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Re: The state of glibc libm

On Wed, 14 Mar 2012, Marc Glisse wrote:

> On Wed, 14 Mar 2012, Joseph S. Myers wrote:
> > I'd say that "better performance with the potential loss of accuracy"
> > should be covered by -ffast-math - that GCC should generate direct use of
> > fsin/fcos instructions for sin/cos for -O2 -funsafe-math-optimizations on
> > x86_64, as it does on x86, unless there is some reason to think they would
> > perform worse than the out-of-line implementation.
> Last time I did some timings (maybe 4 years ago), for double, fsin was slower
> than the libm software implementation compiled for x87, which was itself
> slower than the same implementation compiled for sse. And the software
> implementation was more precise than fsin. My conclusion was to ignore fsin
> from then on.

Interesting - hopefully that means the glibc changes Andreas Jaeger and I 
have been working on to stop using fsin etc. (in the interests of accuracy 
and fixing the sincos issues discussed lately) won't actually make 
performance worse.

Joseph S. Myers

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