Hi! On Mon, Oct 04, 2021 at 04:14:10PM +0200, Jakub Jelinek wrote: > Based on some IRC discussion, yet another option would be bump libgfortran > SONAME (on all arches), make real(kind=16) on powerpc64le-linux mean > always IEEE quad (starting with GCC 12) and if wanted add support for > real(kind=15) meaning double double. > libgfortran would then on powerpc64le-linux use -mabi=ieeelongdouble to make > sure that regardless of the long double choice for C/C++ (whether default > configure time selection or explicit -mabi=*) GFC_REAL_16 is the __float128 > long double. > One problem with that is that I think IEEE quad long double support relies > on glibc 2.32 or later, so not sure what exactly would be done if gcc is > built against older glibc when it needs to call libm routines. Perhaps > convert to __ibm128, call the __ibm128 sinl etc. and convert back (big loss > of precision and range, but at least something).
Eventually we should get a world where kind=16 is IEEE QP float everywhere, and kind=17 (or whatever) is double-double. Some current Power GCC targets support neither. Some support only double-double. Making IEEE QP float work on those (that is, those that are < power8) will require some work still: it should use libquadmath or similar, but that needs to be put into the ABIs, to define how parameter passing works for those types. Just treating it like a struct or an array of ints will work fine, but it needs to be written down. This is more than just Fortran. Mike? Segher
