split: 17 wallclock secs (16.69 usr +  0.02 sys = 16.71 CPU) @ 59844.40/s (n=1000000)
    substr:  0 wallclock secs ( 0.74 usr +  0.00 sys =  0.74 CPU) @ 1351351.35/s (n=1000000)
    unpack:  1 wallclock secs ( 1.02 usr +  0.00 sys =  1.02 CPU) @ 980392.16/s (n=1000000)