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eth2.0-specs/specs/altair/beacon-chain.md

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# Altair -- The Beacon Chain
## Table of contents
<!-- TOC -->
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
- [Introduction](#introduction)
- [Custom types](#custom-types)
- [Constants](#constants)
- [Participation flag indices](#participation-flag-indices)
- [Incentivization weights](#incentivization-weights)
- [Domain types](#domain-types)
- [Misc](#misc)
- [Preset](#preset)
- [Updated penalty values](#updated-penalty-values)
- [Sync committee](#sync-committee)
- [Configuration](#configuration)
- [Inactivity penalties](#inactivity-penalties)
- [Containers](#containers)
- [Modified containers](#modified-containers)
- [`BeaconBlockBody`](#beaconblockbody)
- [`BeaconState`](#beaconstate)
- [New containers](#new-containers)
- [`SyncAggregate`](#syncaggregate)
- [`SyncCommittee`](#synccommittee)
- [Helper functions](#helper-functions)
- [Crypto](#crypto)
- [Misc](#misc-1)
- [`add_flag`](#add_flag)
- [`has_flag`](#has_flag)
- [`get_index_for_new_validator`](#get_index_for_new_validator)
- [`set_or_append_list`](#set_or_append_list)
- [Beacon state accessors](#beacon-state-accessors)
- [`get_next_sync_committee_indices`](#get_next_sync_committee_indices)
- [`get_next_sync_committee`](#get_next_sync_committee)
- [`get_base_reward_per_increment`](#get_base_reward_per_increment)
- [`get_base_reward`](#get_base_reward)
- [`get_unslashed_participating_indices`](#get_unslashed_participating_indices)
- [`get_attestation_participation_flag_indices`](#get_attestation_participation_flag_indices)
- [`get_flag_index_deltas`](#get_flag_index_deltas)
- [Modified `get_inactivity_penalty_deltas`](#modified-get_inactivity_penalty_deltas)
- [Beacon state mutators](#beacon-state-mutators)
- [Modified `slash_validator`](#modified-slash_validator)
- [Block processing](#block-processing)
- [Modified `process_attestation`](#modified-process_attestation)
- [Modified `add_validator_to_registry`](#modified-add_validator_to_registry)
- [Sync aggregate processing](#sync-aggregate-processing)
- [Epoch processing](#epoch-processing)
- [Justification and finalization](#justification-and-finalization)
- [Inactivity scores](#inactivity-scores)
- [Rewards and penalties](#rewards-and-penalties)
- [Slashings](#slashings)
- [Participation flags updates](#participation-flags-updates)
- [Sync committee updates](#sync-committee-updates)
- [Initialize state for pure Altair testnets and test vectors](#initialize-state-for-pure-altair-testnets-and-test-vectors)
<!-- END doctoc generated TOC please keep comment here to allow auto update -->
<!-- /TOC -->
## Introduction
Altair is the first beacon chain hard fork. Its main features are:
* sync committees to support light clients
* incentive accounting reforms to reduce spec complexity
* penalty parameter updates towards their planned maximally punitive values
## Custom types
| Name | SSZ equivalent | Description |
| - | - | - |
| `ParticipationFlags` | `uint8` | a succinct representation of 8 boolean participation flags |
## Constants
### Participation flag indices
| Name | Value |
| - | - |
| `TIMELY_SOURCE_FLAG_INDEX` | `0` |
| `TIMELY_TARGET_FLAG_INDEX` | `1` |
| `TIMELY_HEAD_FLAG_INDEX` | `2` |
### Incentivization weights
| Name | Value |
| - | - |
| `TIMELY_SOURCE_WEIGHT` | `uint64(14)` |
| `TIMELY_TARGET_WEIGHT` | `uint64(26)` |
| `TIMELY_HEAD_WEIGHT` | `uint64(14)` |
| `SYNC_REWARD_WEIGHT` | `uint64(2)` |
| `PROPOSER_WEIGHT` | `uint64(8)` |
| `WEIGHT_DENOMINATOR` | `uint64(64)` |
*Note*: The sum of the weights equal `WEIGHT_DENOMINATOR`.
