xor (char *out, char *in1, char *in2, int n)
{
for (int i = 0; i < n; i++)
  out[i] = in1[i] ^ in2[i];
}
xor (char *out, char *in1, char *in2, int n)
{
for (int i = 0; i < n; i++)
  out[i] = in1[i] ^ in2[i];
}