Attestation committee refactor
* Remove `get_crosslink_committees_at_slot` (that function's ugly man...) * Make the "base" that everything works off instead be `get_crosslink_committee` * Attestations store epoch, start shard and shard, no longer slot (slot can be calculated from the other three) * Retaining start shard in attestations allows `get_attesting_indices` to peek much further back into the past, making it useful for slashings (Phase 1) * Some two-layer-deep nested loops become one-layer-deep loops
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vbuterin
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@ -65,7 +65,8 @@
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- [`get_epoch_committee_count`](#get_epoch_committee_count)
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- [`get_shard_delta`](#get_shard_delta)
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- [`compute_committee`](#compute_committee)
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- [`get_crosslink_committees_at_slot`](#get_crosslink_committees_at_slot)
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- [`get_epoch_start_shard`](#get_epoch_start_shard)
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- [`committee_shard_to_slot`](#committee_shard_to_slot)
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- [`get_block_root_at_slot`](#get_block_root_at_slot)
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- [`get_block_root`](#get_block_root)
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- [`get_state_root`](#get_state_root)
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@ -74,6 +75,7 @@
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- [`generate_seed`](#generate_seed)
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- [`get_beacon_proposer_index`](#get_beacon_proposer_index)
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- [`verify_merkle_branch`](#verify_merkle_branch)
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- [`get_crosslink_committee`](#get_crosslink_committee)
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- [`get_attesting_indices`](#get_attesting_indices)
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- [`int_to_bytes1`, `int_to_bytes2`, ...](#int_to_bytes1-int_to_bytes2-)
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- [`bytes_to_int`](#bytes_to_int)
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@ -307,7 +309,7 @@ The types are defined topologically to aid in facilitating an executable version
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```python
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{
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# LMD GHOST vote
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'slot': 'uint64',
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'epoch': 'uint64',
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'beacon_block_root': 'bytes32',
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# FFG vote
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@ -316,6 +318,7 @@ The types are defined topologically to aid in facilitating an executable version
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'target_root': 'bytes32',
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# Crosslink vote
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'epoch_start_shard': 'uint64',
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'shard': 'uint64',
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'previous_crosslink_root': 'bytes32',
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'crosslink_data_root': 'bytes32',
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@ -805,44 +808,30 @@ def compute_committee(validator_indices: List[ValidatorIndex],
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Note: this definition and the next few definitions are highly inefficient as algorithms, as they re-calculate many sub-expressions. Production implementations are expected to appropriately use caching/memoization to avoid redoing work.
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### `get_crosslink_committees_at_slot`
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### `get_epoch_start_shard`
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```python
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def get_crosslink_committees_at_slot(state: BeaconState,
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slot: Slot) -> List[Tuple[List[ValidatorIndex], Shard]]:
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"""
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Return the list of ``(committee, shard)`` tuples for the ``slot``.
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"""
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epoch = slot_to_epoch(slot)
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current_epoch = get_current_epoch(state)
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previous_epoch = get_previous_epoch(state)
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next_epoch = current_epoch + 1
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def get_epoch_start_shard(state: BeaconState, epoch: Epoch) -> Shard:
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if epoch == get_current_epoch(state):
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return state.latest_start_shard
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elif epoch == get_previous_epoch(state):
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previous_shard_delta = get_shard_delta(state, epoch)
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return (state.latest_start_shard - previous_shard_delta) % SHARD_COUNT
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elif epoch == get_current_epoch(state) + 1:
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current_shard_delta = get_shard_delta(state, get_current_epoch(state))
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return (state.latest_start_shard + current_shard_delta) % SHARD_COUNT
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else:
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raise Exception("Not supported")
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```
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assert previous_epoch <= epoch <= next_epoch
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indices = get_active_validator_indices(state, epoch)
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### `committee_shard_to_slot`
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if epoch == current_epoch:
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start_shard = state.latest_start_shard
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elif epoch == previous_epoch:
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previous_shard_delta = get_shard_delta(state, previous_epoch)
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start_shard = (state.latest_start_shard - previous_shard_delta) % SHARD_COUNT
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elif epoch == next_epoch:
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current_shard_delta = get_shard_delta(state, current_epoch)
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start_shard = (state.latest_start_shard + current_shard_delta) % SHARD_COUNT
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committees_per_epoch = get_epoch_committee_count(state, epoch)
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committees_per_slot = committees_per_epoch // SLOTS_PER_EPOCH
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offset = slot % SLOTS_PER_EPOCH
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slot_start_shard = (start_shard + committees_per_slot * offset) % SHARD_COUNT
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seed = generate_seed(state, epoch)
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return [
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(
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compute_committee(indices, seed, committees_per_slot * offset + i, committees_per_epoch),
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(slot_start_shard + i) % SHARD_COUNT,
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)
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for i in range(committees_per_slot)
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]
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```python
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def committee_shard_to_slot(state: BeaconState, epoch: Epoch, shard: Shard) -> Slot:
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start_shard = get_epoch_start_shard(state, epoch)
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committees_per_slot = get_epoch_committee_count(state, epoch) // SLOTS_PER_EPOCH
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offset = (shard - get_epoch_start_slot(epoch)) % SHARD_COUNT
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return get_epoch_start_slot(epoch) + offset // committees_per_slot
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```
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### `get_block_root_at_slot`
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@ -927,7 +916,9 @@ def get_beacon_proposer_index(state: BeaconState) -> ValidatorIndex:
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Return the beacon proposer index at ``state.slot``.