### Domain types
| Name | Value |
| - | - |
| `DOMAIN_SYNC_COMMITTEE` | `DomainType('0x07000000')` |
| `DOMAIN_SYNC_COMMITTEE_SELECTION_PROOF` | `DomainType('0x08000000')` |
| `DOMAIN_CONTRIBUTION_AND_PROOF` | `DomainType('0x09000000')` |
### Misc
| Name | Value |
| - | - |
| `PARTICIPATION_FLAG_WEIGHTS` | `[TIMELY_SOURCE_WEIGHT, TIMELY_TARGET_WEIGHT, TIMELY_HEAD_WEIGHT]` |
## Preset
### Updated penalty values
This patch updates a few configuration values to move penalty parameters closer to their final, maximum security values.
*Note*: The spec does *not* override previous configuration values but instead creates new values and replaces usage throughout.
| Name | Value |
| - | - |
| `INACTIVITY_PENALTY_QUOTIENT_ALTAIR` | `uint64(3 * 2**24)` (= 50,331,648) |
| `MIN_SLASHING_PENALTY_QUOTIENT_ALTAIR` | `uint64(2**6)` (= 64) |
| `PROPORTIONAL_SLASHING_MULTIPLIER_ALTAIR` | `uint64(2)` |
### Sync committee
| Name | Value | Unit | Duration |
| - | - | - | - |
| `SYNC_COMMITTEE_SIZE` | `uint64(2**9)` (= 512) | validators | |
| `EPOCHS_PER_SYNC_COMMITTEE_PERIOD` | `uint64(2**8)` (= 256) | epochs | ~27 hours |
## Configuration
### Inactivity penalties
| Name | Value | Description |
| - | - | - |
| `INACTIVITY_SCORE_BIAS` | `uint64(2**2)` (= 4) | score points per inactive epoch |
| `INACTIVITY_SCORE_RECOVERY_RATE` | `uint64(2**4)` (= 16) | score points per leak-free epoch |
## Containers
### Modified containers
#### `BeaconBlockBody`
```python
class BeaconBlockBody(Container):
randao_reveal: BLSSignature
eth1_data: Eth1Data # Eth1 data vote
graffiti: Bytes32 # Arbitrary data
# Operations
proposer_slashings: List[ProposerSlashing, MAX_PROPOSER_SLASHINGS]
attester_slashings: List[AttesterSlashing, MAX_ATTESTER_SLASHINGS]
attestations: List[Attestation, MAX_ATTESTATIONS]
deposits: List[Deposit, MAX_DEPOSITS]
voluntary_exits: List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS]
sync_aggregate: SyncAggregate # [New in Altair]
```
#### `BeaconState`
```python
class BeaconState(Container):
# Versioning
genesis_time: uint64
genesis_validators_root: Root
slot: Slot
fork: Fork
# History
latest_block_header: BeaconBlockHeader
block_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT]
state_roots: Vector[Root, SLOTS_PER_HISTORICAL_ROOT]
historical_roots: List[Root, HISTORICAL_ROOTS_LIMIT]
# Eth1
eth1_data: Eth1Data
eth1_data_votes: List[Eth1Data, EPOCHS_PER_ETH1_VOTING_PERIOD * SLOTS_PER_EPOCH]
eth1_deposit_index: uint64
# Registry
validators: List[Validator, VALIDATOR_REGISTRY_LIMIT]
balances: List[Gwei, VALIDATOR_REGISTRY_LIMIT]
# Randomness
randao_mixes: Vector[Bytes32, EPOCHS_PER_HISTORICAL_VECTOR]
# Slashings
slashings: Vector[Gwei, EPOCHS_PER_SLASHINGS_VECTOR] # Per-epoch sums of slashed effective balances
# Participation
previous_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT] # [Modified in Altair]
current_epoch_participation: List[ParticipationFlags, VALIDATOR_REGISTRY_LIMIT] # [Modified in Altair]
# Finality
justification_bits: Bitvector[JUSTIFICATION_BITS_LENGTH] # Bit set for every recent justified epoch
previous_justified_checkpoint: Checkpoint
current_justified_checkpoint: Checkpoint
