(j3.2006) Question about DIM
Bill Long
longb
Tue Jan 12 09:35:06 EST 2016
On Jan 12, 2016, at 12:25 AM, Robert Corbett <robert.corbett at oracle.com> wrote:
> On 01/11/16 05:49, Bill Long wrote:
>> Perhaps a more interesting question is whether this relic is actually used? I can?t remember ever seeing it, though with only 48 years of Fortran programming experience, I?m a relative newcomer. :)
>>
>> If there was any motivation to update DIM, more interesting questions would be
>>
>> 1) If X-Y is -0.0, is the result 0.0 or -0.0?
>>
>> 2) If X-Y is NaN, what is the result?
>
> 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.
I had also thought about potential problems with integers. The current wording seems to just ignore that case. 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.?
Not exactly what we say now.
>
> I wrote my first Fortran program for a DEC PDP-8s in the summer of 1967. I
Mine was an IBM 1130 in the summer of 1968. (NSF Summer Science program for high school students. I wonder of they still have that.)
Cheers,
Bill
> understand that that makes me a latecomer to Fortran relative to some on the
> committee.
>
> Bob Corbett
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Bill Long longb at cray.com
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