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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="math_toolkit.utils.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 Representation Distance Between Two Floating Point Values (ULP) float_distance</a> |
| </h4></div></div></div> |
| <p> |
| Function float_distance finds the number of gaps/bits/ULP between any two |
| floating-point values. If the significands of floating-point numbers are |
| viewed as integers, then their difference is the number of ULP/gaps/bits |
| different. |
| </p> |
| <a name="math_toolkit.utils.next_float.float_distance.synopsis"></a><h5> |
| <a name="id1162327"></a> |
| <a class="link" href="float_distance.html#math_toolkit.utils.next_float.float_distance.synopsis">Synopsis</a> |
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| <p> |
| |
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| <pre class="programlisting"><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">next</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| </pre> |
| <p> |
| </p> |
| <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> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">FPT</span><span class="special">></span> |
| <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> |
| |
| <span class="special">}}</span> <span class="comment">// namespaces |
| </span></pre> |
| <a name="math_toolkit.utils.next_float.float_distance.description___float_distance"></a><h5> |
| <a name="id1162492"></a> |
| <a class="link" href="float_distance.html#math_toolkit.utils.next_float.float_distance.description___float_distance">Description |
| - float_distance</a> |
| </h5> |
| <p> |
| Returns the distance between <span class="emphasis"><em>a</em></span> and <span class="emphasis"><em>b</em></span>: |
| the result is always a signed integer value (stored in floating-point type |
| FPT) representing the number of distinct representations between <span class="emphasis"><em>a</em></span> |
| and <span class="emphasis"><em>b</em></span>. |
| </p> |
| <p> |
| Note that |
| </p> |
| <div class="itemizedlist"><ul type="disc"> |
| <li> |
| <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> |
| always returns 0. |
| </li> |
| <li> |
| <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> |
| always returns 1. |
| </li> |
| <li> |
| <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> |
| always returns -1. |
| </li> |
| </ul></div> |
| <p> |
| The function <code class="computeroutput"><span class="identifier">float_distance</span></code> |
| is equivalent to calculating the number of ULP (Units in the Last Place) |
| between <span class="emphasis"><em>a</em></span> and <span class="emphasis"><em>b</em></span> except that it |
| returns a signed value indicating whether <code class="computeroutput"><span class="identifier">a</span> |
| <span class="special">></span> <span class="identifier">b</span></code> |
| or not. |
| </p> |
| <p> |
| If the distance is too great then it may not be able to be represented |
| as an exact integer by type FPT, but in practice this is unlikely to be |
| a issue. |
| </p> |
| </div> |
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| <td align="right"><div class="copyright-footer">Copyright © 2006 , 2007, 2008, 2009, 2010 John Maddock, Paul A. Bristow, |
| Hubert Holin, Xiaogang Zhang, Bruno Lalande, Johan Råde, Gautam Sewani and |
| Thijs van den Berg<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>) |
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