php emoji怎么转为文字

function utf16_to_entities(){
    $content = mb_convert_encoding($content, 'utf-16');
    $bin = bin2hex($content);
    $arr = str_split($bin, 4);
    $l = count($arr);
    $str = '';
    for ($n = 0; $n < $l; $n++) {
        if (isset($arr[$n + 1]) && (&#39;0x&#39; . $arr[$n] >= 0xd800 && &#39;0x&#39; . $arr[$n] <= 0xdbff && &#39;0x&#39; . $arr[$n + 1] >= 0xdc00 && &#39;0x&#39; . $arr[$n + 1] <= 0xdfff)) {
            $H = &#39;0x&#39; . $arr[$n];
            $L = &#39;0x&#39; . $arr[$n + 1];
            $code = ($H - 0xD800) * 0x400 + 0x10000 + $L - 0xDC00;
            $str.= &#39;&#&#39; . $code . &#39;;&#39;;
            $n++;
        } else {
            $str.=mb_convert_encoding(hex2bin($arr[$n]),&#39;utf-8&#39;,&#39;utf-16&#39;);
        }
    }
    return $str;
}