split:  2 wallclock secs ( 1.16 usr +  0.00 sys =  1.16 CPU) @ 862068.97/s (n=1000000)
    substr:  1 wallclock secs ( 0.70 usr +  0.00 sys =  0.70 CPU) @ 1428571.43/s (n=1000000)
    unpack:  0 wallclock secs ( 0.96 usr +  0.00 sys =  0.96 CPU) @ 1041666.67/s (n=1000000)