faster expf128

[Paul E Murphy]

On 6/22/20 6:02 AM, Paul Zimmermann wrote:
> I have written some expf128 for x86_64 that is more than 10 times faster than
> the current glibc/libquadmath code [1] (see slide 21 of [2]).

I would highly recommend running the benchmarks against ppc64le or s390x 
before replacing the existing implementation.  I think it would improve 
the code to have more explicit separation between implementations 
optimized for soft and hardfp if performance cannot be rectified.  I 
think much of the float128 support assumes the underlying machine does 
not natively support binary128.

> 
> Before making a proper patch for glibc, I'd like to make sure it fits the
> glibc requirements. In particular, the table size is 16kb. Is that ok?
> If too large, what table size would be ok?

I think that is acceptable.  The current tables for expf128 probably 
aren't much smaller, if I recall correctly.