Re: [power-ieee128] OPEN CONV

[Jakub Jelinek <jakub@redhat.com>]

On Sat, Jan 08, 2022 at 11:07:24AM +0100, Thomas Koenig wrote:
> I have tried to unravel the different cases here, I count six
> (lumping together the environment variables, the CONVERT specifier
> and -fconvert, and leaving out the byte swapping)
> 
> Compiler    Convert   Read action     Write action
> 
> IEEE        None      None            None
> IEEE        IEEE      None            None
> IEEE        IBM       IBM->IEEE       IEEE->IBM
> 
> IBM         None      None            None
> IBM         IEEE      IEEE->IBM       IBM->IEEE
> IBM         IBM       None            None
> 
> From this table, it is clear that the compiler has to inform
> the library about the option it is using, I think it is best
> encoded in the number passed to _gfortran_set_convert.

Whether the compiler is using IEEE or IBM real(kind=16) or
complex(kind=16) for a particular spot (which doesn't have to be
the same in the whole program) is known to the library by the
kind argument it provides to the I/O routines, if it is kind=16,
it is IBM, if it is kind=17, it is IEEE.
See the patch I've posted, which does one thing when the runtime
kind (i.e. abi_kind on the compiler side) is 17 and convert
says r16_ibm, and another thing when runtime kind is 16 and
convert says r16_ieee.  Other cases shouldn't need conversion.
And IMHO the default like for byte-swapping should be the native
format, i.e. the one the program actually used.
The only thing that should be encoded in _gfortran_set_convert
is -fconvertWHATEVER command line option IMO.

	Jakub