entropy_code

#include <cstdio>
#include <cstdlib>
#include <iostream>
//#include <omp.h>
//#include <bitset>
#include <cstdint>
//#include <chrono>
//#include <random>
#include <functional>
#include <vector>
#include <cmath>

using namespace std;

//#include <boost/functional/hash.hpp>

uint32_t hash32( uint32_t a)
{
   a = (a+0x7ed55d16) + (a<<12);
   a = (a^0xc761c23c) ^ (a>>19);
   a = (a+0x165667b1) + (a<<5);
   a = (a+0xd3a2646c) ^ (a<<9);
   a = (a+0xfd7046c5) + (a<<3);
   a = (a^0xb55a4f09) ^ (a>>16);
   return a;
}

double HH(int m, int k)
{// entropy of k-bits sequences generated from m bits random variable
     int N = 1<<m;

     int  K =  1<<k;
    vector<int> counts(K );



    for (int i=0;i<N;i++)
    {
        uint32_t x = hash32(i);
       // cout<<x<<" "<<i<<endl;
        counts[(x)%K]++;
    }
    double H=0;
    for (int i=0;i<counts.size();i++)
    {
        double P = counts[i]/(double)N;
        if (P > 0)
            H+= -P*log2(P);
    }
    return H;
}


int main(void)
{

    cout.precision(2);
    std::cout.setf( std::ios::fixed, std:: ios::floatfield );

    cout<<"  ";
    for (int m=1;m<=20;m++)
    {
        std::cout.fill(' ');
        std::cout.width(5);
        cout<<m<<" ";

    }
    cout<<endl;

    for (int k=1;k<25;k++)
    {
        std::cout.fill(' ');
        std::cout.width(2);
        cout<<k<<":";
        for (int m=1;m<=20;m++)
        {
            std::cout.fill(' ');
            std::cout.width(5);
            cout<<(HH(m,k))<<" ";
        }
              cout<<endl;
    }

}