Benchmark: timing 1000000 iterations of regex1, regex2, substr...
    regex1:  4 wallclock secs ( 4.05 usr +  0.00 sys =  4.05 CPU) @ 247096.61/s (n=1000000)
    regex2:  5 wallclock secs ( 3.14 usr +  0.00 sys =  3.14 CPU) @ 318471.34/s (n=1000000)
    substr:  2 wallclock secs ( 0.63 usr +  0.00 sys =  0.63 CPU) @ 1600000.00/s (n=1000000)