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| 4 | <title>Implementation of Float128 type</title> | |
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| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h2 class="title" style="clear: both"> | |
| 27 | <a name="math_toolkit.float128"></a><a class="link" href="float128.html" title="Implementation of Float128 type">Implementation of Float128 type</a> | |
| 28 | </h2></div></div></div> | |
| 29 | <div class="toc"><dl> | |
| 30 | <dt><span class="section"><a href="float128/overloading.html">Overloading template | |
| 31 | functions with float128_t</a></span></dt> | |
| 32 | <dt><span class="section"><a href="float128/exp_function.html">Exponential function</a></span></dt> | |
| 33 | <dt><span class="section"><a href="float128/typeinfo.html"><code class="computeroutput"><span class="identifier">typeinfo</span></code></a></span></dt> | |
| 34 | </dl></div> | |
| 35 | <p> | |
| 36 | Since few compilers implement a true 128-bit floating-point, and language features | |
| 37 | like the suffix Q (which may need an option <code class="computeroutput"><span class="special">-</span><span class="identifier">fext</span><span class="special">-</span><span class="identifier">numeric</span><span class="special">-</span><span class="identifier">literals</span></code> | |
| 38 | to enable), and C++ Standard library functions are as-yet missing or incomplete | |
| 39 | in C++11, this Boost.Math implementation wraps <code class="computeroutput"><span class="identifier">__float128</span></code> | |
| 40 | provided by the GCC compiler <a href="https://gcc.gnu.org/onlinedocs/gcc/Floating-Types.html" target="_top">GCC | |
| 41 | floating-point types</a> or the <code class="computeroutput"><span class="identifier">_Quad</span></code> | |
| 42 | type provided by the Intel compiler. | |
| 43 | </p> | |
| 44 | <p> | |
| 45 | This is provided to in order to demonstrate, and users to evaluate, the feasibility | |
| 46 | and benefits of higher-precision floating-point, especially to allow use of | |
| 47 | the full <cmath> and Boost.Math library of functions and distributions | |
| 48 | at high precision. | |
| 49 | </p> | |
| 50 | <p> | |
| 51 | (It is also possible to use Boost.Math with Boost.Multiprecision decimal and | |
| 52 | binary, but since these are entirely software solutions, allowing much higher | |
| 53 | precision or arbitrary precision, they are likely to be slower). | |
| 54 | </p> | |
| 55 | <p> | |
| 56 | We also provide (we believe full) support for <code class="computeroutput"><span class="special"><</span><span class="identifier">limits</span><span class="special">>,</span> <span class="special"><</span><span class="identifier">cmath</span><span class="special">></span></code>, I/O stream operations in <code class="computeroutput"><span class="special"><</span><span class="identifier">iostream</span><span class="special">></span></code>, and <code class="computeroutput"><span class="special"><</span><span class="identifier">complex</span><span class="special">></span></code>. | |
| 57 | </p> | |
| 58 | <p> | |
| 59 | As a prototype for a future C++ standard, we place all these in <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">std</span></code>. | |
| 60 | This contravenes the existing C++ standard of course, so selecting any compiler | |
| 61 | that promises to check conformance will fail. | |
| 62 | </p> | |
| 63 | <div class="tip"><table border="0" summary="Tip"> | |
| 64 | <tr> | |
| 65 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../doc/src/images/tip.png"></td> | |
| 66 | <th align="left">Tip</th> | |
| 67 | </tr> | |
| 68 | <tr><td align="left" valign="top"><p> | |
| 69 | For GCC, compile with <code class="computeroutput"><span class="special">-</span><span class="identifier">std</span><span class="special">=</span><span class="identifier">gnu</span><span class="special">++</span><span class="number">11</span></code> or <code class="computeroutput"><span class="special">-</span><span class="identifier">std</span><span class="special">=</span><span class="identifier">gnu</span><span class="special">++</span><span class="number">03</span></code> and do | |
| 70 | not use <code class="computeroutput"><span class="special">-</span><span class="identifier">std</span><span class="special">=</span><span class="identifier">stdc</span><span class="special">++</span><span class="number">11</span></code> or any 'strict' options, as these turn off | |
| 71 | full support for <code class="computeroutput"><span class="identifier">__float128</span></code>. | |
| 72 | These requirements also apply to the Intel compiler on Linux, for Intel on | |
| 73 | Windows you need to compile with <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> <span class="special">-</span><span class="identifier">DBOOST_MATH_USE_FLOAT128</span></code> in order to activate | |
