PHP Ascii编码转换

/**
 * ascii 转换
 * @param $c
 * @param string $prefix
 * @return string
 */
function ascii_encode($c, $prefix="&#") {
    $len = strlen($c);
    $a = 0;
    while ($a < $len) {
        $ud = 0;
        if (ord($c{$a}) >= 0 && ord($c{$a}) <= 127) {
            $ud = ord($c{$a});
            $a += 1;
        } else if (ord($c{$a}) >= 192 && ord($c{$a}) <= 223) {
            $ud = (ord($c{$a}) - 192) * 64 + (ord($c{$a + 1}) - 128);
            $a += 2;
        } else if (ord($c{$a}) >= 224 && ord($c{$a}) <= 239) {
            $ud = (ord($c{$a}) - 224) * 4096 + (ord($c{$a + 1}) - 128) * 64 + (ord($c{$a + 2}) - 128);
            $a += 3;
        } else if (ord($c{$a}) >= 240 && ord($c{$a}) <= 247) {
            $ud = (ord($c{$a}) - 240) * 262144 + (ord($c{$a + 1}) - 128) * 4096 + (ord($c{$a + 2}) - 128) * 64 + (ord($c{$a + 3}) - 128);
            $a += 4;
        } else if (ord($c{$a}) >= 248 && ord($c{$a}) <= 251) {
            $ud = (ord($c{$a}) - 248) * 16777216 + (ord($c{$a + 1}) - 128) * 262144 + (ord($c{$a + 2}) - 128) * 4096 + (ord($c{$a + 3}) - 128) * 64 + (ord($c{$a + 4}) - 128);
            $a += 5;
        } else if (ord($c{$a}) >= 252 && ord($c{$a}) <= 253) {
            $ud = (ord($c{$a}) - 252) * 1073741824 + (ord($c{$a + 1}) - 128) * 16777216 + (ord($c{$a + 2}) - 128) * 262144 + (ord($c{$a + 3}) - 128) * 4096 + (ord($c{$a + 4}) - 128) * 64 + (ord($c{$a + 5}) - 128);
            $a += 6;
        } else if (ord($c{$a}) >= 254 && ord($c{$a}) <= 255) { //error
            $ud = false;
        }
        $scill .= $prefix.$ud.";";
    }
    return $scill;
}



 /**
     * 将ascii码转为字符串
     * @param type $str  要解码的字符串
     * @param type $prefix  前缀,默认:&#
     * @return type
     */
    function decode($str, $prefix="&#") {
        $str = str_replace($prefix, "", $str);
        $a = explode(";", $str);
        foreach ($a as $dec) {
            if ($dec < 128) {
                $utf .= chr($dec);
            } else if ($dec < 2048) {
                $utf .= chr(192 + (($dec - ($dec % 64)) / 64));
                $utf .= chr(128 + ($dec % 64));
            } else {
                $utf .= chr(224 + (($dec - ($dec % 4096)) / 4096));
                $utf .= chr(128 + ((($dec % 4096) - ($dec % 64)) / 64));
                $utf .= chr(128 + ($dec % 64));
            }
        }
        return $utf;
    }

ascii_encode("www.blyoo.com")