Le 08/03/2011 23:49, Erik de Castro Lopo a écrit :
> 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?
>
> 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$/
>
> to this:
>
>
> /^([0-9]{1,3}\.){4}\.(dsl\.dynamic\.eranet\.pl|dynamic\.snap\.net\.nz|nat\.umts\.dynamic\.eranet\.pl)$/
>
> 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.
your speculations are wrong. /(joe|foo|bar)/ isn't /3 times faster than
individual tests. but before all, "premature optimisation is the root of
all evil". one should not convert readable stuff to unmaintainable
hieroglyph without measuring the real benefits.
>
> Obviously, a conversion from the first three to the optimised version
> has to be done mechanistically to avoid errors.
>
if it should be done, then it should be done inside the implementation.
> Cheers,
> Erik
