[fpc-devel] Overflow checks and Trunc/Round functions

Jonas Maebe jonas.maebe at elis.ugent.be
Sat Jun 13 13:47:31 CEST 2009

On 13 Jun 2009, at 13:31, Alexander Klenin wrote:

> Currently, Round and Trunc functions ignore the state of  
> compiler directive. The following code prints "-2 -2":
> var
>  a: Integer;
>  b: Double;
> begin
>  b := MaxInt;
>  a := Round(2.0 * b);
>  Writeln(a);
>  a := Trunc(2.0 * b);
>  Writeln(a);
> end.
> This is Delphi-compatible.
> However, I think this is a bug, even if Delphi-inherited, and should
> be fixed in fpc/objfpc mode.
> What do others think?

In Borland-speak, these are not overflow errors, but range errors.  
Turn on range checking, and you will get an error.

The difference between range and overflow errors is as follows:
* range errors occur when an implicit type conversion occurs from one  
type to another (e.g., when assigning, or when using it as a  
parameter), and the value is not legal for the destination type
* overflow errors occur when performing a mathematical operation on a  
value and the result cannot be represented in the type used for  
performing this operation (this "operation type" depends both on the  
target platform and the types of the operands)


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