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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 class="toc">
- <dt><span class="section"><a href="float128/overloading.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 (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>
- to enable), 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 <a href="https://gcc.gnu.org/onlinedocs/gcc/Floating-Types.html" target="_top">GCC
- floating-point types</a> 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 <cmath> and 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++. They also
- 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>
- <span class="identifier">std</span></code>.
- </p>
- <h5>
- <a name="math_toolkit.float128.h0"></a>
- <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
- C __float128 quadmath type</a>
- </h5>
- <p>
- The source code is at <a href="https://gcc.gnu.org/onlinedocs/gcc-9.1.0/libquadmath/quadmath_005fsnprintf.html#quadmath_005fsnprintf" target="_top">quadmath_snprintf.c</a>.
- </p>
- <h5>
- <a name="math_toolkit.float128.h1"></a>
- <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
- C++ <code class="computeroutput"><span class="identifier">float128</span></code> quadmath type</a>
- </h5>
- <p>
- For C++ programs, you will want to use the C++ type <code class="computeroutput"><span class="identifier">float128</span></code>
- </p>
- <p>
- See example at <a href="../../../example/cstdfloat_example.cpp" target="_top">cstdfloat_example.cpp</a>.
- </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 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>.
- </p>
- <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>
- </pre>
- <p>
- See <a href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43622" target="_top">GCC Bug
- 43622 - no C++ typeinfo for __float128</a>. But this is reported (Marc
- Glisse 2015-04-04 ) fixed in GCC 5 (and above).
- </p>
- <p>
- For example, with GCC6.1.1 this works as expected to a <span class="bold"><strong>mangled</strong></span>
- string name, and output (if possible - not always).
- </p>
- <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>
- <span class="comment">//std::cout << tifu128.name() << std::endl; // On GCC, aborts (because not printable string).</span>
- <span class="comment">//std::cout << typeid(__float128).name() << std::endl; // Aborts - string name cannot be output.</span>
- <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>
- <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>
- <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>
- <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>
- <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>
- <span class="comment">// N5boost14multiprecision6numberINS0_8backends16float128_backendELNS0_26expression_template_optionE0EEE</span>
- </pre>
- </td></tr>
- </table></div>
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- Daryle Walker and Xiaogang Zhang<p>
- Distributed under the Boost Software License, Version 1.0. (See accompanying
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