59 lines
2.1 KiB
Nim
59 lines
2.1 KiB
Nim
import
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deques, options, sequtils, tables,
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chronicles,
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./spec/[beaconstate, datatypes, crypto, digest, helpers, validator], extras,
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./attestation_pool, ./beacon_node_types, ./beacon_chain_db, ./ssz
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proc get_ancestor(blck: BlockRef, slot: Slot): BlockRef =
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if blck.slot == slot:
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blck
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elif blck.slot < slot:
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nil
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else:
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get_ancestor(blck.parent, slot)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.4.0/specs/core/0_beacon-chain.md#beacon-chain-fork-choice-rule
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proc lmdGhost*(
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pool: AttestationPool, start_state: BeaconState,
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start_block: BlockRef): BlockRef =
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# TODO: a Fenwick Tree datastructure to keep track of cumulated votes
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# in O(log N) complexity
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# https://en.wikipedia.org/wiki/Fenwick_tree
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# Nim implementation for cumulative frequencies at
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# https://github.com/numforge/laser/blob/990e59fffe50779cdef33aa0b8f22da19e1eb328/benchmarks/random_sampling/fenwicktree.nim
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let
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active_validator_indices =
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get_active_validator_indices(
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start_state.validator_registry, slot_to_epoch(start_state.slot))
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var attestation_targets: seq[tuple[validator: ValidatorIndex, blck: BlockRef]]
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for i in active_validator_indices:
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let pubKey = start_state.validator_registry[i].pubkey
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if (let vote = pool.latestAttestation(pubKey); not vote.isNil):
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attestation_targets.add((i, vote))
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template get_vote_count(blck: BlockRef): uint64 =
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var res: uint64
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for validator_index, target in attestation_targets.items():
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if get_ancestor(target, blck.slot) == blck:
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# The div on the balance is to chop off the insignification bits that
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# fluctuate a lot epoch to epoch to have a more stable fork choice
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res += get_effective_balance(start_state, validator_index) div
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FORK_CHOICE_BALANCE_INCREMENT
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res
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var head = start_block
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while true:
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if head.children.len() == 0:
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return head
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head = head.children[0]
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var
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headCount = get_vote_count(head)
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for i in 1..<head.children.len:
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if (let hc = get_vote_count(head.children[i]); hc > headCount):
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head = head.children[i]
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headCount = hc
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