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Merge pull request #14 from status-im/HelperSpecUpdates 

update some helper functions to current spec, along with a couple of data types that needed tweaking/fixing
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tersec 2018-11-16 22:57:54 +00:00 committed by GitHub
parent 949b24702c d0fd1b4eb7
commit eff23ba182
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2 changed files with 52 additions and 38 deletions
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4
beacon_chain/datatypes.nim
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@ -65,7 +65,7 @@ type
randao_commitment*: Blake2_256_Digest # RANDAO commitment
randao_last_change*: uint64 # Slot the RANDAO commitment was last changed
balance*: uint64 # Balance in Gwei
status*: uint8 # Status code [used to be more enum-like]
status*: ValidatorStatusCodes # Status code
exit_slot*: uint64 # Slot when validator exited (or 0)
CrosslinkRecord* = object
@ -112,7 +112,7 @@ type
fork_slot_number*: uint64
pending_attestations*: seq[AttestationRecord] # Attestations not yet processed
pending_specials*: seq[SpecialRecord] # Specials not yet been processed
recent_block_hashes*: Blake2_256_Digest # recent beacon block hashes needed to process attestations, older to newer
recent_block_hashes*: seq[Blake2_256_Digest] # recent beacon block hashes needed to process attestations, older to newer
randao_mix*: Blake2_256_Digest # RANDAO state
ValidatorStatusCodes* {.pure.} = enum

86
beacon_chain/private/helpers.nim
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@ -8,37 +8,52 @@
# Helper functions
import ../datatypes, sequtils, nimcrypto, math
func get_active_validator_indices(validators: seq[ValidatorRecord], dynasty: int64): seq[Uint24] =
func get_active_validator_indices(validators: seq[ValidatorRecord]): seq[Uint24] =
## Select the active validators
result = @[]
for idx, val in validators:
if val.start_dynasty <= dynasty and
dynasty < val.end_dynasty:
if val.status == ACTIVE:
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
func shuffle(values: seq[Uint24], seed: Blake2_256_Digest): seq[Uint24] {.noInit.}=
## Returns the shuffled ``values`` with seed as entropy.
## TODO: this calls out for tests, but I odn't particularly trust spec
## right now.
const UpperBound = 2^24 # 16777216
assert validators.len <= UpperBound
let values_count = values.len
deepCopy(result, validators)
# Entropy is consumed from the seed in 3-byte (24 bit) chunks
const rand_bytes = 3
let rand_max = 2^(rand_bytes * 8) - 1
# The range of the RNG places an upper-bound on the size of the list that
# may be shuffled. It is a logic error to supply an oversized list.
assert values_count < rand_max
deepCopy(result, values)
var source = seed
var i = 0
while i < validators.len:
while i < values.len - 1:
# Re-hash the `source` to obtain a new pattern of bytes
source = blake2_256.digest source.data
# Iterate through the `source` bytes in 3-byte chunks
for pos in countup(0, 29, 3):
let remaining = validators.len - i
if remaining == 0:
let remaining = values_count - i
if remaining == 1:
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
# Read 3-bytes of `source` as a 24-bit big-endian integer.
let sample_from_source = source.data[pos].Uint24 shl 16 or source.data[pos+1].Uint24 shl 8 or source.data[pos+2].Uint24
if m < randMax:
let replacementPos = m mod remaining + i
swap result[i], result[replacementPos]
# Sample values greater than or equal to `sample_max` will cause
# modulo bias when mapped into the `remaining` range.
let sample_max = rand_max - rand_max mod remaining
# Perform a swap if the consumed entropy will not cause modulo bias.
if sample_from_source < sample_max:
let replacement_position = sample_from_source mod remaining + i
swap result[i], result[replacement_position]
inc i
func split[T](lst: seq[T], N: Positive): seq[seq[T]] =
@ -53,52 +68,51 @@ func get_new_shuffling*(seed: Blake2_256_Digest, validators: seq[ValidatorRecord
## 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
let avs = get_active_validator_indices(validators)
var committees_per_slot, slots_per_committee: uint16
if avs.len >= CYCLE_LENGTH * MIN_COMMITTEE_SIZE:
committees_per_slot = int16 avs.len div CYCLE_LENGTH div (MIN_COMMITTEE_SIZE * 2) + 1
committees_per_slot = uint16 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
while avs.len.uint16 * slots_per_committee < CYCLE_LENGTH * MIN_COMMITTEE_SIZE and
slots_per_committee < CYCLE_LENGTH:
slots_per_committee *= 2
result = @[]
for slot, slot_indices in shuffle(avs, seed).split(CYCLE_LENGTH):
let shard_indices = slot_indices.split(committees_per_slot)
let shard_id_start = crosslinking_start_shard +
slot.int16 * committees_per_slot div slots_per_committee
let shard_id_start = crosslinking_start_shard.uint16 +
slot.uint16 * committees_per_slot div slots_per_committee
var committees = newSeq[ShardAndCommittee](shard_indices.len)
for j, indices in shard_indices:
committees[j].shard_id = (shard_id_start + j.int16) mod SHARD_COUNT
committees[j].shard_id = (shard_id_start + j.uint16) mod SHARD_COUNT
committees[j].committee = indices
result.add committees
func get_shards_and_committees_for_slot*(crystallized_state: CrystallizedState,
slot: uint64): seq[ShardAndCommittee] =
func get_shards_and_committees_for_slot*(state: BeaconState,
slot: uint64): ShardAndCommittee =
# TODO: Spec why is active_state an argument?
# TODO: this returns a scalar, not vector, but its return type in spec is a seq/list?
let start = crystallized_state.last_state_recalc - CYCLE_LENGTH
assert start <= slot
assert slot < start + CYCLE_LENGTH * 2
let earliest_slot_in_array = state.last_state_recalculation_slot - CYCLE_LENGTH
assert earliest_slot_in_array <= slot
assert slot < earliest_slot_in_array + CYCLE_LENGTH * 2
result = crystallized_state.shard_and_committee_for_slots[int slot - start]
return state.shard_and_committee_for_slots[int slot - earliest_slot_in_array]
# TODO, slot is a uint64; 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: uint64): Blake2_256_Digest =
func get_block_hash*(state: BeaconState, current_block: BeaconBlock, slot: int): Blake2_256_Digest =
let earliest_slot_in_array = current_block.slot.int - state.recent_block_hashes.len
assert earliest_slot_in_array <= slot
assert slot < current_block.slot.int
let sback = beacon_block.slot - CYCLE_LENGTH * 2
assert sback <= slot
assert slot < sback + CYCLE_LENGTH * 2
result = active_state.recent_block_hashes[int slot - sback]
return state.recent_block_hashes[slot - earliest_slot_in_array]
func get_new_recent_block_hashes*(
old_block_hashes: seq[Blake2_256_Digest],