Dear list.

Over the last couple of days i've been trying out different things with variants, but I always seem to end up in the same situation: When working with conversion between Extended and Variant, a small part of the precision in the Extended is lost.

This would normally not pose an issue, except for the fact that comparing two Extended variables after one was converted to a variant and back, the two numbers are NOT equal. (I've posted a small example at the bottom of the mail).

I did some digging down the FPC code and found that in the TVarData type has not extended type. Although the assignment operator for variants does include a specific extended version, data is copied into a double type.

Not knowing much about the inner working of variants I don't know the reason for this, is it a bug or does the extended type not work inside the TVarData?

I would be glad if someone could give me some feedback on this.

Kind regards,
Torsten Bonde Christiansen.

DOH! Forgot the example:

procedure TForm1.Button1Click(Sender: TObject);
var
  v: variant;
  x, y: extended;
begin
  x := 1.23456789;
  v := x;
  y := v;
  Label1.Caption := BoolToStr(x = y, 'Same', 'Different');
end;

The extended type does not work inside TVarData. Variants were implemented by Microsoft, and they did not include support for extended.

Michael.

In our previous episode, Michael Van Canneyt said:

Note that extended is x86 specific, and windows has been multi-architecture since the early nineties.

Marco van de Voort wrote

Note that extended is x86 specific, and windows has been multi-architecture since the early nineties.

Does this also mean that Extended does not work on MAC PowerPC?

-Torsten.

It compiles, but it is only 64 bits, like a double.

type
   extended = double;
You can check this at compile time by doing
{$IFDEF FPC_HAS_TYPE_EXTENDED}

Vincent

Ok, Thanks for the answer.

-Torsten.