Benchmark: running rot13builtre, rot13builttr, rot13dynre, rot13dynre2, rot13splitmap, rot13substrfor, rot13tr, each for at least 3 CPU seconds...
rot13builtre:    3 wallclock secs ( 3.13 usr +  0.00 sys =  3.13 CPU) @   572.75/s (n=  1795)
rot13builttr:    4 wallclock secs ( 3.17 usr +  0.00 sys =  3.17 CPU) @ 61539.53/s (n=195388)
rot13dynre:      3 wallclock secs ( 3.07 usr +  0.00 sys =  3.07 CPU) @   567.80/s (n=  1746)
rot13dynre2:     3 wallclock secs ( 3.09 usr +  0.00 sys =  3.09 CPU) @   562.70/s (n=  1741)
rot13splitmap:   3 wallclock secs ( 3.29 usr +  0.00 sys =  3.29 CPU) @   364.99/s (n=  1199)
rot13substrfor:  3 wallclock secs ( 3.22 usr +  0.00 sys =  3.22 CPU) @   491.16/s (n=  1584)
rot13tr:         4 wallclock secs ( 3.09 usr +  0.00 sys =  3.09 CPU) @ 61032.31/s (n=188895)

                  Rate rot13splitmap rot13substrfor rot13dynre2 rot13dynre rot13builtre rot13tr rot13builttr
rot13splitmap    365/s            --           -26%        -35%       -36%         -36%    -99%         -99%
rot13substrfor   491/s           35%             --        -13%       -13%         -14%    -99%         -99%
rot13dynre2      563/s           54%            15%          --        -1%          -2%    -99%         -99%
rot13dynre       568/s           56%            16%          1%         --          -1%    -99%         -99%
rot13builtre     573/s           57%            17%          2%         1%           --    -99%         -99%
rot13tr        61032/s        16622%         12326%      10746%     10649%       10556%      --          -1%
rot13builttr   61540/s        16760%         12429%      10836%     10738%       10645%      1%           --