libs/math/doc/html/math_toolkit/fpclass.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>Floating-Point Classification: Infinities and NaNs</title>
   5 <link rel="stylesheet" href="../math.css" type="text/css">
   6 <meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
   7 <link rel="home" href="../index.html" title="Math Toolkit 2.11.0">
   8 <link rel="up" href="../utils.html" title="Chapter&#160;2.&#160;Floating Point Utilities">
   9 <link rel="prev" href="rounding/modf.html" title="Integer and Fractional Part Splitting (modf)">
  10 <link rel="next" href="sign_functions.html" title="Sign Manipulation Functions">
  11 </head>
  12 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
  13 <table cellpadding="2" width="100%"><tr>
  14 <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
  15 <td align="center"><a href="../../../../../index.html">Home</a></td>
  16 <td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td>
  17 <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
  18 <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
  19 <td align="center"><a href="../../../../../more/index.htm">More</a></td>
  20 </tr></table>
  21 <hr>
  22 <div class="spirit-nav">
  23 <a accesskey="p" href="rounding/modf.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../utils.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="sign_functions.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
  24 </div>
  25 <div class="section">
  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="math_toolkit.fpclass"></a><a class="link" href="fpclass.html" title="Floating-Point Classification: Infinities and NaNs">Floating-Point Classification: Infinities
  28     and NaNs</a>
  29 </h2></div></div></div>
  30 <h5>
  31 <a name="math_toolkit.fpclass.h0"></a>
  32       <span class="phrase"><a name="math_toolkit.fpclass.synopsis"></a></span><a class="link" href="fpclass.html#math_toolkit.fpclass.synopsis">Synopsis</a>
  33     </h5>
  34 <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">FP_ZERO</span>        <span class="comment">/* implementation specific value */</span>
  35 <span class="preprocessor">#define</span> <span class="identifier">FP_NORMAL</span>      <span class="comment">/* implementation specific value */</span>
  36 <span class="preprocessor">#define</span> <span class="identifier">FP_INFINITE</span>    <span class="comment">/* implementation specific value */</span>
  37 <span class="preprocessor">#define</span> <span class="identifier">FP_NAN</span>         <span class="comment">/* implementation specific value */</span>
  38 <span class="preprocessor">#define</span> <span class="identifier">FP_SUBNORMAL</span>   <span class="comment">/* implementation specific value */</span>
  39
  40 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
  41 <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>
  42
  43 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
  44 <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>
  45
  46 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
  47 <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>
  48
  49 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
  50 <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>
  51
  52 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
  53 <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>
  54
  55 <span class="preprocessor">#include</span> <span class="special">&lt;</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">&gt;</span>
  56 </pre>
  57 <p>
  58       to use these functions.
  59     </p>
  60 <h5>
  61 <a name="math_toolkit.fpclass.h1"></a>
  62       <span class="phrase"><a name="math_toolkit.fpclass.description"></a></span><a class="link" href="fpclass.html#math_toolkit.fpclass.description">Description</a>
  63     </h5>
  64 <p>
  65       These functions provide the same functionality as the macros with the same
  66       name in C99, indeed if the C99 macros are available, then these functions are
  67       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">&lt;&gt;</span></code> to function.
  68     </p>
  69 <p>
  70       Note that the definition of these functions <span class="emphasis"><em>does not suppress the
  71       definition of these names as macros by math.h</em></span> on those platforms
  72       that already provide these as macros. That mean that the following have differing
  73       meanings:
  74     </p>
  75 <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>
  76
  77 <span class="comment">// This might call a global macro if defined,</span>
  78 <span class="comment">// but might not work if the type of z is unsupported</span>
  79 <span class="comment">// by the std lib macro:</span>
  80 <span class="identifier">isnan</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
  81 <span class="comment">//</span>
  82 <span class="comment">// This calls the Boost version</span>
  83 <span class="comment">// (found via the "using namespace boost::math" declaration)</span>
  84 <span class="comment">// it works for any type that has numeric_limits support for type z:</span>
  85 <span class="special">(</span><span class="identifier">isnan</span><span class="special">)(</span><span class="identifier">z</span><span class="special">);</span>
  86 <span class="comment">//</span>
  87 <span class="comment">// As above but with explicit namespace qualification.</span>
  88 <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>
  89 <span class="comment">//</span>
  90 <span class="comment">// This will cause a compiler error if isnan is a native macro:</span>
  91 <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>
  92 <span class="comment">// So always use instead:</span>
  93 <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>
  94 <span class="comment">//</span>
  95 <span class="comment">// You can also add a using statement,</span>
  96 <span class="comment">// globally to a .cpp file, or to a local function in a .hpp file.</span>
  97 <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>
  98 <span class="comment">// so you can write the shorter and less cluttered</span>
  99 <span class="special">(</span><span class="identifier">isnan</span><span class="special">)(</span><span class="identifier">z</span><span class="special">)</span>
 100 <span class="comment">// But, as above, if isnan is a native macro, this causes a compiler error,</span>
 101 <span class="comment">// because the macro always 'gets' the name first, unless enclosed in () brackets.</span>
 102 </pre>
 103 <p>
 104       Detailed descriptions for each of these functions follows:
 105     </p>
 106 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
 107 <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>
 108 </pre>
 109 <p>
 110       Returns an integer value that classifies the value <span class="emphasis"><em>t</em></span>:
 111     </p>
 112 <div class="informaltable"><table class="table">
 113 <colgroup>
 114 <col>
 115 <col>
 116 </colgroup>
 117 <thead><tr>
 118 <th>
 119               <p>
 120                 fpclassify value
 121               </p>
 122             </th>
 123 <th>
 124               <p>
 125                 class of t.
