function BSearch($x, $t) {
    if (!is_array($x)) return -1;
    $n = sizeof($x);
    $l = -1;
    $u = $n;
    $p = 0;
    $m = 0;
 
    while ($l + 1 != $u) {
        $m = ceil(($l + $u) / 2);
 
        if ($x[$m] <  $t) {
            $l = $m;
        } else {
            $u = $m;
        }
    }
 
    $p = $u;
    if ($p >= $n || $x[$p] != $t) {
        $p = -1;
    }
    return $p;
}