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<title>Floating-Point Classification: Infinities and NaNs</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="math_toolkit.fpclass"></a><a class="link" href="fpclass.html" title="Floating-Point Classification: Infinities and NaNs">Floating-Point Classification: Infinities
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and NaNs</a>
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</h2></div></div></div>
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<h5>
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<a name="math_toolkit.fpclass.h0"></a>
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<span class="phrase"><a name="math_toolkit.fpclass.synopsis"></a></span><a class="link" href="fpclass.html#math_toolkit.fpclass.synopsis">Synopsis</a>
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</h5>
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<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">FP_ZERO</span> <span class="comment">/* implementation specific value */</span>
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<span class="preprocessor">#define</span> <span class="identifier">FP_NORMAL</span> <span class="comment">/* implementation specific value */</span>
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<span class="preprocessor">#define</span> <span class="identifier">FP_INFINITE</span> <span class="comment">/* implementation specific value */</span>
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<span class="preprocessor">#define</span> <span class="identifier">FP_NAN</span> <span class="comment">/* implementation specific value */</span>
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<span class="preprocessor">#define</span> <span class="identifier">FP_SUBNORMAL</span> <span class="comment">/* implementation specific value */</span>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
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<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>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
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<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="comment">// Neither infinity nor NaN.</span>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
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<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="comment">// Infinity (+ or -).</span>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
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<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="comment">// NaN.</span>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
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<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> <span class="comment">// isfinite and not denormalised.</span>
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<span class="preprocessor">#include</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">special_functions</span><span class="special">\</span><span class="identifier">fpclassify</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
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</pre>
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<p>
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to use these functions.
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</p>
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<h5>
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<a name="math_toolkit.fpclass.h1"></a>
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<span class="phrase"><a name="math_toolkit.fpclass.description"></a></span><a class="link" href="fpclass.html#math_toolkit.fpclass.description">Description</a>
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</h5>
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<p>
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These functions provide the same functionality as the macros with the same
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name in C99, indeed if the C99 macros are available, then these functions are
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implemented in terms of them, otherwise they rely on <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><></span></code> to function.
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</p>
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<p>
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Note that the definition of these functions <span class="emphasis"><em>does not suppress the
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definition of these names as macros by math.h</em></span> on those platforms
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that already provide these as macros. That mean that the following have differing
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meanings:
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</p>
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<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>
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<span class="comment">// This might call a global macro if defined,</span>
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<span class="comment">// but might not work if the type of z is unsupported</span>
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<span class="comment">// by the std lib macro:</span>
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<span class="identifier">isnan</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
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<span class="comment">//</span>
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<span class="comment">// This calls the Boost version</span>
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<span class="comment">// (found via the "using namespace boost::math" declaration)</span>
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<span class="comment">// it works for any type that has numeric_limits support for type z:</span>
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<span class="special">(</span><span class="identifier">isnan</span><span class="special">)(</span><span class="identifier">z</span><span class="special">);</span>
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<span class="comment">//</span>
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<span class="comment">// As above but with explicit namespace qualification.</span>
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<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>
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<span class="comment">//</span>
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<span class="comment">// This will cause a compiler error if isnan is a native macro:</span>
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<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>
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<span class="comment">// So always use instead:</span>
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<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>
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<span class="comment">//</span>
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<span class="comment">// You can also add a using statement,</span>
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<span class="comment">// globally to a .cpp file, or to a local function in a .hpp file.</span>
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<span class="keyword">using</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>
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<span class="comment">// so you can write the shorter and less cluttered</span>
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<span class="special">(</span><span class="identifier">isnan</span><span class="special">)(</span><span class="identifier">z</span><span class="special">)</span>
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<span class="comment">// But, as above, if isnan is a native macro, this causes a compiler error,</span>
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<span class="comment">// because the macro always 'gets' the name first, unless enclosed in () brackets.</span>
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</pre>
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<p>
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Detailed descriptions for each of these functions follows:
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</p>
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<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>
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<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>
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</pre>
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<p>
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Returns an integer value that classifies the value <span class="emphasis"><em>t</em></span>:
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</p>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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fpclassify value
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</p>
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</th>
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<th>
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<p>
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class of t.
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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FP_ZERO
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</p>
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</td>
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<td>
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<p>
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If <span class="emphasis"><em>t</em></span> is zero.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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FP_NORMAL
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</p>
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</td>
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<td>
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<p>
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If <span class="emphasis"><em>t</em></span> is a non-zero, non-denormalised finite
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value.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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FP_INFINITE
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</p>
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</td>
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<td>
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<p>
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If <span class="emphasis"><em>t</em></span> is plus or minus infinity.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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FP_NAN
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</p>
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</td>
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<td>
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<p>
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If <span class="emphasis"><em>t</em></span> is a NaN.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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FP_SUBNORMAL
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</p>
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</td>
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<td>
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<p>
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If <span class="emphasis"><em>t</em></span> is a denormalised number.
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</p>
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</td>
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</tr>
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</tbody>
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</table></div>
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<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>
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<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>
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</pre>
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<p>
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Returns true only if <span class="emphasis"><em>z</em></span> is not an infinity or a NaN.
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</p>
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<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>
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<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>
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</pre>
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<p>
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Returns true only if <span class="emphasis"><em>z</em></span> is plus or minus infinity.
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</p>
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<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>
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<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>
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</pre>
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<p>
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Returns true only if <span class="emphasis"><em>z</em></span> is a <a href="http://en.wikipedia.org/wiki/NaN" target="_top">NaN</a>.
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</p>
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<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>
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<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>
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</pre>
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<p>
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Returns true only if <span class="emphasis"><em>z</em></span> is a normal number (not zero, infinite,
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NaN, or denormalised).
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</p>
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<h6>
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<a name="math_toolkit.fpclass.h2"></a>
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<span class="phrase"><a name="math_toolkit.fpclass.floating_point_format"></a></span><a class="link" href="fpclass.html#math_toolkit.fpclass.floating_point_format">Floating-point
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format</a>
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</h6>
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<p>
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If you wish to find details of the floating-point format for any particular
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processor, there is a program
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</p>
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<p>
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<a href="../../../example/inspect_fp.cpp" target="_top">inspect_fp.cpp</a>
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</p>
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<p>
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by Johan Rade which can be used to print out the processor type, endianness,
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and detailed bit layout of a selection of floating-point values, including
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infinity and NaNs.
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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 © 2006-2019 Nikhar
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Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos,
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Hubert Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Matthew Pulver, Johan
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Råde, Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg,
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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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