Article #16731: Bitwise AND evaluates different under Delphi 3

 Question and Answer Database
FAQ1731D.txt Bitwise AND evaluates different under Delphi 3
Category :Object Pascal
Platform :All
Product :Delphi 3.x
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;
7/16/98 4:31:28 PM

Last Modified: 01-SEP-99