GNU bug report logs - #18013
looking-back is inefficient

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From: npostavs <at> users.sourceforge.net
To: Nicolas Richard <theonewiththeevillook <at> yahoo.fr>
Cc: Andreas Schwab <schwab <at> suse.de>, 18013 <at> debbugs.gnu.org
Subject: bug#18013: 24.3.92; looking-back "[^\n]" taking a lot of time in large buffers
Date: Sat, 25 Mar 2017 16:59:51 -0400

tags 18013 wontfix
close 18013
quit

Nicolas Richard <theonewiththeevillook <at> yahoo.fr> writes:

>
> (looking-back "[^\n]") is bad code, so I totally deserve this. Still, is
> it possible to make the search smarter when the match is supposed to be
> "anchored" at point ? Otherwise let's just close this bug.

`looking-back' would have to analyse "[^\n]" to realize that it could
only match a single character.  I think this is too much effort for too
little benefit to justify implementing this.  For cases like this you
can limit the amount of searching by passing a non-nil LIMIT argument
(as described in the docstring):

    (looking-back "[^\n]" (1- (point)))

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