Mine

use integer;

my $n1 = "758475567567567834";
my $n2 = "5676757345657438";
print "$n1*$n2=",mul($n1,$n2),"\n";

sub mul($$) {
    my ($x,$y) = @_;
    my @a = reverse split(//,$x);
    my @b = reverse split(//,$y);
    my @c;
    for (my $i=0;$i<@a;$i++) {
	for (my $j=0;$j<@b;$j++) {
	    my $carry = $a[$i]*$b[$j];
	    for (my $k = $i+$j;$carry;$k++) {
		$c[$k] += $carry;
		$carry = $c[$k]/10;
		$c[$k] -= $carry*10;
	    }
	}
    }
    return join("",reverse @c);
}