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Justin Drake 2019-04-18 19:33:38 +10:00
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specs/core/0_beacon-chain.md
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@ -1627,33 +1627,34 @@ def get_previous_epoch_matching_head_attestations(state: BeaconState) -> List[Pe
**Note**: Total balances computed for the previous epoch might be marginally different than the actual total balances during the previous epoch transition. Due to the tight bound on validator churn each epoch and small per-epoch rewards/penalties, the potential balance difference is very low and only marginally affects consensus safety. **Note**: Total balances computed for the previous epoch might be marginally different than the actual total balances during the previous epoch transition. Due to the tight bound on validator churn each epoch and small per-epoch rewards/penalties, the potential balance difference is very low and only marginally affects consensus safety.
```python
def get_crosslink_from_attestation_data(state: BeaconState, data: AttestationData) -> Crosslink:
return Crosslink(
epoch=min(slot_to_epoch(data.slot), state.current_crosslinks[data.shard].epoch + MAX_CROSSLINK_EPOCHS),
crosslink_data_root=data.crosslink_data_root,
previous_crosslink_root=data.previous_crosslink_root,
)
```
```python ```python
def get_winning_crosslink_and_attesting_indices(state: BeaconState, epoch: Epoch, shard: Shard) -> Tuple[Crosslink, List[ValidatorIndex]]: def get_winning_crosslink_and_attesting_indices(state: BeaconState, epoch: Epoch, shard: Shard) -> Tuple[Crosslink, List[ValidatorIndex]]:
pending_attestations = state.current_epoch_attestations if epoch == get_current_epoch(state) else state.previous_epoch_attestations pending_attestations = state.current_epoch_attestations if epoch == get_current_epoch(state) else state.previous_epoch_attestations
shard_attestations = [a for a in pending_attestations if a.data.shard == shard] shard_attestations = [a for a in pending_attestations if a.data.shard == shard]
shard_crosslinks = [ shard_crosslinks = [get_crosslink_from_attestation_data(state, a.data) for a in shard_attestations]
Crosslink(
epoch=min(epoch, state.current_crosslinks[shard].epoch + MAX_CROSSLINK_EPOCHS),
crosslink_data_root=a.data.crosslink_data_root,
previous_crosslink_root=a.data.previous_crosslink_root,
) for a in shard_attestations
]
candidate_crosslinks = [c for c in shard_crosslinks if candidate_crosslinks = [c for c in shard_crosslinks if
hash_tree_root(state.current_crosslinks[shard]) in (c.previous_crosslink_root, hash_tree_root(c)) hash_tree_root(state.current_crosslinks[shard]) in (c.previous_crosslink_root, hash_tree_root(c))
] ]
if len(candidate_crosslinks) == 0: if len(candidate_crosslinks) == 0:
return Crosslink(epoch=GENESIS_EPOCH, previous_crosslink_root=ZERO_HASH, crosslink_data_root=ZERO_HASH), [] return Crosslink(epoch=GENESIS_EPOCH, previous_crosslink_root=ZERO_HASH, crosslink_data_root=ZERO_HASH), []
def get_attestations_for(crosslink_data_root) -> List[PendingAttestation]: def get_attestations_for(crosslink: Crosslink) -> List[PendingAttestation]:
return [a for a in shard_attestations if a.data.crosslink_data_root == crosslink_data_root] return [a for a in shard_attestations if get_crosslink_from_attestation_data(state, a.data) == crosslink]
# Winning crosslink has the crosslink data root with the most balance voting for it (ties broken lexicographically) # Winning crosslink has the crosslink data root with the most balance voting for it (ties broken lexicographically)
winning_crosslink = max(candidate_crosslinks, winning_crosslink = max(candidate_crosslinks, key=lambda crosslink: (
key=lambda c: (get_attesting_balance(state, get_attestations_for(c.crosslink_data_root)), c.crosslink_data_root), get_attesting_balance(state, get_attestations_for(crosslink)), crosslink.crosslink_data_root
default=Crosslink(epoch=GENESIS_EPOCH, crosslink_data_root=ZERO_HASH, previous_crosslink_root=ZERO_HASH), ))
)
return winning_crosslink, get_unslashed_attesting_indices(state, get_attestations_for(winning_crosslink.crosslink_data_root)) return winning_crosslink, get_unslashed_attesting_indices(state, get_attestations_for(winning_crosslink))
``` ```
```python ```python