$ perl -del DB<1> x 0+( () = join('','','x'x(1<<30),'') =~ m{}g ) 0 1 DB<2> x 0+( () = join('','','x'x(1<<31),'') =~ m{}g ) 0 0 DB<3> x 0+( () = join('','','x'x((1<<31)-8),'') =~ m{}g ) 0 1 DB<4> x 0+( () = join('','','x'x((1<<31)-7),'') =~ m{}g ) 0 0