Hi Michael,
It adds target hooks so the back end can overwrite the kind number for types.
I made the IBM long double type use KIND=15 instead of KIND=16, and Float128
uses KIND=16 as we've discussed. The tests for long double are still
failing, so I suspect we will need some way of signalling about the long double
which uses a funky kind (king=15).
There is still no conclusion how to deal with the two 16-bit types. I
have also asked on the J3 mailing list, and received a few different
opinions and options as well.
We can:
- Support KIND=16 == IEEE_QP only in the compiler, and supply a CONVERT
option from IBM_QP to IEEE_QP only. People who would need the old
format (why anybody would do that, I have no idea, but some may)
would have to use the old compiler.
- Support KIND=16 == IEEE_QP and KIND=15 = IBM_QP in the compiler, and
implement SELECTED_REAL_KIND according to the Fortran standard. This
would mean that people who put in a precision of 20 digits as a
shorthand for REAL(KIND=16) will get the old version. This will
lead to endless confusion, and penalize people who used
SELECTED_REAL_KIND, so it should be avoided.
- Support KIND=16 == IEEE_QP and KIND=15 = IBM_QP in the compiler, and
have SELECTED_REAL_KIND return 16 for anything above double precision.
This would actually violate the Fortran standard, and has been
generally viewed by J3 as not a good idea. It would, however, work
well for most users. Those who actually need IBM_QP would have to
specify it specifically.
- Have a compiler switch which selects between IEEE_QP and IBM_QP.
This was a suggestion by Steve Lionel formerly of DEC and Intel,
and they did that when they had a few floating point formats on
the Alpha to choose from. We would then have to specially annotate
the KIND=16 library routines, and also maybe indicate the different
argument types in module files. Anything else would be user error.
They also had the CONVERT options to go with it.
Question: Which option would we want to pursue? I actually think the
fourth one (the suggestion by Steve Lionel) is the best one.
Other opinions?
Best regards
Thomas
