Boost C++ Libraries

boost/uuid/random_generator.hpp

// Boost random_generator.hpp header file  ----------------------------------------------//

// Copyright 2010 Andy Tompkins.
// Copyright 2017 James E. King III
// 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/assert.hpp>
#include <boost/core/enable_if.hpp>
#include <boost/core/null_deleter.hpp>
#include <boost/random/mersenne_twister.hpp>
#include <boost/random/uniform_int.hpp>
#include <boost/random/variate_generator.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/tti/has_member_function.hpp>
#include <boost/uuid/detail/random_provider.hpp>
#include <boost/uuid/uuid.hpp>
#include <limits>

namespace boost {
namespace uuids {

namespace detail {
    template<class U>
    U& set_uuid_random_vv(U& u)
    {
        // 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;
    }
    
    BOOST_TTI_HAS_MEMBER_FUNCTION(seed)
}

//! generate a random-based uuid
//! \param[in]  UniformRandomNumberGenerator  see Boost.Random documentation
template <typename UniformRandomNumberGenerator>
class basic_random_generator {
private:
    typedef uniform_int<unsigned long> distribution_type;
    typedef variate_generator<UniformRandomNumberGenerator*, distribution_type> generator_type;

public:
    typedef uuid result_type;

    // default constructor creates the random number generator and
    // if the UniformRandomNumberGenerator is a PseudoRandomNumberGenerator
    // then it gets seeded by a random_provider.
    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 if it is capable
        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, boost::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, boost::null_deleter())
        , generator
          ( pURNG.get()
          , distribution_type
            ( (std::numeric_limits<unsigned long>::min)()
            , (std::numeric_limits<unsigned long>::max)()
            )
          )
    {
        BOOST_ASSERT(pURNG);
    }

    result_type operator()()
    {
        result_type 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);
        }

        return detail::set_uuid_random_vv(u);
    }

private:
    // Detect whether UniformRandomNumberGenerator has a seed() method which indicates that
    // it is a PseudoRandomNumberGenerator and needs a seed to initialize it.  This allows
    // basic_random_generator to take any type of UniformRandomNumberGenerator and still
    // meet the post-conditions for the default constructor.

    template<class MaybePseudoRandomNumberGenerator>
    typename boost::enable_if<detail::has_member_function_seed<MaybePseudoRandomNumberGenerator, void> >::type
        seed(MaybePseudoRandomNumberGenerator& rng)
    {
        detail::random_provider seeder;
        rng.seed(seeder);
    }

    template<class MaybePseudoRandomNumberGenerator>
    typename boost::disable_if<detail::has_member_function_seed<MaybePseudoRandomNumberGenerator, void> >::type
        seed(MaybePseudoRandomNumberGenerator&)
    {
    }

    shared_ptr<UniformRandomNumberGenerator> pURNG;
    generator_type generator;
};

//! \brief a far less complex random generator that uses
//!        operating system provided entropy which will
//!        satisfy the majority of use cases
class random_generator_pure
{
public:
    typedef uuid result_type;

    //! \returns a random, valid uuid
    //! \throws entropy_error
    result_type operator()()
    {
        result_type result;
        prov_.get_random_bytes(&result, sizeof(result_type));
        return detail::set_uuid_random_vv(result);
    }

private:
    detail::random_provider prov_;
};

#if defined(BOOST_UUID_RANDOM_GENERATOR_COMPAT)
typedef basic_random_generator<mt19937> random_generator;
#else
typedef random_generator_pure random_generator;
typedef basic_random_generator<mt19937> random_generator_mt19937;
#endif

}} // namespace boost::uuids

#endif // BOOST_UUID_RANDOM_GENERATOR_HPP