PHP sensitive word filtering code

$f = file('words.txt');
$words = array();
foreach ($f as $w) {
    $words[] = preg_quote(trim($w), '/');
}
$text = file_get_contents('text.txt');

$start = microtime(true);
$reg = '/' . implode('|', $words) . '/S';

preg_match_all($reg, $text, $m);

$result = array();
$total = 0;
foreach ($m[0] as $w) {
    if (!isset($result[$w])) {
        $result[$w] = 1;
    } else {
        $result[$w]++;
    }
    $total++;
}
$end = microtime(true);
echo $end - $start, "n";
echo $total, "n";

print_r($result);

PHP