random_number_generater_test

#include <cmath>
#include <cstdlib>
#include <ctime>
#include <iostream>

using namespace std;

int rand_by_mod(int r, int sup) { return r % sup; }

int rand_by_extend(int r, int sup) { return r * sup / (RAND_MAX + 1); }

double entropy(unsigned counter[], int size, double sum) {
  double ent = 0;

  for (int i = 0; i < size; i++) {
    double freq = counter[i] / sum;
    ent += -freq * log2(freq);
  }

  return ent;
}

int main(int argc, char const *argv[]) {
  constexpr int sup = 16;
  unsigned counter_by_mod[sup] = {0};
  unsigned counter_by_extend[sup] = {0};

  for (int cnt = 0; cnt <= RAND_MAX; cnt++) {
    int r = rand();
    counter_by_mod[rand_by_mod(r, sup)]++;
    counter_by_extend[rand_by_extend(r, sup)]++;
  }

  printf("rand_by_imagine  %.6f \n", -log2(1.0 / sup));
  printf("rand_by_mod      %.6f \n", entropy(counter_by_mod, sup, RAND_MAX));
  printf("rand_by_extend   %.6f \n", entropy(counter_by_extend, sup, RAND_MAX));

  return 0;
}