462 lines
20 KiB
Nim
462 lines
20 KiB
Nim
# beacon_chain
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# Copyright (c) 2018-2020 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 https://opensource.org/licenses/MIT).
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# * Apache v2 license (license terms in the root directory or at https://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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# State transition - epoch processing, as described in
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# https://github.com/ethereum/eth2.0-specs/blob/master/specs/core/0_beacon-chain.md#beacon-chain-state-transition-function
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#
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# The purpose of this code right is primarily educational, to help piece
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# together the mechanics of the beacon state and to discover potential problem
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# areas.
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#
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# The entry point is `process_epoch` which is at the bottom of this file.
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#
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# General notes about the code (TODO):
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# * It's inefficient - we quadratically copy, allocate and iterate when there
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# are faster options
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# * Weird styling - the sections taken from the spec use python styling while
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# the others use NEP-1 - helps grepping identifiers in spec
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# * We mix procedural and functional styles for no good reason, except that the
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# spec does so also.
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# * There are likely lots of bugs.
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# * For indices, we get a mix of uint64, ValidatorIndex and int - this is currently
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# swept under the rug with casts
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# * The spec uses uint64 for data types, but functions in the spec often assume
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# signed bigint semantics - under- and overflows ensue
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# * Sane error handling is missing in most cases (yay, we'll get the chance to
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# debate exceptions again!)
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# When updating the code, add TODO sections to mark where there are clear
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# improvements to be made - other than that, keep things similar to spec for
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# now.
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import
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math, options, sequtils, tables,
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stew/[bitseqs, bitops2], chronicles, json_serialization/std/sets,
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metrics, ../ssz,
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beaconstate, crypto, datatypes, digest, helpers, validator,
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state_transition_helpers,
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../../nbench/bench_lab
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# Logging utilities
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# --------------------------------------------------------
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logScope: topics = "consens"
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# https://github.com/ethereum/eth2.0-metrics/blob/master/metrics.md#interop-metrics
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declareGauge beacon_finalized_epoch, "Current finalized epoch" # On epoch transition
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declareGauge beacon_finalized_root, "Current finalized root" # On epoch transition
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declareGauge beacon_current_justified_epoch, "Current justified epoch" # On epoch transition
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declareGauge beacon_current_justified_root, "Current justified root" # On epoch transition
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declareGauge beacon_previous_justified_epoch, "Current previously justified epoch" # On epoch transition
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declareGauge beacon_previous_justified_root, "Current previously justified root" # On epoch transition
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# Non-spec
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declareGauge epoch_transition_justification_and_finalization, "Epoch transition justification and finalization time"
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declareGauge epoch_transition_times_rewards_and_penalties, "Epoch transition reward and penalty time"
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declareGauge epoch_transition_registry_updates, "Epoch transition registry updates time"
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declareGauge epoch_transition_slashings, "Epoch transition slashings time"
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declareGauge epoch_transition_final_updates, "Epoch transition final updates time"
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# Spec
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# --------------------------------------------------------
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# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#get_total_active_balance
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func get_total_active_balance*(state: BeaconState): Gwei =
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# Return the combined effective balance of the active validators.
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# Note: ``get_total_balance`` returns ``EFFECTIVE_BALANCE_INCREMENT`` Gwei
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# minimum to avoid divisions by zero.
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# TODO it calls get_total_balance with set(g_a_v_i(...))
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get_total_balance(
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state,
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get_active_validator_indices(state, get_current_epoch(state)))
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# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#helper-functions-1
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func get_matching_source_attestations(state: BeaconState, epoch: Epoch):
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seq[PendingAttestation] =
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doAssert epoch in [get_current_epoch(state), get_previous_epoch(state)]
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if epoch == get_current_epoch(state):
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state.current_epoch_attestations
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else:
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state.previous_epoch_attestations
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func get_matching_target_attestations(state: BeaconState, epoch: Epoch):
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seq[PendingAttestation] =
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filterIt(
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get_matching_source_attestations(state, epoch),
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it.data.target.root == get_block_root(state, epoch)
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)
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func get_matching_head_attestations(state: BeaconState, epoch: Epoch):
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seq[PendingAttestation] =
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filterIt(
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get_matching_target_attestations(state, epoch),
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it.data.beacon_block_root ==
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get_block_root_at_slot(state, it.data.slot)
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)
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func get_attesting_balance(
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state: BeaconState, attestations: seq[PendingAttestation],
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stateCache: var StateCache): Gwei =
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# Return the combined effective balance of the set of unslashed validators
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# participating in ``attestations``.
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# Note: ``get_total_balance`` returns ``EFFECTIVE_BALANCE_INCREMENT`` Gwei
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# minimum to avoid divisions by zero.
