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PowerPC IEEE 128-bit floating point: Meta discussion
- From: Michael Meissner <meissner at linux dot vnet dot ibm dot com>
- To: gcc at gcc dot gnu dot org, dje dot gcc at gmail dot com, amodra at gmail dot com, rguenther at suse dot de, jakub at redhat dot com, segher at kernel dot crashing dot org, bergner at vnet dot ibm dot com, rdsandiford at googlemail dot com, pthaugen at us dot ibm dot com, wschmidt at linux dot vnet dot ibm dot com, Ulrich dot Weigand at de dot ibm dot com, stigge at antcom dot de, vmakarov at redhat dot com, andrewd at gentrack dot com, joseph at codesourcery dot com, sjmunroe at us dot ibm dot com, nathan at codesourcery dot com, paul at codesourcery dot com, jason at redhat dot com, stigge at debian dot org, doko at ubuntu dot com, steven at gcc dot gnu dot org, dominiq at lps dot ens dot fr, acsawdey at linux dot vnet dot ibm dot com, azanella at linux dot vnet dot ibm dot com, meissner at linux dot vnet dot ibm dot com
- Date: Fri, 30 May 2014 15:58:16 -0400
- Subject: PowerPC IEEE 128-bit floating point: Meta discussion
- Authentication-results: sourceware.org; auth=none
I'm sorry for a wide angle shotgun approach, but I wanted to discuss with all
of the stakeholders how to phase in IEEE 128-bit floating point to the PowerPC
toolchain. For those of you who are not on the gcc@gcc.gnu.org mailing list,
this thread will be archived at: https://gcc.gnu.org/ml/gcc/
What I'm going to do is break this into several followups that each cover one
topic, so that it is easier to address issues without having to requote the
whole article.
What I want to do in the GCC 4.10 time frame is add the ability of users to use
IEEE 128-bit extended precision support, with as minimal disruption as possible
to existing code. It is unfortunate that we could not have squeezed the
support in the PowerPC little endian support with Elf v2, so that we would not
have backwards compatibility issues on that platform, but alas it did not
happen.
Before IEEE 128-bit can be fully implemented, we will need to modify the
compiler, libgcc, glibc, the debugger, and possibly other tools as well.
Because different teams work on different schedules, it will likely be some
time before all of the pieces are in place. However, we likely will need to
make sure the compiler piece is in place before work can start on the libraries
and debuggers.
In terms of user impact, I really don't know how many people are using long
double, or want to use IEEE 128-bit floating point. I would hope that if a
user program does not use long double, there is not a flag day where they have
to move to a compiler/library combination for a feature they don't use.
--
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.vnet.ibm.com, phone: +1 (978) 899-4797