How to base64 encode php in this format

Question

Can someone please guide me on how to  base64 encode PHP by base64 decode below? 

function fn_one($a){$c='';for ($i=0;$i < strlen($a);$i++) {$b=ord($a[$i]);$c.=chr(--$b);}return $c;}$decode=call_user_func("base64_decode",call_user_func("fn_one","cnGu[R>>"));echo $decode; // Deconde "cnGu[R>>" to "name"

In PHP, the content is encoded as "cnGu[R>>" with the decoding code as below, the output after base64 decoding is "name". 

$encode=call_user_func("base64_encode",call_user_func("fn_one",$decode));echo $encode;// Encode "name" to "cnGu[R>>"

How do I base64 encode "name" in reverse in the format below which results in "name" as "cnGu[R>>"?