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From: Stefan Monnier <monnier@iro.umontreal.ca>
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Subject: Re: Any performance comparison/guide of/for Emacs regex?
Date: Tue, 18 Jan 2011 13:29:35 -0500
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> Any performance comparison/guide of/for Emacs regex?

Not really.  What you need to know is that Emacs's regexp engine is
based on backtracking, so things like .*\\(.*\\).* is insanely
inefficient and will make you think Emacs is frozen.

Generally, you'll prefer to use regexps that don't require backtracking.
E.g. [^(\n]*( works much better than .*( since when encountering an open
parenthesis, the matcher will know for sure that it has to leave the *
loop, rather than having to try both cases in sequence.


        Stefan