183 lines
7.1 KiB
Nim
183 lines
7.1 KiB
Nim
# beacon_chain
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# Copyright (c) 2018 Status Research & Development GmbH
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# Licensed and distributed under either of
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# * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
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# * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
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# at your option. This file may not be copied, modified, or distributed except according to those terms.
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# Uncategorized helper functions from the spec
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import ./datatypes, ./digest, sequtils, math, endians
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# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#integer_squareroot
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func integer_squareroot*(n: SomeInteger): SomeInteger =
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# Return the largest integer ``x`` such that ``x**2 <= n``.
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doAssert n >= 0'u64
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var
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x = n
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y = (x + 1) div 2
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while y < x:
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x = y
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y = (x + n div x) div 2
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x
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# TODO reuse as necessary/useful for merkle proof building
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func merkle_root*(values: openArray[Eth2Digest]): Eth2Digest =
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## Merkleize ``values`` (where ``len(values)`` is a power of two) and return
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## the Merkle root.
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## https://crypto.stackexchange.com/questions/43430/what-is-the-reason-to-separate-domains-in-the-internal-hash-algorithm-of-a-merkl
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let num_values = len(values)
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# Simplifies boundary conditions
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doAssert is_power_of_two(num_values)
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doAssert num_values >= 2
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doAssert num_values mod 2 == 0
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# TODO reverse ``o`` order and use newSeqWith to avoid pointless zero-filling.
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var o = repeat(ZERO_HASH, len(values))
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var hash_buffer: array[2*32, byte]
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# These ``o`` indices get filled from ``values``.
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let highest_internally_filled_index = (num_values div 2) - 1
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doAssert (highest_internally_filled_index + 1) * 2 >= num_values
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for i in countdown(num_values-1, highest_internally_filled_index + 1):
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hash_buffer[0..31] = values[i*2 - num_values].data
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hash_buffer[32..63] = values[i*2+1 - num_values].data
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o[i] = eth2hash(hash_buffer)
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## These ``o`` indices get filled from other ``o`` indices.
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doAssert highest_internally_filled_index * 2 + 1 < num_values
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for i in countdown(highest_internally_filled_index, 1):
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hash_buffer[0..31] = o[i*2].data
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hash_buffer[32..63] = o[i*2+1].data
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o[i] = eth2hash(hash_buffer)
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o[1]
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# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#compute_epoch_of_slot
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func compute_epoch_of_slot*(slot: Slot|uint64): Epoch =
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# Return the epoch number of the given ``slot``.
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(slot div SLOTS_PER_EPOCH).Epoch
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# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#compute_start_slot_of_epoch
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func compute_start_slot_of_epoch*(epoch: Epoch): Slot =
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# Return the start slot of ``epoch``.
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(epoch * SLOTS_PER_EPOCH).Slot
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# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#is_active_validator
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func is_active_validator*(validator: Validator, epoch: Epoch): bool =
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### Check if ``validator`` is active
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validator.activation_epoch <= epoch and epoch < validator.exit_epoch
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# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#get_active_validator_indices
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func get_active_validator_indices*(state: BeaconState, epoch: Epoch):
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seq[ValidatorIndex] =
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# Return the sequence of active validator indices at ``epoch``.
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for idx, val in state.validators:
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if is_active_validator(val, epoch):
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result.add idx.ValidatorIndex
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# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#get_committee_count
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func get_committee_count*(state: BeaconState, epoch: Epoch): uint64 =
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# Return the number of committees at ``epoch``.
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let active_validator_indices = get_active_validator_indices(state, epoch)
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let committees_per_slot = clamp(
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len(active_validator_indices) div SLOTS_PER_EPOCH div TARGET_COMMITTEE_SIZE,
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1, SHARD_COUNT div SLOTS_PER_EPOCH).uint64
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result = committees_per_slot * SLOTS_PER_EPOCH
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# Otherwise, get_crosslink_committee(...) cannot access some committees.
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doAssert SHARD_COUNT >= result
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# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#get_current_epoch
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func get_current_epoch*(state: BeaconState): Epoch =
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# Return the current epoch.
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doAssert state.slot >= GENESIS_SLOT, $state.slot
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compute_epoch_of_slot(state.slot)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.7.1/specs/core/0_beacon-chain.md#get_randao_mix
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func get_randao_mix*(state: BeaconState,
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epoch: Epoch): Eth2Digest =
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## Returns the randao mix at a recent ``epoch``.
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state.randao_mixes[epoch mod EPOCHS_PER_HISTORICAL_VECTOR]
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func bytes_to_int*(data: openarray[byte]): uint64 =
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doAssert data.len == 8
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# Little-endian data representation
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result = 0
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for i in countdown(7, 0):
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result = result * 256 + data[i]
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# Have 1, 4, 8, and 32-byte versions. 1+ more and maybe worth metaprogramming.
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func int_to_bytes32*(x: uint64): array[32, byte] =
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## Little-endian data representation
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## TODO remove uint64 when those callers fade away
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littleEndian64(result[0].addr, x.unsafeAddr)
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func int_to_bytes32*(x: Epoch): array[32, byte] {.borrow.}
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func int_to_bytes8*(x: uint64): array[8, byte] =
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littleEndian64(result[0].addr, x.unsafeAddr)
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func int_to_bytes1*(x: int): array[1, byte] =
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doAssert x >= 0
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doAssert x < 256
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result[0] = x.byte
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func int_to_bytes4*(x: uint64): array[4, byte] =
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doAssert x >= 0'u64
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doAssert x < 2'u64^32
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# Little-endian data representation
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result[0] = ((x shr 0) and 0xff).byte
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result[1] = ((x shr 8) and 0xff).byte
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result[2] = ((x shr 16) and 0xff).byte
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result[3] = ((x shr 24) and 0xff).byte
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# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#compute_domain
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func compute_domain*(
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domain_type: DomainType,
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fork_version: array[4, byte] = [0'u8, 0, 0, 0]): uint64 =
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var buf: array[8, byte]
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buf[0..3] = int_to_bytes4(domain_type.uint64)
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buf[4..7] = fork_version
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bytes_to_int(buf)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#get_domain
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func get_domain*(
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state: BeaconState, domain_type: DomainType, message_epoch: Epoch): Domain =
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## Return the signature domain (fork version concatenated with domain type)
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## of a message.
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let
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epoch = message_epoch
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fork_version = if epoch < state.fork.epoch:
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state.fork.previous_version
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else:
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state.fork.current_version
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compute_domain(domain_type, fork_version)
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func get_domain*(state: BeaconState, domain_type: DomainType): Domain =
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get_domain(state, domain_type, get_current_epoch(state))
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# https://github.com/ethereum/eth2.0-specs/blob/v0.8.3/specs/core/0_beacon-chain.md#get_seed
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func get_seed*(state: BeaconState, epoch: Epoch): Eth2Digest =
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# Generate a seed for the given ``epoch``.
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var seed_input : array[32*3, byte]
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# Detect potential underflow
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doAssert EPOCHS_PER_HISTORICAL_VECTOR >= MIN_SEED_LOOKAHEAD
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seed_input[0..31] =
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get_randao_mix(state,
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epoch + EPOCHS_PER_HISTORICAL_VECTOR - MIN_SEED_LOOKAHEAD - 1).data
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seed_input[32..63] =
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state.active_index_roots[epoch mod EPOCHS_PER_HISTORICAL_VECTOR].data
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seed_input[64..95] = int_to_bytes32(epoch)
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eth2hash(seed_input)
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