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nimbus-eth2/beacon_chain/spec/helpers.nim

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# beacon_chain
# Copyright (c) 2018-2020 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
math,
# Third-party
stew/endians2,
# Internal
./datatypes, ./digest, ../ssz
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/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/v0.11.1/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)
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/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/v0.11.1/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/v0.11.1/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``.
for idx, val in state.validators:
if is_active_validator(val, epoch):
result.add idx.ValidatorIndex
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#get_committee_count_at_slot
func get_committee_count_at_slot*(state: BeaconState, slot: Slot): uint64 =
# Return the number of committees at ``slot``.
# TODO this is mostly used in for loops which have indexes which then need to
# be converted to CommitteeIndex types for get_beacon_committee(...); replace
# with better and more type-safe use pattern, probably beginning with using a
# CommitteeIndex return type here.
let epoch = compute_epoch_at_slot(slot)
let active_validator_indices = get_active_validator_indices(state, epoch)
let committees_per_slot = clamp(
len(active_validator_indices) div SLOTS_PER_EPOCH div TARGET_COMMITTEE_SIZE,
1, MAX_COMMITTEES_PER_SLOT).uint64
result = committees_per_slot
# Otherwise, get_beacon_committee(...) cannot access some committees.
doAssert (SLOTS_PER_EPOCH * MAX_COMMITTEES_PER_SLOT).uint64 >= result
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/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/v0.11.1/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_int*(data: openarray[byte]): uint64 =
doAssert data.len == 8
# Little-endian data representation
result = 0
for i in countdown(7, 0):
result = result * 256 + data[i]
# Have 1, 4, 8, and 32-byte versions. 1+ more and maybe worth metaprogramming.
func int_to_bytes32*(x: uint64): array[32, byte] =
## Little-endian data representation
## TODO remove uint64 when those callers fade away
result[0..<7] = x.toBytesLE()
func int_to_bytes32*(x: Epoch): array[32, byte] {.borrow.}
func int_to_bytes8*(x: uint64): array[8, byte] =
x.toBytesLE()
func int_to_bytes1*(x: int): array[1, byte] =
doAssert x >= 0
doAssert x < 256
result[0] = x.byte
func int_to_bytes4*(x: uint64): array[4, byte] =
doAssert x >= 0'u64
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/v0.11.1/specs/phase0/beacon-chain.md#compute_fork_data_root
func compute_fork_data_root(current_version: array[4, byte],
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/v0.11.1/specs/phase0/beacon-chain.md#compute_fork_digest
func compute_fork_digest*(current_version: array[4, byte],
genesis_validators_root: Eth2Digest): array[4, byte] =
# 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.
result[0..3] =
compute_fork_data_root(current_version, genesis_validators_root).data[0..3]
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#compute_domain
func compute_domain*(
domain_type: DomainType,
fork_version: array[4, byte] = [0'u8, 0, 0, 0],
genesis_validators_root: Eth2Digest = ZERO_HASH): Domain =
# 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] = int_to_bytes4(domain_type.uint64)
result[4..31] = fork_data_root.data[0..27]
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#get_domain
func get_domain*(
fork: Fork, domain_type: DomainType, epoch: Epoch, genesis_validators_root: Eth2Digest): Domain =
## 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): Domain =
## 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/v0.11.1/specs/phase0/beacon-chain.md#compute_signing_root
func compute_signing_root*(ssz_object: auto, domain: Domain): Eth2Digest =
# Return the signing root of an object by calculating the root of the
# object-domain tree.
let domain_wrapped_object = SigningRoot(
object_root: hash_tree_root(ssz_object),
domain: domain
)
hash_tree_root(domain_wrapped_object)
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/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] = int_to_bytes4(domain_type.uint64)
seed_input[4..11] = int_to_bytes8(epoch.uint64)
seed_input[12..43] =
get_randao_mix(state, # Avoid underflow
epoch + EPOCHS_PER_HISTORICAL_VECTOR - MIN_SEED_LOOKAHEAD - 1).data
eth2hash(seed_input)
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