<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Calculating the Representation Distance Between Two Floating Point Values (ULP) float_distance</title> <link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.74.0"> <link rel="home" href="../../../index.html" title="Math Toolkit"> <link rel="up" href="../next_float.html" title="Floating-Point Representation Distance (ULP), and Finding Adjacent Floating-Point Values"> <link rel="prev" href="float_prior.html" title="Finding the Next Smaller Representable Value (float_prior)"> <link rel="next" href="float_advance.html" title="Advancing a Floating Point Value by a Specific Representation Distance (ULP) float_advance"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> <td align="center"><a href="../../../../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="float_prior.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../next_float.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="float_advance.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section" lang="en"> <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="id1165280"></a> <a class="link" href="float_distance.html#math_toolkit.utils.next_float.float_distance.synopsis">Synopsis</a> </h5> <p> </p> <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="id1165445"></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> <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, 2008, 2009 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>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="float_prior.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../next_float.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="float_advance.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>