Rob@desktop ~/pscrpt
$ cat try.pl

use warnings;

$x = 2 ** 54 + 123; # 18014398509482107
$y = 2 ** 54 + 125; # 18014398509482109

if($x + 2 == $y) {print "fine\n"}
else {print "crap\n"}

if($x == $y) {print "crap\n"}
else {print "fine\n"}


Rob@desktop ~/pscrpt
$ perl try.pl
crap
crap