144 lines
5.1 KiB
C++
144 lines
5.1 KiB
C++
/* boost random/random_device.hpp header file
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*
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* Copyright Jens Maurer 2000
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* Copyright Steven Watanabe 2010-2011
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* Distributed under the Boost Software License, Version 1.0. (See
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* accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* $Id$
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*
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* Revision history
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* 2000-02-18 Portability fixes (thanks to Beman Dawes)
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*/
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// See http://www.boost.org/libs/random for documentation.
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#ifndef BOOST_RANDOM_RANDOM_DEVICE_HPP
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#define BOOST_RANDOM_RANDOM_DEVICE_HPP
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#include <string>
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#include <boost/config.hpp>
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#include <boost/noncopyable.hpp>
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#include <boost/random/detail/auto_link.hpp>
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#include <boost/system/config.hpp> // force autolink to find Boost.System
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namespace boost {
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namespace random {
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/**
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* Class \random_device models a \nondeterministic_random_number_generator.
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* It uses one or more implementation-defined stochastic processes to
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* generate a sequence of uniformly distributed non-deterministic random
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* numbers. For those environments where a non-deterministic random number
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* generator is not available, class random_device must not be implemented. See
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*
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* @blockquote
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* "Randomness Recommendations for Security", D. Eastlake, S. Crocker,
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* J. Schiller, Network Working Group, RFC 1750, December 1994
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* @endblockquote
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*
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* for further discussions.
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*
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* @xmlnote
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* Some operating systems abstract the computer hardware enough
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* to make it difficult to non-intrusively monitor stochastic processes.
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* However, several do provide a special device for exactly this purpose.
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* It seems to be impossible to emulate the functionality using Standard
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* C++ only, so users should be aware that this class may not be available
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* on all platforms.
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* @endxmlnote
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*
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* <b>Implementation Note for Linux</b>
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*
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* On the Linux operating system, token is interpreted as a filesystem
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* path. It is assumed that this path denotes an operating system
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* pseudo-device which generates a stream of non-deterministic random
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* numbers. The pseudo-device should never signal an error or end-of-file.
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* Otherwise, @c std::ios_base::failure is thrown. By default,
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* \random_device uses the /dev/urandom pseudo-device to retrieve
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* the random numbers. Another option would be to specify the /dev/random
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* pseudo-device, which blocks on reads if the entropy pool has no more
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* random bits available.
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*
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* <b>Implementation Note for Windows</b>
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*
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* On the Windows operating system, token is interpreted as the name
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* of a cryptographic service provider. By default \random_device uses
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* MS_DEF_PROV.
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*
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* <b>Performance</b>
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*
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* The test program <a href="\boost/libs/random/performance/nondet_random_speed.cpp">
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* nondet_random_speed.cpp</a> measures the execution times of the
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* random_device.hpp implementation of the above algorithms in a tight
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* loop. The performance has been evaluated on an
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* Intel(R) Core(TM) i7 CPU Q 840 \@ 1.87GHz, 1867 Mhz with
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* Visual C++ 2010, Microsoft Windows 7 Professional and with gcc 4.4.5,
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* Ubuntu Linux 2.6.35-25-generic.
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*
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* <table cols="2">
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* <tr><th>Platform</th><th>time per invocation [microseconds]</th></tr>
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* <tr><td> Windows </td><td>2.9</td></tr>
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* <tr><td> Linux </td><td>1.7</td></tr>
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* </table>
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*
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* The measurement error is estimated at +/- 1 usec.
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*/
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class random_device : private noncopyable
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{
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public:
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typedef unsigned int result_type;
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BOOST_STATIC_CONSTANT(bool, has_fixed_range = false);
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/** Returns the smallest value that the \random_device can produce. */
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static result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () { return 0; }
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/** Returns the largest value that the \random_device can produce. */
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static result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () { return ~0u; }
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/** Constructs a @c random_device, optionally using the default device. */
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BOOST_RANDOM_DECL random_device();
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/**
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* Constructs a @c random_device, optionally using the given token as an
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* access specification (for example, a URL) to some implementation-defined
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* service for monitoring a stochastic process.
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*/
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BOOST_RANDOM_DECL explicit random_device(const std::string& token);
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BOOST_RANDOM_DECL ~random_device();
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/**
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* Returns: An entropy estimate for the random numbers returned by
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* operator(), in the range min() to log2( max()+1). A deterministic
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* random number generator (e.g. a pseudo-random number engine)
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* has entropy 0.
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*
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* Throws: Nothing.
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*/
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BOOST_RANDOM_DECL double entropy() const;
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/** Returns a random value in the range [min, max]. */
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BOOST_RANDOM_DECL unsigned int operator()();
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/** Fills a range with random 32-bit values. */
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template<class Iter>
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void generate(Iter begin, Iter end)
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{
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for(; begin != end; ++begin) {
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*begin = (*this)();
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}
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}
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private:
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class impl;
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impl * pimpl;
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};
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} // namespace random
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using random::random_device;
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} // namespace boost
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#endif /* BOOST_RANDOM_RANDOM_DEVICE_HPP */
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