From f31a99c85a958352599ea1e9ed74866c8666a515 Mon Sep 17 00:00:00 2001
From: Hugo van der Sanden <hv@crypt.org>
Date: Thu, 16 Aug 2001 17:27:49 +0100
Subject: [PATCH] Re: [ID 20010803.016] Possible regex bug in 5.6.1 Message-Id:
 <200108161527.f7GFRnH09419@crypt.compulink.co.uk>

p4raw-id: //depot/perl@11697
---
 regexec.c     | 30 +++++++++++++++++-------------
 t/op/re_tests |  4 ++++
 2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/regexec.c b/regexec.c
index e95bd16..3f062ed 100644
--- a/regexec.c
+++ b/regexec.c
@@ -3033,12 +3033,15 @@ S_regmatch(pTHX_ regnode *prog)
 		minmod = 0;
 		if (ln && regrepeat_hard(scan, ln, &l) < ln)
 		    sayNO;
-		if (ln && l == 0 && n >= ln
-		    /* In fact, this is tricky.  If paren, then the
-		       fact that we did/didnot match may influence
-		       future execution. */
-		    && !(paren && ln == 0))
-		    ln = n;
+		/* if we matched something zero-length we don't need to
+		   backtrack - capturing parens are already defined, so
+		   the caveat in the maximal case doesn't apply
+
+		   XXXX if ln == 0, we can redo this check first time
+		   through the following loop
+		*/
+		if (ln && l == 0)
+		    n = ln;	/* don't backtrack */
 		locinput = PL_reginput;
 		if (PL_regkind[(U8)OP(next)] == EXACT) {
 		    c1 = (U8)*STRING(next);
@@ -3060,7 +3063,7 @@ S_regmatch(pTHX_ regnode *prog)
 			UCHARAT(PL_reginput) == c2)
 		    {
 			if (paren) {
-			    if (n) {
+			    if (ln) {
 				PL_regstartp[paren] =
 				    HOPc(PL_reginput, -l) - PL_bostr;
 				PL_regendp[paren] = PL_reginput - PL_bostr;
@@ -3084,12 +3087,13 @@ S_regmatch(pTHX_ regnode *prog)
 	    }
 	    else {
 		n = regrepeat_hard(scan, n, &l);
-		if (n != 0 && l == 0
-		    /* In fact, this is tricky.  If paren, then the
-		       fact that we did/didnot match may influence
-		       future execution. */
-		    && !(paren && ln == 0))
-		    ln = n;
+		/* if we matched something zero-length we don't need to
+		   backtrack, unless the minimum count is zero and we
+		   are capturing the result - in that case the capture
+		   being defined or not may affect later execution
+		*/
+		if (n != 0 && l == 0 && !(paren && ln == 0))
+		    ln = n;	/* don't backtrack */
 		locinput = PL_reginput;
 		DEBUG_r(
 		    PerlIO_printf(Perl_debug_log,
diff --git a/t/op/re_tests b/t/op/re_tests
index cda8790..1e80f50 100644
--- a/t/op/re_tests
+++ b/t/op/re_tests
@@ -792,3 +792,7 @@ tt+$	xxxtt	y	-	-
 ^(a(??{"(?!)"})|(a)(?{1}))b	ab	y	$2	a	# [ID 20010811.006]
 ab(?i)cd	AbCd	n	-	-	# [ID 20010809.023]
 ab(?i)cd	abCd	y	-	-
+(A|B)*(?(1)(CD)|(CD))	CD	y	$2-$3	-CD
+(A|B)*(?(1)(CD)|(CD))	ABCD	y	$2-$3	CD-
+(A|B)*?(?(1)(CD)|(CD))	CD	y	$2-$3	-CD	# [ID 20010803.016]
+(A|B)*?(?(1)(CD)|(CD))	ABCD	y	$2-$3	CD-
-- 
2.7.4