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<title>Finding the Next Representable Value in a Specific Direction (nextafter)</title>
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<div class="titlepage"><div><div><h3 class="title">
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<a name="math_toolkit.next_float.nextafter"></a><a class="link" href="nextafter.html" title="Finding the Next Representable Value in a Specific Direction (nextafter)">Finding the Next Representable
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Value in a Specific Direction (nextafter)</a>
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</h3></div></div></div>
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<h5>
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<a name="math_toolkit.next_float.nextafter.h0"></a>
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<span class="phrase"><a name="math_toolkit.next_float.nextafter.synopsis"></a></span><a class="link" href="nextafter.html#math_toolkit.next_float.nextafter.synopsis">Synopsis</a>
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</h5>
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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>
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</pre>
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<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>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">FPT</span><span class="special">></span>
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<span class="identifier">FPT</span> <span class="identifier">nextafter</span><span class="special">(</span><span class="identifier">FPT</span> <span class="identifier">val</span><span class="special">,</span> <span class="identifier">FPT</span> <span class="identifier">direction</span><span class="special">);</span>
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<span class="special">}}</span> <span class="comment">// namespaces</span>
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</pre>
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<h5>
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<a name="math_toolkit.next_float.nextafter.h1"></a>
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<span class="phrase"><a name="math_toolkit.next_float.nextafter.description_nextafter"></a></span><a class="link" href="nextafter.html#math_toolkit.next_float.nextafter.description_nextafter">Description
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- nextafter</a>
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</h5>
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<p>
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This is an implementation of the <code class="computeroutput"><span class="identifier">nextafter</span></code>
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function included in the C99 standard. (It is also effectively an implementation
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of the C99 <code class="computeroutput"><span class="identifier">nexttoward</span></code> legacy
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function which differs only having a <code class="computeroutput"><span class="keyword">long</span>
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<span class="keyword">double</span></code> direction, and can generally
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serve in its place if required).
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</p>
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<div class="note"><table border="0" summary="Note">
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<tr>
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<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td>
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<th align="left">Note</th>
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</tr>
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<tr><td align="left" valign="top"><p>
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The C99 functions must use suffixes f and l to distinguish <code class="computeroutput"><span class="keyword">float</span></code> and <code class="computeroutput"><span class="keyword">long</span>
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<span class="keyword">double</span></code> versions. C++ uses the template
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mechanism instead.
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</p></td></tr>
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</table></div>
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<p>
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Returns the next representable value after <span class="emphasis"><em>x</em></span> in the
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direction of <span class="emphasis"><em>y</em></span>. If <code class="computeroutput"><span class="identifier">x</span>
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<span class="special">==</span> <span class="identifier">y</span></code>
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then returns <span class="emphasis"><em>x</em></span>. If <span class="emphasis"><em>x</em></span> is non-finite
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then returns the result of a <a class="link" href="../error_handling.html#math_toolkit.error_handling.domain_error">domain_error</a>.
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If there is no such value in the direction of <span class="emphasis"><em>y</em></span> then
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returns an <a class="link" href="../error_handling.html#math_toolkit.error_handling.overflow_error">overflow_error</a>.
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</p>
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<div class="warning"><table border="0" summary="Warning">
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<tr>
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<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../../doc/src/images/warning.png"></td>
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<th align="left">Warning</th>
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</tr>
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<tr><td align="left" valign="top"><p>
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The template parameter FTP must be a floating-point type. An integer type,
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for example, will produce an unhelpful error message.
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</p></td></tr>
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</table></div>
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<div class="tip"><table border="0" summary="Tip">
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<tr>
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<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../../doc/src/images/tip.png"></td>
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<th align="left">Tip</th>
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</tr>
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<tr><td align="left" valign="top"><p>
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Nearly always, you just want the next or prior representable value, so
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instead use <code class="computeroutput"><span class="identifier">float_next</span></code>
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or <code class="computeroutput"><span class="identifier">float_prior</span></code> below.
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</p></td></tr>
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</table></div>
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<h5>
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<a name="math_toolkit.next_float.nextafter.h2"></a>
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<span class="phrase"><a name="math_toolkit.next_float.nextafter.examples_nextafter"></a></span><a class="link" href="nextafter.html#math_toolkit.next_float.nextafter.examples_nextafter">Examples -
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nextafter</a>
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</h5>
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<p>
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The two representations using a 32-bit float either side of unity are:
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</p>
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<pre class="programlisting"><span class="identifier">The</span> <span class="identifier">nearest</span> <span class="special">(</span><span class="identifier">exact</span><span class="special">)</span> <span class="identifier">representation</span> <span class="identifier">of</span> <span class="number">1.F</span> <span class="identifier">is</span> <span class="number">1.00000000</span>
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<span class="identifier">nextafter</span><span class="special">(</span><span class="number">1.F</span><span class="special">,</span> <span class="number">999</span><span class="special">)</span> <span class="identifier">is</span> <span class="number">1.00000012</span>
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<span class="identifier">nextafter</span><span class="special">(</span><span class="number">1</span><span class="special">/</span><span class="identifier">f</span><span class="special">,</span> <span class="special">-</span><span class="number">999</span><span class="special">)</span> <span class="identifier">is</span> <span class="number">0.99999994</span>
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<span class="identifier">The</span> <span class="identifier">nearest</span> <span class="special">(</span><span class="keyword">not</span> <span class="identifier">exact</span><span class="special">)</span> <span class="identifier">representation</span> <span class="identifier">of</span> <span class="number">0.1F</span> <span class="identifier">is</span> <span class="number">0.100000001</span>
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<span class="identifier">nextafter</span><span class="special">(</span><span class="number">0.1F</span><span class="special">,</span> <span class="number">10</span><span class="special">)</span> <span class="identifier">is</span> <span class="number">0.100000009</span>
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<span class="identifier">nextafter</span><span class="special">(</span><span class="number">0.1F</span><span class="special">,</span> <span class="number">10</span><span class="special">)</span> <span class="identifier">is</span> <span class="number">0.099999994</span>
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</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2006-2021 Nikhar Agrawal, Anton Bikineev, Matthew Borland,
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Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert Holin, Bruno
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Lalande, John Maddock, Evan Miller, Jeremy Murphy, Matthew Pulver, Johan Råde,
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Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg, Daryle
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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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