-------- Original-Nachricht --------
> Datum: Wed, 9 Mar 2011 09:49:21 +1100
> Von: Erik de Castro Lopo <mle+to...@mega-nerd.com>
> An: postfix-users@postfix.org
> Betreff: Re: regular expressions was: Kernel Oops
> Wietse Venema wrote:
>
> > If you must match a very large numbers of patterns, you need an
> > implementation that transforms N patterns into one deterministic
> > automaton. This can match 1 pattern in the same time as N patterns.
> > Once the automaton is built (which takes some time) it is blindingly
> > fast. An example of such an implementation is flex.
>
> Is there a limit the the pattern length in the pcre tables?
>
I think there is one (if memory does not fool me then it is somewhere around
1000 characters). But I am not 100% sure.
> If not, it would be possible to convert this (3 only, but could be
> hundreds or even thousands):
>
> /^([0-9]{1,3}\.){4}\.dsl\.dynamic\.eranet\.pl$/
> /^([0-9]{1,3}\.){4}\.dynamic\.snap\.net\.nz$/
> /^([0-9]{1,3}\.){4}\.nat\.umts\.dynamic\.eranet\.pl$/
>
Are you sure the above is correct? You have there a double dot and I think that
is not correct.
> to this:
>
>
> /^([0-9]{1,3}\.){4}\.(dsl\.dynamic\.eranet\.pl|dynamic\.snap\.net\.nz|nat\.umts\.dynamic\.eranet\.pl)$/
>
Or even shorter:
/^([0-9]{1,3}\.){4}((dsl\.dynamic|nat\.umts)\.dynamic\.eranet\.pl|dynamic\.snap\.net\.nz)$/
Maybe using if/endif conditions like Stan Hoeppner has done on his pcre map
could speedup things even more? -> http://www.hardwarefreak.com/fqrdns.pcre
> and that should reject "1.1.1.1.not-found" in 1/3 the time of the
> three original regexes while also matching quicker than the original.
>
> Obviously, a conversion from the first three to the optimised version
> has to be done mechanistically to avoid errors.
>
Well... if the source is already buggy (double dot issue) then automating that
transformation is not going to help you much.
> Cheers,
> Erik
> --
// Steve
> ----------------------------------------------------------------------
> Erik de Castro Lopo
> http://www.mega-nerd.com/
--
GMX DSL Doppel-Flat ab 19,99 Euro/mtl.! Jetzt mit
gratis Handy-Flat! http://portal.gmx.net/de/go/dsl
