mpn_mul is embarrassingly slow

[Niels Möller]

tg at gmplib.org (Torbjörn Granlund) writes:

> More embarrassments.  :-)
>
> I ran some timing tests without my proposed change and with the squqring
> exception code still there.  Please consider the following two
> measurements for doing n x 19 limb (first table) and n x 20 limb
> multiplication.
>
> MUL_TOOM22_THREASHLD is 20 for this machine (compiled in, but also
> measured now).  My comments below.

For n x 20, n pretty large, what strategy does mpn_mul use? I would
expect repeated toom32, but maybe that gives too much overhed. It seems
we don't have any MUL_TOOM32_TO_BASECASE threshold?

Regards,
/Niels

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