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get_total_balance(state, get_unslashed_attesting_indices(
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state, attestations, stateCache))
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# https://github.com/ethereum/eth2.0-specs/blob/v0.9.4/specs/core/0_beacon-chain.md#justification-and-finalization
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proc process_justification_and_finalization*(
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state: var BeaconState, stateCache: var StateCache) {.nbench.}=
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logScope: pcs = "process_justification_and_finalization"
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if get_current_epoch(state) <= GENESIS_EPOCH + 1:
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return
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let
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previous_epoch = get_previous_epoch(state)
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current_epoch = get_current_epoch(state)
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old_previous_justified_checkpoint = state.previous_justified_checkpoint
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old_current_justified_checkpoint = state.current_justified_checkpoint
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# Process justifications
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state.previous_justified_checkpoint = state.current_justified_checkpoint
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## Spec:
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## state.justification_bits[1:] = state.justification_bits[:-1]
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## state.justification_bits[0] = 0b0
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# TODO JUSTIFICATION_BITS_LENGTH is a constant in spec, move there or fix
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# BitVector serialization in SSZ layer
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const JUSTIFICATION_BITS_LENGTH = 4
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state.justification_bits = (state.justification_bits shl 1) and
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cast[uint8]((2^JUSTIFICATION_BITS_LENGTH) - 1)
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# This is a somewhat expensive approach
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let active_validator_indices {.used.} =
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toHashSet(mapIt(
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get_active_validator_indices(state, get_current_epoch(state)), it.int))
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let matching_target_attestations_previous =
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get_matching_target_attestations(state, previous_epoch) # Previous epoch
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## This epoch processing is the last time these previous attestations can
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## matter -- in the next epoch, they'll be 2 epochs old, when BeaconState
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## tracks current_epoch_attestations and previous_epoch_attestations only
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## per
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## https://github.com/ethereum/eth2.0-specs/blob/v0.10.1/specs/phase0/beacon-chain.md#attestations
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## and `get_matching_source_attestations(...)` via
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## https://github.com/ethereum/eth2.0-specs/blob/v0.10.1/specs/phase0/beacon-chain.md#helper-functions-1
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## and
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## https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#final-updates
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## after which the state.previous_epoch_attestations is replaced.
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trace "Non-attesting indices in previous epoch",
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missing_all_validators=
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difference(active_validator_indices,
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toHashSet(mapIt(get_attesting_indices(state,
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matching_target_attestations_previous, stateCache), it.int))),
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missing_unslashed_validators=
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difference(active_validator_indices,
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toHashSet(mapIt(get_unslashed_attesting_indices(state,
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matching_target_attestations_previous, stateCache), it.int))),
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prev_attestations_len=len(state.previous_epoch_attestations),
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cur_attestations_len=len(state.current_epoch_attestations),
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num_active_validators=len(active_validator_indices),
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required_balance = get_total_active_balance(state) * 2,
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attesting_balance_prev = get_attesting_balance(state, matching_target_attestations_previous, stateCache)
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if get_attesting_balance(state, matching_target_attestations_previous,
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stateCache) * 3 >= get_total_active_balance(state) * 2:
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state.current_justified_checkpoint =
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Checkpoint(epoch: previous_epoch,
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root: get_block_root(state, previous_epoch))
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state.justification_bits.setBit 1
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trace "Justified with previous epoch",
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current_epoch = current_epoch,
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checkpoint = shortLog(state.current_justified_checkpoint),
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cat = "justification"
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let matching_target_attestations_current =
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get_matching_target_attestations(state, current_epoch) # Current epoch
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if get_attesting_balance(state, matching_target_attestations_current,
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stateCache) * 3 >= get_total_active_balance(state) * 2:
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state.current_justified_checkpoint =
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Checkpoint(epoch: current_epoch,
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root: get_block_root(state, current_epoch))
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state.justification_bits.setBit 0
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trace "Justified with current epoch",
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current_epoch = current_epoch,
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checkpoint = shortLog(state.current_justified_checkpoint),
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cat = "justification"
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# Process finalizations
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let bitfield = state.justification_bits
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## The 2nd/3rd/4th most recent epochs are justified, the 2nd using the 4th
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## as source
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if (bitfield and 0b1110) == 0b1110 and
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old_previous_justified_checkpoint.epoch + 3 == current_epoch:
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state.finalized_checkpoint = old_previous_justified_checkpoint
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trace "Finalized with rule 234",
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current_epoch = current_epoch,
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checkpoint = shortLog(state.finalized_checkpoint),
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cat = "finalization"
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## The 2nd/3rd most recent epochs are justified, the 2nd using the 3rd as
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## source
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if (bitfield and 0b110) == 0b110 and
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old_previous_justified_checkpoint.epoch + 2 == current_epoch:
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state.finalized_checkpoint = old_previous_justified_checkpoint
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trace "Finalized with rule 23",
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current_epoch = current_epoch,
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checkpoint = shortLog(state.finalized_checkpoint),
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cat = "finalization"
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## The 1st/2nd/3rd most recent epochs are justified, the 1st using the 3rd as
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## source
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if (bitfield and 0b111) == 0b111 and
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old_current_justified_checkpoint.epoch + 2 == current_epoch:
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state.finalized_checkpoint = old_current_justified_checkpoint
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trace "Finalized with rule 123",
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current_epoch = current_epoch,
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checkpoint = shortLog(state.finalized_checkpoint),
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cat = "finalization"
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## The 1st/2nd most recent epochs are justified, the 1st using the 2nd as
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## source
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if (bitfield and 0b11) == 0b11 and
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old_current_justified_checkpoint.epoch + 1 == current_epoch:
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state.finalized_checkpoint = old_current_justified_checkpoint
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trace "Finalized with rule 12",
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current_epoch = current_epoch,
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checkpoint = shortLog(state.finalized_checkpoint),
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cat = "finalization"
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# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#rewards-and-penalties-1
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func get_base_reward(state: BeaconState, index: ValidatorIndex,
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total_balance: auto): Gwei =
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# Spec function recalculates total_balance every time, which creates an
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# O(n^2) situation.