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"""
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current_epoch = get_current_epoch(state)
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first_committee, _ = get_crosslink_committees_at_slot(state, state.slot)[0]
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committees_per_slot = get_epoch_committee_count(state, current_epoch) // SLOTS_PER_EPOCH
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offset = committees_per_slot * (state.slot % EPOCH_LENGTH)
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first_committee = get_crosslink_committee(state, epoch, offset)
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MAX_RANDOM_BYTE = 2**8 - 1
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i = 0
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while True:
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@ -956,6 +947,18 @@ def verify_merkle_branch(leaf: Bytes32, proof: List[Bytes32], depth: int, index:
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return value == root
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```
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### `get_crosslink_committee`
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```python
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def get_crosslink_committee(state: BeaconState, epoch: Epoch, offset: int):
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return compute_committee(
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validator_indices=get_active_validator_indices(state, epoch),
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seed=generate_seed(state, epoch),
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index=offset,
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total_committees=get_epoch_committee_count(state, epoch)
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)
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```
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### `get_attesting_indices`
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```python
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@ -965,10 +968,10 @@ def get_attesting_indices(state: BeaconState,
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"""
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Return the sorted attesting indices corresponding to ``attestation_data`` and ``bitfield``.
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"""
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crosslink_committees = get_crosslink_committees_at_slot(state, attestation_data.slot)
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crosslink_committee = [committee for committee, shard in crosslink_committees if shard == attestation_data.shard][0]
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assert verify_bitfield(bitfield, len(crosslink_committee))
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return sorted([index for i, index in enumerate(crosslink_committee) if get_bitfield_bit(bitfield, i) == 0b1])
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offset = (attestation_data.shard - attestation_data.epoch_start_shard) % SHARD_COUNT
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committee = get_crosslink_committee(state, attestation_data.epoch, offset)
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assert verify_bitfield(bitfield, len(committee))
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return sorted([index for i, index in enumerate(committee) if get_bitfield_bit(bitfield, i) == 0b1])
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```
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### `int_to_bytes1`, `int_to_bytes2`, ...
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@ -1088,7 +1091,7 @@ def verify_indexed_attestation(state: BeaconState, indexed_attestation: IndexedA
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hash_tree_root(AttestationDataAndCustodyBit(data=indexed_attestation.data, custody_bit=0b1)),
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],
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signature=indexed_attestation.signature,
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domain=get_domain(state, DOMAIN_ATTESTATION, slot_to_epoch(indexed_attestation.data.slot)),
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domain=get_domain(state, DOMAIN_ATTESTATION, indexed_attestation.data.epoch),
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)
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```
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@ -1331,7 +1334,7 @@ def get_matching_target_attestations(state: BeaconState, epoch: Epoch) -> List[P
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def get_matching_head_attestations(state: BeaconState, epoch: Epoch) -> List[PendingAttestation]:
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return [
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a for a in get_matching_source_attestations(state, epoch)
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if a.data.beacon_block_root == get_block_root_at_slot(state, a.data.slot)
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if a.data.beacon_block_root == get_block_root_at_slot(state, committee_shard_to_slot(state, epoch, a.data.shard))
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]
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```
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@ -1351,7 +1354,7 @@ def get_attesting_balance(state: BeaconState, attestations: List[PendingAttestat
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```python
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def get_crosslink_from_attestation_data(state: BeaconState, data: AttestationData) -> Crosslink:
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return Crosslink(
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epoch=min(slot_to_epoch(data.slot), state.current_crosslinks[data.shard].epoch + MAX_CROSSLINK_EPOCHS),
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epoch=min(data.epoch, state.current_crosslinks[data.shard].epoch + MAX_CROSSLINK_EPOCHS),
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previous_crosslink_root=data.previous_crosslink_root,
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crosslink_data_root=data.crosslink_data_root,
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)
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@ -1444,8 +1447,10 @@ def process_crosslinks(state: BeaconState) -> None:
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previous_epoch = get_previous_epoch(state)
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next_epoch = get_current_epoch(state) + 1
