[snvzz]

The cores are SiFive U74-MC, the version is, I believe, 21G1.

These are documented.

But that design is configurable. We know B extension (optional) is enabled. I have no idea about every other setting this core can be synthesized with.

[snvzz]

Update: B extension is apparently not actually enabled. Alas.

[moloch-hai]

As usual. Sigh. Just Zpopcnt would go a long way.

[snvzz]

It might have popcnt. It might have Za and Zb.

It just doesn't claim to have B (the whole package).

[moloch-hai]

Looks like Zbb is where the "CPOP" and related instructions (popcount, count leading/trailing zeroes) live.

Zba ("and-not" etc.) and Zbs (single-bit) are more obscure and less important. Zbc (carry-less multiply) is interesting.