# multiplication algorithm to convert decimal number to binary
our @dec2bin1 = qw(0 1 10 11 100 101 110 111 1000 1001);
sub dec2bin {
        $_[0]=~/^(-?)(\d*)/;
        my($sgn, $dec) = ($1, $2);
        $dec=~/(\d)/g;
        my $b = $dec2bin1[$1];
        while($dec=~/(\d)/g) {
                $b = addbin($b . "0", $b . "000"); # multiply by 1010b
                $b = addbin($b, $dec2bin1[$1]);
        }
        $sgn . $b;
}