From b76eae8a71d700ee6bd88867ba21790e6a18dfb9 Mon Sep 17 00:00:00 2001 From: Justin Date: Fri, 23 Nov 2018 15:37:37 +0000 Subject: [PATCH] Update 0_beacon-chain.md --- specs/core/0_beacon-chain.md | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md index 7f4522360..820c20edc 100644 --- a/specs/core/0_beacon-chain.md +++ b/specs/core/0_beacon-chain.md @@ -337,22 +337,23 @@ Beacon block production is significantly different because of the proof of stake ### Beacon chain fork choice rule -The beacon chain fork choice rule is a hybrid that combines justification and finality with Latest Message Driven (LMD) Greediest Heaviest Observed SubTree (GHOST). At any point in time a validator `v` calculates the beacon chain head as follows. +The beacon chain fork choice rule is a hybrid that combines justification and finality with Latest Message Driven (LMD) Greediest Heaviest Observed SubTree (GHOST). At any point in time a validator `v` subjectively calculates the beacon chain head as follows. * Let `store` be the set of attestations and blocks that the validator `v` has observed and verified (in particular, block ancestors must be recursively verified). Attestations not part of any chain are still included in `store`. * Let `finalized_head` be the finalized block with the highest slot number. (A block `B` is finalized if there is a descendant of `B` in `store` the processing of which sets `B` as finalized.) * Let `justified_head` be the descendant of `finalized_head` with the highest slot number that has been justified for at least `CYCLE_LENGTH` slots. (A block `B` is justified is there is a descendant of `B` in `store` the processing of which sets `B` as justified.) If no such descendant exists set `justified_head` to `finalized_head`. * Let `get_ancestor(store, block, slot)` be the ancestor of `block` with slot number `slot`. The `get_ancestor` function can be defined recursively as `def get_ancestor(store, block, slot): return block if block.slot == slot else get_ancestor(store, store.get_parent(block), slot)`. -* Let `get_latest_attestation(store, validator)` be the attestation in `store` from `validator` with the highest slot number. If several such attestations exist use the one the validator `v` verified first. +* Let `get_latest_attestation(store, validator)` be the attestation with the highest slot number in `store` from `validator`. If several such attestations exist use the one the validator `v` observed first. * Let `get_latest_attestation_target(store, validator)` be the target block in the attestation `get_latest_attestation(store, validator)`. * The head is `lmd_ghost(store, justified_head)` where the function `lmd_ghost` is defined below. Note that the implementation below is suboptimal; there are implementations that compute the head in logarithmic time. ```python def lmd_ghost(store, start): - active_validators = [start.state.validators[i] for i in range(get_active_validators(start.state.validators, start.slot))] - latest_attestation_targets = [get_latest_attestation_target(store, validator) for validator in active_validators] + validators = start.state.validators + active_validators = [validators[i] for i in range(get_active_validators(validators, start.slot))] + attestation_targets = [get_latest_attestation_target(store, validator) for validator in active_validators] def get_vote_count(block): - return len([target for target in latest_attestation_targets if get_ancestor(store, target, block.slot) == block]) + return len([target for target in attestation_targets if get_ancestor(store, target, block.slot) == block]) head = start while 1: