213 lines
8.3 KiB
Nim
213 lines
8.3 KiB
Nim
# beacon_chain
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# 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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# Uncategorized helper functions from the spec
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{.push raises: [Defect].}
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import
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# Standard lib
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math,
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# Third-party
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stew/endians2,
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# Internal
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./datatypes, ./digest, ./crypto, ../ssz/merkleization
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type
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# This solves an ambiguous identifier Error in some contexts
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# (other candidate is nativesockets.Domain)
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Domain = datatypes.Domain
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#integer_squareroot
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func integer_squareroot*(n: SomeInteger): SomeInteger =
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# Return the largest integer ``x`` such that ``x**2 <= n``.
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doAssert n >= 0'u64
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var
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x = n
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y = (x + 1) div 2
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while y < x:
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x = y
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y = (x + n div x) div 2
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x
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_epoch_at_slot
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func compute_epoch_at_slot*(slot: Slot|uint64): Epoch =
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# Return the epoch number at ``slot``.
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(slot div SLOTS_PER_EPOCH).Epoch
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template epoch*(slot: Slot): Epoch =
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compute_epoch_at_slot(slot)
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template isEpoch*(slot: Slot): bool =
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(slot mod SLOTS_PER_EPOCH) == 0
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_start_slot_at_epoch
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func compute_start_slot_at_epoch*(epoch: Epoch): Slot =
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# Return the start slot of ``epoch``.
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(epoch * SLOTS_PER_EPOCH).Slot
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#is_active_validator
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func is_active_validator*(validator: Validator, epoch: Epoch): bool =
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### Check if ``validator`` is active
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validator.activation_epoch <= epoch and epoch < validator.exit_epoch
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#get_active_validator_indices
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func get_active_validator_indices*(state: BeaconState, epoch: Epoch):
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seq[ValidatorIndex] =
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# Return the sequence of active validator indices at ``epoch``.
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for idx, val in state.validators:
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if is_active_validator(val, epoch):
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result.add idx.ValidatorIndex
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#get_committee_count_at_slot
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func get_committee_count_at_slot*(num_active_validators: uint64): uint64 =
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clamp(
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num_active_validators div SLOTS_PER_EPOCH div TARGET_COMMITTEE_SIZE,
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1, MAX_COMMITTEES_PER_SLOT).uint64
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func get_committee_count_at_slot*(state: BeaconState, slot: Slot): uint64 =
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# Return the number of committees at ``slot``.
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# TODO this is mostly used in for loops which have indexes which then need to
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# be converted to CommitteeIndex types for get_beacon_committee(...); replace
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# with better and more type-safe use pattern, probably beginning with using a
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# CommitteeIndex return type here.
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let
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epoch = compute_epoch_at_slot(slot)
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active_validator_indices = get_active_validator_indices(state, epoch)
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result = get_committee_count_at_slot(len(active_validator_indices).uint64)
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# Otherwise, get_beacon_committee(...) cannot access some committees.
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doAssert (SLOTS_PER_EPOCH * MAX_COMMITTEES_PER_SLOT).uint64 >= result
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#get_current_epoch
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func get_current_epoch*(state: BeaconState): Epoch =
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# Return the current epoch.
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doAssert state.slot >= GENESIS_SLOT, $state.slot
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compute_epoch_at_slot(state.slot)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#get_randao_mix
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func get_randao_mix*(state: BeaconState,
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epoch: Epoch): Eth2Digest =
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## Returns the randao mix at a recent ``epoch``.
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state.randao_mixes[epoch mod EPOCHS_PER_HISTORICAL_VECTOR]
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func bytes_to_int*(data: openarray[byte]): uint64 =
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doAssert data.len == 8
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# Little-endian data representation
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result = 0
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for i in countdown(7, 0):
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result = result * 256 + data[i]
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# Have 1, 4, 8, and 32-byte versions. 1+ more and maybe worth metaprogramming.
