The inverse is XOR!
If you have:
You can get a or b back if you have the other value available:
a = c^b; // or b^c (order is not important)
b = c^a; // or a^c
For example if a = 5, b = 3 (and thus c = 6 as you mentioned) you get:
b=0011 (3) a=0101 (5)
c=0110 (6) XOR or c=0110 (6) XOR
---------- ----------
a=0101 (5) b=0011 (3)
