Google Sheets - Calculate SUM file size in-between headers

gistfile1.js

//above is inline code from filesize.js

function MODPACK_SIZE(column, targetColumn, name) {
  var sh = SpreadsheetApp.getActiveSheet();
  var data = sh.getDataRange().getValues();
  
  var iStart = -1;
  var iEnd = data.length;
  
  // Find start
  for(n=0; n < data.length; ++n){
    if(data[n][column].toString().match(name)==name) {
      iStart = n + 1;
      break;
    }
  }
  
  // Find end
  for(n=iStart; n < data.length; ++n){
    if(data[n][column].toString().match('@')=='@') {
      iEnd = n - 1;
      break;
    }
  }
  
  if (iEnd === data.length) {
    iEnd = data.length - 1;
  };
  
  var totalSize = 0; //bytes
  
  // Parse in-between
  if (iStart >= 0) {
    
    var ret = '';
    
    for(n=iStart; n < iEnd + 1; ++n){
      var exp = data[n][targetColumn].toString().split(' ');
      
      var val = Number(exp[0]);
      var type = exp[1];
      
      switch (type) {
        case "KB":
          totalSize += (val * 1000);
          break;
        case "MB":
          totalSize += (val * 1000000);
          break;
        case "GB":
          totalSize += (val * 1000000000);
          break;
      }
    }
    
    return filesize(totalSize, {base: 10});
  }
  
  return 'Failed: ' + name;
}