text: // Boost random_generator.hpp header file  ----------------------------------------------//
  
  // Copyright 2010 Andy Tompkins.
  // 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)
  
  #ifndef BOOST_UUID_RANDOM_GENERATOR_HPP
  #define BOOST_UUID_RANDOM_GENERATOR_HPP
  
  #include <boost/uuid/uuid.hpp>
  #include <boost/uuid/seed_rng.hpp>
  #include <boost/random/uniform_int.hpp>
  #include <boost/random/variate_generator.hpp>
  #include <boost/random/mersenne_twister.hpp>
  #include <boost/assert.hpp>
  #include <boost/shared_ptr.hpp>
  #include <limits>
  
  namespace boost {
  namespace uuids {
  
  // generate a random-based uuid
  template <typename UniformRandomNumberGenerator>
  class basic_random_generator {
  private:
      typedef uniform_int<unsigned long> distribution_type;
      typedef variate_generator<UniformRandomNumberGenerator*, distribution_type> generator_type;
  
      struct null_deleter
      {
          void operator()(void const *) const {}
      };
  
  public:
      typedef uuid result_type;
      
      // default constructor creates the random number generator
      basic_random_generator()
          : pURNG(new UniformRandomNumberGenerator)
          , generator
            ( pURNG.get()
            , distribution_type
              ( (std::numeric_limits<unsigned long>::min)()
              , (std::numeric_limits<unsigned long>::max)()
              )
            )
      {
          // seed the random number generator
          detail::seed(*pURNG);
      }
      
      // keep a reference to a random number generator
      // don't seed a given random number generator
      explicit basic_random_generator(UniformRandomNumberGenerator& gen)
          : pURNG(&gen, null_deleter())
          , generator
            ( pURNG.get()
            , distribution_type
              ( (std::numeric_limits<unsigned long>::min)()
              , (std::numeric_limits<unsigned long>::max)()
              )
            )
      {}
      
      // keep a pointer to a random number generator
      // don't seed a given random number generator
      explicit basic_random_generator(UniformRandomNumberGenerator* pGen)
          : pURNG(pGen, null_deleter())
          , generator
            ( pURNG.get()
            , distribution_type
              ( (std::numeric_limits<unsigned long>::min)()
              , (std::numeric_limits<unsigned long>::max)()
              )
            )
      {
          BOOST_ASSERT(pURNG);
      }
      
      uuid operator()()
      {
          uuid u;
          
          int i=0;
          unsigned long random_value = generator();
          for (uuid::iterator it=u.begin(); it!=u.end(); ++it, ++i) {
              if (i==sizeof(unsigned long)) {
                  random_value = generator();
                  i = 0;
              }
  
  			// static_cast gets rid of warnings of converting unsigned long to boost::uint8_t
              *it = static_cast<uuid::value_type>((random_value >> (i*8)) & 0xFF);
          }
  
          // set variant
          // must be 0b10xxxxxx
          *(u.begin()+8) &= 0xBF;
          *(u.begin()+8) |= 0x80;
  
          // set version
          // must be 0b0100xxxx
          *(u.begin()+6) &= 0x4F; //0b01001111
          *(u.begin()+6) |= 0x40; //0b01000000
  
          return u;
      }
  
  private:
      shared_ptr<UniformRandomNumberGenerator> pURNG;
      generator_type generator;
  };
  
  typedef basic_random_generator<mt19937> random_generator;
  
  }} // namespace boost::uuids
  
  #endif //BOOST_UUID_RANDOM_GENERATOR_HPP
  