algorithm - c# using bitwise XOR for swapping

Question

void swap(ref int x, ref int y)
{       x = x ^ y;   y = y ^ x;   x = x ^ y;  }

im learning about bitwise XOR. how is this swapping occurring? it's blowing my mind. this method is supposed to swap the contents of X and Y, but i dont understand AT ALL what is going on?

Answer 1

Beware. This method has a very very nasty property. It was used in one of the Underhanded C Contest entries. It will work happily... until one day someone tries something like swapping two array elements a[i] and a[j] without assuring that i!=j.

When both references refer to the same variable, this method zeroes it.