On 2017-02-02 04:37, Franklin? Lee wrote:
On Thu, Jan 26, 2017 at 4:13 PM, Sven R. Kunze <srku...@mail.de> wrote:
Hi folks,
I recently refreshed regular expressions theoretical basics *indulging in
reminiscences* So, I read https://swtch.com/~rsc/regexp/regexp1.html
However, reaching the chart in the lower third of the article, I saw Python
2.4 measured against a naive Thompson matching implementation. And I was
surprised about how bad it performed compared to an unoptimized version of
an older than dirt algorithm.
From my perspective, I can say, that regular expressions might worth
optimizing especially for web applications (url matching usually uses
regexes) but also for other applications where I've seen many tight loops
using regexes as well. So, I am probing interest on this topic here.
What I (think I) know:
- Both re and regex use the same C backend, which is not based on NFA.
- The re2 library, which the writer of that article made, allows
capture groups (but only up to a limit) and bounded repetitions (up to
a limit).
- Perl has started to optimize some regex patterns.
[snip]
re and regex use different C backends. Both are based on NFA.
re2 is based on DFA, with a fallback to re.
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