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Frequently Asked Questions

Bitwise AND evaluates different under Delphi 3

Question:

Under Delphi 3 (all versions), on some occasions, bitwise arithmetic using "AND" against integers does not always render the same results as Delphi 2. How can I get around this?

Answer:

This is a known problem, where in certain circumstances, the

compiler produces a sign extended negative result in a bitwise 

"AND" operation. The solution is to compare the result against 

zero, instead of comparing the result as being greater than 

zero. The following example demonstrates both the problem and 

the solution.



procedure TForm1.Button1Click(Sender: TObject);

var

  IntVal : Integer;

begin

  IntVal := 128 + 1;

  if (IntVal and 128) > 0 then

    ShowMessage('This never executes!');

end;



procedure TForm1.Button2Click(Sender: TObject);

var

  IntVal : Integer;

begin

  IntVal := 128 + 1;

  if (IntVal and 128) <> 0 then

    ShowMessage('This is correct!');

end;

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