Optimisations and bug fixes for state advance

This commit is reasonably performant on Prater!

consensus/state_processing/src/common/altair.rs

@@ -5,15 +5,13 @@ use types::*;
 /// Returns the base reward for some validator.
 ///
 /// Spec v1.1.0
-pub fn get_base_reward<T: EthSpec>(
-    state: &BeaconState<T>,
-    index: usize,
+pub fn get_base_reward(
+    validator_effective_balance: u64,
     // Should be == get_total_active_balance(state, spec)
     total_active_balance: u64,
     spec: &ChainSpec,
 ) -> Result<u64, Error> {
-    state
-        .get_effective_balance(index)?
+    validator_effective_balance
         .safe_div(spec.effective_balance_increment)?
         .safe_mul(get_base_reward_per_increment(total_active_balance, spec)?)
         .map_err(Into::into)

consensus/state_processing/src/common/mod.rs

@@ -24,8 +24,7 @@ pub fn increase_balance<E: EthSpec>(
     index: usize,
     delta: u64,
 ) -> Result<(), BeaconStateError> {
-    state.get_balance_mut(index)?.safe_add_assign(delta)?;
-    Ok(())
+    increase_balance_directly(state.get_balance_mut(index)?, delta)
 }
 
 /// Decrease the balance of a validator, saturating upon overflow, as per the spec.
@@ -34,7 +33,17 @@ pub fn decrease_balance<E: EthSpec>(
     index: usize,
     delta: u64,
 ) -> Result<(), BeaconStateError> {
-    let balance = state.get_balance_mut(index)?;
+    decrease_balance_directly(state.get_balance_mut(index)?, delta)
+}
+
+/// Increase the balance of a validator, erroring upon overflow, as per the spec.
+pub fn increase_balance_directly(balance: &mut u64, delta: u64) -> Result<(), BeaconStateError> {
+    balance.safe_add_assign(delta)?;
+    Ok(())
+}
+
+/// Decrease the balance of a validator, saturating upon overflow, as per the spec.
+pub fn decrease_balance_directly(balance: &mut u64, delta: u64) -> Result<(), BeaconStateError> {
     *balance = balance.saturating_sub(delta);
     Ok(())
 }