Simplify fork choice's `calculate_committee_fraction`

[michaelsproul]

Description

The v1.3.0 spec simplified the calculation of proposer boost in a way that is almost equivalent to the previous definition. We are still using the old definition but could update at any time to the simpler version.

Our impl:

lighthouse/consensus/proto_array/src/proto_array.rs

Lines 1054 to 1068 in a53830f

	pub fn calculate_committee_fraction<E: EthSpec>(
	justified_balances: &JustifiedBalances,
	proposer_score_boost: u64,
	) -> Option<u64> {
	let average_balance = justified_balances
	.total_effective_balance
	.checked_div(justified_balances.num_active_validators)?;
	let committee_size = justified_balances
	.num_active_validators
	.checked_div(E::slots_per_epoch())?;
	let committee_weight = committee_size.checked_mul(average_balance)?;
	committee_weight
	.checked_mul(proposer_score_boost)?
	.checked_div(100)
	}

Spec: https://github.com/ethereum/consensus-specs/blob/v1.3.0/specs/phase0/fork-choice.md#get_weight

Discussion: ethereum/consensus-specs#3034 (comment)

Version

v4.0.1

[eserilev]

@michaelsproul hi, i'd like to pick this one up

so if I'm understanding the spec correctly, the additional calculations of average_balance and committee_size can be removed

instead committee_weight is just simply total_effective_balance which is the sum of the effective balance of all validators in the network that are in a given "justified" state

[michaelsproul]

yep!

[michaelsproul]

Closed by #4213