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[Bug ports/2749] powerpc32 does not build --without-fp
- From: "joseph at codesourcery dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: 15 Sep 2006 21:28:23 -0000
- Subject: [Bug ports/2749] powerpc32 does not build --without-fp
- References: <20060609223502.2749.sjmunroe@us.ibm.com>
- Reply-to: sourceware-bugzilla at sourceware dot org
------- Additional Comments From joseph at codesourcery dot com 2006-09-15 21:28 -------
Subject: Re: powerpc32 does not build --without-fp
On Fri, 15 Sep 2006, jakub at redhat dot com wrote:
> glibc on many arches doesn't have a standard conforming fma(3) - for float
Yes - that's what the Debian bug report I mentioned is about. A new bug
report should probably be opened in glibc Bugzilla for this issue.
> just using double multiplication and addition should be good enough, but
The standard says the result is rounded once, so double rounding isn't
correct, but still a lot better than what we have right now.
> especially for long double the current implementation is wrong. So, if there was
> a soft-fp FMA that could be used on all the targets that can't do this in
> hardware, it would be great.
To do it for long double you'd need to add more operations to op-8.h (and
invent an oct-float type), since you need an intermediate type with twice
the precision. Also you'd need to add appropriate packing/unpacking for
IBM long double (which soft-fp doesn't natively support).
We do have various sfp-machine.h files for targets not currently using
soft-fp sitting around and ready to use as part of using soft-fp for
generic fma (on all targets without fma instructions).
Now, we have the immediate problem that soft-fp patches are very hard to
get into glibc (I have one unreviewed from June, bug 2831) and the same
applies to other generic fixes to mathematical functions (bug 2592,
likewise fix waiting since June) - and the glibc patches attached to this
bug report have also mostly been ready for some time to go in as a clear
improvement on the present state of affairs (with any subsequent fixes
likely to be comparatively small and confined to either soft-fp or ports).
So while I've considered generically fixing fma in glibc and adding
appropriate testcases, I wouldn't be confident of such fixes actually
getting anywhere.
--
http://sourceware.org/bugzilla/show_bug.cgi?id=2749
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