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func int_to_bytes32*(x: uint64): array[32, byte] =
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## Little-endian data representation
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## TODO remove uint64 when those callers fade away
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result[0..<7] = x.toBytesLE()
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func int_to_bytes32*(x: Epoch): array[32, byte] {.borrow.}
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func int_to_bytes8*(x: uint64): array[8, byte] =
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x.toBytesLE()
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func int_to_bytes1*(x: int): array[1, byte] =
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doAssert x >= 0
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doAssert x < 256
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result[0] = x.byte
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func int_to_bytes4*(x: uint64): array[4, byte] =
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doAssert x >= 0'u64
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doAssert x < 2'u64^32
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# Little-endian data representation
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result[0] = ((x shr 0) and 0xff).byte
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result[1] = ((x shr 8) and 0xff).byte
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result[2] = ((x shr 16) and 0xff).byte
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result[3] = ((x shr 24) and 0xff).byte
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_fork_data_root
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func compute_fork_data_root(current_version: Version,
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genesis_validators_root: Eth2Digest): Eth2Digest =
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# Return the 32-byte fork data root for the ``current_version`` and
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# ``genesis_validators_root``.
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# This is used primarily in signature domains to avoid collisions across
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# forks/chains.
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hash_tree_root(ForkData(
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current_version: current_version,
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genesis_validators_root: genesis_validators_root
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))
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_fork_digest
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func compute_fork_digest*(current_version: Version,
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genesis_validators_root: Eth2Digest): ForkDigest =
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# Return the 4-byte fork digest for the ``current_version`` and
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# ``genesis_validators_root``.
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# This is a digest primarily used for domain separation on the p2p layer.
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# 4-bytes suffices for practical separation of forks/chains.
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array[4, byte](result)[0..3] =
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compute_fork_data_root(
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current_version, genesis_validators_root).data.toOpenArray(0, 3)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_domain
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func compute_domain*(
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domain_type: DomainType,
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fork_version: Version,
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genesis_validators_root: Eth2Digest = ZERO_HASH): Domain =
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# Return the domain for the ``domain_type`` and ``fork_version``.
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let fork_data_root =
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compute_fork_data_root(fork_version, genesis_validators_root)
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result[0..3] = int_to_bytes4(domain_type.uint64)
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result[4..31] = fork_data_root.data[0..27]
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#get_domain
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func get_domain*(
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fork: Fork, domain_type: DomainType, epoch: Epoch, genesis_validators_root: Eth2Digest): Domain =
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## Return the signature domain (fork version concatenated with domain type)
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## of a message.
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let fork_version =
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if epoch < fork.epoch:
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fork.previous_version
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else:
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fork.current_version
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compute_domain(domain_type, fork_version, genesis_validators_root)
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func get_domain*(
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state: BeaconState, domain_type: DomainType, epoch: Epoch): Domain =
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## Return the signature domain (fork version concatenated with domain type)
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## of a message.
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get_domain(state.fork, domain_type, epoch, state.genesis_validators_root)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.11.3/specs/phase0/beacon-chain.md#compute_signing_root
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func compute_signing_root*(ssz_object: auto, domain: Domain): Eth2Digest =
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# Return the signing root of an object by calculating the root of the
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# object-domain tree.
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let domain_wrapped_object = SigningData(
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object_root: hash_tree_root(ssz_object),
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domain: domain
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)
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hash_tree_root(domain_wrapped_object)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#get_seed
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func get_seed*(state: BeaconState, epoch: Epoch, domain_type: DomainType): Eth2Digest =
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# Return the seed at ``epoch``.
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var seed_input : array[4+8+32, byte]
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# Detect potential underflow
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static:
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doAssert EPOCHS_PER_HISTORICAL_VECTOR > MIN_SEED_LOOKAHEAD
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seed_input[0..3] = int_to_bytes4(domain_type.uint64)
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seed_input[4..11] = int_to_bytes8(epoch.uint64)
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seed_input[12..43] =
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get_randao_mix(state, # Avoid underflow
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epoch + EPOCHS_PER_HISTORICAL_VECTOR - MIN_SEED_LOOKAHEAD - 1).data
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eth2digest(seed_input)
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