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let effective_balance = state.validators[index].effective_balance
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effective_balance * BASE_REWARD_FACTOR div
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integer_squareroot(total_balance) div BASE_REWARDS_PER_EPOCH
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# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#rewards-and-penalties-1
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func get_attestation_deltas(state: BeaconState, stateCache: var StateCache):
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tuple[a: seq[Gwei], b: seq[Gwei]] {.nbench.}=
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let
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previous_epoch = get_previous_epoch(state)
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total_balance = get_total_active_balance(state)
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var
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rewards = repeat(0'u64, len(state.validators))
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penalties = repeat(0'u64, len(state.validators))
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eligible_validator_indices : seq[ValidatorIndex] = @[]
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for index, v in state.validators:
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if is_active_validator(v, previous_epoch) or
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(v.slashed and previous_epoch + 1 < v.withdrawable_epoch):
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eligible_validator_indices.add index.ValidatorIndex
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# Micro-incentives for matching FFG source, FFG target, and head
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let
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matching_source_attestations =
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get_matching_source_attestations(state, previous_epoch)
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matching_target_attestations =
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get_matching_target_attestations(state, previous_epoch)
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matching_head_attestations =
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get_matching_head_attestations(state, previous_epoch)
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for attestations in
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[matching_source_attestations, matching_target_attestations,
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matching_head_attestations]:
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let
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unslashed_attesting_indices =
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get_unslashed_attesting_indices(state, attestations, stateCache)
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attesting_balance = get_total_balance(state, unslashed_attesting_indices)
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for index in eligible_validator_indices:
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if index in unslashed_attesting_indices:
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# Factored out from balance totals to avoid uint64 overflow
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const increment = EFFECTIVE_BALANCE_INCREMENT
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let reward_numerator = get_base_reward(state, index, total_balance) *
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(attesting_balance div increment)
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rewards[index] += reward_numerator div (total_balance div increment)
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else:
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penalties[index] += get_base_reward(state, index, total_balance)
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# Proposer and inclusion delay micro-rewards
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## This depends on matching_source_attestations being an indexable seq, not a
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## set, hash table, etc.
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let source_attestation_attesting_indices =
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mapIt(
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matching_source_attestations,
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get_attesting_indices(state, it.data, it.aggregation_bits, stateCache))
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for index in get_unslashed_attesting_indices(
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state, matching_source_attestations, stateCache):
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# Translation of attestation = min([...])
