Re: Do not define -mlong-double-128 on ppc when --without-fp specified?

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Wed, 15 Mar 2006, Roland McGrath wrote:

> Sorry, it's going to be broken until someone volunteers to fill in the
> missing pieces.  We do not want to have different glibc ABIs for different
> powerpc configurations.

Note that the function-call ABI for soft-float and hard-float PowerPC is 
in any case incompatible, you can't mix soft-float binaries with 
hard-float libc or vice versa.

> The glibc ABI for powerpc will use IBM extended
> format for long double from now on, regardless of the particular hardware
> constraints you are configuring for.  To restore working support for
> --without-fpu powerpc configurations, GCC needs to be made to support it.
> This will require writing the soft-fp support for IBM extended format that
> GCC will generate calls to.  

Rather than trying to fit support for a fundamentally non-IEEE 
floating-point format into an IEEE software floating point library, I 
think it would be simpler and more compatible with the hard-float case to 
use the existing IBM long double support in libgcc (darwin-ldouble.c) 
(falling back to soft-fp operations on double) for +-*/, plus simple 
functions for the cases the .md file can expand directly (conversions, 
negation, comparison).  Then, the only soft-fp support you need to add is 
for fused multiply-add.

-- 
Joseph S. Myers
joseph@codesourcery.com