Where $begtagidx is out to 4 billion and have not seen problem.

Okay. It seems that limitation has been lifted with 5.16 (I still use 5.10.1 as my primary Perl where it is the case):

say $];;
5.016001

$s = 'fred'; $s x= 1024**3;;

print substr( $s, -4 );;
fred
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But the 2GB limit on regex still persists in 5.16:

[19:51:25.70] C:\test>\perl64-16\bin\perl \perl64\bin\p1.pl
[0] Perl> say $];;
5.016001
[0] Perl> $s = 'fred'; $s x= 1024**3;;
[0] Perl> ++$n while $s =~ /fred/g; say $n;;
Use of uninitialized value $n in say at (eval 9) line 1, <STDIN> line 
+3.

[0] Perl> $s = 'fr'; $s x= 1024**3;;
[0] Perl> ++$n while $s =~ /fr/g; say $n;;
Use of uninitialized value $n in say at (eval 11) line 1, <STDIN> line
+ 5.

[0] Perl> $s = 'fr'; $s x= 1020**3;;
[0] Perl> ++$n while $s =~ /fr/g; say $n;;
1061208000
[0] Perl>
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