 126               </p>
 127             </th>
 128 </tr></thead>
 129 <tbody>
 130 <tr>
 131 <td>
 132               <p>
 133                 FP_ZERO
 134               </p>
 135             </td>
 136 <td>
 137               <p>
 138                 If <span class="emphasis"><em>t</em></span> is zero.
 139               </p>
 140             </td>
 141 </tr>
 142 <tr>
 143 <td>
 144               <p>
 145                 FP_NORMAL
 146               </p>
 147             </td>
 148 <td>
 149               <p>
 150                 If <span class="emphasis"><em>t</em></span> is a non-zero, non-denormalised finite
 151                 value.
 152               </p>
 153             </td>
 154 </tr>
 155 <tr>
 156 <td>
 157               <p>
 158                 FP_INFINITE
 159               </p>
 160             </td>
 161 <td>
 162               <p>
 163                 If <span class="emphasis"><em>t</em></span> is plus or minus infinity.
 164               </p>
 165             </td>
 166 </tr>
 167 <tr>
 168 <td>
 169               <p>
 170                 FP_NAN
 171               </p>
 172             </td>
 173 <td>
 174               <p>
 175                 If <span class="emphasis"><em>t</em></span> is a NaN.
 176               </p>
 177             </td>
 178 </tr>
 179 <tr>
 180 <td>
 181               <p>
 182                 FP_SUBNORMAL
 183               </p>
 184             </td>
 185 <td>
 186               <p>
 187                 If <span class="emphasis"><em>t</em></span> is a denormalised number.
 188               </p>
 189             </td>
 190 </tr>
 191 </tbody>
 192 </table></div>
 193 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
 194 <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>
 195 </pre>
 196 <p>
 197       Returns true only if <span class="emphasis"><em>z</em></span> is not an infinity or a NaN.
 198     </p>
 199 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
 200 <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>
 201 </pre>
 202 <p>
 203       Returns true only if <span class="emphasis"><em>z</em></span> is plus or minus infinity.
 204     </p>
 205 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
 206 <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>
 207 </pre>
 208 <p>
 209       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>.
 210     </p>
 211 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
 212 <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>
 213 </pre>
 214 <p>
 215       Returns true only if <span class="emphasis"><em>z</em></span> is a normal number (not zero, infinite,
 216       NaN, or denormalised).
 217     </p>
 218 <h6>
 219 <a name="math_toolkit.fpclass.h2"></a>
 220       <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
 221       format</a>
 222     </h6>
 223 <p>
 224       If you wish to find details of the floating-point format for any particular
 225       processor, there is a program
 226     </p>
 227 <p>
 228       <a href="../../../example/inspect_fp.cpp" target="_top">inspect_fp.cpp</a>
 229     </p>
 230 <p>
 231       by Johan Rade which can be used to print out the processor type, endianness,
 232       and detailed bit layout of a selection of floating-point values, including
 233       infinity and NaNs.
 234     </p>
 235 </div>
 236 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 237 <td align="left"></td>
 238 <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2019 Nikhar
 239       Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos,
 240       Hubert Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Matthew Pulver, Johan
 241       R&#229;de, Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg,
 242       Daryle Walker and Xiaogang Zhang<p>
 243         Distributed under the Boost Software License, Version 1.0. (See accompanying
 244         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>)
 245       </p>
 246 </div></td>
 247 </tr></table>
 248 <hr>
 249 <div class="spirit-nav">
 250 <a accesskey="p" href="rounding/modf.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../utils.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="sign_functions.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
 251 </div>
 252 </body>
 253 </html>