Using In-place Value Permutation in Assembly

Can be used in assembly programming to exchange the

value of two registers in place:

R1 ?? R1?R2

R2 ?? R1?R2

R1 ?? R1?R2

The In-place Value Permutation Property of the exclusive-OR:

(X?Y)?Y = X

(X?Y)?X= Y

If we do back substitution in the second and third operations,

we will find out that (assuming R1=A and R2=B initially):

R1 ? (A ? B)

R2 ? (A ? B) ? B = A

R1 ? (A ? B) ? A = B

Thus, if initially R1 = A and R2 = B, then after this sequence

of operations, R1 = B and R2 = A.