Milter-greylist

AIDA Shinra wrote:
 > Matt Kettler wrote:
 > > > 
 > > > But this:
 > > > 
 > > >   acl greylist domain /[0-9][0-9]*\-[0-9][0-9]*\-[0-9][0-9]*/
 > > >   acl greylist domain /[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*/
 > > > 
 > > > which I still firmly believe are terrible for performance.
 > > 
 > > Agreed. Those could be terrible, at least for some inputs.

No, they're perfectly OK.

 > A little offtopic: they are not too bad. No backtracking for any
 > input. * don't do harm if * part and its following part are mutually
 > exclusive. For example:
 > \[.*\] causes backtracking
 > \[[^]]*\] doesn't cause any backtracking

It depends entirely on the implementation of the regex
library.  You can implement them in a way that an NFA
is built that _never_ requires any backtracking for "*"
(including both cases mentioned above).

See any good book on formal languages and automatons.

Best regards
   Oliver

-- 
Oliver Fromme,  secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
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