How to decode PHP file?

Question

PHP

Help solve the following problem, there is a PHP file that contains several hundred such encoded fragments: $_[in____(base64_decode('Yw=='))], respectively, a 2-encoder is used, after exporting the processed code with readable values:

1) function in____
2) base64_decode
Function in____:

function in____($_){
  $__='';
  for($____=0; $____<strlen($_); $____++){
    $___=ord($_[$____]);
    $__.=chr(--$___);
  }
  return $__;
}

The task is to automate the decoding of one large file, in which there are several hundred encoded fragments, how to decide what to do I do not understand from base64 to normal code, I don't know how to implement it in JavaScript.