From 7b99588b8affbfaad119c00a0be04e611a7bdafc Mon Sep 17 00:00:00 2001
From: Eitan Seri-Levi <eserilev@ucsc.edu>
Date: Wed, 3 May 2023 09:02:58 +0000
Subject: [PATCH] simplify calculate_committee_fraction (#4213)

## Issue Addressed

[#4211](https://github.com/sigp/lighthouse/issues/4211)

## Proposed Changes

This PR conforms the helper function `calculate_committee_fraction` to the [v1.3.0 spec](https://github.com/ethereum/consensus-specs/blob/v1.3.0/specs/phase0/fork-choice.md#get_weight)

## Additional Info

the old definition of `calculate_committee_fraction` is almost identical, but the new definition is simpler.
---
 .../src/fork_choice_test_definition/execution_status.rs     | 6 +++---
 consensus/proto_array/src/proto_array.rs                    | 6 +-----
 2 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/consensus/proto_array/src/fork_choice_test_definition/execution_status.rs b/consensus/proto_array/src/fork_choice_test_definition/execution_status.rs
index ede5bb39481..aa26a843069 100644
--- a/consensus/proto_array/src/fork_choice_test_definition/execution_status.rs
+++ b/consensus/proto_array/src/fork_choice_test_definition/execution_status.rs
@@ -987,11 +987,11 @@ pub fn get_execution_status_test_definition_03() -> ForkChoiceTestDefinition {
 
     ops.push(Operation::AssertWeight {
         block_root: get_root(0),
-        weight: 33_000,
+        weight: 33_250,
     });
     ops.push(Operation::AssertWeight {
         block_root: get_root(1),
-        weight: 33_000,
+        weight: 33_250,
     });
     ops.push(Operation::AssertWeight {
         block_root: get_root(2),
@@ -1000,7 +1000,7 @@ pub fn get_execution_status_test_definition_03() -> ForkChoiceTestDefinition {
     ops.push(Operation::AssertWeight {
         block_root: get_root(3),
         // This is a "magic number" generated from `calculate_committee_fraction`.
-        weight: 31_000,
+        weight: 31_250,
     });
 
     // Invalidate the payload of 3.
diff --git a/consensus/proto_array/src/proto_array.rs b/consensus/proto_array/src/proto_array.rs
index 2c19206cb75..1cc34beff0c 100644
--- a/consensus/proto_array/src/proto_array.rs
+++ b/consensus/proto_array/src/proto_array.rs
@@ -1055,13 +1055,9 @@ pub fn calculate_committee_fraction<E: EthSpec>(
     justified_balances: &JustifiedBalances,
     proposer_score_boost: u64,
 ) -> Option<u64> {
-    let average_balance = justified_balances
+    let committee_weight = 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)