| 74 | 128-bit floating point support. | |
| 75 | </p></td></tr> | |
| 76 | </table></div> | |
| 77 | <p> | |
| 78 | The <code class="computeroutput"><span class="identifier">__float128</span></code> type is provided | |
| 79 | by the <a href="http://gcc.gnu.org/onlinedocs/libquadmath/" target="_top">libquadmath | |
| 80 | library</a> on GCC or by Intel's FORTRAN library with Intel C++. THey also | |
| 81 | provide a full set of <code class="computeroutput"><span class="special"><</span><span class="identifier">cmath</span><span class="special">></span></code> functions in <code class="computeroutput"><span class="keyword">namespace</span> | |
| 82 | <span class="identifier">std</span></code>. | |
| 83 | </p> | |
| 84 | <h5> | |
| 85 | <a name="math_toolkit.float128.h0"></a> | |
| 86 | <span class="phrase"><a name="math_toolkit.float128.using_c_float128_quadmath_type"></a></span><a class="link" href="float128.html#math_toolkit.float128.using_c_float128_quadmath_type">Using | |
| 87 | C __float128 quadmath type</a> | |
| 88 | </h5> | |
| 89 | <p> | |
| 90 | [quadmath_snprintf_1] | |
| 91 | </p> | |
| 92 | <p> | |
| 93 | The source code is at <a href="../../../example/quadmath_snprintf.c" target="_top">quadmath_snprintf.c</a>. | |
| 94 | </p> | |
| 95 | <h5> | |
| 96 | <a name="math_toolkit.float128.h1"></a> | |
| 97 | <span class="phrase"><a name="math_toolkit.float128.using_c_float128_quadmath_type0"></a></span><a class="link" href="float128.html#math_toolkit.float128.using_c_float128_quadmath_type0">Using | |
| 98 | C++ <code class="computeroutput"><span class="identifier">float128</span></code> quadmath type</a> | |
| 99 | </h5> | |
| 100 | <p> | |
| 101 | For C++ programs, you will want to use the C++ type <code class="computeroutput"><span class="identifier">float128</span></code> | |
| 102 | </p> | |
| 103 | <p> | |
| 104 | See example at <a href="../../../example/cstdfloat_example.cpp" target="_top">cstdfloat_example.cpp</a>. | |
| 105 | </p> | |
| 106 | <p> | |
| 107 | A typical invocation of the compiler is | |
| 108 | </p> | |
| 109 | <pre class="programlisting"><span class="identifier">g</span><span class="special">++</span> <span class="special">-</span><span class="identifier">O3</span> <span class="special">-</span><span class="identifier">std</span><span class="special">=</span><span class="identifier">gnu</span><span class="special">++</span><span class="number">11</span> <span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span> <span class="special">-</span><span class="identifier">I</span><span class="special">/</span><span class="identifier">c</span><span class="special">/</span><span class="identifier">modular</span><span class="special">-</span><span class="identifier">boost</span> <span class="special">-</span><span class="identifier">lquadmath</span> <span class="special">-</span><span class="identifier">o</span> <span class="identifier">test</span><span class="special">.</span><span class="identifier">exe</span> | |
| 110 | </pre> | |
| 111 | <div class="tip"><table border="0" summary="Tip"> | |
| 112 | <tr> | |
| 113 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../doc/src/images/tip.png"></td> | |
| 114 | <th align="left">Tip</th> | |
| 115 | </tr> | |
| 116 | <tr><td align="left" valign="top"><p> | |
| 117 | If you are trying to use the develop branch of Boost.Math, then make <code class="computeroutput"><span class="special">-</span><span class="identifier">I</span><span class="special">/</span><span class="identifier">c</span><span class="special">/</span><span class="identifier">modular</span><span class="special">-</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">libs</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">include</span></code> | |
| 118 | the <span class="bold"><strong>first</strong></span> include directory. | |
| 119 | </p></td></tr> | |
| 120 | </table></div> | |
| 121 | <pre class="programlisting"><span class="identifier">g</span><span class="special">++</span> <span class="special">-</span><span class="identifier">O3</span> <span class="special">-</span><span class="identifier">std</span><span class="special">=</span><span class="identifier">gnu</span><span class="special">++</span><span class="number">11</span> <span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span> <span class="special">-</span><span class="identifier">I</span><span class="special">/</span><span class="identifier">c</span><span class="special">/</span><span class="identifier">modular</span><span class="special">-</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">libs</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">include</span> <span class="special">-</span><span class="identifier">I</span><span class="special">/</span><span class="identifier">c</span><span class="special">/</span><span class="identifier">modular</span><span class="special">-</span><span class="identifier">boost</span> <span class="special">-</span><span class="identifier">lquadmath</span> <span class="special">-</span><span class="identifier">o</span> <span class="identifier">test</span><span class="special">.</span><span class="identifier">exe</span> | |
