Files
lighthouse/eth2/state_processing/src/per_epoch_processing/apply_rewards.rs
2020-04-20 12:35:11 +10:00

245 lines
8.0 KiB
Rust

use super::super::common::get_base_reward;
use super::validator_statuses::{TotalBalances, ValidatorStatus, ValidatorStatuses};
use super::Error;
use safe_arith::SafeArith;
use types::*;
/// Use to track the changes to a validators balance.
#[derive(Default, Clone)]
pub struct Delta {
rewards: u64,
penalties: u64,
}
impl Delta {
/// Reward the validator with the `reward`.
pub fn reward(&mut self, reward: u64) -> Result<(), Error> {
self.rewards = self.rewards.safe_add(reward)?;
Ok(())
}
/// Penalize the validator with the `penalty`.
pub fn penalize(&mut self, penalty: u64) -> Result<(), Error> {
self.penalties = self.penalties.safe_add(penalty)?;
Ok(())
}
/// Combine two deltas.
fn combine(&mut self, other: Delta) -> Result<(), Error> {
self.reward(other.rewards)?;
self.penalize(other.penalties)
}
}
/// Apply attester and proposer rewards.
///
/// Spec v0.11.1
pub fn process_rewards_and_penalties<T: EthSpec>(
state: &mut BeaconState<T>,
validator_statuses: &mut ValidatorStatuses,
spec: &ChainSpec,
) -> Result<(), Error> {
if state.current_epoch() == T::genesis_epoch() {
return Ok(());
}
// Guard against an out-of-bounds during the validator balance update.
if validator_statuses.statuses.len() != state.balances.len()
|| validator_statuses.statuses.len() != state.validators.len()
{
return Err(Error::ValidatorStatusesInconsistent);
}
let mut deltas = vec![Delta::default(); state.balances.len()];
get_attestation_deltas(&mut deltas, state, &validator_statuses, spec)?;
get_proposer_deltas(&mut deltas, state, validator_statuses, spec)?;
// Apply the deltas, erroring on overflow above but not on overflow below (saturating at 0
// instead).
for (i, delta) in deltas.iter().enumerate() {
state.balances[i] = state.balances[i].safe_add(delta.rewards)?;
state.balances[i] = state.balances[i].saturating_sub(delta.penalties);
}
Ok(())
}
/// For each attesting validator, reward the proposer who was first to include their attestation.
///
/// Spec v0.11.1
fn get_proposer_deltas<T: EthSpec>(
deltas: &mut Vec<Delta>,
state: &BeaconState<T>,
validator_statuses: &mut ValidatorStatuses,
spec: &ChainSpec,
) -> Result<(), Error> {
for (index, validator) in validator_statuses.statuses.iter().enumerate() {
if validator.is_previous_epoch_attester && !validator.is_slashed {
let inclusion = validator
.inclusion_info
.expect("It is a logic error for an attester not to have an inclusion delay.");
let base_reward = get_base_reward(
state,
index,
validator_statuses.total_balances.current_epoch(),
spec,
)?;
if inclusion.proposer_index >= deltas.len() {
return Err(Error::ValidatorStatusesInconsistent);
}
deltas[inclusion.proposer_index]
.reward(base_reward.safe_div(spec.proposer_reward_quotient)?)?;
}
}
Ok(())
}
/// Apply rewards for participation in attestations during the previous epoch.
///
/// Spec v0.11.1
fn get_attestation_deltas<T: EthSpec>(
deltas: &mut Vec<Delta>,
state: &BeaconState<T>,
validator_statuses: &ValidatorStatuses,
spec: &ChainSpec,
) -> Result<(), Error> {
let finality_delay = (state.previous_epoch() - state.finalized_checkpoint.epoch).as_u64();
for (index, validator) in validator_statuses.statuses.iter().enumerate() {
let base_reward = get_base_reward(
state,
index,
validator_statuses.total_balances.current_epoch(),
spec,
)?;
let delta = get_attestation_delta::<T>(
&validator,
&validator_statuses.total_balances,
base_reward,
finality_delay,
spec,
)?;
deltas[index].combine(delta)?;
}
Ok(())
}
/// Determine the delta for a single validator, sans proposer rewards.