finalized_checkpoint: Checkpoint
# Inactivity
inactivity_scores: List[uint64, VALIDATOR_REGISTRY_LIMIT] # [New in Altair]
# Sync
current_sync_committee: SyncCommittee # [New in Altair]
next_sync_committee: SyncCommittee # [New in Altair]
```
### New containers
#### `SyncAggregate`
```python
class SyncAggregate(Container):
sync_committee_bits: Bitvector[SYNC_COMMITTEE_SIZE]
sync_committee_signature: BLSSignature
```
#### `SyncCommittee`
```python
class SyncCommittee(Container):
pubkeys: Vector[BLSPubkey, SYNC_COMMITTEE_SIZE]
aggregate_pubkey: BLSPubkey
```
## Helper functions
### Crypto
Refer to the definitions in the [phase 0 document regarding BLS signatures](../phase0/beacon-chain.md#bls-signatures)
and the extensions defined in the [Altair BLS document](./bls.md). This specification assumes knowledge of
the functionality described in those documents.
### Misc
#### `add_flag`
```python
def add_flag(flags: ParticipationFlags, flag_index: int) -> ParticipationFlags:
"""
Return a new ``ParticipationFlags`` adding ``flag_index`` to ``flags``.
"""
flag = ParticipationFlags(2**flag_index)
return flags | flag
```
#### `has_flag`
```python
def has_flag(flags: ParticipationFlags, flag_index: int) -> bool:
"""
Return whether ``flags`` has ``flag_index`` set.
"""
flag = ParticipationFlags(2**flag_index)
return flags & flag == flag
```
#### `get_index_for_new_validator`
```python
def get_index_for_new_validator(state: BeaconState) -> ValidatorIndex:
return ValidatorIndex(len(state.validators))
```
#### `set_or_append_list`
```python
def set_or_append_list(list: List, index: ValidatorIndex, value: Any) -> None:
if index == len(list):
list.append(value)
else:
list[index] = value
```
### Beacon state accessors
#### `get_next_sync_committee_indices`
```python
def get_next_sync_committee_indices(state: BeaconState) -> Sequence[ValidatorIndex]:
"""
Return the sync committee indices, with possible duplicates, for the next sync committee.
"""
epoch = Epoch(get_current_epoch(state) + 1)
MAX_RANDOM_BYTE = 2**8 - 1
active_validator_indices = get_active_validator_indices(state, epoch)
active_validator_count = uint64(len(active_validator_indices))
seed = get_seed(state, epoch, DOMAIN_SYNC_COMMITTEE)
i = 0
sync_committee_indices: List[ValidatorIndex] = []
while len(sync_committee_indices) < SYNC_COMMITTEE_SIZE:
shuffled_index = compute_shuffled_index(uint64(i % active_validator_count), active_validator_count, seed)
candidate_index = active_validator_indices[shuffled_index]
random_byte = hash(seed + uint_to_bytes(uint64(i // 32)))[i % 32]
effective_balance = state.validators[candidate_index].effective_balance
if effective_balance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE * random_byte:
sync_committee_indices.append(candidate_index)
i += 1
return sync_committee_indices
```
#### `get_next_sync_committee`
*Note*: The function `get_next_sync_committee` should only be called at sync committee period boundaries and when [upgrading state to Altair](./fork.md#upgrading-the-state).
```python
def get_next_sync_committee(state: BeaconState) -> SyncCommittee:
"""
Return the next sync committee, with possible pubkey duplicates.
