  A two-player one-round binary game consists of two cooperative players who
each replies by one bit to a message that he receives privately; they win the
game if both questions and answers satisfy some predetermined property. A game
is called entangled if the players are allowed to share a priori entanglement.
It is well-known that the maximum winning probability (value) of entangled
XOR-games (binary games in which the predetermined property depends only on the
XOR of the two output bits) can be computed by a semidefinite program. In this
paper we extend this result in the following sense; if a binary game is
uniform, meaning that in an optimal strategy the marginal distributions of the
output of each player are uniform, then its entangled value can be efficiently
computed by a semidefinite program. We also introduce a lower bound on the
entangled value of a general two-player one-round game; this bound depends on
the size of the output set of each player and can be computed by a semidefinite
program. In particular, we show that if the game is binary, w_q is its
entangled value, and w_{sdp} is the optimum value of the corresponding
semidefinite program, then 0.68w_{sdp} < w_q <= w_{sdp}.