| 122 | </pre> | |
| 123 | <div class="note"><table border="0" summary="Note"> | |
| 124 | <tr> | |
| 125 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> | |
| 126 | <th align="left">Note</th> | |
| 127 | </tr> | |
| 128 | <tr><td align="left" valign="top"> | |
| 129 | <p> | |
| 130 | So far, the only missing detail that we had noted was in trying to use <code class="computeroutput"><span class="special"><</span><span class="identifier">typeinfo</span><span class="special">></span></code>, for example for <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="keyword">typeid</span><span class="special"><</span><span class="identifier">__float_128</span><span class="special">>.</span><span class="identifier">name</span><span class="special">();</span></code>. | |
| 131 | </p> | |
| 132 | <pre class="programlisting"><span class="identifier">Link</span> <span class="identifier">fails</span><span class="special">:</span> <span class="identifier">undefined</span> <span class="identifier">reference</span> <span class="identifier">to</span> <span class="identifier">typeinfo</span> <span class="keyword">for</span> <span class="identifier">__float128</span><span class="special">.</span> | |
| 133 | </pre> | |
| 134 | <p> | |
| 135 | See <a href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43622" target="_top">GCC Bug | |
| 136 | 43622 - no C++ typeinfo for __float128</a>. But this is reported (Marc | |
| 137 | Glisse 2015-04-04 ) fixed in GCC 5 (and above). | |
| 138 | </p> | |
| 139 | <p> | |
| 140 | For example, with GCC6.1.1 this works as expected to a <span class="bold"><strong>mangled</strong></span> | |
| 141 | string name, and output (if possible - not always). | |
| 142 | </p> | |
| 143 | <pre class="programlisting"><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">type_info</span><span class="special">&</span> <span class="identifier">tifu128</span> <span class="special">=</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">__float128</span><span class="special">);</span> <span class="comment">// OK.</span> | |
| 144 | <span class="comment">//std::cout << tifu128.name() << std::endl; // On GCC, aborts (because not printable string).</span> | |
| 145 | <span class="comment">//std::cout << typeid(__float128).name() << std::endl; // Aborts - string name cannot be output.</span> | |
| 146 | ||
| 147 | <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">type_info</span><span class="special">&</span> <span class="identifier">tif128</span> <span class="special">=</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">float128</span><span class="special">);</span> <span class="comment">// OK.</span> | |
| 148 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">tif128</span><span class="special">.</span><span class="identifier">name</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">// OK.</span> | |
| 149 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">float128</span><span class="special">).</span><span class="identifier">name</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">// OK.</span> | |
| 150 | ||
| 151 | <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">type_info</span><span class="special">&</span> <span class="identifier">tpi</span> <span class="special">=</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">pi1</span><span class="special">);</span> <span class="comment">// OK GCC 6.1.1 (from GCC 5 according to http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43622)</span> | |
| 152 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">tpi</span><span class="special">.</span><span class="identifier">name</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">// Output mangled name:</span> | |
| 153 | ||
| 154 | <span class="comment">// N5boost14multiprecision6numberINS0_8backends16float128_backendELNS0_26expression_template_optionE0EEE</span> | |
| 155 | </pre> | |
| 156 | </td></tr> | |
| 157 | </table></div> | |
| 158 | </div> | |
| 159 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 160 | <td align="left"></td> | |
| 161 | <td align="right"><div class="copyright-footer">Copyright © 2006-2010, 2012-2014 Nikhar Agrawal, | |
| 162 | Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert | |
| 163 | Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan Råde, Gautam Sewani, | |
| 164 | Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p> | |
| 165 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 166 | 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>) | |
| 167 | </p> | |
| 168 | </div></td> | |
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