Benchmark: timing 5000000 iterations of sub1, sub2, sub3...
      sub1:  8 wallclock secs ( 7.49 usr +  0.00 sys =  7.49 CPU) @ 667467.63/s (n=5000000)
      sub2:  7 wallclock secs ( 7.27 usr + -0.01 sys =  7.26 CPU) @ 688800.11/s (n=5000000)
      sub3:  5 wallclock secs ( 5.12 usr +  0.01 sys =  5.13 CPU) @ 975419.43/s (n=5000000)