New n log n algorithm for high-precision multiplication

[paul zimmermann]

       Dear Niels,

> There's also unfinished work on small-prime FFT, motivated mainly to get
> better cache locality (for huge numbers, field elements in
> Schönhage-Strassen get so large that they exceed the L1 cache, slowing
> down the supposedly very efficient field operations).

Schönhage-Strassen can be implemented with good cache locality:

https://hal.inria.fr/inria-00126462

Paul