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boost/uuid/random_generator.hpp

// 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