On 15.10.21 20:11, Jakub Jelinek wrote:
On Fri, Oct 15, 2021 at 08:05:38PM +0200, Thomas Koenig wrote:
with -mabi=ibmlongdouble, I see 31 and 291, while with -mabi=ieeelongdouble
33 and 4931. The 0.0_8 precision/range values are 15 and 307, so neither
precision of C long double if it is double-double nor range matches anything.
If we do implement double-double support, I think KIND=15 would be better
than KIND=17, it is true that double-double has for certain numbers much
higher precision than IEEE quad, but the precision depends on the numbers
and most of the time is smaller, the range is always smaller. And
the PRECISION/RANGE intrinsic numbers are also both smaller.
There is one potential problem: selected_real_kind.
The standard says about that...
# If more than one kind type parameter value meets the criteria, the
# value returned is the one with the smallest decimal precision, unless
# there are several such values, in which case the smallest of these
# kind values is returned
So, selected_real_kind(25) would yield double double, and we would
have to violate the standard there if we wanted people to have
IEEE QP in that case.
That would be true if some kind exist for double double, whether
it is kind == 15 or kind == 17, no?
Correct. The authors probably did not think of this particular
case when they wrote the standard.
We can ask the J3 standards committee to change the wording. I think
I will just do that, to see what they have to say.
Best regards
Thomas
