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| <a name="boost.random_device"></a><div class="titlepage"></div> |
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| <h2><span class="refentrytitle">Class random_device</span></h2> |
| <p>boost::random_device</p> |
| </div> |
| <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> |
| <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="../boost_random/reference.html#header.boost.nondet_random_hpp" title="Header <boost/nondet_random.hpp>">boost/nondet_random.hpp</a>> |
| |
| </span> |
| <span class="keyword">class</span> <a class="link" href="random_device.html" title="Class random_device">random_device</a> <span class="special">{</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="comment">// types</span> |
| <span class="keyword">typedef</span> <span class="keyword">unsigned</span> <span class="keyword">int</span> <a name="boost.random_device.result_type"></a><span class="identifier">result_type</span><span class="special">;</span> |
| |
| <span class="comment">// <a class="link" href="random_device.html#boost.random_deviceconstruct-copy-destruct">construct/copy/destruct</a></span> |
| <a class="link" href="random_device.html#id1168472-bb"><span class="identifier">random_device</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&</span> <span class="special">=</span> <span class="identifier">default_token</span><span class="special">)</span><span class="special">;</span> |
| <a class="link" href="random_device.html#id1168491-bb"><span class="special">~</span><span class="identifier">random_device</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> |
| |
| <span class="comment">// <a class="link" href="random_device.html#id1168403-bb">public member functions</a></span> |
| <span class="identifier">result_type</span> <a class="link" href="random_device.html#id1168407-bb"><span class="identifier">min</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="identifier">result_type</span> <a class="link" href="random_device.html#id1168425-bb"><span class="identifier">max</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="identifier">BOOST_RANDOM_DECL</span> <span class="keyword">double</span> <a class="link" href="random_device.html#id1168442-bb"><span class="identifier">entropy</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="identifier">BOOST_RANDOM_DECL</span> <span class="keyword">unsigned</span> <span class="keyword">int</span> <a class="link" href="random_device.html#id1168460-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> has_fixed_range<span class="special">;</span> |
| <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">result_type</span> min_value<span class="special">;</span> |
| <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">result_type</span> max_value<span class="special">;</span> |
| <span class="special">}</span><span class="special">;</span></pre></div> |
| <div class="refsect1"> |
| <a name="id2471249"></a><h2>Description</h2> |
| <p>Class <a class="link" href="random_device.html" title="Class random_device">random_device</a> models a <a class="link" href="../boost_random/reference.html#boost_random.reference.concepts.non_deterministic_uniform_random_number_generator" title="Non-deterministic Uniform Random Number Generator">non-deterministic random number generator</a> . It uses one or more implementation-defined stochastic processes to generate a sequence of uniformly distributed non-deterministic random numbers. For those environments where a non-deterministic random number generator is not available, class random_device must not be implemented. See</p> |
| <p> </p> |
| <div class="blockquote"><blockquote class="blockquote"><p> "Randomness Recommendations for Security", D. Eastlake, S. Crocker, J. Schiller, Network Working Group, RFC 1750, December 1994 </p></blockquote></div> |
| <p> </p> |
| <p>for further discussions.</p> |
| <p> </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> Some operating systems abstract the computer hardware enough to make it difficult to non-intrusively monitor stochastic processes. However, several do provide a special device for exactly this purpose. It seems to be impossible to emulate the functionality using Standard C++ only, so users should be aware that this class may not be available on all platforms. </p></td></tr> |
| </table></div> |
| <p> </p> |
| <p><span class="bold"><strong>Implementation Note for Linux</strong></span></p> |
| <p>On the Linux operating system, token is interpreted as a filesystem path. It is assumed that this path denotes an operating system pseudo-device which generates a stream of non-deterministic random numbers. The pseudo-device should never signal an error or end-of-file. Otherwise, <code class="computeroutput">std::ios_base::failure</code> is thrown. By default, <a class="link" href="random_device.html" title="Class random_device">random_device</a> uses the /dev/urandom pseudo-device to retrieve the random numbers. Another option would be to specify the /dev/random pseudo-device, which blocks on reads if the entropy pool has no more random bits available.</p> |
| <p><span class="bold"><strong>Implementation Note for Windows</strong></span></p> |
| <p>On the Windows operating system, token is interpreted as the name of a cryptographic service provider. By default <a class="link" href="random_device.html" title="Class random_device">random_device</a> uses MS_DEF_PROV.</p> |
| <p><span class="bold"><strong>Performance</strong></span></p> |
| <p>The test program <a href="../../../libs/random/performance/nondet_random_speed.cpp" target="_top">nondet_random_speed.cpp</a> measures the execution times of the nondet_random.hpp implementation of the above algorithms in a tight loop. The performance has been evaluated on a Pentium Pro 200 MHz with gcc 2.95.2, Linux 2.2.13, glibc 2.1.2.</p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td><span class="bold"><strong>class</strong></span></td> |
| <td><span class="bold"><strong>time per invocation [usec] </strong></span></td> |
| </tr> |
| <tr> |
| <td> <a class="link" href="random_device.html" title="Class random_device">random_device</a> </td> |
| <td>92.0 </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <p> |
| </p> |
| <p>The measurement error is estimated at +/- 1 usec. </p> |
| <div class="refsect2"> |
| <a name="id2471409"></a><h3> |
| <a name="boost.random_deviceconstruct-copy-destruct"></a><code class="computeroutput">random_device</code> |
| public |
| construct/copy/destruct</h3> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| <pre class="literallayout"><a name="id1168472-bb"></a><span class="identifier">random_device</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&</span> token <span class="special">=</span> <span class="identifier">default_token</span><span class="special">)</span><span class="special">;</span></pre> |
| <p>Constructs a <code class="computeroutput">random_device</code>, optionally using the given token as an access specification (for example, a URL) to some implementation-defined service for monitoring a stochastic process. </p> |
| </li> |
| <li class="listitem"><pre class="literallayout"><a name="id1168491-bb"></a><span class="special">~</span><span class="identifier">random_device</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre></li> |
| </ol></div> |
| </div> |
| <div class="refsect2"> |
| <a name="id2471536"></a><h3> |
| <a name="id1168403-bb"></a><code class="computeroutput">random_device</code> public member functions</h3> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="identifier">result_type</span> <a name="id1168407-bb"></a><span class="identifier">min</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> |
| <p>Returns: The smallest value that the <code class="computeroutput"><a class="link" href="random_device.html" title="Class random_device">random_device</a></code> can produce. </p> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="identifier">result_type</span> <a name="id1168425-bb"></a><span class="identifier">max</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> |
| <p>Returns: The largest value that the <code class="computeroutput"><a class="link" href="random_device.html" title="Class random_device">random_device</a></code> can produce. </p> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="identifier">BOOST_RANDOM_DECL</span> <span class="keyword">double</span> <a name="id1168442-bb"></a><span class="identifier">entropy</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> |
| <p>Returns: An entropy estimate for the random numbers returned by operator(), in the range min() to log2( max()+1). A deterministic random number generator (e.g. a pseudo-random number engine) has entropy 0.</p> |
| <p>Throws: Nothing. </p> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="identifier">BOOST_RANDOM_DECL</span> <span class="keyword">unsigned</span> <span class="keyword">int</span> <a name="id1168460-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre> |
| <p>Returns: A random value in the range [min, max] </p> |
| </li> |
| </ol></div> |
| </div> |
| </div> |
| </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 © 2000 -2005 Jens Maurer, 2009 Steven Watanabe<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> |
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