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<title>Floating-Point Constant Macros</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="math_toolkit.macros"></a><a class="link" href="macros.html" title="Floating-Point Constant Macros">Floating-Point Constant Macros</a>
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</h2></div></div></div>
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<p>
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All macros of the type <code class="computeroutput"><span class="identifier">BOOST_FLOAT16_C</span><span class="special">,</span> <span class="identifier">BOOST_FLOAT32_C</span><span class="special">,</span> <span class="identifier">BOOST_FLOAT64_C</span><span class="special">,</span> <span class="identifier">BOOST_FLOAT80_C</span><span class="special">,</span> <span class="identifier">BOOST_FLOAT128_C</span><span class="special">,</span> </code> and <code class="computeroutput"><span class="identifier">BOOST_FLOATMAX_C</span></code>
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are always defined after inclusion of <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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<p>
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These allow floating-point <span class="bold"><strong>constants of at least the
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specified width</strong></span> to be declared:
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</p>
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<pre class="programlisting"><span class="comment">// Declare Archimedes' constant using float32_t with approximately 7 decimal digits of precision.</span>
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<span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">float32_t</span> <span class="identifier">pi</span> <span class="special">=</span> <span class="identifier">BOOST_FLOAT32_C</span><span class="special">(</span><span class="number">3.1415926536</span><span class="special">);</span>
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<span class="comment">// Declare the Euler-gamma constant with approximately 15 decimal digits of precision.</span>
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<span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">float64_t</span> <span class="identifier">euler</span> <span class="special">=</span>
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<span class="identifier">BOOST_FLOAT64_C</span><span class="special">(</span><span class="number">0.57721566490153286060651209008240243104216</span><span class="special">);</span>
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<span class="comment">// Declare the Golden Ratio constant with the maximum decimal digits of precision that the platform supports.</span>
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<span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">floatmax_t</span> <span class="identifier">golden_ratio</span> <span class="special">=</span>
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<span class="identifier">BOOST_FLOATMAX_C</span><span class="special">(</span><span class="number">1.61803398874989484820458683436563811772</span><span class="special">);</span>
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</pre>
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<th align="left">Tip</th>
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</tr>
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<tr><td align="left" valign="top"><p>
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Boost.Math provides many constants 'built-in', so always use Boost.Math constants
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if available, for example:
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<pre class="programlisting"><span class="comment">// Display the constant pi to the maximum available precision.</span>
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<span class="identifier">boost</span><span class="special">::</span><span class="identifier">floatmax_t</span> <span class="identifier">pi_max</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">constants</span><span class="special">::</span><span class="identifier">pi</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">floatmax_t</span><span class="special">>();</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">.</span><span class="identifier">precision</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">boost</span><span class="special">::</span><span class="identifier">floatmax_t</span><span class="special">>::</span><span class="identifier">digits10</span><span class="special">);</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Most precise pi = "</span> <span class="special"><<</span> <span class="identifier">pi_max</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
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<span class="comment">// If floatmax_t is float_128_t, then</span>
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<span class="comment">// Most precise pi = 3.141592653589793238462643383279503</span>
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</pre>
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<p>
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from <a href="../../../example/cstdfloat_example.cpp" target="_top">cstdfloat_example.cpp</a>.
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</p>
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<p>
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See the complete list of <a class="link" href="constants.html" title="The Mathematical Constants">constants</a>.
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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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