236 lines
10 KiB
Nim
236 lines
10 KiB
Nim
# beacon_chain
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# Copyright (c) 2018 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 http://opensource.org/licenses/MIT).
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# * Apache v2 license (license terms in the root directory or at http://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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import ./datatypes, ./digest, sequtils, math
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#split
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func split*[T](lst: openArray[T], N: Positive): seq[seq[T]] =
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## split lst in N pieces, with each piece having `len(lst) div N` or
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## `len(lst) div N + 1` pieces
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# TODO: implement as an iterator
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result = newSeq[seq[T]](N)
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for i in 0 ..< N:
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result[i] = lst[lst.len * i div N ..< lst.len * (i+1) div N] # TODO: avoid alloc via toOpenArray
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func get_new_recent_block_roots*(old_block_roots: seq[Eth2Digest],
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parent_slot, current_slot: int64,
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parent_hash: Eth2Digest
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): seq[Eth2Digest] =
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# Should throw for `current_slot - CYCLE_LENGTH * 2 - 1` according to spec comment
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let d = current_slot - parent_slot
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result = old_block_roots[d .. ^1]
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for _ in 0 ..< min(d, old_block_roots.len):
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result.add parent_hash
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#integer_squareroot
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func integer_squareroot*(n: SomeInteger): SomeInteger =
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## The largest integer ``x`` such that ``x**2`` is less than ``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/v0.5.0/specs/core/0_beacon-chain.md#get_fork_version
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func get_fork_version*(fork: Fork, epoch: Epoch): array[4, byte] =
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## Return the fork version of the given ``epoch``.
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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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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#is_power_of_two
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func is_power_of_2*(v: uint64): bool = (v > 0'u64) and (v and (v-1)) == 0
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func merkle_root*(values: openArray[Eth2Digest]): Eth2Digest =
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## Merkleize ``values`` (where ``len(values)`` is a power of two) and return
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## the Merkle root.
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## https://crypto.stackexchange.com/questions/43430/what-is-the-reason-to-separate-domains-in-the-internal-hash-algorithm-of-a-merkl
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let num_values = len(values)
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# Simplifies boundary conditions
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doAssert is_power_of_two(num_values)
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doAssert num_values >= 2
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doAssert num_values mod 2 == 0
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# TODO reverse ``o`` order and use newSeqWith to avoid pointless zero-filling.
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var o = repeat(ZERO_HASH, len(values))
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var hash_buffer: array[2*32, byte]
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# These ``o`` indices get filled from ``values``.
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let highest_internally_filled_index = (num_values div 2) - 1
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doAssert (highest_internally_filled_index + 1) * 2 >= num_values
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for i in countdown(num_values-1, highest_internally_filled_index + 1):
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hash_buffer[0..31] = values[i*2 - num_values].data
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hash_buffer[32..63] = values[i*2+1 - num_values].data
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o[i] = eth2hash(hash_buffer)
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## These ``o`` indices get filled from other ``o`` indices.
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doAssert highest_internally_filled_index * 2 + 1 < num_values
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for i in countdown(highest_internally_filled_index, 1):
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hash_buffer[0..31] = o[i*2].data
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hash_buffer[32..63] = o[i*2+1].data
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o[i] = eth2hash(hash_buffer)
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o[1]
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#slot_to_epoch
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func slot_to_epoch*(slot: Slot|uint64): Epoch =
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(slot div SLOTS_PER_EPOCH).Epoch
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#get_epoch_start_slot
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func get_epoch_start_slot*(epoch: Epoch): Slot =
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# Return the starting slot of the given ``epoch``.
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(epoch * SLOTS_PER_EPOCH).Slot
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#is_double_vote
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func is_double_vote*(attestation_data_1: AttestationData,
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attestation_data_2: AttestationData): bool =
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## Check if ``attestation_data_1`` and ``attestation_data_2`` have the same
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## target.
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let
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# RLP artifact
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target_epoch_1 = slot_to_epoch(attestation_data_1.slot)
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target_epoch_2 = slot_to_epoch(attestation_data_2.slot)
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target_epoch_1 == target_epoch_2
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#is_surround_vote
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func is_surround_vote*(attestation_data_1: AttestationData,
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attestation_data_2: AttestationData): bool =
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## Check if ``attestation_data_1`` surrounds ``attestation_data_2``.
