Entropy of Quantum random numbers

qrnd.cc

#include <iostream>
#include <iterator>
#include <fstream>
#include <algorithm>
#include <cstdio>
#include <vector>
#include <cmath>
#include <limits>
#include <iomanip>
#include <string>
#include <map>

#define VERBOSE 1
#define ENTROPY 0

double log2( double number ) {
   return log( number ) / log( 2 ) ;
}
 
int entropy(std::string &str, bool disp) {

    std::map<char, int> frequencies;

    for (char c : str) {
        frequencies[c]++;
    }

    int numlen = str.length();
    double entropy = 0;

    for (std::pair<char, int> p : frequencies) {
        double freq = static_cast<double>(p.second) / numlen;
        entropy += freq * log2(freq);
    }

    if (disp) {
        std::cout << "Entropy is: " << fabs(entropy) << std::endl;
    } else {
        std::cout << fabs(entropy) << std::endl;
    }   

    return 0 ;
}

int main () {

    float min = std::numeric_limits<float>::min();
    float max = std::numeric_limits<float>::max();

    std::cout << std::setprecision(16);
    std::cout.setf(std::ios::fixed, std:: ios::floatfield);

    #if VERBOSE
        std::cout << "Minimum value for float: " << min << "\n";
        std::cout << "Maximum value for float: " << max << "\n";
    #endif

    FILE * f;
    f = fopen("/home/gecemmo/Downloads/ANU_25Jun2014_1000MB/ANU_25Jun2014_100MB_1", "rb");

    double sum = 0;
    int count = 500000;

    std::string content;

    for (int i=0;i<count;i++) {
        
        unsigned char *ptr = new unsigned char[4];

        if (f != NULL) {

            size_t nr = fread(ptr, sizeof(char), 4, f);

            if (nr < 4) break;

            content += std::string((const char*)ptr);

            unsigned int ui = *reinterpret_cast<unsigned int*>(ptr);
            float fp = ui / (float)(0xffffffff - 1);

            #if VERBOSE
                std::cout << "[" <<  i << "] "<< fp << std::endl;
            #endif

            sum += fp;
            
            #if ENTROPY
                if (i % 5000 == 0) entropy(content, false); 
            #endif     
        }
    }

    std::cout << "Average value: " << (sum/count) << " (" << count << " numbers)" << std::endl;

    #if ENTROPY
        entropy(content, true);
    #endif
    
    fclose(f);

    return 0;
}