How to swap without a third variable?

Question

I have to swap two variables with a number value without using a third variable. What is the simple solution?

Answer 1

Here we have this in MIPS assembler. The first solution is long and bad. The second one with XOR is better.

addi $t0, $0, -5
addi $t1, $0, 15

add $t0, $t0, $t1
sub $t1, $t1, $t0
nor $t1, $0, $t1
addi $t1, $t1, 1
sub $t0, $t0, $t1

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xor $t0, $t0, $t1
xor $t1, $t0, $t1
xor $t0, $t0, $t1