If we're allowed to cheat then the difference moves into the realms of run to run variability 
    Rate     b     a     d     c
b 82.7/s    --  -97%  -97%  -99%
a 2657/s 3112%    --   -3%  -56%
d 2748/s 3222%    3%    --  -54%
c 5982/s 7132%  125%  118%    --
388200:12000:829800:389700

[download]
I'm not sure what cheating is in this context, but that's not the point. The only "run to run" variability I see is between cases a and d, which are almost identical. Case c is more than twice as fast of any of the other variants.

In reply to Re^10: Regex match at the beginning or end of string by JavaFan
in thread Regex match at the beginning or end of string by cyber-guard

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