function GetCheckSum(FileName: string): DWORD;
var
 F: file of DWORD;
 P: Pointer;
 Fsize: DWORD;
 Buffer: array[0..500] of DWORD;
begin
 FileMode := 0;
 AssignFile(F, FileName);
 Reset(F);
 Seek(F, FileSize(F) div 2);
 Fsize := FileSize(F) - 1 - FilePos(F);
 if Fsize > 500 then
 Fsize := 500;
 BlockRead(F, Buffer, Fsize);
 Close(F);
 P := @Buffer;
 asm
 xor eax, eax
 xor ecx, ecx
 mov edi , p
 @again:
 add eax, [edi + 4*ecx]
 inc ecx
 cmp ecx, fsize
 jl @again
 mov @result, eax
 end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
 ShowMessage(IntToStr(GetCheckSum('c:\Autoexec.bat')));
end;