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<title>Floating Point Classification: Infinities and NaN's</title>
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<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="math_toolkit.special.fpclass"></a><a href="fpclass.html" title="Floating Point Classification: Infinities and NaN's"> Floating Point Classification:
Infinities and NaN's</a>
</h3></div></div></div>
<a name="math_toolkit.special.fpclass.synopsis"></a><h5>
<a name="id696749"></a>
<a href="fpclass.html#math_toolkit.special.fpclass.synopsis">Synopsis</a>
</h5>
<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">FP_ZERO</span> <span class="comment">/* implementation specific value */</span>
<span class="preprocessor">#define</span> <span class="identifier">FP_NORMAL</span> <span class="comment">/* implementation specific value */</span>
<span class="preprocessor">#define</span> <span class="identifier">FP_INFINITE</span> <span class="comment">/* implementation specific value */</span>
<span class="preprocessor">#define</span> <span class="identifier">FP_NAN</span> <span class="comment">/* implementation specific value */</span>
<span class="preprocessor">#define</span> <span class="identifier">FP_SUBNORMAL</span> <span class="comment">/* implementation specific value */</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">int</span> <span class="identifier">fpclassify</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">bool</span> <span class="identifier">isfinite</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">z</span><span class="special">);</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">bool</span> <span class="identifier">isinf</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">bool</span> <span class="identifier">isnan</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">bool</span> <span class="identifier">isnormal</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
</pre>
<a name="math_toolkit.special.fpclass.description"></a><h5>
<a name="id697189"></a>
<a href="fpclass.html#math_toolkit.special.fpclass.description">Description</a>
</h5>
<p>
These functions provide the same functionality as the macros with the same
name in C99, indeed if the C99 macros are available, then these functions
are implemented in terms of them, otherwise they rely on std::numeric_limits<>
to function.
</p>
<p>
Note that the definition of these functions <span class="emphasis"><em>does not suppress the
definition of these names as macros by math.h</em></span> on those platforms
that already provide these as macros. That mean that the following have differing
meanings:
</p>
<pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">;</span>
<span class="comment">// This might call a global macro if defined,
</span><span class="comment">// but might not work if the type of z is unsupported
</span><span class="comment">// by the std lib macro:
</span><span class="identifier">isnan</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
<span class="comment">//
</span><span class="comment">// This calls the Boost version
</span><span class="comment">// (found via the "using namespace boost::math" declaration)
</span><span class="comment">// it works for any type that has numeric_limits support for type z:
</span><span class="special">(</span><span class="identifier">isnan</span><span class="special">)(</span><span class="identifier">z</span><span class="special">);</span>
<span class="comment">//
</span><span class="comment">// As above but with namespace qualification.
</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">isnan</span><span class="special">)(</span><span class="identifier">z</span><span class="special">);</span>
<span class="comment">//
</span><span class="comment">// This will cause a compiler error is isnan is a native macro:
</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">isnan</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
<span class="comment">// So always use (boost::math::isnan)(z); instead.
</span></pre>
<p>
Detailed descriptions for each of these functions follows:
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">int</span> <span class="identifier">fpclassify</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
</pre>
<p>
Returns an integer value that classifies the value <span class="emphasis"><em>t</em></span>:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
fpclassify value
</p>
</th>
<th>
<p>
class of t.
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
FP_ZERO
</p>
</td>
<td>
<p>
If <span class="emphasis"><em>t</em></span> is zero.
</p>
</td>
</tr>
<tr>
<td>
<p>
FP_NORMAL
</p>
</td>
<td>
<p>
If <span class="emphasis"><em>t</em></span> is a non-zero, non-denormalised finite
value.
</p>
</td>
</tr>
<tr>
<td>
<p>
FP_INFINITE
</p>
</td>
<td>
<p>
If <span class="emphasis"><em>t</em></span> is plus or minus infinity.
</p>
</td>
</tr>
<tr>
<td>
<p>
FP_NAN
</p>
</td>
<td>
<p>
If <span class="emphasis"><em>t</em></span> is a NaN.
</p>
</td>
</tr>
<tr>
<td>
<p>
FP_SUBNORMAL
</p>
</td>
<td>
<p>
If <span class="emphasis"><em>t</em></span> is a denormalised number.
</p>
</td>
</tr>
</tbody>
</table></div>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">bool</span> <span class="identifier">isfinite</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">z</span><span class="special">);</span>
</pre>
<p>
Returns true only if <span class="emphasis"><em>z</em></span> is not an infinity or a NaN.
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">bool</span> <span class="identifier">isinf</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
</pre>
<p>
Returns true only if <span class="emphasis"><em>z</em></span> is plus or minus infinity.
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">bool</span> <span class="identifier">isnan</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
</pre>
<p>
Returns true only if <span class="emphasis"><em>z</em></span> is a NaN.
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">bool</span> <span class="identifier">isnormal</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">t</span><span class="special">);</span>
</pre>
<p>
Returns true only if <span class="emphasis"><em>z</em></span> is a normal number (not zero,
infinite, NaN, or denormalised).
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright 2006 -2007 John Maddock, Paul A. Bristow, Hubert Holin
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>)
</p>
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