266 lines
11 KiB
Nim
266 lines
11 KiB
Nim
# Copyright (c) 2018-2020 Status Research & Development GmbH
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# Licensed and distributed under either of
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# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
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# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
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# at your option. This file may not be copied, modified, or distributed except according to those terms.
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# Helpers and functions pertaining to managing the validator set
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{.push raises: [Defect].}
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import
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algorithm, options, sequtils, math, tables, sets,
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./datatypes, ./digest, ./helpers
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_shuffled_index
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_committee
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func get_shuffled_seq*(seed: Eth2Digest,
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list_size: uint64,
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): seq[ValidatorIndex] =
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## Via https://github.com/protolambda/eth2-shuffle/blob/master/shuffle.go
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## Shuffles ``validators`` into beacon committees, seeded by ``seed`` and
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## ``slot``.
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## Returns a list of ``SLOTS_PER_EPOCH * committees_per_slot`` committees
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## where each committee is itself a list of validator indices.
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##
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## Invert the inner/outer loops from the spec, essentially. Most useful
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## hash result re-use occurs within a round.
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# Empty size -> empty list.
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if list_size == 0:
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return
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var
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# Share these buffers.
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# TODO: Redo to follow spec.
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# We can have an "Impl" private version that takes buffer as parameters
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# so that we avoid alloc on repeated calls from compute_committee
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pivot_buffer: array[(32+1), byte]
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source_buffer: array[(32+1+4), byte]
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shuffled_active_validator_indices = mapIt(
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0 ..< list_size.int, it.ValidatorIndex)
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sources = repeat(Eth2Digest(), (list_size div 256) + 1)
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## The pivot's a function of seed and round only.
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## This doesn't change across rounds.
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pivot_buffer[0..31] = seed.data
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source_buffer[0..31] = seed.data
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for round in 0 ..< SHUFFLE_ROUND_COUNT:
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let round_bytes1 = int_to_bytes1(round)[0]
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pivot_buffer[32] = round_bytes1
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source_buffer[32] = round_bytes1
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# Only one pivot per round.
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let pivot = bytes_to_int(eth2digest(pivot_buffer).data.toOpenArray(0, 7)) mod list_size
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## Only need to run, per round, position div 256 hashes, so precalculate
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## them. This consumes memory, but for low-memory devices, it's possible
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## to mitigate by some light LRU caching and similar.
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for reduced_position in 0 ..< sources.len:
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source_buffer[33..36] = int_to_bytes4(reduced_position.uint64)
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sources[reduced_position] = eth2digest(source_buffer)
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## Iterate over all the indices. This was in get_permuted_index, but large
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## efficiency gains exist in caching and re-using data.
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for index in 0 ..< list_size.int:
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let
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cur_idx_permuted = shuffled_active_validator_indices[index]
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flip = ((list_size + pivot) - cur_idx_permuted.uint64) mod list_size
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position = max(cur_idx_permuted.int, flip.int)
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let
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source = sources[position div 256].data
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byte_value = source[(position mod 256) div 8]
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bit = (byte_value shr (position mod 8)) mod 2
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if bit != 0:
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shuffled_active_validator_indices[index] = flip.ValidatorIndex
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result = shuffled_active_validator_indices
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func get_shuffled_active_validator_indices*(state: BeaconState, epoch: Epoch):
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seq[ValidatorIndex] =
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# Non-spec function, to cache a data structure from which one can cheaply
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# compute both get_active_validator_indexes() and get_beacon_committee().
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let active_validator_indices = get_active_validator_indices(state, epoch)
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mapIt(
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get_shuffled_seq(
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get_seed(state, epoch, DOMAIN_BEACON_ATTESTER),
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active_validator_indices.len.uint64),
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active_validator_indices[it])
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#get_previous_epoch
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func get_previous_epoch*(state: BeaconState): Epoch =
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# Return the previous epoch (unless the current epoch is ``GENESIS_EPOCH``).
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let current_epoch = get_current_epoch(state)
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if current_epoch == GENESIS_EPOCH:
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current_epoch
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else:
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current_epoch - 1
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_committee
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func compute_committee(indices: seq[ValidatorIndex], seed: Eth2Digest,
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index: uint64, count: uint64): seq[ValidatorIndex] =
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## Return the committee corresponding to ``indices``, ``seed``, ``index``,
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## and committee ``count``.
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# indices only used here for its length, or for the shuffled version,
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# so unlike spec, pass the shuffled version in directly.
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let
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start = (len(indices).uint64 * index) div count
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endIdx = (len(indices).uint64 * (index + 1)) div count
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# These assertions from compute_shuffled_index(...)
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let index_count = indices.len().uint64
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doAssert endIdx <= index_count
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doAssert index_count <= 2'u64^40
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# In spec, this calls get_shuffled_index() every time, but that's wasteful
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# Here, get_beacon_committee() gets the shuffled version.
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try:
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indices[start.int .. (endIdx.int-1)]
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except KeyError:
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raiseAssert("Cached entries are added before use")
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#get_beacon_committee
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func get_beacon_committee*(
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state: BeaconState, slot: Slot, index: CommitteeIndex,
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cache: var StateCache): seq[ValidatorIndex] =
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# Return the beacon committee at ``slot`` for ``index``.
