(j3.2006) Question about DIM

[Cohen Malcolm]

> I have not only seen DIM used, I have seen a bug report filed against it. 
> The
> user called the function with integer arguments that overflowed when the
> subtraction was done.  The function result was negative because of the
> overflow.  The user claimed that the Fortran standard required the result 
> to be
> nonnegative.

Obviously not.

<<<
I had also thought about potential problems with integers. The current 
wording seems to just ignore that case.
>>>

The same problem arises with non-IEEE reals too.  The current wording does 
not ignore that case either (see below).

<<<
  I suspect that we really intend something like

?If X > Y and X - Y is representable by the type and kind of X, the result 
is X - Y; otherwise the result is zero.?
>>>

Definitely not.  Apart from giving the wrong answer, it would also slow down 
everyone's integer DIM for the sake of giving a value to an erroneous 
calculation.  What a waste.

The "current wording" includes 13.8.1p2 which already covers the situation 
of an out of range result for any intrinsic function, viz "shall not".

Cheers,
-- 
........................Malcolm Cohen, Nihon NAG, Tokyo.