Calculate Checksum from PE Executables

uses ImageHlp

function ComputePEChecksum(FileName: string): DWORD;
var
  h, hMap: Cardinal;
  pMem: Pointer;
  headersum, checksum, fsizehigh, fsizelow: DWORD;
  nth: PImageNtHeaders;
Label
  cleanup;
begin
  pMem := nil;

  Result := 0;

  headersum := 0;
  checksum  := 0;

  h := Windows.CreateFile(PChar(FileName), GENERIC_READ, FILE_SHARE_READ,
    nil, OPEN_EXISTING, 0, 0);
  if (h = INVALID_HANDLE_VALUE) then
    Exit;

  fsizelow := Windows.GetFileSize(h, Pointer(@fsizehigh));

  hMap := Windows.CreateFileMapping(h, nil, PAGE_READONLY, fsizeHigh, fsizeLow, nil);
  if (hMap = 0) then
    goto cleanup;

  pMem := Windows.MapViewOfFile(hMap, FILE_MAP_READ, 0, 0, 0);
  if (pMem = nil) then
    goto cleanup;

  nth := CheckSumMappedFile(pMem, fsizeLow, @headersum, @checksum);

  if (nth = nil) then
    checksum := 0;

  cleanup:
  if (pMem <> nil) then
    Windows.UnmapViewOfFile(pMem);
  if (hMap <> 0) then
    Windows.CloseHandle(hMap);
  if (h <> 0) then
    Windows.CloseHandle(h);

  Result := checksum;
end;

Beispiel :

procedure TForm1.Button1Click(Sender: TObject);
var
  x1, x2: DWORD;
begin
  if OpenDialog1.Execute then
  x1 := ComputePEChecksum(OpenDialog1.FileName); // original filename
  // original filename but has a string in it lightly modified
    Label1.Caption :=  FloatToStr(x1);
  //WriteLn('Checksum 1: ', x1, #13#10'Checksum 2: ', x2);
end;