spec: Draft FMA extension field accelerator

[RobinJadoul]

No description provided.

[github-actions]

Kimi Code Review

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[github-actions]

Codex Code Review

• High – FMA drops two coefficients of c (fext_fma.toml): output[1] and output[2] omit c[1] and c[2]. Thus the chip computes a*b + (c₀,0,0), not a*b+c. Add the missing terms to both constraints and polynomials.

[erik-3milabs]

Am I correct in understanding that this PR is not yet complete? Right now, there does not seem to be a way to get the information out of the "Extension Field Realm" back to RAM/MEMORY land and interact with it. (I seem to recall we considered having assertions in the Fext-Realm, instead of the load-back, but I don't see any signs this PR introduces that solution yet)

[RobinJadoul]

Indeed, the intention was to have an FEXT_ZERO or similar chip. I'm now unsure if I had a reason to delay that, or if I was just forgetful.

[erik-3milabs]

You forgot to recompute #nr_variables, #nr_columns, and #nr_interactions.

[erik-3milabs]

Also, please highlight that the addr is read from A0.

[erik-3milabs]

Please rebase against spec/reg and update the six register accesses introduced in the fext_*.toml files.