From: "Stephen J. Turnbull" <turnbull@sk.tsukuba.ac.jp>
To: "Andreas Röhler" <andreas.roehler@online.de>
Cc: Emacs developers <emacs-devel@gnu.org>
Subject: Re: Possible problem with looking-back function
Date: Thu, 19 Aug 2010 18:02:24 +0900 [thread overview]
Message-ID: <8739ubug9r.fsf@uwakimon.sk.tsukuba.ac.jp> (raw)
In-Reply-To: <4C6CCA8B.5060106@online.de>
Andreas Röhler writes:
> that surprises me. Check must be done against the string already
> found. So workload should grow lineary resp. slightly ascending.
That's incorrect. In regexp matching abstractly defined, there is no
"string already matched." In general backtracking must be done to get
a correct POSIX match, and it's potentially very expensive. It would
be sometimes possible (as in this case) to identify a non-backtracking
algorithm as you suggest, but that would mean that different regexps
would be treated differently, or that some regexps would be
ridiculously expensive.
next prev parent reply other threads:[~2010-08-19 9:02 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-19 1:15 Possible problem with looking-back function Vinicius Jose Latorre
2010-08-19 2:43 ` Davis Herring
2010-08-19 6:09 ` Andreas Röhler
2010-08-19 8:01 ` Stefan Monnier
2010-08-19 9:02 ` Stephen J. Turnbull [this message]
2010-08-19 9:32 ` Andreas Röhler
2010-08-20 2:11 ` Vinicius Jose Latorre
2010-08-20 13:07 ` Stefan Monnier
2010-08-21 0:08 ` Vinicius Jose Latorre
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