"Benchmarked variations include some of those used by kcott"

I'm assuming you're referring to cg_ncg with (?: ... ) and cg_atomic with (?> ... ).

Prior to posting yesterday, and purely out of curiousity, I ran /atg(.+?)(?:taa|tag|tga)/ and /atg(.+?)(?>taa|tag|tga)/ through Regexp::Debugger looking at the matching process step-by-step. From memory, ?: took 64 steps (in total) to complete the match while ?> took 66 steps. That probably accounts for the cg_atomic vs. cg_ncg 3% (66/64 = 1.03125).

Again from memory, the two extra steps occurred after failing to match taa|tag|tga after either the 'a' or 't' of 'atg'. For the ?: case, the steps were something like: "(?:" start non-capture group; "taa" no match; "|" next alt; ...; "tga" no match. For the ?> case: "(?>" start non-backtracking group; ... as for ?: ...; (then the additional step) ")" end non-backtracking group.

Obviously, you can check that yourself if you're so inclined. I wasn't inclined to repeat the process. :-)

[I haven't analysed your benchmarking further.]

-- Ken

In reply to Re^4: Simple regex question. Grouping with a negative lookahead assertion. by kcott
in thread Simple regex question. Grouping with a negative lookahead assertion. by Anonymous Monk

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