prev -> previous, cur -> current, get_shard_committee_at_slot rework, get_randao_mix rework

This commit is contained in:
Vitalik Buterin 2019-01-10 11:01:19 -06:00
parent 0b16430cf5
commit e2886bf3d3
1 changed files with 66 additions and 52 deletions

View File

@ -67,10 +67,11 @@
- [`split`](#split)
- [`get_committees_per_slot`](#get_committees_per_slot)
- [`get_shuffling`](#get_shuffling)
- [`get_prev_epoch_committees_per_slot`](#get_prev_epoch_committees_per_slot)
- [`get_cur_epoch_committees_per_slot`](#get_cur_epoch_committees_per_slot)
- [`get_previous_epoch_committees_per_slot`](#get_previous_epoch_committees_per_slot)
- [`get_current_epoch_committees_per_slot`](#get_current_epoch_committees_per_slot)
- [`get_shard_committees_at_slot`](#get_shard_committees_at_slot)
- [`get_block_root`](#get_block_root)
- [`get_randao_mix`](#get_randao_mix)
- [`get_beacon_proposer_index`](#get_beacon_proposer_index)
- [`merkle_root`](#merkle_root)
- [`get_attestation_participants`](#get_attestation_participants)
@ -480,12 +481,12 @@ Unless otherwise indicated, code appearing in `this style` is to be interpreted
# Randomness and committees
'latest_randao_mixes': ['hash32'],
'latest_vdf_outputs': ['hash32'],
'prev_epoch_start_shard': 'uint64',
'cur_epoch_start_shard': 'uint64',
'prev_epoch_calculation_slot': 'uint64',
'cur_epoch_calculation_slot': 'uint64',
'prev_epoch_randao_mix': 'hash32',
'cur_epoch_randao_mix': 'hash32',
'previous_epoch_start_shard': 'uint64',
'current_epoch_start_shard': 'uint64',
'previous_epoch_calculation_slot': 'uint64',
'current_epoch_calculation_slot': 'uint64',
'previous_epoch_randao_mix': 'hash32',
'current_epoch_randao_mix': 'hash32',
# Custody challenges
'custody_challenges': [CustodyChallenge],
@ -891,27 +892,27 @@ def get_shuffling(seed: Hash32,
**Note**: this definition and the next few definitions make heavy use of repetitive computing. Production implementations are expected to appropriately use caching/memoization to avoid redoing work.
#### `get_prev_epoch_committees_per_slot`
#### `get_previous_epoch_committees_per_slot`
```python
def get_prev_epoch_committees_per_slot(state: BeaconState) -> int:
prev_active_validators = get_active_validator_indices(validators, state.prev_epoch_calculation_slot)
return get_committees_per_slot(len(prev_active_validators))
def get_previous_epoch_committees_per_slot(state: BeaconState) -> int:
previous_active_validators = get_active_validator_indices(validators, state.previous_epoch_calculation_slot)
return get_committees_per_slot(len(previous_active_validators))
```
#### `get_cur_epoch_committees_per_slot`
#### `get_current_epoch_committees_per_slot`
```python
def get_cur_epoch_committees_per_slot(state: BeaconState) -> int:
cur_active_validators = get_active_validator_indices(validators, state.cur_epoch_calculation_slot)
return get_committees_per_slot(len(cur_active_validators))
def get_current_epoch_committees_per_slot(state: BeaconState) -> int:
current_active_validators = get_active_validator_indices(validators, state.current_epoch_calculation_slot)
return get_committees_per_slot(len(current_active_validators))
```
#### `get_shard_committees_at_slot`
```python
def get_shard_committees_at_slot(state: BeaconState,
slot: int) -> Tuple[List[List[int]], int]:
slot: int) -> List[Tuple[List[int], int]]:
"""
Returns (i) the list of committees and (ii) the shard associated with the first committee for the ``slot``.
"""
@ -920,22 +921,22 @@ def get_shard_committees_at_slot(state: BeaconState,
offset = slot % EPOCH_LENGTH
if slot < earliest_slot + EPOCH_LENGTH:
committees_per_slot = get_prev_epoch_committees_per_slot(state)
shuffling = get_shuffling(state.prev_epoch_randao_mix,
committees_per_slot = get_previous_epoch_committees_per_slot(state)
shuffling = get_shuffling(state.previous_epoch_randao_mix,
state.validator_registry,
state.prev_epoch_calculation_slot)
start_shard = state.prev_epoch_start_shard
state.previous_epoch_calculation_slot)
slot_start_shard = (state.previous_epoch_start_shard + committees_per_slot * offset) % SHARD_COUNT
else:
committees_per_slot = get_cur_epoch_committees_per_slot(state)
shuffling = get_shuffling(state.cur_epoch_randao_mix,
committees_per_slot = get_current_epoch_committees_per_slot(state)
shuffling = get_shuffling(state.current_epoch_randao_mix,
state.validator_registry,
state.cur_epoch_calculation_slot)
start_shard = state.cur_epoch_start_shard
state.current_epoch_calculation_slot)
slot_start_shard = (state.current_epoch_start_shard + committees_per_slot * offset) % SHARD_COUNT
return (
shuffling[committees_per_slot * offset: committees_per_slot * (offset + 1)],
(start_shard + committees_per_slot * offset) % SHARD_COUNT
)
return [
(shuffling[committees_per_slot * offset + i], (slot_start_shard + i) % SHARD_COUNT)
for i in range(committees_per_slot)
]
```
**Note**: we plan to replace the shuffling algorithm with a pointwise-evaluable shuffle (see https://github.com/ethereum/eth2.0-specs/issues/323), which will allow calculation of the committees for each slot individually.
