"(x == A) ^ (x == B)", if A != B, is equivalent to

"(x == A) ^ (x == B)", if A != B, is equivalent to
"(x == A) || (x == B)", as x cannot simultaneously be equal to A and B.

"x == A ^ x == B" produces a compiler warning from GCC, so fix it by
using || instead - "x == A || x == B" doesn't produce such a warning.