mpn_sqrtrem{1,2} - rounding mode

[Adrien Prost-Boucle]

> Il Ven, 24 Marzo 2017 11:54 pm, Adrien Prost-Boucle ha scritto:
> > This page, at the end, tends to discourage playing with rounding mode too
> > frequently:
> > https://www.gnu.org/software/libc/manual/html_node/Rounding.html
> 
> This page is about writing portable code using libc, here we have a quite
> specific hardware: CPUs supporting SSE/SSE2.

Yes, this needs some benchmarking.
I tested with a function that repeatedly sets all rounding modes.
The result is: 995413 calls to fesetround() per second on my laptop
That's extremely slow given the speed of the sqrt function!

So, I think that for these floating-point investigations,
we have to keep rounding mode set by the user (or default),
and do all necessary corrections to work under any rounding mode.

Adrien