Benchmark: timing 1000000 iterations of Eval, S_op...
      Eval: 140 wallclock secs (133.80 usr +  0.03 sys = 133.83 CPU) @ 7472.17/s (n=1000000)
      S_op:  1 wallclock secs ( 0.81 usr +  0.00 sys =  0.81 CPU) @ 1234567.90/s (n=1000000)