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<title>Implementation of Float128 type</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="math_toolkit.float128"></a><a class="link" href="float128.html" title="Implementation of Float128 type">Implementation of Float128 type</a>
</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="float128/overloading_template_functions_w.html">Overloading
template functions with float128_t</a></span></dt>
<dt><span class="section"><a href="float128/exp_function.html">Exponential function</a></span></dt>
<dt><span class="section"><a href="float128/typeinfo.html"><code class="computeroutput"><span class="identifier">typeinfo</span></code></a></span></dt>
</dl></div>
<p>
Since few compilers implement a true 128-bit floating-point, and language features
like the suffix Q, and C++ Standard library functions are as-yet missing or
incomplete in C++11, this Boost.Math implementation wraps <code class="computeroutput"><span class="identifier">__float128</span></code>
provided by the GCC compiler or the <code class="computeroutput"><span class="identifier">_Quad</span></code>
type provided by the Intel compiler.
</p>
<p>
This is provided to in order to demonstrate, and users to evaluate, the feasibility
and benefits of higher-precision floating-point, especially to allow use of
the full Boost.Math library of functions and distributions at high precision.
</p>
<p>
(It is also possible to use Boost.Math with Boost.Multiprecision decimal and
binary, but since these are entirely software solutions, allowing much higher
precision or arbitrary precision, they are likely to be slower).
</p>
<p>
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>.
</p>
<p>
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>.
This contravenes the existing C++ standard of course, so selecting any compiler
that promises to check conformance will fail.
</p>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../doc/src/images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top"><p>
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
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
full support for <code class="computeroutput"><span class="identifier">__float128</span></code>.
These requirements also apply to the Intel compiler on Linux, for Intel on
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
128-bit floating point support.
</p></td></tr>
</table></div>
<p>
The <code class="computeroutput"><span class="identifier">__float128</span></code> type is provided
by the <a href="http://gcc.gnu.org/onlinedocs/libquadmath/" target="_top">libquadmath
library</a> on GCC or by Intel's FORTRAN library with Intel C++.
</p>
<p>
A typical invocation of the compiler is
</p>
<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>
</pre>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../doc/src/images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top"><p>
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>
the <span class="bold"><strong>first</strong></span> include directory.
</p></td></tr>
</table></div>
<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>
</pre>
<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>
So far, the only missing detail that we have noted is 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>. Link fails: undefined reference to <code class="computeroutput"><span class="identifier">typeinfo</span> <span class="keyword">for</span>
<span class="identifier">__float128</span></code>. See <a href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43622" target="_top">GCC
Bug 43622 - no C++ typeinfo for __float128</a>.
</p></td></tr>
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<td align="right"><div class="copyright-footer">Copyright © 2006-2010, 2012-2014 Nikhar Agrawal,
Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert
Holin, Bruno Lalande, John Maddock, Johan Råde, Gautam Sewani, Benjamin Sobotta,
Thijs van den Berg, Daryle Walker and Xiaogang Zhang<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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