Re: [power-ieee128] OPEN CONV

[Thomas Koenig <tkoenig@netcologne.de>]

On 07.01.22 22:48, Jakub Jelinek wrote:
> On Fri, Jan 07, 2022 at 10:40:50PM +0100, Thomas Koenig wrote:
>> One thing that one has to watch out for is a big-endian IBM long double
>> file, so the byte swapping will have to be done before assigning
>> the value.
> 
> I've tried to handle that right, i.e. on unformatted read with
> byte-swapping and r16 <-> r17 conversions first do byte-swapping
> and then r16 <-> r17 conversions, while for unformatted writes
> first r16 <-> r17 conversions and then byte-swapping.

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.

Old programs should continue to run with the new library, so
the absence of a call to _gfortran_set_convert, or a call
which sets byte swapping, should have the old meaning, i.e
IBM long double. A program which uses IEEE long double should
then call _gfortran_set_convert with a suitable argument to
let the library know what to do, just in case.

I think this is what I will start working on.

Best regards

	Thomas