[pcre-dev] [Bug 547] full regular expression support inside …

Top Page

Reply to this message
Author: admin
To: pcre-dev
Subject: [pcre-dev] [Bug 547] full regular expression support inside lookbehind

--- Comment #5 from Philip Hazel <Philip.Hazel@???> ---
Fixed-length lookbehind is (relatively) simple: you move back a fixed number of
characters, then apply the normal matching algorithms. That's what PCRE and
Perl (until recently) do. I see that Perl 5.3 has some experimental support for
variable length. The documentation says this: "Prior to Perl 5.30, it worked
only for fixed-width lookbehind, but starting in that release, it can handle
variable lengths from 1 to 255." It goes on to say that this is experimental
and may be removed if insurmountable problems arise. I have no idea how it is
implemented, but the 255 limit suggests it is perhaps trying a minimum length
and then continuing to move backwards (up to the limit). If something similar
were implemented in PCRE I'm sure the performance would be lousy.

You are receiving this mail because:
You are on the CC list for the bug.