Does GHASH use XOR or addition? I've been looking into GHASH and some sites describe it as a polynomial:

A1*(H* *M-1)+A2*(H* *M-2)...C1*H(H* *M-N)+C2*H(H* *(M-N-1))...+len(A||C)*H+E(0)=t


while other sites replace the + with the XOR symbol, ^:

A1*(H* *M-1)^A2*(H* *M-2)...C1*H(H* *M-N)^C2*H(H* *(M-N-1))...^len(A||C)^H+E(0)=t


Which one is the correct one?
There is no difference in this context. XOR is sometimes called "carryless addition" because one bit addition mod 2 is identical to the one bit XOR operation. Multiplication is also carryless in this context.