Update rewards processing to v0.5.0

eth2/state_processing/src/per_epoch_processing/apply_rewards.rs

@@ -0,0 +1,317 @@
+use super::validator_statuses::{TotalBalances, ValidatorStatus, ValidatorStatuses};
+use super::{Error, WinningRootHashSet};
+use integer_sqrt::IntegerSquareRoot;
+use types::*;
+
+#[derive(Default, Clone)]
+pub struct Delta {
+    pub rewards: u64,
+    pub penalties: u64,
+}
+
+impl std::ops::AddAssign for Delta {
+    /// Use wrapping addition as that is how it's defined in the spec.
+    fn add_assign(&mut self, other: Delta) {
+        self.rewards += other.rewards;
+        self.penalties += other.penalties;
+    }
+}
+
+/// Apply attester and proposer rewards.
+///
+/// Spec v0.5.0
+pub fn apply_rewards(
+    state: &mut BeaconState,
+    validator_statuses: &mut ValidatorStatuses,
+    winning_root_for_shards: &WinningRootHashSet,
+    spec: &ChainSpec,
+) -> Result<(), Error> {
+    // Guard against an out-of-bounds during the validator balance update.
+    if validator_statuses.statuses.len() != state.validator_balances.len() {
+        return Err(Error::ValidatorStatusesInconsistent);
+    }
+    // Guard against an out-of-bounds during the attester inclusion balance update.
+    if validator_statuses.statuses.len() != state.validator_registry.len() {
+        return Err(Error::ValidatorStatusesInconsistent);
+    }
+
+    let mut deltas = vec![Delta::default(); state.validator_balances.len()];
+
+    get_justification_and_finalization_deltas(&mut deltas, state, &validator_statuses, spec)?;
+    get_crosslink_deltas(&mut deltas, state, &validator_statuses, spec)?;
+
+    // Apply the proposer deltas if we are finalizing normally.
+    //
+    // This is executed slightly differently to the spec because of the way our functions are
+    // structured. It should be functionally equivalent.
+    if epochs_since_finality(state, spec) <= 4 {
+        get_proposer_deltas(
+            &mut deltas,
+            state,
+            validator_statuses,
+            winning_root_for_shards,
+            spec,
+        )?;
+    }
+
+    // Apply the deltas, over-flowing but not under-flowing (saturating at 0 instead).
+    for (i, delta) in deltas.iter().enumerate() {
+        state.validator_balances[i] += delta.rewards;
+        state.validator_balances[i] = state.validator_balances[i].saturating_sub(delta.penalties);
+    }
+
+    Ok(())
+}
+
+/// Applies the attestation inclusion reward to each proposer for every validator who included an
+/// attestation in the previous epoch.
+///
+/// Spec v0.5.0
+fn get_proposer_deltas(
+    deltas: &mut Vec<Delta>,
+    state: &mut BeaconState,
+    validator_statuses: &mut ValidatorStatuses,
+    winning_root_for_shards: &WinningRootHashSet,
+    spec: &ChainSpec,
+) -> Result<(), Error> {
+    // Update statuses with the information from winning roots.
+    validator_statuses.process_winning_roots(state, winning_root_for_shards, spec)?;
+
+    for (index, validator) in validator_statuses.statuses.iter().enumerate() {
+        let mut delta = Delta::default();
+
+        if validator.is_previous_epoch_attester {
+            let inclusion = validator
+                .inclusion_info
+                .expect("It is a logic error for an attester not to have an inclusion distance.");
+
+            let base_reward = get_base_reward(
+                state,
+                inclusion.proposer_index,
+                validator_statuses.total_balances.previous_epoch,
+                spec,
+            )?;
+
+            if inclusion.proposer_index >= deltas.len() {
+                return Err(Error::ValidatorStatusesInconsistent);
+            }
+
+            delta.rewards += base_reward / spec.attestation_inclusion_reward_quotient;
+        }
+
+        deltas[index] += delta;
+    }
+
+    Ok(())
+}
+
+/// Apply rewards for participation in attestations during the previous epoch.
+///
+/// Spec v0.5.0
+fn get_justification_and_finalization_deltas(
+    deltas: &mut Vec<Delta>,
+    state: &BeaconState,
+    validator_statuses: &ValidatorStatuses,
+    spec: &ChainSpec,
+) -> Result<(), Error> {
+    let epochs_since_finality = epochs_since_finality(state, spec);
+
+    for (index, validator) in validator_statuses.statuses.iter().enumerate() {
+        let base_reward = get_base_reward(
+            state,
+            index,
+            validator_statuses.total_balances.previous_epoch,
+            spec,
+        )?;
+        let inactivity_penalty = get_inactivity_penalty(
+            state,
+            index,
+            epochs_since_finality.as_u64(),
+            validator_statuses.total_balances.previous_epoch,
+            spec,
+        )?;
+
+        let delta = if epochs_since_finality <= 4 {
+            compute_normal_justification_and_finalization_delta(
+                &validator,
+                &validator_statuses.total_balances,
+                base_reward,
+                spec,
+            )
+        } else {
+            compute_inactivity_leak_delta(&validator, base_reward, inactivity_penalty, spec)
+        };
+
+        deltas[index] += delta;
+    }
+
+    Ok(())
+}
+
+/// Determine the delta for a single validator, if the chain is finalizing normally.
