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 /* 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 BOOST_CONSTEXPR result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () { return 0; }
     /** Returns the largest value that the \random_device can produce. */
     static BOOST_CONSTEXPR 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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