Benchmark: running substr, vec for at least 60 CPU seconds...
    substr: 61 wallclock secs (62.41 usr +  0.02 sys = 62.42 CPU) @  1.09/s (n=68)
       vec: 58 wallclock secs (60.64 usr +  0.02 sys = 60.66 CPU) @  0.73/s (n=44)
       s/iter    vec substr
vec      1.38     --   -33%
substr  0.918    50%     --