+///
+/// Spec v0.5.0
+fn compute_normal_justification_and_finalization_delta(
+    validator: &ValidatorStatus,
+    total_balances: &TotalBalances,
+    base_reward: u64,
+    spec: &ChainSpec,
+) -> Delta {
+    let mut delta = Delta::default();
+
+    let boundary_attesting_balance = total_balances.previous_epoch_boundary_attesters;
+    let total_balance = total_balances.previous_epoch;
+    let total_attesting_balance = total_balances.previous_epoch_attesters;
+    let matching_head_balance = total_balances.previous_epoch_boundary_attesters;
+
+    // Expected FFG source.
+    if validator.is_previous_epoch_attester {
+        delta.rewards += base_reward * total_attesting_balance / total_balance;
+        // Inclusion speed bonus
+        let inclusion = validator
+            .inclusion_info
+            .expect("It is a logic error for an attester not to have an inclusion distance.");
+        delta.rewards +=
+            base_reward * spec.min_attestation_inclusion_delay / inclusion.distance.as_u64();
+    } else if validator.is_active_in_previous_epoch {
+        delta.penalties += base_reward;
+    }
+
+    // Expected FFG target.
+    if validator.is_previous_epoch_boundary_attester {
+        delta.rewards += base_reward / boundary_attesting_balance / total_balance;
+    } else if validator.is_active_in_previous_epoch {
+        delta.penalties += base_reward;
+    }
+
+    // Expected head.
+    if validator.is_previous_epoch_head_attester {
+        delta.rewards += base_reward * matching_head_balance / total_balance;
+    } else if validator.is_active_in_previous_epoch {
+        delta.penalties += base_reward;
+    };
+
+    // Proposer bonus is handled in `apply_proposer_deltas`.
+    //
+    // This function only computes the delta for a single validator, so it cannot also return a
+    // delta for a validator.
+
+    delta
+}
+
+/// Determine the delta for a single delta, assuming the chain is _not_ finalizing normally.
+///
+/// Spec v0.5.0
+fn compute_inactivity_leak_delta(
+    validator: &ValidatorStatus,
+    base_reward: u64,
+    inactivity_penalty: u64,
+    spec: &ChainSpec,
+) -> Delta {
+    let mut delta = Delta::default();
+
+    if validator.is_active_in_previous_epoch {
+        if !validator.is_previous_epoch_attester {
+            delta.penalties += inactivity_penalty;
+        } else {
+            // If a validator did attest, apply a small penalty for getting attestations included
+            // late.
+            let inclusion = validator
+                .inclusion_info
+                .expect("It is a logic error for an attester not to have an inclusion distance.");
+            delta.rewards +=
+                base_reward * spec.min_attestation_inclusion_delay / inclusion.distance.as_u64();
+            delta.penalties += base_reward;
+        }
+
+        if !validator.is_previous_epoch_boundary_attester {
+            delta.penalties += inactivity_penalty;
+        }
+
+        if !validator.is_previous_epoch_head_attester {
+            delta.penalties += inactivity_penalty;
+        }
+    }
+
+    // Penalize slashed-but-inactive validators as though they were active but offline.
+    if !validator.is_active_in_previous_epoch
+        & validator.is_slashed
+        & !validator.is_withdrawable_in_current_epoch
+    {
+        delta.penalties += 2 * inactivity_penalty + base_reward;
+    }
+
+    delta
+}
+
+/// Calculate the deltas based upon the winning roots for attestations during the previous epoch.
+///
+/// Spec v0.5.0
+fn get_crosslink_deltas(
+    deltas: &mut Vec<Delta>,
+    state: &BeaconState,
+    validator_statuses: &ValidatorStatuses,
+    spec: &ChainSpec,
+) -> Result<(), Error> {
+    for (index, validator) in validator_statuses.statuses.iter().enumerate() {
+        let mut delta = Delta::default();
+
+        let base_reward = get_base_reward(
+            state,
+            index,
+            validator_statuses.total_balances.previous_epoch,
+            spec,
+        )?;
+
+        if let Some(ref winning_root) = validator.winning_root_info {
+            delta.rewards += base_reward * winning_root.total_attesting_balance
+                / winning_root.total_committee_balance
+        } else {
+            delta.penalties += base_reward;
+        }
+
+        deltas[index] += delta;
+    }
+
+    Ok(())
+}
+
+/// Returns the base reward for some validator.
+///
+/// Spec v0.5.0
+fn get_base_reward(
+    state: &BeaconState,
+    index: usize,
+    previous_total_balance: u64,
+    spec: &ChainSpec,
+) -> Result<u64, BeaconStateError> {
+    if previous_total_balance == 0 {
+        Ok(0)
+    } else {
+        let adjusted_quotient = previous_total_balance.integer_sqrt() / spec.base_reward_quotient;
+        Ok(state.get_effective_balance(index, spec)? / adjusted_quotient / 5)
+    }
+}
+
+/// Returns the inactivity penalty for some validator.
+///
+/// Spec v0.5.0
+fn get_inactivity_penalty(
+    state: &BeaconState,
+    index: usize,
+    epochs_since_finality: u64,
+    previous_total_balance: u64,
+    spec: &ChainSpec,
+) -> Result<u64, BeaconStateError> {
+    Ok(get_base_reward(state, index, previous_total_balance, spec)?
+        + state.get_effective_balance(index, spec)? * epochs_since_finality
+            / spec.inactivity_penalty_quotient
+            / 2)
+}
+
+/// Returns the epochs since the last finalized epoch.
+///
+/// Spec v0.5.0
+fn epochs_since_finality(state: &BeaconState, spec: &ChainSpec) -> Epoch {
+    state.current_epoch(spec) + 1 - state.finalized_epoch
+}