Delphi - Detect Int64 Overflow Error

Question

In Delphi how can I detect overflow errors for Int64?

For Integers we could do:

type
MyInt = Integer; //Int64

function TryMaxTimes10(out Res: MyInt): boolean;
var
  a, b: MyInt;
begin
  {$Q+}
  try
    a := High(MyInt);
    b := 10;
    Res := a * b; //REF1
    Result := True; 
  except
    Result := False;
  end;
  {$Q-}
end;

For MyInt = Integer, line REF1 gives an exception and so TryMaxTimes10 returns false.

But if we change MyInt to MyInt = Int64, then REF1 does not give an exception and TryMaxTimes10 returns true!

I understand that the help for {$Q+} does not specifically mention Int64: ... {$Q+} state, certain integer arithmetic operations ... are checked for overflow.

QUESTION: So my question is, how can we detect overflow errors for Int64?

(I'm using Delphi 7. Does the same thing happen in newer versions of Delphi?)

Answer 1

This is a known issue. See http://qc.embarcadero.com/wc/qcmain.aspx?d=10185, and the comments Andy wrote at the bottom.

My suggestion would be to create a function (I did not compile nor test this - just an example):

function Foo(A, B : Int64) : Int64;
var bNeg : boolean;
begin
  // Do we expect a negative result?
  bNeg := ((a < 0) xor (b < 0));
  // Get the real result
  Result := a * b;
  // If the result is wrong, raise an error
  if ((Result < 0) xor bNeg) then begin
    // Raise EOverFlow
  end;
end;