[Octave-bug-tracker] [bug #39430] regexp: performance for cell arrays is slow

[Rik]

URL:
  <http://savannah.gnu.org/bugs/?39430>

                 Summary: regexp: performance for cell arrays is slow
                 Project: GNU Octave
            Submitted by: rik5
            Submitted on: Sun 07 Jul 2013 04:55:02 PM PDT
                Category: Libraries
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Performance
                  Status: Confirmed
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Any

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Details:

The performance of regexp is an order of magnitude slower than the same
functionality in strfind.  Some performance penalty is expected, but not this
great.

Sample Code:



octave:71> xc = cellstr (char (randi( [65 65+25], [1e5, 20])));
octave:72> tic; yr = regexp (xc, 'ABC'); toc
Elapsed time is 2.5726881 seconds.
octave:73> tic; y = strfind (xc, 'ABC'); toc
Elapsed time is 0.20126295 seconds.


There seem to be several causes.  It appears that Octave is re-compiling the
PCRE pattern every time it does a match for one row.  Octave is also bothering
to process and restore all possible return values (start, end, tokens,
tokenextents, match, and splits) even if only a subsection is desired.  I
haven't done a hotspot analysis though.





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