Optimization: The running instance does not need to absorbed.

[srinathsetty]

Given that the public IO of the incoming R1CS instance contains the hash of the running instance in addition to (params, U, i, z0, zi), we can skip absorbing the running instance.

[varunthakore]

Hi @srinathsetty, can I work on this issue ?

My understanding is that since u.x[0] = Hash(params, U, i, z0, zi) and we are absorbing u at line 241, we can avoid absorbing U at line 240.

Nova/src/gadgets/r1cs.rs

Lines 240 to 241 in 48065b0

	self.absorb_in_ro(cs.namespace(|| "absorb running instance"), &mut ro)?;
	u.absorb_in_ro(&mut ro);

Similarly in NIFS::prove and NIFS::verify, we can avoid absorbing the RelaxedR1CSInstance U1.

Nova/src/nifs.rs

Line 49 in 48065b0

U1.absorb_in_ro(&mut ro);

Nova/src/nifs.rs

Line 95 in 48065b0

U1.absorb_in_ro(&mut ro);

We will have to update the const NUM_FE_FOR_RO and expected values in tests accordingly.

Let me know if this is fine. I can create a PR.

[srinathsetty]

@varunthakore Yes, that sounds great!