#include <stdio.h>
#include <math.h>

long state = 42;
long lcg() {
  state = (1103515245L * state + 12345L) % 2147483648L;
  return state;
}
double uniform() { return (double)lcg() / 2147483648.0; }

double exp_sample(double lambda) {
  double u = uniform();
  if (u < 1e-12) u = 1e-12;
  return -log(u) / lambda;
}

int main() {
  double lambda = 0.5;
  double sum = 0;
  int n = 1000;
  for (int i = 0; i < n; i++) {
    double x = exp_sample(lambda);
    if (i < 10) printf("%.3f\n", x);
    sum += x;
  }
  printf("mean = %.3f (expected 2.0)\n", sum / n);
  return 0;
}