nimbus-eth2/beacon_chain/spec/helpers.nim

236 lines
10 KiB
Nim

# beacon_chain
# Copyright (c) 2018 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at http://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
import ./datatypes, ./digest, sequtils, math
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#split
func split*[T](lst: openArray[T], N: Positive): seq[seq[T]] =
## split lst in N pieces, with each piece having `len(lst) div N` or
## `len(lst) div N + 1` pieces
# TODO: implement as an iterator
result = newSeq[seq[T]](N)
for i in 0 ..< N:
result[i] = lst[lst.len * i div N ..< lst.len * (i+1) div N] # TODO: avoid alloc via toOpenArray
func get_new_recent_block_roots*(old_block_roots: seq[Eth2Digest],
parent_slot, current_slot: int64,
parent_hash: Eth2Digest
): seq[Eth2Digest] =
# Should throw for `current_slot - CYCLE_LENGTH * 2 - 1` according to spec comment
let d = current_slot - parent_slot
result = old_block_roots[d .. ^1]
for _ in 0 ..< min(d, old_block_roots.len):
result.add parent_hash
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#integer_squareroot
func integer_squareroot*(n: SomeInteger): SomeInteger =
## The largest integer ``x`` such that ``x**2`` is less than ``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/v0.5.0/specs/core/0_beacon-chain.md#get_fork_version
func get_fork_version*(fork: Fork, epoch: Epoch): array[4, byte] =
## Return the fork version of the given ``epoch``.
if epoch < fork.epoch:
fork.previous_version
else:
fork.current_version
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#is_power_of_two
func is_power_of_2*(v: uint64): bool = (v > 0'u64) and (v and (v-1)) == 0
func merkle_root*(values: openArray[Eth2Digest]): Eth2Digest =
## Merkleize ``values`` (where ``len(values)`` is a power of two) and return
## the Merkle root.
## https://crypto.stackexchange.com/questions/43430/what-is-the-reason-to-separate-domains-in-the-internal-hash-algorithm-of-a-merkl
let num_values = len(values)
# Simplifies boundary conditions
doAssert is_power_of_two(num_values)
doAssert num_values >= 2
doAssert num_values mod 2 == 0
# TODO reverse ``o`` order and use newSeqWith to avoid pointless zero-filling.
var o = repeat(ZERO_HASH, len(values))
var hash_buffer: array[2*32, byte]
# These ``o`` indices get filled from ``values``.
let highest_internally_filled_index = (num_values div 2) - 1
doAssert (highest_internally_filled_index + 1) * 2 >= num_values
for i in countdown(num_values-1, highest_internally_filled_index + 1):
hash_buffer[0..31] = values[i*2 - num_values].data
hash_buffer[32..63] = values[i*2+1 - num_values].data
o[i] = eth2hash(hash_buffer)
## These ``o`` indices get filled from other ``o`` indices.
doAssert highest_internally_filled_index * 2 + 1 < num_values
for i in countdown(highest_internally_filled_index, 1):
hash_buffer[0..31] = o[i*2].data
hash_buffer[32..63] = o[i*2+1].data
o[i] = eth2hash(hash_buffer)
o[1]
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#slot_to_epoch
func slot_to_epoch*(slot: Slot|uint64): Epoch =
(slot div SLOTS_PER_EPOCH).Epoch
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#get_epoch_start_slot
func get_epoch_start_slot*(epoch: Epoch): Slot =
# Return the starting slot of the given ``epoch``.
(epoch * SLOTS_PER_EPOCH).Slot
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#is_double_vote
func is_double_vote*(attestation_data_1: AttestationData,
attestation_data_2: AttestationData): bool =
## Check if ``attestation_data_1`` and ``attestation_data_2`` have the same
## target.
let
# RLP artifact
target_epoch_1 = slot_to_epoch(attestation_data_1.slot)
target_epoch_2 = slot_to_epoch(attestation_data_2.slot)
