fix flawed substitution-loop detection on zero-length matches

	Message-Id: <199807171755.NAA27720@monk.mps.ohio-state.edu>
	Subject: [PATCH 5.004_72] Substitution loop in devel branch

p4raw-id: //depot/perl@1560

2 files changed, 8 insertions, 2 deletions

diff --git a/pp_hot.c b/pp_hot.c
index 3ecb5b3e40..d2a7af53d8 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -1590,7 +1590,9 @@ PP(pp_subst)
 	DIE("panic: do_subst");
 
     strend = s + len;
-    maxiters = (strend - s) + 10;
+    maxiters = 2*(strend - s) + 10;	/* We can match twice at each 
+					   position, once with zero-length,
+					   second time with non-zero. */
 
     if (!rx->prelen && curpm) {
 	pm = curpm;
diff --git a/t/op/subst.t b/t/op/subst.t
index 57a956dda6..2d42eeb386 100755
--- a/t/op/subst.t
+++ b/t/op/subst.t
@@ -6,7 +6,7 @@ BEGIN {
     @INC = '../lib' if -d '../lib';
 }
 
-print "1..70\n";
+print "1..71\n";
 
 $x = 'foo';
 $_ = "x";
@@ -302,3 +302,7 @@ s{  \d+          \b [,.;]? (?{ 'digits' })
 }{$^R}xg;
 print ($_ eq $foo ? "ok 70\n" : "not ok 70\n#'$_'\n#'$foo'\n");
 
+$_ = 'x' x 20; 
+s/\d*|x/<$&>/g; 
+$foo = '<>' . ('<x><>' x 20) ;
+print ($_ eq $foo ? "ok 71\n" : "not ok 71\n#'$_'\n#'$foo'\n");