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let
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epoch = compute_epoch_at_slot(slot)
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# This is a somewhat more fragile, but high-ROI, caching setup --
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# get_active_validator_indices() is slow to run in a loop and only
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# changes once per epoch. It is not, in the general case, possible
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# to precompute these arbitrarily far out so still need to pick up
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# missing cases here.
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if epoch notin cache.shuffled_active_validator_indices:
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cache.shuffled_active_validator_indices[epoch] =
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get_shuffled_active_validator_indices(state, epoch)
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try:
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let committee_count = get_committee_count_at_slot(
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cache.shuffled_active_validator_indices[epoch].len)
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compute_committee(
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cache.shuffled_active_validator_indices[epoch],
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get_seed(state, epoch, DOMAIN_BEACON_ATTESTER),
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(slot mod SLOTS_PER_EPOCH) * committee_count +
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index.uint64,
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committee_count * SLOTS_PER_EPOCH
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)
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except KeyError:
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raiseAssert "values are added to cache before using them"
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# Not from spec
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func get_empty_per_epoch_cache*(): StateCache =
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result.shuffled_active_validator_indices =
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initTable[Epoch, seq[ValidatorIndex]]()
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_proposer_index
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func compute_proposer_index(state: BeaconState, indices: seq[ValidatorIndex],
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seed: Eth2Digest): Option[ValidatorIndex] =
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# Return from ``indices`` a random index sampled by effective balance.
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const MAX_RANDOM_BYTE = 255
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if len(indices) == 0:
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return none(ValidatorIndex)
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let
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seq_len = indices.len.uint64
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shuffled_seq = mapIt(get_shuffled_seq(seed, seq_len), indices[it])
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doAssert seq_len == shuffled_seq.len.uint64
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var
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i = 0
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buffer: array[32+8, byte]
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buffer[0..31] = seed.data
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while true:
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buffer[32..39] = int_to_bytes8(i.uint64 div 32)
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let
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candidate_index = shuffled_seq[(i.uint64 mod seq_len).int]
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random_byte = (eth2digest(buffer).data)[i mod 32]
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effective_balance =
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state.validators[candidate_index].effective_balance
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if effective_balance * MAX_RANDOM_BYTE >=
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MAX_EFFECTIVE_BALANCE * random_byte:
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return some(candidate_index)
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i += 1
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#get_beacon_proposer_index
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func get_beacon_proposer_index*(state: BeaconState, cache: var StateCache, slot: Slot):
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Option[ValidatorIndex] =
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try:
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if slot in cache.beacon_proposer_indices:
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return cache.beacon_proposer_indices[slot]
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except KeyError:
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raiseAssert("Cached entries are added before use")
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# Return the beacon proposer index at the current slot.
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let epoch = get_current_epoch(state)
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var buffer: array[32 + 8, byte]
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buffer[0..31] = get_seed(state, epoch, DOMAIN_BEACON_PROPOSER).data
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buffer[32..39] = int_to_bytes8(slot.uint64)
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# TODO fixme; should only be run once per slot and cached
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# There's exactly one beacon proposer per slot.
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if epoch notin cache.shuffled_active_validator_indices:
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cache.shuffled_active_validator_indices[epoch] =
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get_shuffled_active_validator_indices(state, epoch)
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try:
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let
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seed = eth2digest(buffer)
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indices =
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sorted(cache.shuffled_active_validator_indices[epoch], system.cmp)
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cache.beacon_proposer_indices[slot] =
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compute_proposer_index(state, indices, seed)
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cache.beacon_proposer_indices[slot]
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except KeyError:
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raiseAssert("Cached entries are added before use")
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#get_beacon_proposer_index
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func get_beacon_proposer_index*(state: BeaconState, cache: var StateCache):
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Option[ValidatorIndex] =
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get_beacon_proposer_index(state, cache, state.slot)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/validator.md#validator-assignments
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func get_committee_assignment*(
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state: BeaconState, epoch: Epoch,
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validator_indices: HashSet[ValidatorIndex]):
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Option[tuple[a: seq[ValidatorIndex], b: CommitteeIndex, c: Slot]] {.used.} =
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# Return the committee assignment in the ``epoch`` for ``validator_index``.
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# ``assignment`` returned is a tuple of the following form:
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# * ``assignment[0]`` is the list of validators in the committee
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# * ``assignment[1]`` is the index to which the committee is assigned
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# * ``assignment[2]`` is the slot at which the committee is assigned
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# Return None if no assignment.
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#
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# Slightly adapted from spec version to support multiple validator indices,
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# since each beacon_node supports many validators.
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let next_epoch = get_current_epoch(state) + 1
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doAssert epoch <= next_epoch
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var cache = get_empty_per_epoch_cache()
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let start_slot = compute_start_slot_at_epoch(epoch)
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for slot in start_slot ..< start_slot + SLOTS_PER_EPOCH:
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for index in 0 ..< get_committee_count_at_slot(state, slot):
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let idx = index.CommitteeIndex
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let committee = get_beacon_committee(state, slot, idx, cache)
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if not disjoint(validator_indices, toHashSet(committee)):
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return some((committee, idx, slot))
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none(tuple[a: seq[ValidatorIndex], b: CommitteeIndex, c: Slot])
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/validator.md#validator-assignments
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func is_proposer(
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state: BeaconState, validator_index: ValidatorIndex): bool {.used.} =
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var cache = get_empty_per_epoch_cache()
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let proposer_index = get_beacon_proposer_index(state, cache)
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proposer_index.isSome and proposer_index.get == validator_index
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