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Simplify justification and finalization accounting logic 

Much of the simplification is cosmetic. The following changes are substantive:

* Inactivity leak penalty specifically on missing the target, not both the target and the source
* Even outside of quadratic leak scenarios, slashing victims suffer offline penalties
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vbuterin 2019-03-21 15:11:05 -05:00 committed by GitHub
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94
specs/core/0_beacon-chain.md
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@ -1883,10 +1883,11 @@ def get_base_reward(state: BeaconState, index: ValidatorIndex) -> Gwei:
```python
def get_inactivity_penalty(state: BeaconState, index: ValidatorIndex, epochs_since_finality: int) -> Gwei:
return (
get_base_reward(state, index) +
get_effective_balance(state, index) * epochs_since_finality // INACTIVITY_PENALTY_QUOTIENT // 2
)
if epochs_since_finality <= 4:
extra_penalty = 0
else:
extra_penalty = get_effective_balance(state, index) * min(epochs_since_finality // INACTIVITY_PENALTY_QUOTIENT // 2
return get_base_reward(state, index) + extra_penalty
```
Note: When applying penalties in the following balance recalculations implementers should make sure the `uint64` does not underflow.
@ -1896,22 +1897,8 @@ Note: When applying penalties in the following balance recalculations implemente
```python
def get_justification_and_finalization_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:
epochs_since_finality = get_current_epoch(state) + 1 - state.finalized_epoch
if epochs_since_finality <= 4:
return compute_normal_justification_and_finalization_deltas(state)
else:
return compute_inactivity_leak_deltas(state)
```
When blocks are finalizing normally...
```python
def compute_normal_justification_and_finalization_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:
# deltas[0] for rewards
# deltas[1] for penalties
deltas = [
[0 for index in range(len(state.validator_registry))],
[0 for index in range(len(state.validator_registry))]
]
rewards = [0 for index in range(len(state.validator_registry))]
penalties = [0 for index in range(len(state.validator_registry))]
# Some helper variables
boundary_attestations = get_previous_epoch_boundary_attestations(state)
boundary_attesting_balance = get_attesting_balance(state, boundary_attestations)
@ -1919,76 +1906,37 @@ def compute_normal_justification_and_finalization_deltas(state: BeaconState) ->
total_attesting_balance = get_attesting_balance(state, state.previous_epoch_attestations)
matching_head_attestations = get_previous_epoch_matching_head_attestations(state)
matching_head_balance = get_attesting_balance(state, matching_head_attestations)
eligible_validators = [
i for i,v in enumerate(state.validator_registry) if is_active_validator(v, get_current_epoch(state)) or
(v.slashed and get_current_epoch(state) < v.withdrawable_epoch)
]
# Process rewards or penalties for all validators
for index in get_active_validator_indices(state.validator_registry, get_previous_epoch(state)):
for index in eligible_validators:
# Expected FFG source
if index in get_attesting_indices(state, state.previous_epoch_attestations):
deltas[0][index] += get_base_reward(state, index) * total_attesting_balance // total_balance
rewards[index] += get_base_reward(state, index) * total_attesting_balance // total_balance
# Inclusion speed bonus
deltas[0][index] += (
rewards[index] += (
get_base_reward(state, index) * MIN_ATTESTATION_INCLUSION_DELAY //
inclusion_distance(state, index)
)
else:
deltas[1][index] += get_base_reward(state, index)
penalties[index] += get_base_reward(state, index)
# Expected FFG target
if index in get_attesting_indices(state, boundary_attestations):
deltas[0][index] += get_base_reward(state, index) * boundary_attesting_balance // total_balance
rewards[index] += get_base_reward(state, index) * boundary_attesting_balance // total_balance
else:
deltas[1][index] += get_base_reward(state, index)
penalties[index] += get_inactivity_penalty(state, index, epochs_since_finality)
# Expected head
if index in get_attesting_indices(state, matching_head_attestations):
deltas[0][index] += get_base_reward(state, index) * matching_head_balance // total_balance
rewards[index] += get_base_reward(state, index) * matching_head_balance // total_balance
else:
deltas[1][index] += get_base_reward(state, index)
penalties[index] += get_base_reward(state, index)
# Proposer bonus
if index in get_attesting_indices(state, state.previous_epoch_attestations):
proposer_index = get_beacon_proposer_index(state, inclusion_slot(state, index))
deltas[0][proposer_index] += get_base_reward(state, index) // ATTESTATION_INCLUSION_REWARD_QUOTIENT
return deltas
```
When blocks are not finalizing normally...
```python
def compute_inactivity_leak_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:
# deltas[0] for rewards
# deltas[1] for penalties
deltas = [
[0 for index in range(len(state.validator_registry))],
[0 for index in range(len(state.validator_registry))]
]
boundary_attestations = get_previous_epoch_boundary_attestations(state)
matching_head_attestations = get_previous_epoch_matching_head_attestations(state)
active_validator_indices = get_active_validator_indices(state.validator_registry, get_previous_epoch(state))
epochs_since_finality = get_current_epoch(state) + 1 - state.finalized_epoch
for index in active_validator_indices:
if index not in get_attesting_indices(state, state.previous_epoch_attestations):
deltas[1][index] += get_inactivity_penalty(state, index, epochs_since_finality)
else:
# If a validator did attest, apply a small penalty for getting attestations included late
deltas[0][index] += (
get_base_reward(state, index) * MIN_ATTESTATION_INCLUSION_DELAY //
inclusion_distance(state, index)
)
deltas[1][index] += get_base_reward(state, index)
if index not in get_attesting_indices(state, boundary_attestations):
deltas[1][index] += get_inactivity_penalty(state, index, epochs_since_finality)
if index not in get_attesting_indices(state, matching_head_attestations):
deltas[1][index] += get_base_reward(state, index)
# Penalize slashed-but-inactive validators as though they were active but offline
for index in range(len(state.validator_registry)):
eligible = (
index not in active_validator_indices and
state.validator_registry[index].slashed and
get_current_epoch(state) < state.validator_registry[index].withdrawable_epoch
)
if eligible:
deltas[1][index] += (
2 * get_inactivity_penalty(state, index, epochs_since_finality) +
get_base_reward(state, index)
)
return deltas
rewards[proposer_index] += get_base_reward(state, index) // ATTESTATION_INCLUSION_REWARD_QUOTIENT
return [rewards, penalties]
```
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