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nimbus-eth2/beacon_chain/spec/helpers.nim

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# beacon_chain
# Copyright (c) 2018-2021 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
# Uncategorized helper functions from the spec
{.push raises: [Defect].}
import
# Standard lib
std/[math, tables],
# Third-party
stew/endians2,
# Internal
./datatypes/[phase0, altair], ./digest, ./crypto, ../ssz/merkleization
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#integer_squareroot
func integer_squareroot*(n: SomeInteger): SomeInteger =
## Return the largest integer ``x`` such that ``x**2 <= n``.
doAssert n >= 0'u64
var
x = n
y = (x + 1) div 2
while y < x:
x = y
y = (x + n div x) div 2
x
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#compute_epoch_at_slot
func compute_epoch_at_slot*(slot: Slot|uint64): Epoch =
## Return the epoch number at ``slot``.
(slot div SLOTS_PER_EPOCH).Epoch
template epoch*(slot: Slot): Epoch =
compute_epoch_at_slot(slot)
template isEpoch*(slot: Slot): bool =
(slot mod SLOTS_PER_EPOCH) == 0
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#compute_start_slot_at_epoch
func compute_start_slot_at_epoch*(epoch: Epoch): Slot =
## Return the start slot of ``epoch``.
(epoch * SLOTS_PER_EPOCH).Slot
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#is_active_validator
func is_active_validator*(validator: Validator, epoch: Epoch): bool =
## Check if ``validator`` is active
validator.activation_epoch <= epoch and epoch < validator.exit_epoch
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#get_active_validator_indices
func get_active_validator_indices*(state: BeaconState, epoch: Epoch):
seq[ValidatorIndex] =
## Return the sequence of active validator indices at ``epoch``.
result = newSeqOfCap[ValidatorIndex](state.validators.len)
for idx in 0..<state.validators.len:
if is_active_validator(state.validators[idx], epoch):
result.add idx.ValidatorIndex
func get_active_validator_indices_len*(state: BeaconState, epoch: Epoch): uint64 =
for idx in 0..<state.validators.len:
if is_active_validator(state.validators[idx], epoch):
inc result
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#get_current_epoch
func get_current_epoch*(state: BeaconState): Epoch =
## Return the current epoch.
doAssert state.slot >= GENESIS_SLOT, $state.slot
compute_epoch_at_slot(state.slot)
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#get_randao_mix
func get_randao_mix*(state: BeaconState,
epoch: Epoch): Eth2Digest =
## Returns the randao mix at a recent ``epoch``.
state.randao_mixes[epoch mod EPOCHS_PER_HISTORICAL_VECTOR]
func bytes_to_uint64*(data: openArray[byte]): uint64 =
doAssert data.len == 8
# Little-endian data representation
uint64.fromBytesLE(data)
# Have 1, 4, and 8-byte versions. Spec only defines 8-byte version, but useful
# to check invariants on rest.
func uint_to_bytes8*(x: uint64): array[8, byte] =
x.toBytesLE()
func uint_to_bytes4*(x: uint64): array[4, byte] =
doAssert x < 2'u64^32
# Little-endian data representation
result[0] = ((x shr 0) and 0xff).byte
result[1] = ((x shr 8) and 0xff).byte
result[2] = ((x shr 16) and 0xff).byte
result[3] = ((x shr 24) and 0xff).byte
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#compute_fork_data_root
func compute_fork_data_root(current_version: Version,
genesis_validators_root: Eth2Digest): Eth2Digest =
## Return the 32-byte fork data root for the ``current_version`` and
## ``genesis_validators_root``.
## This is used primarily in signature domains to avoid collisions across
## forks/chains.
hash_tree_root(ForkData(
current_version: current_version,
genesis_validators_root: genesis_validators_root
))
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#compute_fork_digest
func compute_fork_digest*(current_version: Version,
genesis_validators_root: Eth2Digest): ForkDigest =
## Return the 4-byte fork digest for the ``current_version`` and
## ``genesis_validators_root``.
## This is a digest primarily used for domain separation on the p2p layer.
## 4-bytes suffices for practical separation of forks/chains.
array[4, byte](result)[0..3] =
compute_fork_data_root(
current_version, genesis_validators_root).data.toOpenArray(0, 3)
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#compute_domain
func compute_domain*(
domain_type: DomainType,
fork_version: Version,
genesis_validators_root: Eth2Digest = ZERO_HASH): Eth2Domain =
## Return the domain for the ``domain_type`` and ``fork_version``.
let fork_data_root =
compute_fork_data_root(fork_version, genesis_validators_root)
result[0..3] = uint_to_bytes4(domain_type.uint64)
result[4..31] = fork_data_root.data.toOpenArray(0, 27)
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#get_domain
func get_domain*(
fork: Fork,
domain_type: DomainType,
epoch: Epoch,
genesis_validators_root: Eth2Digest): Eth2Domain =
## Return the signature domain (fork version concatenated with domain type)
## of a message.
let fork_version =
if epoch < fork.epoch:
fork.previous_version
else:
fork.current_version
compute_domain(domain_type, fork_version, genesis_validators_root)
func get_domain*(
state: BeaconState, domain_type: DomainType, epoch: Epoch): Eth2Domain =
## Return the signature domain (fork version concatenated with domain type)
## of a message.
get_domain(state.fork, domain_type, epoch, state.genesis_validators_root)
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#compute_signing_root
func compute_signing_root*(ssz_object: auto, domain: Eth2Domain): Eth2Digest =
## Return the signing root of an object by calculating the root of the
## object-domain tree.
let domain_wrapped_object = SigningData(
object_root: hash_tree_root(ssz_object),
domain: domain
)
hash_tree_root(domain_wrapped_object)
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.1/specs/phase0/beacon-chain.md#get_seed
func get_seed*(state: BeaconState, epoch: Epoch, domain_type: DomainType): Eth2Digest =
## Return the seed at ``epoch``.
var seed_input : array[4+8+32, byte]
# Detect potential underflow
static:
doAssert EPOCHS_PER_HISTORICAL_VECTOR > MIN_SEED_LOOKAHEAD
seed_input[0..3] = uint_to_bytes4(domain_type.uint64)
seed_input[4..11] = uint_to_bytes8(epoch.uint64)
seed_input[12..43] =
get_randao_mix(state, # Avoid underflow
epoch + EPOCHS_PER_HISTORICAL_VECTOR - MIN_SEED_LOOKAHEAD - 1).data
eth2digest(seed_input)
# https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#get_flag_indices_and_weights
iterator get_flag_indices_and_weights*(): (ParticipationFlag, int) =
for item in [
(TIMELY_HEAD_FLAG_INDEX, TIMELY_HEAD_WEIGHT),
(TIMELY_SOURCE_FLAG_INDEX, TIMELY_SOURCE_WEIGHT),
(TIMELY_TARGET_FLAG_INDEX, TIMELY_TARGET_WEIGHT)]:
yield item
# https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#add_flag
func add_flag*(flags: ParticipationFlags, flag_index: int): ParticipationFlags =
let flag = ParticipationFlags(1'u8 shl flag_index)
flags or flag
# https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.2/specs/altair/beacon-chain.md#has_flag
func has_flag*(flags: ParticipationFlags, flag_index: int): bool =
let flag = ParticipationFlags(1'u8 shl flag_index)
(flags and flag) == flag
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