> | |
| 68 | Things you should know when using this type: | |
| 69 | </p> | |
| 70 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
| 71 | <li class="listitem"> | |
| 72 | Default constructed <code class="computeroutput"><span class="identifier">float128</span></code>s | |
| 73 | have the value zero. | |
| 74 | </li> | |
| 75 | <li class="listitem"> | |
| 76 | This backend supports rvalue-references and is move-aware, making instantiations | |
| 77 | of <code class="computeroutput"><span class="identifier">number</span></code> on this backend | |
| 78 | move aware. | |
| 79 | </li> | |
| 80 | <li class="listitem"> | |
| 81 | It is not possible to round-trip objects of this type to and from a | |
| 82 | string and get back exactly the same value when compiled with Intel's | |
| 83 | C++ compiler and using <code class="computeroutput"><span class="identifier">_Quad</span></code> | |
| 84 | as the underlying type: this is a current limitation of our code. Round | |
| 85 | tripping when using <code class="computeroutput"><a class="link" href="float128.html" title="float128">float128</a></code> | |
| 86 | as the underlying type is possible (both for GCC and Intel). | |
| 87 | </li> | |
| 88 | <li class="listitem"> | |
| 89 | 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> | |
| 90 | being thrown if the string can not be interpreted as a valid floating-point | |
| 91 | number. | |
| 92 | </li> | |
| 93 | <li class="listitem"> | |
| 94 | Division by zero results in an infinity being produced. | |
| 95 | </li> | |
| 96 | <li class="listitem"> | |
| 97 | Type <code class="computeroutput"><span class="identifier">float128</span></code> can be | |
| 98 | used as a literal type (constexpr support). | |
| 99 | </li> | |
| 100 | <li class="listitem"> | |
| 101 | When using the Intel compiler, the underlying type defaults to <code class="computeroutput"><a class="link" href="float128.html" title="float128">float128</a></code> | |
| 102 | if it's available and <code class="computeroutput"><span class="identifier">_Quad</span></code> | |
| 103 | if not. You can override the default by defining either <code class="computeroutput"><span class="identifier">BOOST_MP_USE_FLOAT128</span></code> or <code class="computeroutput"><span class="identifier">BOOST_MP_USE_QUAD</span></code>. | |
| 104 | </li> | |
| 105 | <li class="listitem"> | |
| 106 | When the underlying type is Intel's <code class="computeroutput"><span class="identifier">_Quad</span></code> | |
| 107 | type, the code must be compiled with the compiler option <code class="computeroutput"><span class="special">-</span><span class="identifier">Qoption</span><span class="special">,</span><span class="identifier">cpp</span><span class="special">,--</span><span class="identifier">extended_float_type</span></code>. | |
| 108 | </li> | |
| 109 | </ul></div> | |
| 110 | <h6> | |
| 111 | <a name="boost_multiprecision.tut.floats.float128.h0"></a> | |
| 112 | <span class="phrase"><a name="boost_multiprecision.tut.floats.float128.float128_example"></a></span><a class="link" href="float128.html#boost_multiprecision.tut.floats.float128.float128_example">float128 | |
| 113 | example:</a> | |
| 114 | </h6> | |
| 115 | <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">float128</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> | |
| 116 | <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> | |
| 117 | <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> | |
| 118 | ||
| 119 | <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> | |
| 120 | <span class="special">{</span> | |
| 121 | <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> | |
| 122 | ||
| 123 | <span class="comment">// Operations at 128-bit precision and full numeric_limits support:</span> | |
| 124 | <span class="identifier">float128</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span> | |
| 125 | <span class="comment">// There are 113-bits of precision:</span> | |
| 126 | <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">float128</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> | |
| 127 | <span class="comment">// Or 34 decimal places:</span> | |
| 128 | <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">float128</span><span class="special">>::</span><span class="identifier">digits10</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> | |
| 129 | <span class="comment">// We can use any C++ std lib function, lets print all the digits as well:</span> | |
| 130 | <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">setprecision</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">float128</span><span class="special">>::</span><span class="identifier">max_digits10</span><span class="special">)</span> | |
| 131 | <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) = 0.693147180559945309417232121458176575</span> | |
| 132 | <span class="comment">// We can also use any function from Boost.Math:</span> | |
| 133 | <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> | |
| 134 | <span class="comment">// And since we have an extended exponent range we can generate some really large </span> | |
| 135 | <span class="comment">// numbers here (4.02387260077093773543702433923004111e+2564):</span> | |
| 136 | <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">float128</span><span class="special">(</span><span class="number">1000</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> | |
| 137 | <span class="comment">//</span> | |
| 138 | <span class="comment">// We can declare constants using GCC or Intel's native types, and the Q suffix,</span> | |
| 139 | <span class="comment">// these can be declared constexpr if required:</span> | |
| 140 | ||
| 141 | <span class="keyword">constexpr</span> <span class="identifier">float128</span> <span class="identifier">pi</span> <span class="special">=</span> <span class="number">3.1415926535897932384626433832795028841971693993751058</span><span class="identifier">Q</span><span class="special">;</span> | |
| 142 | ||
| 143 | <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> | |
| 144 | <span class="special">}</span> | |
| 145 | </pre> | |
| 146 | <div class="footnotes"> | |
| 147 | <br><hr style="width:100; align:left;"> | |
| 148 | <div id="ftn.boost_multiprecision.tut.floats.float128.f0" class="footnote"><p><a href="#boost_multiprecision.tut.floats.float128.f0" class="para"><sup class="para">[3] </sup></a> | |
| 149 | On 64-bit Ubuntu 11.10, GCC-4.8.0, Intel Core 2 Duo T5800. | |
| 150 | </p></div> | |
| 151 | </div> | |
| 152 | </div> | |
| 153 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 154 | <td align="left"></td> | |
| 155 | <td align="right"><div class="copyright-footer">Copyright © 2002-2013 John Maddock and Christopher Kormanyos<p> | |
| 156 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 157 | 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>) | |
| 158 | </p> | |
| 159 | </div></td> | |
| 160 | </tr></table> | |
| 161 | <hr> | |
| 162 | <div class="spirit-nav"> | |
| 163 | <a accesskey="p" href="mpfr_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="fp_eg.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> | |
| 164 | </div> | |
| 165 | </body> | |
| 166 | </html> |