The Birthday Attack (Approximation)

birthday.cc

#include <cmath>
#include <cstdlib>
#include <iostream>
 
int main(int argc, char ** argv) {
  if (argc != 3) {
    std::cerr << "Usage: " << argv[0] << " probability-exponent bits" << std::endl;
    return 1;
  }
 
  long probabilityExponent = strtol(argv[1], NULL, 10);
  double probability = pow(10, probabilityExponent);
 
  long bits = strtol(argv[2], NULL, 10);
  double outputs = pow(2, bits);
 
  std::cout << sqrt(2.0 * outputs * -log1p(-probability)) << std::endl;
 
  return 0;
}