ceph/src/boost/libs/math/doc/html/math_toolkit/next_float/float_distance.html

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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="math_toolkit.next_float.float_distance"></a><a class="link" href="float_distance.html" title="Calculating the Representation Distance Between Two floating-point Values (ULP) float_distance">Calculating the
  28       Representation Distance Between Two floating-point Values (ULP) float_distance</a>
  29 </h3></div></div></div>
  30 <p>
  31         Function float_distance finds the number of gaps/bits/ULP between any two
  32         floating-point values. If the significands of floating-point numbers are
  33         viewed as integers, then their difference is the number of ULP/gaps/bits
  34         different.
  35       </p>
  36 <h5>
  37 <a name="math_toolkit.next_float.float_distance.h0"></a>
  38         <span class="phrase"><a name="math_toolkit.next_float.float_distance.synopsis"></a></span><a class="link" href="float_distance.html#math_toolkit.next_float.float_distance.synopsis">Synopsis</a>
  39       </h5>
  40 <pre class="programlisting"><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">next</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  41 </pre>
  42 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span>
  43
  44 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">FPT</span><span class="special">&gt;</span>
  45 <span class="identifier">FPT</span> <span class="identifier">float_distance</span><span class="special">(</span><span class="identifier">FPT</span> <span class="identifier">a</span><span class="special">,</span> <span class="identifier">FPT</span> <span class="identifier">b</span><span class="special">);</span>
  46
  47 <span class="special">}}</span> <span class="comment">// namespaces</span>
  48 </pre>
  49 <h5>
  50 <a name="math_toolkit.next_float.float_distance.h1"></a>
  51         <span class="phrase"><a name="math_toolkit.next_float.float_distance.description_float_distance"></a></span><a class="link" href="float_distance.html#math_toolkit.next_float.float_distance.description_float_distance">Description
  52         - float_distance</a>
  53       </h5>
  54 <p>
  55         Returns the distance between <span class="emphasis"><em>a</em></span> and <span class="emphasis"><em>b</em></span>:
  56         the result is always a signed integer value (stored in floating-point type
  57         FPT) representing the number of distinct representations between <span class="emphasis"><em>a</em></span>
  58         and <span class="emphasis"><em>b</em></span>.
  59       </p>
  60 <p>
  61         Note that
  62       </p>
  63 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  64 <li class="listitem">
  65             <code class="computeroutput"><span class="identifier">float_distance</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">a</span><span class="special">)</span></code>
  66             always returns 0.
  67           </li>
  68 <li class="listitem">
  69             <code class="computeroutput"><span class="identifier">float_distance</span><span class="special">(</span><span class="identifier">float_next</span><span class="special">(</span><span class="identifier">a</span><span class="special">),</span> <span class="identifier">a</span><span class="special">)</span></code>
  70             always returns -1.
  71           </li>
  72 <li class="listitem">
  73             <code class="computeroutput"><span class="identifier">float_distance</span><span class="special">(</span><span class="identifier">float_prior</span><span class="special">(</span><span class="identifier">a</span><span class="special">),</span> <span class="identifier">a</span><span class="special">)</span></code>
  74             always returns 1.
  75           </li>
  76 </ul></div>
  77 <p>
  78         The function <code class="computeroutput"><span class="identifier">float_distance</span></code>
  79         is equivalent to calculating the number of ULP (Units in the Last Place)
  80         between <span class="emphasis"><em>a</em></span> and <span class="emphasis"><em>b</em></span> except that it
  81         returns a signed value indicating whether <code class="computeroutput"><span class="identifier">a</span>
  82         <span class="special">&gt;</span> <span class="identifier">b</span></code>
  83         or not.
  84       </p>
  85 <p>
  86         If the distance is too great then it may not be able to be represented as
  87         an exact integer by type FPT, but in practice this is unlikely to be a issue.
  88       </p>
  89 </div>
  90 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
  91 <td align="left"></td>
  92 <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2010, 2012-2014 Nikhar Agrawal,
  93       Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert
  94       Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan R&#229;de, Gautam Sewani,
  95       Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p>
  96         Distributed under the Boost Software License, Version 1.0. (See accompanying
  97         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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