procedure SwapVars1(var u, v; Size: Integer);
var
 x: Pointer;
begin
 GetMem(x, Size);
 try
  System.move(u, x^, Size);
  System.move(v, u, Size);
  System.move(x^, v, Size);
 finally
  FreeMem(x);
 end;
end;

procedure SwapVars2(var Source, Dest; Size: Integer);
 // By Mike Heydon, <a href="mailto:mheydon@eoh.co.za">mheydon@eoh.co.za</a>
begin
 asm
  push edi
  push esi
  mov esi,Source
  mov edi,Dest
  mov ecx,Size
  cld
 @1:
  mov al,[edi]
  xchg [esi],al
  inc si
  stosb
  loop @1
  pop esi
  pop edi
 end;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
 SwapVars1(X1, X2, SizeOf(Integer));
end;

var

 X1, X2: Byte;

begin

 X1 := X2 xor X2;

 X2 := X1 xor X2; // X2 = X1

 X1 := X1 xor X2; // X1 = X2