1 /* boost nondet_random.hpp header file
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)
8 * $Id: nondet_random.hpp 62347 2010-05-31 16:44:36Z steven_watanabe $
11 * 2000-02-18 Portability fixes (thanks to Beman Dawes)
14 // See http://www.boost.org/libs/random for documentation.
17 #ifndef BOOST_NONDET_RANDOM_HPP
18 #define BOOST_NONDET_RANDOM_HPP
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>
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
38 * "Randomness Recommendations for Security", D. Eastlake, S. Crocker,
39 * J. Schiller, Network Working Group, RFC 1750, December 1994
42 * for further discussions.
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
53 * <b>Implementation Note for Linux</b>
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.
65 * <b>Implementation Note for Windows</b>
67 * On the Windows operating system, token is interpreted as the name
68 * of a cryptographic service provider. By default \random_device uses
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.
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>
84 * The measurement error is estimated at +/- 1 usec.
86 class random_device : private noncopyable
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);
95 * Returns: The smallest value that the \random_device can produce.
97 result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return min_value; }
99 * Returns: The largest value that the \random_device can produce.
101 result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return max_value; }
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.
107 BOOST_RANDOM_DECL explicit random_device(const std::string& token = default_token);
108 BOOST_RANDOM_DECL ~random_device();
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)
117 BOOST_RANDOM_DECL double entropy() const;
119 * Returns: A random value in the range [min, max]
121 BOOST_RANDOM_DECL unsigned int operator()();
124 BOOST_RANDOM_DECL static const char * const default_token;
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.
138 // TODO: put Schneier's Yarrow-160 algorithm here.
142 #endif /* BOOST_NONDET_RANDOM_HPP */