232 lines
10 KiB
Nim
232 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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# TODO spec candidate? there's bits in nim-ranges but that one has some API
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# issues regarding bit endianess that need resolving..
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func bitSet*(bitfield: var openArray[byte], index: int) =
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bitfield[index div 8] = bitfield[index div 8] or 1'u8 shl (7 - (index mod 8))
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# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#get_bitfield_bit
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func get_bitfield_bit*(bitfield: openarray[byte], i: int): byte =
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# Extract the bit in ``bitfield`` at position ``i``.
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assert 0 <= i div 8, "i: " & $i & " i div 8: " & $(i div 8)
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assert i div 8 < bitfield.len, "i: " & $i & " i div 8: " & $(i div 8)
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(bitfield[i div 8] shr (7 - (i mod 8))) mod 2
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# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#verify_bitfield
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func verify_bitfield*(bitfield: openarray[byte], committee_size: int): bool =
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# Verify ``bitfield`` against the ``committee_size``.
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if len(bitfield) != (committee_size + 7) div 8:
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return false
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for i in committee_size + 1 ..< committee_size - (committee_size mod 8) + 8:
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if get_bitfield_bit(bitfield, i) == 0b1:
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return false
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true
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# https://github.com/ethereum/eth2.0-specs/blob/v0.2.0/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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# TODO remove; cascades through randao.nim, validator_pool.nim, etc
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func repeat_hash*(v: Eth2Digest, n: SomeInteger): Eth2Digest =
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# Spec version:
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# if n == 0: v
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# else: repeat_hash(eth2hash(v.data), n - 1)
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# Nim is pretty bad at recursion though (max 2k levels / no tco), so:
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result = v
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var n = n
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while n != 0:
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result = eth2hash(result.data)
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dec n
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func ceil_div8*(v: int): int = (v + 7) div 8 # TODO use a proper bitarray!
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# https://github.com/ethereum/eth2.0-specs/blob/v0.1/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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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/v0.1/specs/core/0_beacon-chain.md#get_fork_version
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func get_fork_version*(fork: Fork, epoch: EpochNumber): uint64 =
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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/v0.1/specs/core/0_beacon-chain.md#get_domain
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func get_domain*(
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fork: Fork, epoch: EpochNumber, domain_type: SignatureDomain): uint64 =
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# TODO Slot overflow? Or is slot 32 bits for all intents and purposes?
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# Get the domain number that represents the fork meta and signature domain.
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(get_fork_version(fork, epoch) shl 32) + domain_type.uint32
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# https://github.com/ethereum/eth2.0-specs/blob/v0.2.0/specs/core/0_beacon-chain.md#is_power_of_two
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func is_power_of_2*(v: uint64): bool = (v and (v-1)) == 0
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# https://github.com/ethereum/eth2.0-specs/blob/v0.1/specs/core/0_beacon-chain.md#merkle_root
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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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#var o = array[len(values) * 2, Eth2Digest]
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#o[len(values) .. 2*len(values)] = values
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#for i in countdown(len(values)-1, 0):
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# discard
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#o[i] = hash(o[i*2] + o[i*2+1])
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#return o[1]
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#TODO
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discard
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# https://github.com/ethereum/eth2.0-specs/blob/v0.2.0/specs/core/0_beacon-chain.md#slot_to_epoch
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func slot_to_epoch*(slot: SlotNumber): EpochNumber =
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slot div EPOCH_LENGTH
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# https://github.com/ethereum/eth2.0-specs/blob/v0.1/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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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/v0.1/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.justified_epoch
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source_epoch_2 = attestation_data_2.justified_epoch
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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/v0.2.0/specs/core/0_beacon-chain.md#is_active_validator
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func is_active_validator*(validator: Validator, epoch: EpochNumber): bool =
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### Checks 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/v0.2.0/specs/core/0_beacon-chain.md#get_active_validator_indices
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func get_active_validator_indices*(validators: openArray[Validator], epoch: EpochNumber): 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/v0.2.0/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 EPOCH_LENGTH div TARGET_COMMITTEE_SIZE,
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1, SHARD_COUNT div EPOCH_LENGTH).uint64 * EPOCH_LENGTH
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# https://github.com/ethereum/eth2.0-specs/blob/v0.2.0/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_calculation_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/v0.2.0/specs/core/0_beacon-chain.md#get_current_epoch
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func get_current_epoch*(state: BeaconState): EpochNumber =
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# Return the current epoch of the given ``state``.
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slot_to_epoch(state.slot)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.2.0/specs/core/0_beacon-chain.md#get_randao_mix
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func get_randao_mix*(state: BeaconState,
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epoch: EpochNumber): 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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assert get_current_epoch(state) - LATEST_RANDAO_MIXES_LENGTH < epoch
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assert 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/v0.2.0/specs/core/0_beacon-chain.md#get_active_index_root
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func get_active_index_root(state: BeaconState, epoch: EpochNumber): 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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assert get_current_epoch(state) - LATEST_INDEX_ROOTS_LENGTH < epoch
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assert epoch <= get_current_epoch(state) + ENTRY_EXIT_DELAY
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state.latest_index_roots[epoch mod LATEST_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: seq[byte]): uint64 =
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assert 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/v0.2.0/specs/core/0_beacon-chain.md#int_to_bytes1-int_to_bytes2-
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# Have 1, 4, and 32-byte versions. 2+ 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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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_bytes1*(x: int): array[1, byte] =
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assert x >= 0
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assert 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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assert x >= 0'u64
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assert 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/v0.2.0/specs/core/0_beacon-chain.md#generate_seed
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func generate_seed*(state: BeaconState, epoch: EpochNumber): 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 > SEED_LOOKAHEAD
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seed_input[0..31] = get_randao_mix(state, epoch - 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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