8.1 KiB
8.1 KiB
Phase 1 miscellaneous beacon chain changes
Table of contents
Configuration
| Name | Value | Unit | Duration |
|---|---|---|---|
MAX_SHARD_RECEIPT_PROOFS |
2**0 (= 1) |
- | - |
PERSISTENT_COMMITTEE_ROOT_LENGTH |
2**8 (= 256) |
periods | ~9 months |
Classes
CompactCommittee
class CompactCommittee(Container):
pubkeys: List[BLSPubkey, MAX_VALIDATORS_PER_COMMITTEE]
compact_validators: List[uint64, MAX_VALIDATORS_PER_COMMITTEE]
ShardReceiptProof
class ShardReceiptProof(Container):
shard: Shard
proof: List[Hash, PLACEHOLDER]
receipt: List[ShardReceiptDelta, PLACEHOLDER]
Helpers
pack_compact_validator
def pack_compact_validator(index: int, slashed: bool, balance_in_increments: int) -> int:
"""
Creates a compact validator object representing index, slashed status, and compressed balance.
Takes as input balance-in-increments (// EFFECTIVE_BALANCE_INCREMENT) to preserve symmetry with
the unpacking function.
"""
return (index << 16) + (slashed << 15) + balance_in_increments
unpack_compact_validator
def unpack_compact_validator(compact_validator: int) -> Tuple[int, bool, int]:
"""
Returns validator index, slashed, balance // EFFECTIVE_BALANCE_INCREMENT
"""
return compact_validator >> 16, (compact_validator >> 15) % 2, compact_validator & (2**15 - 1)
committee_to_compact_committee
def committee_to_compact_committee(state: BeaconState, committee: Sequence[ValidatorIndex]) -> CompactCommittee:
"""
Given a state and a list of validator indices, outputs the CompactCommittee representing them.
"""
validators = [state.validators[i] for i in committee]
compact_validators = [
pack_compact_validator(i, v.slashed, v.effective_balance // EFFECTIVE_BALANCE_INCREMENT)
for i, v in zip(committee, validators)
]
pubkeys = [v.pubkey for v in validators]
return CompactCommittee(pubkeys=pubkeys, compact_validators=compact_validators)
get_previous_power_of_2
def get_previous_power_of_2(x: int) -> int:
return x if x <= 2 else 2 * get_previous_power_of_2(x // 2)
verify_merkle_proof
def verify_merkle_proof(leaf: Hash, proof: Sequence[Hash], index: GeneralizedIndex, root: Hash) -> bool:
assert len(proof) == get_generalized_index_length(index)
for i, h in enumerate(proof):
if get_generalized_index_bit(index, i):
leaf = hash(h + leaf)
else:
leaf = hash(leaf + h)
return leaf == root
compute_historical_state_generalized_index
def compute_historical_state_generalized_index(earlier: ShardSlot, later: ShardSlot) -> GeneralizedIndex:
"""
Computes the generalized index of the state root of slot `frm` based on the state root of slot `to`.
Relies on the `history_acc` in the `ShardState`, where `history_acc[i]` maintains the most recent 2**i'th
slot state. Works by tracing a `log(later-earlier)` step path from `later` to `earlier` through intermediate
blocks at the next available multiples of descending powers of two.
"""
o = GeneralizedIndex(1)
for i in range(63, -1, -1):
if (later - 1) & 2**i > (earlier - 1) & 2**i:
later = later - ((later - 1) % 2**i) - 1
o = concat_generalized_indices(o, get_generalized_index(ShardState, 'history_acc', i))
return o
get_generalized_index_of_crosslink_header
def get_generalized_index_of_crosslink_header(index: int) -> GeneralizedIndex:
"""
Gets the generalized index for the root of the index'th header in a crosslink.
"""
MAX_CROSSLINK_SIZE = SHARD_BLOCK_SIZE_LIMIT * SHARD_SLOTS_PER_BEACON_SLOT * SLOTS_PER_EPOCH * MAX_EPOCHS_PER_CROSSLINK
assert MAX_CROSSLINK_SIZE == get_previous_power_of_2(MAX_CROSSLINK_SIZE)
return GeneralizedIndex(MAX_CROSSLINK_SIZE // SHARD_HEADER_SIZE + index)
process_shard_receipt_proof
def process_shard_receipt_proof(state: BeaconState, receipt_proof: ShardReceiptProof):
"""
Processes a ShardReceipt object.
"""
receipt_slot = state.next_shard_receipt_period[receipt_proof.shard] * SLOTS_PER_EPOCH * EPOCHS_PER_SHARD_PERIOD
first_slot_in_last_crosslink = state.current_crosslinks[receipt_proof.shard].start_epoch * SLOTS_PER_EPOCH
gindex = concat_generalized_indices(
get_generalized_index_of_crosslink_header(0),
get_generalized_index(ShardBlockHeader, 'state_root'),
compute_historical_state_generalized_index(receipt_slot, first_slot_in_last_crosslink),
get_generalized_index(ShardState, 'receipt_root')
)
assert verify_merkle_proof(
leaf=hash_tree_root(receipt_proof.receipt),
proof=receipt_proof.proof,
index=gindex,
root=state.current_crosslinks[shard].data_root
)
for delta in receipt_proof.receipt:
if get_current_epoch(state) < state.validators[delta.index].withdrawable_epoch:
increase_balance(state, delta.index, state.validators[delta.index].effective_balance * delta.reward_coefficient // REWARD_COEFFICIENT_BASE)
decrease_balance(state, delta.index, delta.block_fee)
state.next_shard_receipt_period[receipt_proof.shard] += 1
increase_balance(state, get_beacon_proposer_index(state), MICRO_REWARD)
Changes
Persistent committees
Add to the beacon state the following fields:
# begin insert @persistent_committee_fields
persistent_committee_roots: Vector[Hash, PERSISTENT_COMMITTEE_ROOT_LENGTH]
next_shard_receipt_period: Vector[uint, SHARD_COUNT]
# end insert @persistent_committee_fields
next_shard_receipt_period values initialized to PHASE_1_FORK_SLOT // SLOTS_PER_EPOCH // EPOCHS_PER_SHARD_PERIOD
Run update_persistent_committee immediately before process_final_updates:
# begin insert @update_persistent_committee
update_persistent_committee(state)
# end insert @update_persistent_committee
def update_persistent_committee(state: BeaconState) -> None:
"""
Updates persistent committee roots at boundary blocks.
"""
if (get_current_epoch(state) + 1) % EPOCHS_PER_SHARD_PERIOD == 0:
period = (get_current_epoch(state) + 1) // EPOCHS_PER_SHARD_PERIOD
committees = Vector[CompactCommittee, SHARD_COUNT]([
committee_to_compact_committee(state, get_period_committee(state, get_current_epoch(state) + 1, i))
for i in range(SHARD_COUNT)
])
state.persistent_committee_roots[period % PERSISTENT_COMMITTEE_ROOT_LENGTH] = hash_tree_root(committees)
Shard receipt processing
Add the shard_receipt_proofs operation to BeaconBlockBody:
# begin insert @shard_receipts
shard_receipt_proofs: List[ShardReceiptProof, MAX_SHARD_RECEIPT_PROOFS]
# end insert @shard_receipts
Use process_shard_receipt_proof to process each receipt.
# begin insert @process_shard_receipts
(body.shard_receipt_proofs, process_shard_receipt_proofs),
# end insert @process_shard_receipts