1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Class random_device</title> 6<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../../boost_random/reference.html#header.boost.random.random_device_hpp" title="Header <boost/random/random_device.hpp>"> 10<link rel="prev" href="poisson_distribution/param_type.html" title="Class param_type"> 11<link rel="next" href="random_number_generator.html" title="Class template random_number_generator"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ 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alt="Next"></a> 25</div> 26<div class="refentry"> 27<a name="boost.random.random_device"></a><div class="titlepage"></div> 28<div class="refnamediv"> 29<h2><span class="refentrytitle">Class random_device</span></h2> 30<p>boost::random::random_device</p> 31</div> 32<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> 33<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.random.random_device_hpp" title="Header <boost/random/random_device.hpp>">boost/random/random_device.hpp</a>> 34 35</span> 36<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">private</span> <span class="identifier">noncopyable</span> <span class="special">{</span> 37<span class="keyword">public</span><span class="special">:</span> 38 <span class="comment">// types</span> 39 <span class="keyword">typedef</span> <span class="keyword">unsigned</span> <span class="keyword">int</span> <a name="boost.random.random_device.result_type"></a><span class="identifier">result_type</span><span class="special">;</span> 40 41 <span class="comment">// <a class="link" href="random_device.html#boost.random.random_deviceconstruct-copy-destruct">construct/copy/destruct</a></span> 42 <a class="link" href="random_device.html#id-1_3_34_5_6_34_1_1_1_7-bb"><span class="identifier">random_device</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 43 <span class="keyword">explicit</span> <a class="link" href="random_device.html#id-1_3_34_5_6_34_1_1_1_8-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="special">;</span> 44 <a class="link" href="random_device.html#id-1_3_34_5_6_34_1_1_1_9-bb"><span class="special">~</span><span class="identifier">random_device</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 45 46 <span class="comment">// <a class="link" href="random_device.html#id-1_3_34_5_6_34_1_1_1_5-bb">public static functions</a></span> 47 <span class="keyword">static</span> <span class="identifier">result_type</span> <a class="link" href="random_device.html#id-1_3_34_5_6_34_1_1_1_5_1-bb"><span class="identifier">min</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 48 <span class="keyword">static</span> <span class="identifier">result_type</span> <a class="link" href="random_device.html#id-1_3_34_5_6_34_1_1_1_5_2-bb"><span class="identifier">max</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 49 50 <span class="comment">// <a class="link" href="random_device.html#id-1_3_34_5_6_34_1_1_1_6-bb">public member functions</a></span> 51 <span class="keyword">double</span> <a class="link" href="random_device.html#id-1_3_34_5_6_34_1_1_1_6_1-bb"><span class="identifier">entropy</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> 52 <span class="keyword">unsigned</span> <span class="keyword">int</span> <a class="link" href="random_device.html#id-1_3_34_5_6_34_1_1_1_6_2-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> 53 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Iter<span class="special">></span> <span class="keyword">void</span> <a class="link" href="random_device.html#id-1_3_34_5_6_34_1_1_1_6_3-bb"><span class="identifier">generate</span></a><span class="special">(</span><span class="identifier">Iter</span><span class="special">,</span> <span class="identifier">Iter</span><span class="special">)</span><span class="special">;</span> 54 55 <span class="comment">// public data members</span> 56 <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">has_fixed_range</span><span class="special">;</span> 57<span class="special">}</span><span class="special">;</span></pre></div> 58<div class="refsect1"> 59<a name="id-1.3.34.5.6.33.3.4"></a><h2>Description</h2> 60<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 <a class="link" href="random_device.html" title="Class random_device">random_device</a> must not be implemented. See</p> 61<p> </p> 62<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> 63<p> </p> 64<p>for further discussions.</p> 65<p> </p> 66<div class="note"><table border="0" summary="Note"> 67<tr> 68<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../doc/src/images/note.png"></td> 69<th align="left">Note</th> 70</tr> 71<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> 72</table></div> 73<p> </p> 74<p><span class="bold"><strong>Implementation Note for Linux</strong></span></p> 75<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> 76<p><span class="bold"><strong>Implementation Note for Windows</strong></span></p> 77<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> 78<p><span class="bold"><strong>Performance</strong></span></p> 79<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 random_device.hpp implementation of the above algorithms in a tight loop. The performance has been evaluated on an Intel(R) Core(TM) i7 CPU Q 840 @ 1.87GHz, 1867 Mhz with Visual C++ 2010, Microsoft Windows 7 Professional and with gcc 4.4.5, Ubuntu Linux 2.6.35-25-generic.