Benchmark: timing 1048576 iterations of sub, zwa...
       sub: 16 wallclock secs (15.07 usr +  0.00 sys = 15.07 CPU) @ 69580.36/s
       zwa: 13 wallclock secs (12.58 usr +  0.00 sys = 12.58 CPU) @ 83352.62/s
       Rate  sub  zwa
sub 69580/s   -- -17%
zwa 83353/s  20%   --