"""
indices = get_next_sync_committee_indices(state)
pubkeys = [state.validators[index].pubkey for index in indices]
aggregate_pubkey = eth_aggregate_pubkeys(pubkeys)
return SyncCommittee(pubkeys=pubkeys, aggregate_pubkey=aggregate_pubkey)
```
#### `get_base_reward_per_increment`
```python
def get_base_reward_per_increment(state: BeaconState) -> Gwei:
return Gwei(EFFECTIVE_BALANCE_INCREMENT * BASE_REWARD_FACTOR // integer_squareroot(get_total_active_balance(state)))
```
#### `get_base_reward`
*Note*: The function `get_base_reward` is modified with the removal of `BASE_REWARDS_PER_EPOCH` and the use of increment based accounting.
*Note*: On average an optimally performing validator earns one base reward per epoch.
```python
def get_base_reward(state: BeaconState, index: ValidatorIndex) -> Gwei:
"""
Return the base reward for the validator defined by ``index`` with respect to the current ``state``.
"""
increments = state.validators[index].effective_balance // EFFECTIVE_BALANCE_INCREMENT
return Gwei(increments * get_base_reward_per_increment(state))
```
#### `get_unslashed_participating_indices`
```python
def get_unslashed_participating_indices(state: BeaconState, flag_index: int, epoch: Epoch) -> Set[ValidatorIndex]:
"""
Return the set of validator indices that are both active and unslashed for the given ``flag_index`` and ``epoch``.
"""
assert epoch in (get_previous_epoch(state), get_current_epoch(state))
if epoch == get_current_epoch(state):
epoch_participation = state.current_epoch_participation
else:
epoch_participation = state.previous_epoch_participation
active_validator_indices = get_active_validator_indices(state, epoch)
participating_indices = [i for i in active_validator_indices if has_flag(epoch_participation[i], flag_index)]
return set(filter(lambda index: not state.validators[index].slashed, participating_indices))
```
#### `get_attestation_participation_flag_indices`
```python
def get_attestation_participation_flag_indices(state: BeaconState,
data: AttestationData,
inclusion_delay: uint64) -> Sequence[int]:
"""
Return the flag indices that are satisfied by an attestation.
"""
if data.target.epoch == get_current_epoch(state):
justified_checkpoint = state.current_justified_checkpoint
else:
justified_checkpoint = state.previous_justified_checkpoint
# Matching roots
is_matching_source = data.source == justified_checkpoint
is_matching_target = is_matching_source and data.target.root == get_block_root(state, data.target.epoch)
is_matching_head = is_matching_target and data.beacon_block_root == get_block_root_at_slot(state, data.slot)
assert is_matching_source
participation_flag_indices = []
if is_matching_source and inclusion_delay <= integer_squareroot(SLOTS_PER_EPOCH):
participation_flag_indices.append(TIMELY_SOURCE_FLAG_INDEX)
if is_matching_target and inclusion_delay <= SLOTS_PER_EPOCH:
participation_flag_indices.append(TIMELY_TARGET_FLAG_INDEX)
if is_matching_head and inclusion_delay == MIN_ATTESTATION_INCLUSION_DELAY:
participation_flag_indices.append(TIMELY_HEAD_FLAG_INDEX)
return participation_flag_indices
```
#### `get_flag_index_deltas`
```python
def get_flag_index_deltas(state: BeaconState, flag_index: int) -> Tuple[Sequence[Gwei], Sequence[Gwei]]:
"""
Return the deltas for a given ``flag_index`` by scanning through the participation flags.
