DELPHI - How get greatest common divisor (for two digits)

The function returns greatest common divisor for two digits. When it does not found it, returns 1.

function GCD( _iNumber1, _iNumber2 : integer ) : integer;
var
  iTemp : integer;
begin
  if _iNumber1 < 0 then _iNumber1 := -_iNumber1;
  if _iNumber2 < 0 then _iNumber2 := -_iNumber2;

  repeat

    if _iNumber1 < _iNumber2 then
      begin
        iTemp := _iNumber1;
        _iNumber1 := _iNumber2;
        _iNumber2 := iTemp;
      end;

    _iNumber1 := _iNumber1 mod _iNumber2;

  until ( _iNumber1 = 0 );

  result := _iNumber2;
end;

Calling:

var
  i : integer;
begin
  i := GCD( 12, 16 );

  ShowMessage( IntToStr( i ) );
end;

Output: