[curves] Balancing reduced-radix and full-radix performance for extra-strength primes

[Watson Ladd]

So I remember a while ago we had a list of high performance primes. I
don't remember 2^379-19 being on it, but can check to see if there are
obviously dominated choices.

But it seems that any prime with exponent between 352 and 384 will
have the same full-width performance. (I imagine the reduction is a
variant of Barrett reduction). I do think that 2^389-21 probably
wasn't the best choice: it was one of two suggested primes, the other
being 2^383-31, which has similar properties to 2^379-19.

On Mon, Jan 19, 2015 at 3:20 PM, Michael Hamburg <mike at shiftleft.org> wrote:
>
> On Jan 19, 2015, at 3:08 PM, Michael Hamburg <mike at shiftleft.org> wrote:
>
> Seems fine to me.  The prime 2^398 - 21 did bug me a little bit for this
> reason.
>
>
> Err,  2^389 - 21.
>
> — Mike
>
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