Hi,

I'm using the following code:

function mycalc( num1,num2: real):integer;
begin
  Result:=trunc(num1*num2);
end;

How can I protect from the product of the two numbers being too big?

If it's too big I want to discard it anyway.

function mycalc( num1,num2: real):integer;
 begin
   Result:=trunc(num1*num2);
  if result > maxint then result := 0;
 end;

Would this do what you want?

Howard Page-Clark

Yes, great, thanks.

Would there be any error or would Lazarus just continue as if nothing had happened?

2009/2/14 Howard Page-Clark :

Actually the code I fired off is useless - since result is an integer it is never going to be more than maxint! What you need is

function mycalc( num1,num2: real):integer;
var tmp: int64;
 begin
   tmp :=trunc(num1*num2);
   if (tmp <= maxint) then
    result := tmp
  else result := 0;
 end;

Errors will only be flagged up if you compile with -Co or tick the appropriate overflow check box in the compiler options dialog, Code tab, "Checks" panel.

----
Howard Page-Clark

My application is to use first REAL arithmetic :

Var V : Extended  ;
 or
Var V : Real ;
or
Var V : Double ;

...

  V := num1 ;
  V := V * num2 ;

If ( V < Your_Maximum_Allowed_Value )
Then Result := trunc ( num1 * num2 )
Else Message ... about overflow ...

If you compare run1 * run2 directly maxint ,
multiplication may give overflow when result of multiplication is theoretically large than maxint .

Thank you very much .

Mehmet Erol Sanliturk

Thanks Howard.

If the result is never going to be more than maxint anyway, then I don't have to do anything at all, that will be perfectly acceptable to me as it would already be beyond what is usable.

What would screw me up would be if I just lose the topmost bit and it all resets to zero again.

2009/2/14 Howard Page-Clark :