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let
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source_epoch_1 = attestation_data_1.source_epoch
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source_epoch_2 = attestation_data_2.source_epoch
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# RLP artifact
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target_epoch_1 = slot_to_epoch(attestation_data_1.slot)
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target_epoch_2 = slot_to_epoch(attestation_data_2.slot)
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source_epoch_1 < source_epoch_2 and target_epoch_2 < target_epoch_1
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_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/v0.5.0/specs/core/0_beacon-chain.md#get_active_validator_indices
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func get_active_validator_indices*(validators: openArray[Validator], epoch: Epoch): seq[ValidatorIndex] =
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## Gets indices of active validators from validators
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for idx, val in 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/v0.5.1/specs/core/0_beacon-chain.md#get_epoch_committee_count
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func get_epoch_committee_count*(active_validator_count: int): uint64 =
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clamp(
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active_validator_count div SLOTS_PER_EPOCH div TARGET_COMMITTEE_SIZE,
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1, SHARD_COUNT div SLOTS_PER_EPOCH).uint64 * SLOTS_PER_EPOCH
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#get_current_epoch_committee_count
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func get_current_epoch_committee_count*(state: BeaconState): uint64 =
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# Return the number of committees in the current epoch of the given ``state``.
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let current_active_validators = get_active_validator_indices(
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state.validator_registry,
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state.current_shuffling_epoch,
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)
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get_epoch_committee_count(len(current_active_validators))
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_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 of the given ``state``.
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doAssert state.slot >= GENESIS_SLOT, $state.slot
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slot_to_epoch(state.slot)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_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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# Cannot underflow, since GENESIS_EPOCH > LATEST_RANDAO_MIXES_LENGTH
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doAssert get_current_epoch(state) - LATEST_RANDAO_MIXES_LENGTH < epoch
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doAssert epoch <= get_current_epoch(state)
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state.latest_randao_mixes[epoch mod LATEST_RANDAO_MIXES_LENGTH]
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#get_active_index_root
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func get_active_index_root(state: BeaconState, epoch: Epoch): Eth2Digest =
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# Returns the index root at a recent ``epoch``.
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## Cannot underflow, since GENESIS_EPOCH > LATEST_RANDAO_MIXES_LENGTH
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## and ACTIVATION_EXIT_DELAY > 0.
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doAssert get_current_epoch(state) - LATEST_ACTIVE_INDEX_ROOTS_LENGTH +
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ACTIVATION_EXIT_DELAY < epoch
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doAssert epoch <= get_current_epoch(state) + ACTIVATION_EXIT_DELAY
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state.latest_active_index_roots[epoch mod LATEST_ACTIVE_INDEX_ROOTS_LENGTH]
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# https://github.com/ethereum/eth2.0-specs/blob/v0.2.0/specs/core/0_beacon-chain.md#bytes_to_int
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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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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#int_to_bytes1-int_to_bytes2-
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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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for i in 0 ..< 8:
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result[24 + i] = byte((x shr i*8) and 0xff)
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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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for i in 0 ..< 8:
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result[i] = byte((x shr i*8) and 0xff)
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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/v0.5.0/specs/core/0_beacon-chain.md#get_domain
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func get_domain*(
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fork: Fork, epoch: Epoch, domain_type: SignatureDomain): uint64 =
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# Get the domain number that represents the fork meta and signature domain.
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var buf: array[8, byte]
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buf[0..3] = get_fork_version(fork, epoch)
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buf[4..7] = int_to_bytes4(domain_type.uint64)
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bytes_to_int(buf)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#generate_seed
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func generate_seed*(state: BeaconState, epoch: Epoch): Eth2Digest =
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# Generate a seed for the given ``epoch``.
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var seed_input : array[32*3, byte]
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# Cannot underflow, since GENESIS_EPOCH > MIN_SEED_LOOKAHEAD
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seed_input[0..31] = get_randao_mix(state, epoch - MIN_SEED_LOOKAHEAD).data
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seed_input[32..63] = get_active_index_root(state, epoch).data
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seed_input[64..95] = int_to_bytes32(epoch)
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eth2hash(seed_input)
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