Re: why a.pl is faster than b.pl

On Thu, 29 Dec 2005, Bob Showalter wrote:

> Jeff Pang wrote:
> > Hi,bob,
> >
> > You said:
> >
> > 3. It will probably be faster to use a single regex of the format:
> >
> > /pata|patb|patc|patd/
> >
> >
> > In fact maybe you are wrong on this.
>
> Darn. First time this year :-)
>
> > Based on my test case,the RE written as below:
> >
> > /pata/ || /patb/ || /patc/ || /patd/
> >
> > is much faster than yours.
>
> OK. Perhaps its due to backtracking. Go with what works!

Several Perl books, including _Mastering Regular Expressions_ and, if I
remember correctly, _Learning Perl_, use variants of this example. In
essence, yes, if you want to match one of several constant strings like
this, the match will happen faster with a series of static regexes than
it would wwith one compound regex with alternation.


--
Chris Devers
DO NOT LEAVE IT IS NOT REAL
.