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From: Rui Zhu <sprache@iname.com>
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Subject: Re: Scoring is horribly slowed down by this entry. Why?
Date: 03 Aug 1999 01:36:37 +0200
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Felix Lee <flee@teleport.com> writes:

> Rui Zhu <sprache@iname.com>:
> > ("\\([-_0-9A-Za-z]+\.\\)+\\(com\\|net\\) *$" -1000 nil r)
> 
> 1. there are N possible starting points for the [...]+
> pattern, and greedy-match semantics will have it doing N
> attempts for each possible starting point.  the (...)+
> pattern around it forces each of these N attempts to be done
> N times, so the best case performance is something like
> O(N**3).  this is going to be terrible, because N is pretty
> large, since alphanumeric characters are common.
> 
> 2. "\." should be "\\.".  "\." == ".", which makes the
> regexp behavior worse, since it will need to try matching
> any character, not just alphanumerics, which makes N bigger,
> sort of.

Oops, how silly am I.  I really want `\\.', it is this forgotten
backslash that causes almost the whole trouble.

Thanks,
        Rui