"""
rewards = [Gwei(0)] * len(state.validators)
penalties = [Gwei(0)] * len(state.validators)
previous_epoch = get_previous_epoch(state)
unslashed_participating_indices = get_unslashed_participating_indices(state, flag_index, previous_epoch)
weight = PARTICIPATION_FLAG_WEIGHTS[flag_index]
unslashed_participating_balance = get_total_balance(state, unslashed_participating_indices)
unslashed_participating_increments = unslashed_participating_balance // EFFECTIVE_BALANCE_INCREMENT
active_increments = get_total_active_balance(state) // EFFECTIVE_BALANCE_INCREMENT
for index in get_eligible_validator_indices(state):
base_reward = get_base_reward(state, index)
if index in unslashed_participating_indices:
if not is_in_inactivity_leak(state):
reward_numerator = base_reward * weight * unslashed_participating_increments
rewards[index] += Gwei(reward_numerator // (active_increments * WEIGHT_DENOMINATOR))
elif flag_index != TIMELY_HEAD_FLAG_INDEX:
penalties[index] += Gwei(base_reward * weight // WEIGHT_DENOMINATOR)
return rewards, penalties
```
#### Modified `get_inactivity_penalty_deltas`
```python
def get_inactivity_penalty_deltas(state: BeaconState) -> Tuple[Sequence[Gwei], Sequence[Gwei]]:
"""
Return the inactivity penalty deltas by considering timely target participation flags and inactivity scores.
"""
rewards = [Gwei(0) for _ in range(len(state.validators))]
penalties = [Gwei(0) for _ in range(len(state.validators))]
previous_epoch = get_previous_epoch(state)
matching_target_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, previous_epoch)
for index in get_eligible_validator_indices(state):
if index not in matching_target_indices:
penalty_numerator = state.validators[index].effective_balance * state.inactivity_scores[index]
penalty_denominator = INACTIVITY_SCORE_BIAS * INACTIVITY_PENALTY_QUOTIENT_ALTAIR
penalties[index] += Gwei(penalty_numerator // penalty_denominator)
return rewards, penalties
```
### Beacon state mutators
#### Modified `slash_validator`
*Note*: The function `slash_validator` is modified to use `MIN_SLASHING_PENALTY_QUOTIENT_ALTAIR`
and use `PROPOSER_WEIGHT` when calculating the proposer reward.
```python
def slash_validator(state: BeaconState,
slashed_index: ValidatorIndex,
whistleblower_index: ValidatorIndex=None) -> None:
"""
Slash the validator with index ``slashed_index``.
"""
epoch = get_current_epoch(state)
initiate_validator_exit(state, slashed_index)
validator = state.validators[slashed_index]
validator.slashed = True
validator.withdrawable_epoch = max(validator.withdrawable_epoch, Epoch(epoch + EPOCHS_PER_SLASHINGS_VECTOR))
state.slashings[epoch % EPOCHS_PER_SLASHINGS_VECTOR] += validator.effective_balance
decrease_balance(state, slashed_index, validator.effective_balance // MIN_SLASHING_PENALTY_QUOTIENT_ALTAIR)
# Apply proposer and whistleblower rewards
proposer_index = get_beacon_proposer_index(state)
if whistleblower_index is None:
whistleblower_index = proposer_index
whistleblower_reward = Gwei(validator.effective_balance // WHISTLEBLOWER_REWARD_QUOTIENT)
proposer_reward = Gwei(whistleblower_reward * PROPOSER_WEIGHT // WEIGHT_DENOMINATOR)
increase_balance(state, proposer_index, proposer_reward)
increase_balance(state, whistleblower_index, Gwei(whistleblower_reward - proposer_reward))
```
### Block processing
```python
def process_block(state: BeaconState, block: BeaconBlock) -> None:
process_block_header(state, block)
process_randao(state, block.body)
process_eth1_data(state, block.body)
process_operations(state, block.body) # [Modified in Altair]
process_sync_aggregate(state, block.body.sync_aggregate) # [New in Altair]
```
#### Modified `process_attestation`
*Note*: The function `process_attestation` is modified to do incentive accounting with epoch participation flags.
