bignum's oct function does not perform a conversion if its argument
doesn't start with '0'.
$ perl -e 'print oct(100)," ",hex(100),"\n"'
64 256
$ perl -Mbignum -e 'print oct(100)," ",hex(100),"\n"'
100 256
$ perl -Mbignum -e 'print oct("0100")," ",hex(100),"\n"'
64 256