Quoting "Jason A. Donenfeld" <ja...@zx2c4.com>:
Hi Armando,

I've started importing your precomputation implementation into kernel
space for use in kbench9000 (and in WireGuard and the kernel crypto
library too, of course).

- The first problem remains the license. The kernel requires
GPLv2-compatible code. GPLv3 isn't compatible with GPLv2. This isn't
up to me at all, unfortunately, so this stuff will have to be licensed
differently in order to be useful.

The rfc7748_precomputed library is now released under LGPLv2.1.
We are happy to see our code integrated in more projects.

Quoting "Jason A. Donenfeld" <ja...@zx2c4.com>:
- It looks like the precomputation implementation is failing some unit
tests! Perhaps it's not properly reducing incoming public points?

There's the vector if you'd like to play with it. The other test
vectors I have do pass, though, which is good I suppose.

Thanks, for this observation. The code was missing to handle some carry bits,
producing incorrect outputs for numbers between 2p and 2^256. Now, I have
rewritten some operations for GF(2^255-19) considering all of these cases.
More tests were added and fuzz test against HACL implementation.

Code is available at:
  https://github.com/armfazh/rfc7748_precomputed  (commit c79ca5e...)

*Disclaimer: More test and work is needed for the GF(2^448-2^224-1) arithmetic.

On the plus side, the implementation is super fast:
With turbo on, on my E3-1505Mv5, I'm getting:

donna64: 121793 cycles per call
 hacl64: 109793 cycles per call
 fiat64: 108937 cycles per call
sandy2x: 103003 cycles per call
  amd64: 108688 cycles per call
precomp: 83391 cycles per call
 fiat32: 232835 cycles per call
donna32: 411511 cycles per call

The benchmark of your precomputation implementation has what's
referred to by medical doctors as "less digits".

Due to the bug's corrections, a slight loss of performance was observed;
however, other operations were optimized too counteracting the losses.
Let us know about your new measurements.

Armando Faz Hernández, PhD Candidate.
Instituto de Computação, Unicamp.
Campinas, Brasil.

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