From: Oleksandr Gavenko <gavenkoa@gmail.com>
To: help-gnu-emacs@gnu.org
Subject: Re: Any performance comparison/guide of/for Emacs regex?
Date: Tue, 18 Jan 2011 23:48:47 +0200 [thread overview]
Message-ID: <ih51s3$g1v$1@dough.gmane.org> (raw)
In-Reply-To: <jwv8vyi2hm5.fsf-monnier+gnu.emacs.help@gnu.org>
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!
next prev parent reply other threads:[~2011-01-18 21:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.16.1295365226.21909.help-gnu-emacs@gnu.org>
2011-01-18 18:29 ` Any performance comparison/guide of/for Emacs regex? Stefan Monnier
2011-01-18 21:48 ` Oleksandr Gavenko [this message]
[not found] ` <mailman.3.1295387371.19799.help-gnu-emacs@gnu.org>
2011-01-19 1:22 ` Stefan Monnier
2011-01-18 21:27 ` Tim X
2011-01-18 15:38 Oleksandr Gavenko
2011-01-18 15:59 ` Deniz Dogan
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