  Using the latest LHCb measurements of time-dependent CP violation in the
B^0_s -> K^+K^- decay, a U-spin relation between the decay amplitudes of B^0_s
-> K^+K^- and B^0 -> \pi^+\pi^- decay processes allows constraints to be placed
on the angle gamma of the unitarity triangle and on the B^0_s mixing phase
-2\beta_s. Results from an extended approach, which uses additional inputs on
B^0 -> \pi^0\pi^0 and B^+ -> \pi^+\pi^0 decays from other experiments and
exploits isospin symmetry, are also presented. The dependence of the results on
the maximum allowed amount of U-spin breaking is studied. At 68% probability,
the value \gamma = ( 63.5 +7.2 -6.7 ) degrees modulo 180 degrees is determined.
In an alternative analysis, the value -2\beta_s = -0.12 +0.14 -0.16 rad is
found. In both measurements, the uncertainties due to U-spin breaking effects
up to 50% are included.
