testing checksum

test.php

@@ -17,12 +17,44 @@ require_once './src/D2DocGenerator.php';
 define('DB_FILE', "ironman-dev.db");
 PDO_Connect("sqlite:" . DB_FILE);
 
-$fp = fopen("x", "rb+");
+$filename = "D:\Diablo II\MODS\ironman-dev\save\Test.d2s";
+$fp = fopen($filename, "rb+");
+$filesize = filesize($filename);
+$pucData = unpack("C*",file_get_contents($filename));
+
+ // ddump($pucData);
 
 
-fseek($fp, 0);
-$y = fread($fp, 1);
+// ddump(fseek($fp, 1));
+ 
+// pucData - pointer to the byte stream of the .d2s file
+// iSize - number of bytes in the stream ( filesize )
+function checksum($fp, $pucData, $iSize){
+    // delete old checksum at offset 0x0C - byte 12
+    fseek($fp, 12);
+    // (I) unsigned integer (machine dependent size and byte order)
+    fwrite($fp, pack('I', 0)); // produces 4 bytes 
+    
+    $uiCS = 0b00000000000000000000000000000000; 
+    
+    // this is the whole checksum calculation
+    for ($j = 1; $j <= $iSize; ++$j ){
+        $uiCS = (($uiCS << 1)|( $uiCS >> 31)) + decbin($pucData[$j]);
+        // dump(decbin($pucData[$j]));
+    }
+    
+    
+    dump(decbin($uiCS));
+    
+    //fseek($fp, 12);
+    //fwrite($fp, pack('I', $uiCS));     
+}
+
+fseek($fp, 347);
+fwrite($fp, pack('C', 0xFD));
+fseek($fp, 348);
+fwrite($fp, pack('C', 0x9F));
+
+checksum($fp, $pucData, $filesize);
 
-fseek($fp, 4);
-fwrite($fp, "__");
 fclose($fp);