bf_F
#define ROUND(a, b, n) ({ b ^= P[n]; a ^= bf_F(b); })
#define ROUND(a, b, n) ({ b ^= P[n]; a ^= bf_F(b); })
#define EROUND(a, b, n) do { b ^= P[n]; a ^= bf_F(b); } while (0)
#define DROUND(a, b, n) do { a ^= bf_F(b); b ^= P[n]; } while (0)