Investigate the use of portable_simd

[tlepoint]

Rust has an experimental portable SIMD abstraction which could be particularly useful to speed up some of the vector modular operations / NTTs in a "generic" way (i.e., without needing to specialize for AVX2 or Neon). I did some minimal investigation in the branch simd-2, and observe some speedup in a virtual machine with Intel CPU when enabling avx2 and avx512f in RUSTFLAGS. Such a feature may require a lot of care to properly handle alignment, and this issue is created to centralize the discussions about SIMD.

[fionser]

How about the ntt libray from Zama ?

[tlepoint]

Yes! Now that the latest bug in concrete-ntt is fixed, it should be easy to integrate it. I had a local branch with this integration a few weeks ago and need to revive it, but I also need to solve #229 before that.