@ -955,6 +956,19 @@ def get_block_root(state: BeaconState,
`get_block_root(_, s)` should always return `hash_tree_root` of the block in the beacon chain at slot `s`, and `get_shard_committees_at_slot(_, s)` should not change unless the [validator](#dfn-validator) registry changes.
#### `get_randao_mix`
```python
def get_randao_mix(state: BeaconState,
slot: int) -> Hash32:
"""
Returns the randao mix at a recent ``slot``.
"""
assert state.slot <= slot + LATEST_RANDAO_MIXES_LENGTH
assert slot < state.slot
return state.latest_block_roots[slot % LATEST_RANDAO_MIXES_LENGTH]
```
#### `get_beacon_proposer_index`
```python
@ -963,8 +977,8 @@ def get_beacon_proposer_index(state: BeaconState,
"""
Returns the beacon proposer index for the ``slot``.
"""
committees, shard = get_shard_committees_at_slot(state, slot)
return committees[0][slot % len(committees[0])]
first_committee, _ = get_shard_committees_at_slot(state, slot)[0]
return first_committee[slot % len(first_committee)]
```
#### `merkle_root`
@ -990,9 +1004,9 @@ def get_attestation_participants(state: BeaconState,
Returns the participant indices at for the ``attestation_data`` and ``participation_bitfield``.
"""
# Find the relevant committee
shard_committees, start_shard = get_shard_committees_at_slot(state, attestation_data.slot)
shard_committee = shard_committee[(attestation_data.shard - start_shard) % SHARD_COUNT]
# Find the committee in the list with the desired shard
shard_committees = get_shard_committees_at_slot(state, attestation_data.slot)
shard_committee = [committee for committee, shard in shard_committees if shard == attestation_data.shard][0]
assert len(participation_bitfield) == ceil_div8(len(shard_committee))
# Find the participating attesters in the committee
@ -1182,12 +1196,12 @@ def get_initial_beacon_state(initial_validator_deposits: List[Deposit],
# Randomness and committees
latest_randao_mixes=[ZERO_HASH for _ in range(LATEST_RANDAO_MIXES_LENGTH)],
latest_vdf_outputs=[ZERO_HASH for _ in range(LATEST_RANDAO_MIXES_LENGTH // EPOCH_LENGTH)],
prev_epoch_start_shard=0,
cur_epoch_start_shard=GENESIS_START_SHARD,
prev_epoch_calculation_slot=GENESIS_SLOT,
cur_epoch_calculation_slot=GENESIS_SLOT,
prev_epoch_randao_mix=ZERO_HASH,
cur_epoch_randao_mix=ZERO_HASH,
previous_epoch_start_shard=0,
current_epoch_start_shard=GENESIS_START_SHARD,
previous_epoch_calculation_slot=GENESIS_SLOT,
current_epoch_calculation_slot=GENESIS_SLOT,
previous_epoch_randao_mix=ZERO_HASH,
current_epoch_randao_mix=ZERO_HASH,
# Custody challenges
custody_challenges=[],
@ -1572,7 +1586,7 @@ All [validators](#dfn-validator):
**Note**: `previous_epoch_boundary_attesting_balance` balance might be marginally different than `current_epoch_boundary_attesting_balance` 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.
For every `slot in range(state.slot - 2 * EPOCH_LENGTH, state.slot)`, let `shard_committee_at_slot, start_shard = get_shard_committees_at_slot(slot)`. For every `index in range(len(shard_committee_at_slot))`, let `shard_committee = shard_committee_at_slot[index]`, `shard = (start_shard + index) % SHARD_COUNT`, and compute:
For every `slot in range(state.slot - 2 * EPOCH_LENGTH, state.slot)`, let `shard_committee_at_slot = get_shard_committees_at_slot(slot)`. For every `(shard_committee, shard)` in `shard_committee_at_slot`, compute:
* Let `shard_block_root` be `state.latest_crosslinks[shard].shard_block_root`
* Let `attesting_validator_indices(shard_committee, shard_block_root)` be the union of the [validator](#dfn-validator) index sets given by `[get_attestation_participants(state, a.data, a.participation_bitfield) for a in current_epoch_attestations + previous_epoch_attestations if a.shard == shard and a.shard_block_root == shard_block_root]`.
