This is a trick using the exclusive or operator ^ that was used when computers were short on memory.
a = (a ^ b) /* a^b, b */
b = (a ^ b) /* a^b, a */
a = (a ^ b) /* b, a */
You can also do it using subtraction for numeric values
a = a – b /* a – b, b */
b = b -a /* a-b, a */
a = b – a /* b, a */