Exchanging two integers with no scratch variable

How can you swap the values of two integer variables a and b without using a third variable?

Arithmetic: a = a + b; b = a - b; a = a - b;, or XOR: a ^= b; b ^= a; a ^= b;. After the first step a holds the combination, from which each original value can be recovered. The addition version can overflow, and both fail if a and b refer to the same memory (the value becomes $0$), so check for aliasing.