Benchmark: timing 500000 iterations of absolute, negate, regex...
  absolute:  1 wallclock secs ( 1.24 usr +  0.00 sys =  1.24 CPU) @ 404858.30/s (n=500000)
    negate:  1 wallclock secs ( 1.15 usr +  0.00 sys =  1.15 CPU) @ 433275.56/s (n=500000)
     regex:  3 wallclock secs ( 3.16 usr +  0.00 sys =  3.16 CPU) @ 158328.06/s (n=500000)
             Rate    regex absolute   negate
regex    158328/s       --     -61%     -63%
absolute 404858/s     156%       --      -7%
negate   433276/s     174%       7%       --