Ticket #6801: mersenne_twister_bug.cpp

#include <iostream>
#include <sstream>
using namespace std;

#include <boost/random/mersenne_twister.hpp>
using namespace boost::random;

int main(int argc, char * argv[])
{
        typedef mt11213b Engine;

        // an MT engine with the default seed
        Engine boost_mt;

        stringstream boost_ss;

        boost_ss << boost_mt;

        typedef Engine::result_type UIntType;

        static const size_t n = Engine::state_size;

        UIntType x[n], * y = x;
        for (size_t i = 0; i < n; ++i)
                boost_ss >> x[i] >> ws;

        Engine boost_mtOther;
        // alter the high w - r bits of y[0] (for mt11213b, w = 32 and r = 19)
        y[0] |= 0x00030000;
        boost_mtOther.seed(y, y + n);

        // operator== returns false
        cout << "boost_mt == boost_mtOther: " << (boost_mt == boost_mtOther) << endl;

        const size_t boost_testSize = 1000000;

        // however the two engines are equivalent:
        for (size_t i = 0; i < boost_testSize; ++i)
        {
                UIntType result = boost_mt();
                UIntType resultOther = boost_mtOther();
                if (result != resultOther)
                        cout << "critical check boost_mt() == boost_mtOther() ["
                        << result << " != " << resultOther << "] failed at iteration " << i << endl;
        }
}