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Re: Any performance comparison/guide of/for Emacs regex?
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From: |
Oleksandr Gavenko |
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Subject: |
Re: Any performance comparison/guide of/for Emacs regex? |
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Date: |
Tue, 18 Jan 2011 23:48:47 +0200 |
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User-agent: |
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.2.12) Gecko/20101027 Thunderbird/3.1.6 |
On 2011-01-18 20:29, Stefan Monnier wrote:
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.
Thanks for answer!
How about if \\(.*\\) used to enclose a set of `\|'
alternatives or for referencing in font-lock expressions?
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.
I get basic understand but read more about backtracking
in regex engine some later. Thanks.
--
Best regards!