Anomaly in mpn_sqrtrem and mpn_rottrem

[Niels Möller]

tg at gmplib.org (Torbjörn Granlund) writes:

> Surely, we could make mpn_rootrem run faster, in particular for small
> arguments.  But also for large arguments, 2x slowdown seems like a lot.

I've had a quick look. Both mpn_dc_sqrtrem and mpn_rootrem_internal
(which seem to be the work horses for larger operands) do a division in
the loop. The latter is organized as a newton iteration, the former
isn't (but I guess the computation is more or less equivalent to a
Newton iteration).

The code is a bit too complex for me to really compare them...

For larger operands, I imagine a rewrite to use a division-free
Newton-iteration for an approximation of the inverse root would be
faster.

Regards,
/Niels

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