```python
def process_attestation(state: BeaconState, attestation: Attestation) -> None:
data = attestation.data
assert data.target.epoch in (get_previous_epoch(state), get_current_epoch(state))
assert data.target.epoch == compute_epoch_at_slot(data.slot)
assert data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot <= data.slot + SLOTS_PER_EPOCH
assert data.index < get_committee_count_per_slot(state, data.target.epoch)
committee = get_beacon_committee(state, data.slot, data.index)
assert len(attestation.aggregation_bits) == len(committee)
# Participation flag indices
participation_flag_indices = get_attestation_participation_flag_indices(state, data, state.slot - data.slot)
# Verify signature
assert is_valid_indexed_attestation(state, get_indexed_attestation(state, attestation))
# Update epoch participation flags
if data.target.epoch == get_current_epoch(state):
epoch_participation = state.current_epoch_participation
else:
epoch_participation = state.previous_epoch_participation
proposer_reward_numerator = 0
for index in get_attesting_indices(state, attestation):
for flag_index, weight in enumerate(PARTICIPATION_FLAG_WEIGHTS):
if flag_index in participation_flag_indices and not has_flag(epoch_participation[index], flag_index):
epoch_participation[index] = add_flag(epoch_participation[index], flag_index)
proposer_reward_numerator += get_base_reward(state, index) * weight
# Reward proposer
proposer_reward_denominator = (WEIGHT_DENOMINATOR - PROPOSER_WEIGHT) * WEIGHT_DENOMINATOR // PROPOSER_WEIGHT
proposer_reward = Gwei(proposer_reward_numerator // proposer_reward_denominator)
increase_balance(state, get_beacon_proposer_index(state), proposer_reward)
```
#### Modified `add_validator_to_registry`
*Note*: The function `add_validator_to_registry` is modified to initialize `inactivity_scores`, `previous_epoch_participation`, and `current_epoch_participation`.
```python
def add_validator_to_registry(state: BeaconState,
pubkey: BLSPubkey,
withdrawal_credentials: Bytes32,
amount: uint64) -> None:
index = get_index_for_new_validator(state)
validator = get_validator_from_deposit(pubkey, withdrawal_credentials, amount)
set_or_append_list(state.validators, index, validator)
set_or_append_list(state.balances, index, amount)
# [New in Altair]
set_or_append_list(state.previous_epoch_participation, index, ParticipationFlags(0b0000_0000))
set_or_append_list(state.current_epoch_participation, index, ParticipationFlags(0b0000_0000))
set_or_append_list(state.inactivity_scores, index, uint64(0))
```
#### Sync aggregate processing
*Note*: The function `process_sync_aggregate` is new.
```python
def process_sync_aggregate(state: BeaconState, sync_aggregate: SyncAggregate) -> None:
# Verify sync committee aggregate signature signing over the previous slot block root
committee_pubkeys = state.current_sync_committee.pubkeys
participant_pubkeys = [pubkey for pubkey, bit in zip(committee_pubkeys, sync_aggregate.sync_committee_bits) if bit]
previous_slot = max(state.slot, Slot(1)) - Slot(1)
domain = get_domain(state, DOMAIN_SYNC_COMMITTEE, compute_epoch_at_slot(previous_slot))
signing_root = compute_signing_root(get_block_root_at_slot(state, previous_slot), domain)
assert eth_fast_aggregate_verify(participant_pubkeys, signing_root, sync_aggregate.sync_committee_signature)
# Compute participant and proposer rewards
total_active_increments = get_total_active_balance(state) // EFFECTIVE_BALANCE_INCREMENT
total_base_rewards = Gwei(get_base_reward_per_increment(state) * total_active_increments)
max_participant_rewards = Gwei(total_base_rewards * SYNC_REWARD_WEIGHT // WEIGHT_DENOMINATOR // SLOTS_PER_EPOCH)
participant_reward = Gwei(max_participant_rewards // SYNC_COMMITTEE_SIZE)
proposer_reward = Gwei(participant_reward * PROPOSER_WEIGHT // (WEIGHT_DENOMINATOR - PROPOSER_WEIGHT))
