Re: regex performance

From: Eric Niebler (yg-boost-users_at_[hidden])
Date: 2002-04-20 12:29:34

"Thomas Maeder" <yg-boost-users_at_[hidden]> wrote in message
news:m3hem67oa3.fsf_at_madbox.local...
> Eric Niebler <yg-boost-users_at_[hidden]> writes:
>
> > Slightly off-topic, but ...
>
> Would you be interested in getting this back on topic? <evil grin>
>

Getting there.  :-)  See below.

>
> > ... have a look at GRETA, my own regular expression template library.  I
have
> > found it to be as much as 7x faster than boost regex.  It's
> > free for non-commercial use.
>
> Does this mean that it (or something derived from it) couldn't be
boostified?
>

Since you asked ... I fought tooth and nail to get permission to submit to
Boost, but our layers wouldn't budge. But the winds are changing in the VC++
group -- there are some who would like to see this happen.  I'd still like
very much to combine the best of boost regex with the best of GRETA and make
it publically available, either in boost or with a boost-like license.
We'll see.

>
> > I'd love any feedback you might have.  The interface is not nearly as
> > nice or as rich as Dr. Maddock's, but it's just about the fastest C/C++
> > regex library I've tested. Wide chars, backreferences, full Perl 5
> > syntax, etc., etc.
>
> IMHO, it would be nice to have sort of regex light (less rich
functionality,
> better performance) in boost, and GRETA might be a good starting point. It
> would be helpful if the parts of the interface common to both libraries
> were harmonized. Do you think this would be possible?
>

The interfaces are vastly different, unfortunately.  I would like to put a
more boost-ish interface on GRETA, because the boost interface is nicer.
And it would give me perspective on regex interface issues that will be
valuable during the standardization process, which I plan to be involved in.
If I can find the time, I'll do it.  (GRETA is a labor of love that I pursue
in my spare time -- it has next to nothing to do with my job.)

Note that "harmonizing" boost regex and GRETA would be difficult because
their flavors of regular expressions have slightly different semantics.
Boost has POSIX-like semantics, which makes stronger guarantees about the
"left-most longest" rule.  GRETA has Perl-like semantics, which makes weaker
guarantees, but lets me cut some corners.

FYI -- GRETA isn't "regex lite."  It's a backtracking regex engine, so it's
heavier-weight than, say, a DFA-based regex engine that doesn't do
backreferences.  It's faster than boost, but that's more because I use a
different implementation, not a fundamentally different algorithm per se.

Eric