PHP checksum working need to refactor and make more useful, easier to use, refactor lots of code

src/D2Functions.php

@@ -87,10 +87,14 @@ function setBit(int $n, int $p, bool $b){
 function getBit(int $b, int $p){
     return intval(($b & (1 << $p)) !== 0);
 }
-
-function checksum($fileData) {
+/**
+ * Calculate D2S Checksum
+ * @param $data
+ * @return string
+ */
+function checksum($data) : string {
     $nSignature = 0;
-    foreach($fileData as $byte){            
+    foreach($data as $byte){            
         $nSignature = ((($nSignature << 1) | ($nSignature >> 31)) + $byte) & 0xFFFFFFFF;        
     }
     return swapEndianness(dechex($nSignature));