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<title>Overview</title>
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<link rel="home" href="../index.html" title="Math Toolkit 2.5.0">
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<link rel="up" href="../cstdfloat.html" title="Chapter 3. Specified-width floating-point typedefs">
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<table cellpadding="2" width="100%"><tr>
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<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
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<td align="center"><a href="../../../../../index.html">Home</a></td>
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<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
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<a accesskey="p" href="../cstdfloat.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../cstdfloat.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="rationale.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="math_toolkit.overview"></a><a class="link" href="overview.html" title="Overview">Overview</a>
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</h2></div></div></div>
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<p>
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The header <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">cstdfloat</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
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provides <span class="bold"><strong>optional</strong></span> standardized floating-point
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<code class="computeroutput"><span class="keyword">typedef</span></code>s having <span class="bold"><strong>specified
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widths</strong></span>. These are useful for writing portable code because they
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should behave identically on all platforms. These <code class="computeroutput"><span class="keyword">typedef</span></code>s
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are the floating-point analog of specified-width integers in <code class="computeroutput"><span class="special"><</span><span class="identifier">cstdint</span><span class="special">></span></code> and <code class="computeroutput"><span class="identifier">stdint</span><span class="special">.</span><span class="identifier">h</span></code>.
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</p>
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<p>
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The <code class="computeroutput"><span class="keyword">typedef</span></code>s are based on <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3626.pdf" target="_top">N3626</a>
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proposed for a new C++14 standard header <code class="computeroutput"><span class="special"><</span><span class="identifier">cstdfloat</span><span class="special">></span></code>
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and <a href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1703.pdf" target="_top">N1703</a>
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proposed for a new C language standard header <code class="computeroutput"><span class="special"><</span><span class="identifier">stdfloat</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span></code>.
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</p>
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<p>
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All <code class="computeroutput"><span class="keyword">typedef</span></code>s are in <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">boost</span></code>
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(would be in namespace <code class="computeroutput"><span class="identifier">std</span></code>
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if eventually standardized).
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</p>
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<p>
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The <code class="computeroutput"><span class="keyword">typedef</span></code>s include <code class="computeroutput"><span class="identifier">float16_t</span><span class="special">,</span> <span class="identifier">float32_t</span><span class="special">,</span> <span class="identifier">float64_t</span><span class="special">,</span> <span class="identifier">float80_t</span><span class="special">,</span> <span class="identifier">float128_t</span></code>, their corresponding least and
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fast types, and the corresponding maximum-width type. The <code class="computeroutput"><span class="keyword">typedef</span></code>s
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are based on underlying built-in types such as <code class="computeroutput"><span class="keyword">float</span></code>,
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<code class="computeroutput"><span class="keyword">double</span></code>, or <code class="computeroutput"><span class="keyword">long</span>
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<span class="keyword">double</span></code>, or the proposed <a href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2016.pdf" target="_top">N2016
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short float type</a>, or based on other compiler-specific non-standardized
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types such as <code class="computeroutput"><span class="identifier">__float128</span></code>. The
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underlying types of these <code class="computeroutput"><span class="keyword">typedef</span></code>s
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must conform with the corresponding specifications of binary16, binary32, binary64,
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and binary128 in <a href="http://en.wikipedia.org/wiki/IEEE_floating_point" target="_top">IEEE_floating_point</a>
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floating-point format, and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><>::</span><span class="identifier">is_iec559</span>
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<span class="special">==</span> <span class="keyword">true</span></code>.
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</p>
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<p>
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The 128-bit floating-point type (of great interest in scientific and numeric
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programming) is not required in the Boost header, and may not be supplied for
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all platforms/compilers, because compiler support for a 128-bit floating-point
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type is not mandated by either the C standard or the C++ standard.
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</p>
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<p>
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See <a class="link" href="examples.html#math_toolkit.examples.je_lambda">Jahnke-Emden-Lambda function
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example</a> for an example using both a <code class="computeroutput"><span class="special"><</span><span class="identifier">cmath</span><span class="special">></span></code>
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function and a Boost.Math function to evaluate a moderately interesting function,
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the <a href="http://mathworld.wolfram.com/LambdaFunction.html" target="_top">Jahnke-Emden-Lambda
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function</a> and <a class="link" href="examples.html#math_toolkit.examples.normal_table">normal
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distribution</a> as an example of a statistical distribution from Boost.Math.
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</p>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2006-2010, 2012-2014 Nikhar Agrawal,
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Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert
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Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan Råde, Gautam Sewani,
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Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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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</p>
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</div></td>
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</tr></table>
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<hr>
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