squaring vs multiply

[Zimmermann Paul]

       Hi Torbjörn,

> A significant fraction of the point-wise products' time will be spent in
> mpn_mul_basecase/mpn_sqr_basecase.  The time ration for those is close
> to 1/2.  This ratio seems to be reflected in toom functions.

this is a very good point. As a consequence, we should have S/M = 2/3
asymptotically, whatever the kind of FFT algorithm used (i.e., with
negligible or non-negligible pointwise products).

Paul