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Postings from September 2011
On Sun Sep 18 13:33:28 2011, sprout wrote:
> On Mon Sep 12 06:24:25 2011, ph10@hermes.cam.ac.uk wrote:
> > another oddity of (*THEN).
> >
> > Pattern: /a+?(*THEN)c/
> > Subject: aaac
> > Result: Perl 5.012003 matches "aaac"
>
> That’s strange. In 5.14 it doesn’t match. I don’t know which is worse.
The change occurred with this commit:
commit d1c771f5a95fddf225347623798f65884aa6eee7
Author: Bram <p5p@perl.wizbit.be>
Date: Thu Aug 26 13:27:24 2010 +0200
VERB nodes in the regex engine should NOT be marked as JUMPABLE.
JUMPABLE nodes can be ignored during certain phases of regex execution,
including ones where backtracking is affected. This change disables this
behviour so that the VERBS can perform their desired results.
Committer has taken the liberty of modifying the patch so that all
VERBS are jumped, thus making the JUMPABLE expression a little simpler.
I have left Bram's change to JUMPABLE intact, but inside of a comment
for now.
See discussion in thread for [perl #71942] *COMMIT bypasses optimisation
for futher details.
http://rt.perl.org/rt3/Ticket/Display.html?id=71942
There appears to be room for futher optimisation here
by moving the JUMPABLE logic to regex-compile time. Currently
it is arguable that the "optimisation" this patch seeks to avoid
is actually not an optimisation at all, as it happens OVER AND OVER
during execution of a match, thus the extra effort might actually
outweight the benefit, especially on large strings.
diff --git a/regexec.c b/regexec.c
index 35ef8d4..ec4c4b0 100644
--- a/regexec.c
+++ b/regexec.c
@@ -252,7 +252,8 @@
OP(rn) == EVAL || \
OP(rn) == SUSPEND || OP(rn) == IFMATCH || \
OP(rn) == PLUS || OP(rn) == MINMOD || \
- OP(rn) == KEEPS || (PL_regkind[OP(rn)] == VERB) || \
+ OP(rn) == KEEPS || \
+ /*(PL_regkind[OP(rn)] == VERB && OP(rn) != PRUNE && OP(rn) !=
COMMIT && OP(rn) != MARKPOINT && OP(rn) != SKIP && OP(rn) != CUTGROUP)
|| */\
(PL_regkind[OP(rn)] == CURLY && ARG1(rn) > 0) \
)
#define IS_EXACT(rn) (PL_regkind[OP(rn)] == EXACT)
diff --git a/t/re/pat_advanced.t b/t/re/pat_advanced.t
...snipped...
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