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Editing: random_device.hpp
/* boost random/random_device.hpp header file * * Copyright Jens Maurer 2000 * Copyright Steven Watanabe 2010-2011 * Distributed under the Boost Software License, Version 1.0. (See * accompanying file LICENSE_1_0.txt or copy at * http://www.boost.org/LICENSE_1_0.txt) * * $Id$ * * Revision history * 2000-02-18 Portability fixes (thanks to Beman Dawes) */ // See http://www.boost.org/libs/random for documentation. #ifndef BOOST_RANDOM_RANDOM_DEVICE_HPP #define BOOST_RANDOM_RANDOM_DEVICE_HPP #include <string> #include <boost/config.hpp> #include <boost/noncopyable.hpp> #include <boost/random/detail/auto_link.hpp> #include <boost/system/config.hpp> // force autolink to find Boost.System namespace boost { namespace random { /** * Class \random_device models a \nondeterministic_random_number_generator. * 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 * * @blockquote * "Randomness Recommendations for Security", D. Eastlake, S. Crocker, * J. Schiller, Network Working Group, RFC 1750, December 1994 * @endblockquote * * for further discussions. * * @xmlnote * 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. * @endxmlnote * * <b>Implementation Note for Linux</b> * * 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, @c std::ios_base::failure is thrown. By default, * \random_device 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. * * <b>Implementation Note for Windows</b> * * On the Windows operating system, token is interpreted as the name * of a cryptographic service provider. By default \random_device uses * MS_DEF_PROV. * * <b>Performance</b> * * The test program <a href="\boost/libs/random/performance/nondet_random_speed.cpp"> * 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. * * <table cols="2"> * <tr><th>Platform</th><th>time per invocation [microseconds]</th></tr> * <tr><td> Windows </td><td>2.9</td></tr> * <tr><td> Linux </td><td>1.7</td></tr> * </table> * * The measurement error is estimated at +/- 1 usec. */ class random_device : private noncopyable { public: typedef unsigned int result_type; BOOST_STATIC_CONSTANT(bool, has_fixed_range = false); /** Returns the smallest value that the \random_device can produce. */ static result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () { return 0; } /** Returns the largest value that the \random_device can produce. */ static result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () { return ~0u; } /** Constructs a @c random_device, optionally using the default device. */ BOOST_RANDOM_DECL random_device(); /** * Constructs a @c random_device, optionally using the given token as an * access specification (for example, a URL) to some implementation-defined * service for monitoring a stochastic process. */ BOOST_RANDOM_DECL explicit random_device(const std::string& token); BOOST_RANDOM_DECL ~random_device(); /** * 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. * * Throws: Nothing. */ BOOST_RANDOM_DECL double entropy() const; /** Returns a random value in the range [min, max]. */ BOOST_RANDOM_DECL unsigned int operator()(); /** Fills a range with random 32-bit values. */ template<class Iter> void generate(Iter begin, Iter end) { for(; begin != end; ++begin) { *begin = (*this)(); } } private: class impl; impl * pimpl; }; } // namespace random using random::random_device; } // namespace boost #endif /* BOOST_RANDOM_RANDOM_DEVICE_HPP */
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