sub dec2bin {
    my $str = unpack("B32", pack("N", shift));
    $str =~ s/^0+(?=\d)//;   # otherwise you'll get leading zeros
    return $str;
}

sub bin2dec {
    return unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
}
print bin2dec("101")," ",bin2dec("111"),"\n";
print dec2bin(5),    " ",dec2bin(7)    ,"\n";

##</code><code>##

5 7
101 111