</p> 80<div class="informaltable"><table class="table"> 81<colgroup> 82<col> 83<col> 84</colgroup> 85<tbody> 86<tr> 87<td><span class="bold"><strong>Platform</strong></span></td> 88<td><span class="bold"><strong>time per invocation [microseconds] </strong></span></td> 89</tr> 90<tr> 91<td>Windows </td> 92<td>2.9 </td> 93</tr> 94<tr> 95<td>Linux </td> 96<td>1.7 </td> 97</tr> 98</tbody> 99</table></div> 100<p> 101</p> 102<p>The measurement error is estimated at +/- 1 usec. </p> 103<div class="refsect2"> 104<a name="id-1.3.34.5.6.33.3.4.14"></a><h3> 105<a name="boost.random.random_deviceconstruct-copy-destruct"></a><code class="computeroutput">random_device</code> 106 public 107 construct/copy/destruct</h3> 108<div class="orderedlist"><ol class="orderedlist" type="1"> 109<li class="listitem"> 110<pre class="literallayout"><a name="id-1_3_34_5_6_34_1_1_1_7-bb"></a><span class="identifier">random_device</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre> 111<p>Constructs a <code class="computeroutput"><code class="computeroutput"><a class="link" href="random_device.html" title="Class random_device">random_device</a></code></code>, optionally using the default device. </p> 112</li> 113<li class="listitem"> 114<pre class="literallayout"><span class="keyword">explicit</span> <a name="id-1_3_34_5_6_34_1_1_1_8-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="special">;</span></pre> 115<p>Constructs a <code class="computeroutput"><code class="computeroutput"><a class="link" href="random_device.html" title="Class random_device">random_device</a></code></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> 116</li> 117<li class="listitem"><pre class="literallayout"><a name="id-1_3_34_5_6_34_1_1_1_9-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> 118</ol></div> 119</div> 120<div class="refsect2"> 121<a name="id-1.3.34.5.6.33.3.4.15"></a><h3> 122<a name="id-1_3_34_5_6_34_1_1_1_5-bb"></a><code class="computeroutput">random_device</code> public static functions</h3> 123<div class="orderedlist"><ol class="orderedlist" type="1"> 124<li class="listitem"> 125<pre class="literallayout"><span class="keyword">static</span> <span class="identifier">result_type</span> <a name="id-1_3_34_5_6_34_1_1_1_5_1-bb"></a><span class="identifier">min</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre> 126<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> 127</li> 128<li class="listitem"> 129<pre class="literallayout"><span class="keyword">static</span> <span class="identifier">result_type</span> <a name="id-1_3_34_5_6_34_1_1_1_5_2-bb"></a><span class="identifier">max</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre> 130<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> 131</li> 132</ol></div> 133</div> 134<div class="refsect2"> 135<a name="id-1.3.34.5.6.33.3.4.16"></a><h3> 136<a name="id-1_3_34_5_6_34_1_1_1_6-bb"></a><code class="computeroutput">random_device</code> public member functions</h3> 137<div class="orderedlist"><ol class="orderedlist" type="1"> 138<li class="listitem"> 139<pre class="literallayout"><span class="keyword">double</span> <a name="id-1_3_34_5_6_34_1_1_1_6_1-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> 140<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> 141<p>Throws: Nothing. </p> 142</li> 143<li class="listitem"> 144<pre class="literallayout"><span class="keyword">unsigned</span> <span class="keyword">int</span> <a name="id-1_3_34_5_6_34_1_1_1_6_2-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> 145<p>Returns a random value in the range [min, max]. </p> 146</li> 147<li class="listitem"> 148<pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Iter<span class="special">></span> <span class="keyword">void</span> <a name="id-1_3_34_5_6_34_1_1_1_6_3-bb"></a><span class="identifier">generate</span><span class="special">(</span><span class="identifier">Iter</span> begin<span class="special">,</span> <span class="identifier">Iter</span> end<span class="special">)</span><span class="special">;</span></pre> 149<p>Fills a range with random 32-bit values. </p> 150</li> 151</ol></div> 152</div> 153</div> 154</div> 155<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 156<td align="left"></td> 157<td align="right"><div class="copyright-footer">Copyright © 2000-2005 Jens Maurer<br>Copyright © 2009, 2010 Steven Watanabe<p> 158 Distributed under the Boost Software License, Version 1.0. (See accompanying 159 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>) 160 </p> 161</div></td> 162</tr></table> 163<hr> 164<div class="spirit-nav"> 165<a accesskey="p" href="poisson_distribution/param_type.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../boost_random/reference.html#header.boost.random.random_device_hpp"><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="random_number_generator.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 166</div> 167</body> 168</html> 169
