Lookup table for calculating amount commitments

[Boog900]

What

When retrieving pre-RCT outputs from the DB we need to calculate an amount commitment for use in RCT rings, this is currently done manually:

cuprate/storage/blockchain/src/ops/output.rs

Lines 158 to 160 in 2776769

	// FIXME: implement lookup table for common values:
	// <https://github.com/monero-project/monero/blob/c8214782fb2a769c57382a999eaf099691c836e7/src/ringct/rctOps.cpp#L322>
	let commitment = ED25519_BASEPOINT_POINT + H() * Scalar::from(amount);

Also when adding V2 miner txs:

cuprate/storage/blockchain/src/ops/tx.rs

Lines 123 to 129 in 2776769

	// Create commitment.
	// <https://github.com/Cuprate/cuprate/pull/102#discussion_r1559489302>
	// FIXME: implement lookup table for common values:
	// <https://github.com/monero-project/monero/blob/c8214782fb2a769c57382a999eaf099691c836e7/src/ringct/rctOps.cpp#L322>
	let commitment = (ED25519_BASEPOINT_POINT
	+ monero_serai::H() * Scalar::from(amount))
	.compress()

This issue is for creating a lookup table for common amounts (the validly decomposed amounts).

Why

Calculating commitments is slower than using a look up table.

How

I did this in our test sync branch:

cuprate/helper/src/commitment.rs

Lines 55 to 62 in 1eaf32b

	pub fn compute_zero_commitment(amount: u64) -> EdwardsPoint {
	precomputed_commitments()
	.get(&amount)
	.copied()
	.unwrap_or_else(|| {
	h_precomp().vartime_multiscalar_mul([Scalar::from(amount), Scalar::from(1_u8)])
	})
	}

However performance tests should be conducted to see if the slow path (line 60) is actually faster than our current method

[willco-1]

I'd like to take a shot at this if that's okay

[Boog900]

We currently have someone working on this sorry, #178 is slightly larger but currently has no one working on it, if that interests you?

[willco-1]

I’d probably need a little help on this one but feel free to assign it to me and i’ll take a shot at it! cheers. On Sep 6, 2024, at 17:05, Boog900 ***@***.***> wrote: We currently have someone working on this sorry, #178 is slightly larger but currently has no one working on it, if that interests you? —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you commented.Message ID: ***@***.***>

[Boog900]

Nice, you will have to comment on the issue for me to assign it. You are welcome to join our matrix server: https://matrix.to/#/#cuprate:monero.social, out of the 4 tasks listed in #178 Persist banned peers would probably be the easiest to start on.