TITLE: Meaning of function with circle and cross
QUESTION [5 upvotes]: I've seen this function M2 = tmp ⊕ Pi. What does the circle with cross do?

REPLY [11 votes]: In logic and CompSci, $\oplus$ is used to denote the "exclusive or" or "XOR": $\quad x \lor y \land \lnot(x \land y)$.
In set theory, $\oplus$ denotes the disjoint union.
In linear algebra/vector analysis, it's used to denote the direct sum of two vector spaces. 
It's also used to denote parity: see P Parity.

Clearly, the context in which it's used is crucial.

In $LaTeX$: use \oplus.