nimbus-eth2/beacon_chain/private/helpers.nim

114 lines
4.3 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.
# Helper functions
import ../datatypes, sequtils, nimcrypto, math
func get_active_validator_indices(validators: seq[ValidatorRecord], dynasty: int64): seq[Uint24] =
## Select the active validators
result = @[]
for idx, val in validators:
if val.start_dynasty <= dynasty and
dynasty < val.end_dynasty:
result.add idx.Uint24
func shuffle(validators: seq[Uint24], seed: Blake2_256_Digest): seq[Uint24] {.noInit.}=
## Pseudorandomly shuffles the validator set based on some seed
const UpperBound = 2^24 # 16777216
assert validators.len <= UpperBound
deepCopy(result, validators)
var source = seed
var i = 0
while i < validators.len:
source = blake2_256.digest source.data
for pos in countup(0, 29, 3):
let remaining = validators.len - i
if remaining == 0:
break
let m = source.data[pos].Uint24 shl 16 or source.data[pos+1].Uint24 shl 8 or source.data[pos+2].Uint24
let rand_max = Uint24 UpperBound - UpperBound mod remaining
if m < randMax:
let replacementPos = m mod remaining + i
swap result[i], result[replacementPos]
inc i
func split[T](lst: seq[T], N: Positive): seq[seq[T]] =
# 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_shuffling*(seed: Blake2_256_Digest, validators: seq[ValidatorRecord],
dynasty: int64, crosslinking_start_shard: int16): seq[seq[ShardAndCommittee]] {.noInit.} =
## Split up validators into groups at the start of every epoch,
## determining at what height they can make attestations and what shard they are making crosslinks for
## Implementation should do the following: http://vitalik.ca/files/ShuffleAndAssign.png
let avs = get_active_validator_indices(validators, dynasty)
var committees_per_slot, slots_per_committee: int16
if avs.len >= CYCLE_LENGTH * MIN_COMMITTEE_SIZE:
committees_per_slot = int16 avs.len div CYCLE_LENGTH div (MIN_COMMITTEE_SIZE * 2) + 1
slots_per_committee = 1
else:
committees_per_slot = 1
slots_per_committee = 1
while avs.len * slots_per_committee < CYCLE_LENGTH * MIN_COMMITTEE_SIZE and
slots_per_committee < CYCLE_LENGTH:
slots_per_committee *= 2
result = @[]
for slot, height_indices in shuffle(avs, seed).split(CYCLE_LENGTH):
let shard_indices = height_indices.split(committees_per_slot)
var committees = newSeq[ShardAndCommittee](shard_indices.len)
for j, indices in shard_indices:
committees[j].shard_id = crosslinking_start_shard +
slot.int16 * committees_per_slot div slots_per_committee + j.int16
committees[j].committee = indices
result.add committees
func get_indices_for_slot*(crystallized_state: CrystallizedState,
slot: int64): seq[ShardAndCommittee] {.noInit.}=
# TODO: Spec why is active_state an argument?
let start = crystallized_state.last_state_recalc - CYCLE_LENGTH
assert start <= slot
assert slot < start + CYCLE_LENGTH * 2
result = crystallized_state.indices_for_slots[int slot - start]
# TODO, slot is an int64 will be an issue on int32 arch.
# Clarify with EF if light clients will need the beacon chain
func get_block_hash*(active_state: ActiveState,
beacon_block: BeaconBlock, slot: int64): Blake2_256_Digest =
let sback = beacon_block.slot_number - CYCLE_LENGTH * 2
assert sback <= slot
assert slot < sback + CYCLE_LENGTH * 2
result = active_state.recent_block_hashes[int slot - sback]
func get_new_recent_block_hashes*(
old_block_hashes: seq[Blake2_256_Digest],
parent_slot, current_slot: int64,
parent_hash: Blake2_256_Digest
): seq[Blake2_256_Digest] =
# Should throw for `current_slot - CYCLE_LENGTH * 2 - 1` according to spec comment
let d = current_slot - parent_slot
result = old_block_hashes[d .. ^1]
for _ in 0 ..< min(d, old_block_hashes.len):
result.add parent_hash