///
/// Spec v0.11.1
fn get_attestation_delta<T: EthSpec>(
validator: &ValidatorStatus,
total_balances: &TotalBalances,
base_reward: u64,
finality_delay: u64,
spec: &ChainSpec,
) -> Result<Delta, Error> {
let mut delta = Delta::default();
// Is this validator eligible to be rewarded or penalized?
// Spec: validator index in `eligible_validator_indices`
let is_eligible = validator.is_active_in_previous_epoch
|| (validator.is_slashed && !validator.is_withdrawable_in_current_epoch);
if !is_eligible {
return Ok(delta);
}
// Handle integer overflow by dividing these quantities by EFFECTIVE_BALANCE_INCREMENT
// Spec:
// - increment = EFFECTIVE_BALANCE_INCREMENT
// - reward_numerator = get_base_reward(state, index) * (attesting_balance // increment)
// - rewards[index] = reward_numerator // (total_balance // increment)
let total_balance_ebi = total_balances
.current_epoch()
.safe_div(spec.effective_balance_increment)?;
let total_attesting_balance_ebi = total_balances
.previous_epoch_attesters()
.safe_div(spec.effective_balance_increment)?;
let matching_target_balance_ebi = total_balances
.previous_epoch_target_attesters()
.safe_div(spec.effective_balance_increment)?;
let matching_head_balance_ebi = total_balances
.previous_epoch_head_attesters()
.safe_div(spec.effective_balance_increment)?;
// Expected FFG source.
// Spec:
// - validator index in `get_unslashed_attesting_indices(state, matching_source_attestations)`
if validator.is_previous_epoch_attester && !validator.is_slashed {
delta.reward(
base_reward
.safe_mul(total_attesting_balance_ebi)?
.safe_div(total_balance_ebi)?,
)?;
// Inclusion speed bonus
let proposer_reward = base_reward.safe_div(spec.proposer_reward_quotient)?;
let max_attester_reward = base_reward.safe_sub(proposer_reward)?;
let inclusion = validator
.inclusion_info
.expect("It is a logic error for an attester not to have an inclusion delay.");
delta.reward(max_attester_reward.safe_div(inclusion.delay)?)?;
} else {
delta.penalize(base_reward)?;
}
// Expected FFG target.
// Spec:
// - validator index in `get_unslashed_attesting_indices(state, matching_target_attestations)`
if validator.is_previous_epoch_target_attester && !validator.is_slashed {
delta.reward(
base_reward
.safe_mul(matching_target_balance_ebi)?
.safe_div(total_balance_ebi)?,
)?;
} else {
delta.penalize(base_reward)?;
}
// Expected head.
// Spec:
// - validator index in `get_unslashed_attesting_indices(state, matching_head_attestations)`
if validator.is_previous_epoch_head_attester && !validator.is_slashed {
delta.reward(
base_reward
.safe_mul(matching_head_balance_ebi)?
.safe_div(total_balance_ebi)?,
)?;
} else {
delta.penalize(base_reward)?;
}
// Inactivity penalty
if finality_delay > spec.min_epochs_to_inactivity_penalty {
// All eligible validators are penalized
delta.penalize(spec.base_rewards_per_epoch.safe_mul(base_reward)?)?;
// Additionally, all validators whose FFG target didn't match are penalized extra
if !validator.is_previous_epoch_target_attester {
delta.penalize(
validator
.current_epoch_effective_balance
.safe_mul(finality_delay)?
.safe_div(spec.inactivity_penalty_quotient)?,
)?;
}
}
// Proposer bonus is handled in `get_proposer_deltas`.
//
// This function only computes the delta for a single validator, so it cannot also return a
// delta for a validator.
Ok(delta)
}