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/src/contrib/boost/nondet_random.hpp

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  1/* boost nondet_random.hpp header file
  2 *
  3 * Copyright Jens Maurer 2000
  4 * Distributed under the Boost Software License, Version 1.0. (See
  5 * accompanying file LICENSE_1_0.txt or copy at
  6 * http://www.boost.org/LICENSE_1_0.txt)
  7 *
  8 * $Id: nondet_random.hpp 60755 2010-03-22 00:45:06Z steven_watanabe $
  9 *
 10 * Revision history
 11 *  2000-02-18  Portability fixes (thanks to Beman Dawes)
 12 */
 13
 14//  See http://www.boost.org/libs/random for documentation.
 15
 16
 17#ifndef BOOST_NONDET_RANDOM_HPP
 18#define BOOST_NONDET_RANDOM_HPP
 19
 20#include <string>                       // std::abs
 21#include <algorithm>                    // std::min
 22#include <boost/config/no_tr1/cmath.hpp>
 23#include <boost/config.hpp>
 24#include <boost/utility.hpp>            // noncopyable
 25#include <boost/integer_traits.hpp>     // compile-time integral limits
 26#include <boost/random/detail/auto_link.hpp>
 27
 28namespace boost {
 29
 30/**
 31 * Class \random_device models a \nondeterministic_random_number_generator.
 32 * It uses one or more implementation-defined stochastic processes to
 33 * generate a sequence of uniformly distributed non-deterministic random
 34 * numbers. For those environments where a non-deterministic random number
 35 * generator is not available, class random_device must not be implemented. See
 36 *
 37 *  @blockquote
 38 *  "Randomness Recommendations for Security", D. Eastlake, S. Crocker,
 39 *  J. Schiller, Network Working Group, RFC 1750, December 1994
 40 *  @endblockquote
 41 *
 42 * for further discussions. 
 43 *
 44 * @xmlnote
 45 * Some operating systems abstract the computer hardware enough
 46 * to make it difficult to non-intrusively monitor stochastic processes.
 47 * However, several do provide a special device for exactly this purpose.
 48 * It seems to be impossible to emulate the functionality using Standard
 49 * C++ only, so users should be aware that this class may not be available
 50 * on all platforms.
 51 * @endxmlnote
 52 *
 53 * <b>Implementation Note for Linux</b>
 54 *
 55 * On the Linux operating system, token is interpreted as a filesystem
 56 * path. It is assumed that this path denotes an operating system
 57 * pseudo-device which generates a stream of non-deterministic random
 58 * numbers. The pseudo-device should never signal an error or end-of-file.
 59 * Otherwise, @c std::ios_base::failure is thrown. By default,
 60 * \random_device uses the /dev/urandom pseudo-device to retrieve
 61 * the random numbers. Another option would be to specify the /dev/random
 62 * pseudo-device, which blocks on reads if the entropy pool has no more
 63 * random bits available.
 64 *
 65 * <b>Inplementation Note for Windows</b>
 66 *
 67 * On the Windows operating system, token is interpreted as the name
 68 * of a cryptographic service provider.  By default \random_device uses
 69 * MS_DEF_PROV.
 70 *
 71 * <b>Performance</b>
 72 *
 73 * The test program <a href="\boost/libs/random/performance/nondet_random_speed.cpp">
 74 * nondet_random_speed.cpp</a> measures the execution times of the
 75 * nondet_random.hpp implementation of the above algorithms in a tight
 76 * loop. The performance has been evaluated on a Pentium Pro 200 MHz
 77 * with gcc 2.95.2, Linux 2.2.13, glibc 2.1.2.
 78 *
 79 * <table cols="2">
 80 *   <tr><th>class</th><th>time per invocation [usec]</th></tr>
 81 *   <tr><td> @xmlonly <classname alt="boost::random_device">random_device</classname> @endxmlonly </td><td>92.0</td></tr>
 82 * </table>
 83 *
 84 * The measurement error is estimated at +/- 1 usec.
 85 */
 86class random_device : private noncopyable
 87{
 88public:
 89  typedef unsigned int result_type;
 90  BOOST_STATIC_CONSTANT(bool, has_fixed_range = true);
 91  BOOST_STATIC_CONSTANT(result_type, min_value = integer_traits<result_type>::const_min);
 92  BOOST_STATIC_CONSTANT(result_type, max_value = integer_traits<result_type>::const_max);
 93
 94  /**
 95   * Returns: The smallest value that the \random_device can produce.
 96   */
 97  result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return min_value; }
 98  /**
 99   * Returns: The largest value that the \random_device can produce.
100   */
101  result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return max_value; }
102  /** 
103   * Constructs a @c random_device, optionally using the given token as an
104   * access specification (for example, a URL) to some implementation-defined
105   * service for monitoring a stochastic process. 
106   */
107  BOOST_RANDOM_DECL explicit random_device(const std::string& token = default_token);
108  BOOST_RANDOM_DECL ~random_device();
109  /**
110   * Returns: An entropy estimate for the random numbers returned by
111   * operator(), in the range min() to log2( max()+1). A deterministic
112   * random number generator (e.g. a pseudo-random number engine)
113   * has entropy 0.
114   *
115   * Throws: Nothing.
116   */
117  BOOST_RANDOM_DECL double entropy() const;
118  /**
119   * Returns: A random value in the range [min, max]
120   */
121  BOOST_RANDOM_DECL unsigned int operator()();
122
123private:
124  BOOST_RANDOM_DECL static const char * const default_token;
125
126  /*
127   * std:5.3.5/5 [expr.delete]: "If the object being deleted has incomplete
128   * class type at the point of deletion and the complete class has a
129   * non-trivial destructor [...], the behavior is undefined".
130   * This disallows the use of scoped_ptr<> with pimpl-like classes
131   * having a non-trivial destructor.
132   */
133  class impl;
134  impl * pimpl;
135};
136
137
138// TODO: put Schneier's Yarrow-160 algorithm here.
139
140} // namespace boost
141
142#endif /* BOOST_NONDET_RANDOM_HPP */