target_epoch_1 == target_epoch_2
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#is_surround_vote
func is_surround_vote*(attestation_data_1: AttestationData,
attestation_data_2: AttestationData): bool =
## Check if ``attestation_data_1`` surrounds ``attestation_data_2``.
let
source_epoch_1 = attestation_data_1.source_epoch
source_epoch_2 = attestation_data_2.source_epoch
# RLP artifact
target_epoch_1 = slot_to_epoch(attestation_data_1.slot)
target_epoch_2 = slot_to_epoch(attestation_data_2.slot)
source_epoch_1 < source_epoch_2 and target_epoch_2 < target_epoch_1
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_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/v0.5.0/specs/core/0_beacon-chain.md#get_active_validator_indices
func get_active_validator_indices*(validators: openArray[Validator], epoch: Epoch): seq[ValidatorIndex] =
## Gets indices of active validators from validators
for idx, val in validators:
if is_active_validator(val, epoch):
result.add idx.ValidatorIndex
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.1/specs/core/0_beacon-chain.md#get_epoch_committee_count
func get_epoch_committee_count*(active_validator_count: int): uint64 =
clamp(
active_validator_count div SLOTS_PER_EPOCH div TARGET_COMMITTEE_SIZE,
1, SHARD_COUNT div SLOTS_PER_EPOCH).uint64 * SLOTS_PER_EPOCH
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#get_current_epoch_committee_count
func get_current_epoch_committee_count*(state: BeaconState): uint64 =
# Return the number of committees in the current epoch of the given ``state``.
let current_active_validators = get_active_validator_indices(
state.validator_registry,
state.current_shuffling_epoch,
)
get_epoch_committee_count(len(current_active_validators))
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#get_current_epoch
func get_current_epoch*(state: BeaconState): Epoch =
# Return the current epoch of the given ``state``.
doAssert state.slot >= GENESIS_SLOT, $state.slot
slot_to_epoch(state.slot)
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#get_randao_mix
func get_randao_mix*(state: BeaconState,
epoch: Epoch): Eth2Digest =
## Returns the randao mix at a recent ``epoch``.
# Cannot underflow, since GENESIS_EPOCH > LATEST_RANDAO_MIXES_LENGTH
doAssert get_current_epoch(state) - LATEST_RANDAO_MIXES_LENGTH < epoch
doAssert epoch <= get_current_epoch(state)
state.latest_randao_mixes[epoch mod LATEST_RANDAO_MIXES_LENGTH]
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#get_active_index_root
func get_active_index_root(state: BeaconState, epoch: Epoch): Eth2Digest =
# Returns the index root at a recent ``epoch``.
## Cannot underflow, since GENESIS_EPOCH > LATEST_RANDAO_MIXES_LENGTH
## and ACTIVATION_EXIT_DELAY > 0.
doAssert get_current_epoch(state) - LATEST_ACTIVE_INDEX_ROOTS_LENGTH +
ACTIVATION_EXIT_DELAY < epoch
doAssert epoch <= get_current_epoch(state) + ACTIVATION_EXIT_DELAY
state.latest_active_index_roots[epoch mod LATEST_ACTIVE_INDEX_ROOTS_LENGTH]
# https://github.com/ethereum/eth2.0-specs/blob/v0.2.0/specs/core/0_beacon-chain.md#bytes_to_int
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]
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#int_to_bytes1-int_to_bytes2-
# 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
for i in 0 ..< 8:
result[24 + i] = byte((x shr i*8) and 0xff)
func int_to_bytes32*(x: Epoch): array[32, byte] {.borrow.}
func int_to_bytes8*(x: uint64): array[8, byte] =
for i in 0 ..< 8:
result[i] = byte((x shr i*8) and 0xff)
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/v0.5.0/specs/core/0_beacon-chain.md#get_domain
func get_domain*(
fork: Fork, epoch: Epoch, domain_type: SignatureDomain): uint64 =
# Get the domain number that represents the fork meta and signature domain.
var buf: array[8, byte]
buf[0..3] = get_fork_version(fork, epoch)
buf[4..7] = int_to_bytes4(domain_type.uint64)
bytes_to_int(buf)
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#generate_seed
func generate_seed*(state: BeaconState, epoch: Epoch): Eth2Digest =
# Generate a seed for the given ``epoch``.
var seed_input : array[32*3, byte]
# Cannot underflow, since GENESIS_EPOCH > MIN_SEED_LOOKAHEAD
seed_input[0..31] = get_randao_mix(state, epoch - MIN_SEED_LOOKAHEAD).data
seed_input[32..63] = get_active_index_root(state, epoch).data
seed_input[64..95] = int_to_bytes32(epoch)
eth2hash(seed_input)