Anomaly in mpn_sqrtrem and mpn_rootrem
nisse at lysator.liu.se
Thu Jul 9 08:00:39 UTC 2015
tg at gmplib.org (Torbjörn Granlund) writes:
> nisse at lysator.liu.se (Niels Möller) writes:
> There are divisions also in the newton iteration, right? Then a single
> division in the computation of the initial value is likely a win, if it
> saves two or more iterations in the loop.
> There are GMP division operations, but these are not likely going to hit
> any hardware division.
They're doing an expensive preinv per iteration, IIRC. So a preinv (or
even plain division) involving k should pay off, if it saves a few
> Surely the most important k is 3 (assuming 2 is always handled by the
> sqrt code).
Elaborate? Are you thinking of any particular algorithm using cube
roots, or just the general observation that smaller numbers tend to be
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