# Apply participant and proposer rewards
all_pubkeys = [v.pubkey for v in state.validators]
committee_indices = [ValidatorIndex(all_pubkeys.index(pubkey)) for pubkey in state.current_sync_committee.pubkeys]
for participant_index, participation_bit in zip(committee_indices, sync_aggregate.sync_committee_bits):
if participation_bit:
increase_balance(state, participant_index, participant_reward)
increase_balance(state, get_beacon_proposer_index(state), proposer_reward)
else:
decrease_balance(state, participant_index, participant_reward)
```
### Epoch processing
```python
def process_epoch(state: BeaconState) -> None:
process_justification_and_finalization(state) # [Modified in Altair]
process_inactivity_updates(state) # [New in Altair]
process_rewards_and_penalties(state) # [Modified in Altair]
process_registry_updates(state)
process_slashings(state) # [Modified in Altair]
process_eth1_data_reset(state)
process_effective_balance_updates(state)
process_slashings_reset(state)
process_randao_mixes_reset(state)
process_historical_roots_update(state)
process_participation_flag_updates(state) # [New in Altair]
process_sync_committee_updates(state) # [New in Altair]
```
#### Justification and finalization
*Note*: The function `process_justification_and_finalization` is modified to adapt to the new participation records.
```python
def process_justification_and_finalization(state: BeaconState) -> None:
# Initial FFG checkpoint values have a `0x00` stub for `root`.
# Skip FFG updates in the first two epochs to avoid corner cases that might result in modifying this stub.
if get_current_epoch(state) <= GENESIS_EPOCH + 1:
return
previous_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_previous_epoch(state))
current_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_current_epoch(state))
total_active_balance = get_total_active_balance(state)
previous_target_balance = get_total_balance(state, previous_indices)
current_target_balance = get_total_balance(state, current_indices)
weigh_justification_and_finalization(state, total_active_balance, previous_target_balance, current_target_balance)
```
#### Inactivity scores
*Note*: The function `process_inactivity_updates` is new.
```python
def process_inactivity_updates(state: BeaconState) -> None:
# Skip the genesis epoch as score updates are based on the previous epoch participation
if get_current_epoch(state) == GENESIS_EPOCH:
return
for index in get_eligible_validator_indices(state):
# Increase the inactivity score of inactive validators
if index in get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_previous_epoch(state)):
state.inactivity_scores[index] -= min(1, state.inactivity_scores[index])
else:
state.inactivity_scores[index] += INACTIVITY_SCORE_BIAS
# Decrease the inactivity score of all eligible validators during a leak-free epoch
if not is_in_inactivity_leak(state):
state.inactivity_scores[index] -= min(INACTIVITY_SCORE_RECOVERY_RATE, state.inactivity_scores[index])
```
#### Rewards and penalties
*Note*: The function `process_rewards_and_penalties` is modified to support the incentive accounting reforms.
```python
def process_rewards_and_penalties(state: BeaconState) -> None:
# No rewards are applied at the end of `GENESIS_EPOCH` because rewards are for work done in the previous epoch
if get_current_epoch(state) == GENESIS_EPOCH:
return
flag_deltas = [get_flag_index_deltas(state, flag_index) for flag_index in range(len(PARTICIPATION_FLAG_WEIGHTS))]
deltas = flag_deltas + [get_inactivity_penalty_deltas(state)]
for (rewards, penalties) in deltas:
for index in range(len(state.validators)):
increase_balance(state, ValidatorIndex(index), rewards[index])
decrease_balance(state, ValidatorIndex(index), penalties[index])
```
#### Slashings
*Note*: The function `process_slashings` is modified to use `PROPORTIONAL_SLASHING_MULTIPLIER_ALTAIR`.
