for my $i (0 .. length($str1)) {
	if (substr($str1, $i, 1) ne substr($str2, $i, 1)) {
		$val++;
	}
}

##</code><code>##

my $step = 5;
my $bound = int (length($str1) / $step);

for my $i (0 .. $bound) {
	if (substr($str1, ($i * $step), $step) ne (substr($str2, ($i * $step), $step)) {
		$val++;
	}
}

##</code><code>##

for my $i (0 .. $bound) {
	my $substr1 = substr($str1, ($i * $step), $step);
	my $substr2 = substr($str2, ($i * $step), $step);
	if ($substr1 ne $substr2) {
		for my $j (0 .. ($step - 1)) {
			if (substr($substr1, $j, 1) ne
			    substr($substr2, $j, 1)) {
				$val++;
			}
		}
	}
}