gmp.i

unsigned long long my_pow(unsigned int x, unsigned int n) {
  int res = 1;
  while (n) {
    if (n & 1) res *= x;
    n >>= 1;
    x *= x;
  }
  return res;
}

int main(void) {
  unsigned long long x = my_pow(2, 63);
  /*@ assert (2 * x + 1) % 2 == 1; */
  return 0;
}