my $bignum = Math::BigInt->new('9007199254740991');

print $bignum->as_bin(),"\n";

######################################################## 

use bigint;

my $bignum = 9007199254740991;
print $bignum->as_bin(),"\n";

##</code><code>##

0b11111111111111111111111111111111111111111111111111111
0b11111111111111111111111111111111111111111111111111111