input: Write a python function to swap two numbers using bitwise operators.
  assert swap(10, 5) == (5, 10)
  assert swap(20, 30) == (30, 20)
  assert swap(0, 0) == (0, 0)
output: def swap(a, b):
      a = a ^ b
      b = a ^ b
      a = a ^ b
      return a, b