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for slot in range(get_epoch_start_slot(previous_epoch), get_epoch_start_slot(next_epoch)):
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epoch = slot_to_epoch(slot)
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for crosslink_committee, shard in get_crosslink_committees_at_slot(state, slot):
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for epoch in (get_previous_epoch(state), get_current_epoch(state)):
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for offset in range(get_epoch_committee_count(state, epoch)):
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shard = (get_epoch_start_shard(epoch) + offset) % SHARD_COUNT
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crosslink_committee = get_crosslink_committee(state, epoch, offset)
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winning_crosslink, attesting_indices = get_winning_crosslink_and_attesting_indices(state, shard, epoch)
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if 3 * get_total_balance(state, attesting_indices) >= 2 * get_total_balance(state, crosslink_committee):
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state.current_crosslinks[shard] = winning_crosslink
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@ -1492,7 +1497,8 @@ def get_attestation_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:
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for index in get_unslashed_attesting_indices(state, matching_source_attestations):
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earliest_attestation = get_earliest_attestation(state, matching_source_attestations, index)
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rewards[earliest_attestation.proposer_index] += get_base_reward(state, index) // PROPOSER_REWARD_QUOTIENT
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inclusion_delay = earliest_attestation.inclusion_slot - earliest_attestation.data.slot
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attestation_slot = committee_shard_to_slot(state, earliest_attestation.data.epoch, earliest_attestation.data.shard)
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inclusion_delay = earliest_attestation.inclusion_slot - attestation_slot
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rewards[index] += get_base_reward(state, index) * MIN_ATTESTATION_INCLUSION_DELAY // inclusion_delay
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# Inactivity penalty
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@ -1511,9 +1517,10 @@ def get_attestation_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:
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def get_crosslink_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:
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rewards = [0 for index in range(len(state.validator_registry))]
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penalties = [0 for index in range(len(state.validator_registry))]
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for slot in range(get_epoch_start_slot(get_previous_epoch(state)), get_epoch_start_slot(get_current_epoch(state))):
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epoch = slot_to_epoch(slot)
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for crosslink_committee, shard in get_crosslink_committees_at_slot(state, slot):
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epoch = get_previous_epoch(state)
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for offset in range(get_epoch_committee_count(state, epoch)):
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shard = (get_epoch_start_shard(epoch) + offset) % SHARD_COUNT
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crosslink_committee = get_crosslink_committee(state, epoch, offset)
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winning_crosslink, attesting_indices = get_winning_crosslink_and_attesting_indices(state, shard, epoch)
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attesting_balance = get_total_balance(state, attesting_indices)
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committee_balance = get_total_balance(state, crosslink_committee)
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@ -1770,16 +1777,20 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
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Note that this function mutates ``state``.
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"""
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data = attestation.data
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attestation_slot = committee_shard_to_slot(state, data.epoch, attestation.shard)
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min_slot = state.slot - SLOTS_PER_EPOCH if get_current_epoch(state) > GENESIS_EPOCH else GENESIS_SLOT
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assert min_slot <= data.slot <= state.slot - MIN_ATTESTATION_INCLUSION_DELAY
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assert min_slot <= attestation_slot <= state.slot - MIN_ATTESTATION_INCLUSION_DELAY
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# Check target epoch, source epoch, source root, and source crosslink
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target_epoch = slot_to_epoch(data.slot)
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assert (target_epoch, data.source_epoch, data.source_root, data.previous_crosslink_root) in {
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assert (data.epoch, data.source_epoch, data.source_root, data.previous_crosslink_root) in {
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(get_current_epoch(state), state.current_justified_epoch, state.current_justified_root, hash_tree_root(state.current_crosslinks[data.shard])),
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(get_previous_epoch(state), state.previous_justified_epoch, state.previous_justified_root, hash_tree_root(state.previous_crosslinks[data.shard])),
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}
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# Check shard and epoch start shard
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assert data.epoch_start_shard == get_epoch_start_shard(state, data.epoch)
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assert (data.shard - data.epoch_start_shard) % SHARD_COUNT < get_epoch_committee_count(state, data.epoch)
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# Check crosslink data root
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assert data.crosslink_data_root == ZERO_HASH # [to be removed in phase 1]
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