How to filter out characters that are not UTF8 in PHP (code)

function utf8_filter($data) { $str = ""; for($n = 0; $n < strlen($data);) { $s = substr($data, $n, 1); $v = ord($s); if($v >= 127) { ++$n; $cnt = 0; $tmp = $v; while($tmp & 0x80) { $tmp = $tmp << 1; ++$cnt; } $x = 0; while($x < $cnt && $n < strlen($data)) { $s = substr($data, $n, 1); if((ord($s) & 0xC0) == 0x80) { ++$n; ++$x; }else{ break; } } if($x + 1 == $cnt) { $str = $str . substr($data, $n - $cnt, $cnt); }else{ while($n < strlen($data)) { $s = substr($data, $n, 1); if(ord($s) & 0x80) { ++$n; }else{ break; } } } }else{ $str = $str. $s; ++$n; } } return $str; }