```python
def process_slashings(state: BeaconState) -> None:
epoch = get_current_epoch(state)
total_balance = get_total_active_balance(state)
adjusted_total_slashing_balance = min(sum(state.slashings) * PROPORTIONAL_SLASHING_MULTIPLIER_ALTAIR, total_balance)
for index, validator in enumerate(state.validators):
if validator.slashed and epoch + EPOCHS_PER_SLASHINGS_VECTOR // 2 == validator.withdrawable_epoch:
increment = EFFECTIVE_BALANCE_INCREMENT # Factored out from penalty numerator to avoid uint64 overflow
penalty_numerator = validator.effective_balance // increment * adjusted_total_slashing_balance
penalty = penalty_numerator // total_balance * increment
decrease_balance(state, ValidatorIndex(index), penalty)
```
#### Participation flags updates
*Note*: The function `process_participation_flag_updates` is new.
```python
def process_participation_flag_updates(state: BeaconState) -> None:
state.previous_epoch_participation = state.current_epoch_participation
state.current_epoch_participation = [ParticipationFlags(0b0000_0000) for _ in range(len(state.validators))]
```
#### Sync committee updates
*Note*: The function `process_sync_committee_updates` is new.
```python
def process_sync_committee_updates(state: BeaconState) -> None:
next_epoch = get_current_epoch(state) + Epoch(1)
if next_epoch % EPOCHS_PER_SYNC_COMMITTEE_PERIOD == 0:
state.current_sync_committee = state.next_sync_committee
state.next_sync_committee = get_next_sync_committee(state)
```
## Initialize state for pure Altair testnets and test vectors
This helper function is only for initializing the state for pure Altair testnets and tests.
*Note*: The function `initialize_beacon_state_from_eth1` is modified: (1) using `ALTAIR_FORK_VERSION` as the previous and current fork version, (2) utilizing the Altair `BeaconBlockBody` when constructing the initial `latest_block_header`, and (3) adding initial sync committees.
```python
def initialize_beacon_state_from_eth1(eth1_block_hash: Hash32,
eth1_timestamp: uint64,
deposits: Sequence[Deposit]) -> BeaconState:
fork = Fork(
previous_version=ALTAIR_FORK_VERSION, # [Modified in Altair] for testing only
current_version=ALTAIR_FORK_VERSION, # [Modified in Altair]
epoch=GENESIS_EPOCH,
)
state = BeaconState(
genesis_time=eth1_timestamp + GENESIS_DELAY,
fork=fork,
eth1_data=Eth1Data(block_hash=eth1_block_hash, deposit_count=uint64(len(deposits))),
latest_block_header=BeaconBlockHeader(body_root=hash_tree_root(BeaconBlockBody())),
randao_mixes=[eth1_block_hash] * EPOCHS_PER_HISTORICAL_VECTOR, # Seed RANDAO with Eth1 entropy
)
# Process deposits
leaves = list(map(lambda deposit: deposit.data, deposits))
for index, deposit in enumerate(deposits):
deposit_data_list = List[DepositData, 2**DEPOSIT_CONTRACT_TREE_DEPTH](*leaves[:index + 1])
state.eth1_data.deposit_root = hash_tree_root(deposit_data_list)
process_deposit(state, deposit)
# Process activations
for index, validator in enumerate(state.validators):
balance = state.balances[index]
validator.effective_balance = min(balance - balance % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE)
if validator.effective_balance == MAX_EFFECTIVE_BALANCE:
validator.activation_eligibility_epoch = GENESIS_EPOCH
validator.activation_epoch = GENESIS_EPOCH
# Set genesis validators root for domain separation and chain versioning
state.genesis_validators_root = hash_tree_root(state.validators)
# [New in Altair] Fill in sync committees
# Note: A duplicate committee is assigned for the current and next committee at genesis
state.current_sync_committee = get_next_sync_committee(state)
state.next_sync_committee = get_next_sync_committee(state)
return state
```
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