nimbus-eth2/beacon_chain/spec/helpers.nim

183 lines
7.1 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, endians
# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_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
# TODO reuse as necessary/useful for merkle proof building
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/v0.8.3/specs/core/0_beacon-chain.md#compute_epoch_of_slot
func compute_epoch_of_slot*(slot: Slot|uint64): Epoch =
# Return the epoch number of the given ``slot``.
(slot div SLOTS_PER_EPOCH).Epoch
# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#compute_start_slot_of_epoch
func compute_start_slot_of_epoch*(epoch: Epoch): Slot =
# Return the start slot of ``epoch``.
(epoch * SLOTS_PER_EPOCH).Slot
# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/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/v0.8.3/specs/core/0_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/v0.8.3/specs/core/0_beacon-chain.md#get_committee_count
func get_committee_count*(state: BeaconState, epoch: Epoch): uint64 =
# Return the number of committees at ``epoch``.
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, SHARD_COUNT div SLOTS_PER_EPOCH).uint64
result = committees_per_slot * SLOTS_PER_EPOCH
# Otherwise, get_crosslink_committee(...) cannot access some committees.
doAssert SHARD_COUNT >= result
# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_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_of_slot(state.slot)
# https://github.com/ethereum/eth2.0-specs/blob/v0.7.1/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``.
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
littleEndian64(result[0].addr, x.unsafeAddr)
func int_to_bytes32*(x: Epoch): array[32, byte] {.borrow.}
func int_to_bytes8*(x: uint64): array[8, byte] =
littleEndian64(result[0].addr, x.unsafeAddr)
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/v0.8.3/specs/core/0_beacon-chain.md#compute_domain
func compute_domain*(
domain_type: DomainType,
fork_version: array[4, byte] = [0'u8, 0, 0, 0]): uint64 =
var buf: array[8, byte]
buf[0..3] = int_to_bytes4(domain_type.uint64)
buf[4..7] = fork_version
bytes_to_int(buf)
# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#get_domain
func get_domain*(
state: BeaconState, domain_type: DomainType, message_epoch: Epoch): Domain =
## Return the signature domain (fork version concatenated with domain type)
## of a message.
let
epoch = message_epoch
fork_version = if epoch < state.fork.epoch:
state.fork.previous_version
else:
state.fork.current_version
compute_domain(domain_type, fork_version)
func get_domain*(state: BeaconState, domain_type: DomainType): Domain =
get_domain(state, domain_type, get_current_epoch(state))
# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#get_seed
func get_seed*(state: BeaconState, epoch: Epoch): Eth2Digest =
# Generate a seed for the given ``epoch``.
var seed_input : array[32*3, byte]
# Detect potential underflow
doAssert EPOCHS_PER_HISTORICAL_VECTOR >= MIN_SEED_LOOKAHEAD
seed_input[0..31] =
get_randao_mix(state,
epoch + EPOCHS_PER_HISTORICAL_VECTOR - MIN_SEED_LOOKAHEAD - 1).data
seed_input[32..63] =
state.active_index_roots[epoch mod EPOCHS_PER_HISTORICAL_VECTOR].data
seed_input[64..95] = int_to_bytes32(epoch)
eth2hash(seed_input)