@ -1605,7 +1619,7 @@ Set `state.finalized_slot = state.previous_justified_slot` if any of the followi
### Crosslinks
For every `slot in range(state.slot - 2 * EPOCH_LENGTH, state.slot)`, let `shard_committee_at_slot, start_shard = get_shard_committees_at_slot(slot)`. For every `index in range(len(shard_committee_at_slot))`, let `shard_committee = shard_committee_at_slot[index]`, `shard = (start_shard + index) % SHARD_COUNT`, and compute:
For every `slot in range(state.slot - 2 * EPOCH_LENGTH, state.slot)`, let `shard_committee_at_slot = get_shard_committees_at_slot(slot)`. For every `(shard_committee, shard)` in `shard_committee_at_slot`, compute:
* Set `state.latest_crosslinks[shard] = CrosslinkRecord(slot=state.slot, shard_block_root=winning_root(shard_committee))` if `3 * total_attesting_balance(shard_committee) >= 2 * total_balance(shard_committee)`.
@ -1676,7 +1690,7 @@ def process_ejections(state: BeaconState) -> None:
If the following are satisfied:
* `state.finalized_slot > state.validator_registry_latest_change_slot`
* `state.latest_crosslinks[shard].slot > state.validator_registry_latest_change_slot` for every shard number `shard` in `[(state.cur_epoch_start_shard + i) % SHARD_COUNT for i in range(get_cur_epoch_committees_per_slot(state) * EPOCH_LENGTH)]` (that is, for every shard in the current committees)
* `state.latest_crosslinks[shard].slot > state.validator_registry_latest_change_slot` for every shard number `shard` in `[(state.current_epoch_start_shard + i) % SHARD_COUNT for i in range(get_current_epoch_committees_per_slot(state) * EPOCH_LENGTH)]` (that is, for every shard in the current committees)
update the validator registry and associated fields by running
@ -1726,19 +1740,19 @@ def update_validator_registry(state: BeaconState) -> None:
and perform the following updates:
* Set `state.prev_epoch_calculation_slot = state.cur_epoch_calculation_slot`
* Set `state.prev_epoch_start_shard = state.cur_epoch_start_shard`
* Set `state.prev_epoch_randao_mix = state.cur_epoch_randao_mix`
* Set `state.cur_epoch_calculation_slot = state.slot`
* Set `state.cur_epoch_start_shard = (state.cur_epoch_start_shard + get_cur_epoch_committees_per_slot(state) * EPOCH_LENGTH) % SHARD_COUNT`
* Set `state.cur_epoch_randao_mix = state.latest_randao_mixes[(state.cur_epoch_calculation_slot - SEED_LOOKAHEAD) % LATEST_RANDAO_MIXES_LENGTH]`
* Set `state.previous_epoch_calculation_slot = state.current_epoch_calculation_slot`
* Set `state.previous_epoch_start_shard = state.current_epoch_start_shard`
* Set `state.previous_epoch_randao_mix = state.current_epoch_randao_mix`
* Set `state.current_epoch_calculation_slot = state.slot`
* Set `state.current_epoch_start_shard = (state.current_epoch_start_shard + get_current_epoch_committees_per_slot(state) * EPOCH_LENGTH) % SHARD_COUNT`
* Set `state.current_epoch_randao_mix = get_randao_mix(state, state.current_epoch_calculation_slot - SEED_LOOKAHEAD)`
If a validator registry update does _not_ happen do the following:
* Set `state.prev_epoch_calculation_slot = state.cur_epoch_calculation_slot`
* Set `state.prev_epoch_start_shard = state.cur_epoch_start_shard`
* Set `state.previous_epoch_calculation_slot = state.current_epoch_calculation_slot`
* Set `state.previous_epoch_start_shard = state.current_epoch_start_shard`
* Let `epochs_since_last_registry_change = (state.slot - state.validator_registry_latest_change_slot) // EPOCH_LENGTH`.
* If `epochs_since_last_registry_change` is an exact power of 2, set `state.cur_epoch_calculation_slot = state.slot` and `state.cur_epoch_randao_mix = state.latest_randao_mixes[(state.cur_epoch_calculation_slot - SEED_LOOKAHEAD) % LATEST_RANDAO_MIXES_LENGTH]`. Note that `state.cur_epoch_start_shard` is left unchanged.
* If `epochs_since_last_registry_change` is an exact power of 2, set `state.current_epoch_calculation_slot = state.slot` and `state.current_epoch_randao_mix = state.latest_randao_mixes[(state.current_epoch_calculation_slot - SEED_LOOKAHEAD) % LATEST_RANDAO_MIXES_LENGTH]`. Note that `state.current_epoch_start_shard` is left unchanged.
Regardless of whether or not a validator set change happens, run the following: