Re: [PATCH], PowerPC IEEE 128-bit fp, patch #10 (comparison, documentation, conversion, debug)

[Joseph Myers <joseph at codesourcery dot com>]

On Tue, 29 Dec 2015, Michael Meissner wrote:

> Going forward, patch #11 will enable the software emulation library.  At the
> moment, there is no support for converting between decimal types and
> __float128, nor for the complex __float128 support.  These are being worked on,
> and should be done in the GCC 7.x time frame.  However, it is important to add
> the software emulation support in GCC 6.x so that most users that want to use
> IEEE 128-bit floating point can use it, and that we can work on the glibc
> issues to fully support __float128 in the GCC 7.x time frame.

While of course glibc issues can be worked on in the GCC 7.x time frame 
even in the absence of a GCC release with the required support (and 
functions could be added to glibc e.g. for x86_64 where the GCC support 
already exists), to be clear, as the glibc ABI can't depend on the GCC 
version used to build glibc, it won't be possible to add any __float128 
functions to glibc for powerpc until there is glibc community consensus 
that we can require GCC 7.x (or whatever version has all the required 
features, which certainly include complex __float128 support) as the 
minimum version for building glibc for powerpc64 (and the symbol version 
for any new functions will be that of the first glibc release including 
them, as usual).  That may not be for a few years.

(I exclude the idea of adding real functions to glibc before complex 
functions as unlikely to get consensus, although there's certainly a lot 
of careful design and consensus-building work to determine the precise set 
of functions that makes logical sense, especially as regards float128 
equivalents of glibc functions outside ISO C, or ISO C functions where TS 
18661-3 nevertheless doesn't include *f128 functions - and to resolve a 
great many other tricky design issues.)

-- 
Joseph S. Myers
joseph@codesourcery.com