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doAssert matching_source_attestations.len > 0
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# Start by filtering the right attestations
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var filtered_matching_source_attestations: seq[PendingAttestation]
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for source_attestation_index, a in matching_source_attestations:
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if index notin
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source_attestation_attesting_indices[source_attestation_index]:
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continue
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filtered_matching_source_attestations.add a
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# The first filtered attestation serves as min until we find something
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# better
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var attestation = filtered_matching_source_attestations[0]
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for source_attestation_index, a in filtered_matching_source_attestations:
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if a.inclusion_delay < attestation.inclusion_delay:
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attestation = a
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let
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base_reward = get_base_reward(state, index, total_balance)
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proposer_reward = (base_reward div PROPOSER_REWARD_QUOTIENT).Gwei
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rewards[attestation.proposer_index.int] += proposer_reward
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let max_attester_reward = base_reward - proposer_reward
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rewards[index] += max_attester_reward div attestation.inclusion_delay
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# Inactivity penalty
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let finality_delay = previous_epoch - state.finalized_checkpoint.epoch
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if finality_delay > MIN_EPOCHS_TO_INACTIVITY_PENALTY:
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let matching_target_attesting_indices =
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get_unslashed_attesting_indices(
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state, matching_target_attestations, stateCache)
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for index in eligible_validator_indices:
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penalties[index] +=
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BASE_REWARDS_PER_EPOCH.uint64 * get_base_reward(state, index, total_balance)
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if index notin matching_target_attesting_indices:
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penalties[index] +=
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state.validators[index].effective_balance *
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finality_delay div INACTIVITY_PENALTY_QUOTIENT
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(rewards, penalties)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.10.1/specs/phase0/beacon-chain.md#rewards-and-penalties-1
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func process_rewards_and_penalties(
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state: var BeaconState, cache: var StateCache) {.nbench.}=
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if get_current_epoch(state) == GENESIS_EPOCH:
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return
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let (rewards, penalties) = get_attestation_deltas(state, cache)
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for i in 0 ..< len(state.validators):
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increase_balance(state, i.ValidatorIndex, rewards[i])
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decrease_balance(state, i.ValidatorIndex, penalties[i])
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# https://github.com/ethereum/eth2.0-specs/blob/v0.9.4/specs/core/0_beacon-chain.md#slashings
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func process_slashings*(state: var BeaconState) {.nbench.}=
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let
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epoch = get_current_epoch(state)
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total_balance = get_total_active_balance(state)
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for index, validator in state.validators:
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if validator.slashed and epoch + EPOCHS_PER_SLASHINGS_VECTOR div 2 ==
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validator.withdrawable_epoch:
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let increment = EFFECTIVE_BALANCE_INCREMENT # Factored out from penalty
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# numerator to avoid uint64 overflow
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let penalty_numerator =
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validator.effective_balance div increment *
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min(sum(state.slashings) * 3, total_balance)
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let penalty = penalty_numerator div total_balance * increment
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decrease_balance(state, index.ValidatorIndex, penalty)
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# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#final-updates
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func process_final_updates*(state: var BeaconState) {.nbench.}=
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let
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current_epoch = get_current_epoch(state)
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next_epoch = current_epoch + 1
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# Reset eth1 data votes
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if next_epoch mod EPOCHS_PER_ETH1_VOTING_PERIOD == 0:
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state.eth1_data_votes = @[]
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# Update effective balances with hysteresis
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for index, validator in state.validators:
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let balance = state.balances[index]
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const
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HYSTERESIS_INCREMENT =
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EFFECTIVE_BALANCE_INCREMENT div HYSTERESIS_QUOTIENT
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DOWNWARD_THRESHOLD =
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HYSTERESIS_INCREMENT * HYSTERESIS_DOWNWARD_MULTIPLIER
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UPWARD_THRESHOLD = HYSTERESIS_INCREMENT * HYSTERESIS_UPWARD_MULTIPLIER
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if balance + DOWNWARD_THRESHOLD < validator.effective_balance or
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validator.effective_balance + UPWARD_THRESHOLD < balance:
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state.validators[index].effective_balance =
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min(
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balance - balance mod EFFECTIVE_BALANCE_INCREMENT,
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MAX_EFFECTIVE_BALANCE)
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# Reset slashings
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state.slashings[next_epoch mod EPOCHS_PER_SLASHINGS_VECTOR] = 0.Gwei
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# Set randao mix
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state.randao_mixes[next_epoch mod EPOCHS_PER_HISTORICAL_VECTOR] =
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get_randao_mix(state, current_epoch)
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# Set historical root accumulator
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if next_epoch mod (SLOTS_PER_HISTORICAL_ROOT div SLOTS_PER_EPOCH).uint64 == 0:
|
|
let historical_batch = HistoricalBatch(
|
|
block_roots: state.block_roots,
|
|
state_roots: state.state_roots,
|
|
)
|
|
state.historical_roots.add (hash_tree_root(historical_batch))
|
|
|
|
# Rotate current/previous epoch attestations
|
|
state.previous_epoch_attestations = state.current_epoch_attestations
|
|
state.current_epoch_attestations = @[]
|
|
|
|
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#epoch-processing
|
|
proc process_epoch*(state: var BeaconState) {.nbench.}=
|
|
trace "process_epoch",
|
|
current_epoch = get_current_epoch(state)
|
|
|
|
var per_epoch_cache = get_empty_per_epoch_cache()
|
|
|
|
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#justification-and-finalization
|
|
process_justification_and_finalization(state, per_epoch_cache)
|
|
|
|
trace "ran process_justification_and_finalization",
|
|
current_epoch = get_current_epoch(state)
|
|
|
|
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#rewards-and-penalties-1
|
|
process_rewards_and_penalties(state, per_epoch_cache)
|
|
|
|
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#registry-updates
|
|
# Don't rely on caching here.
|
|
process_registry_updates(state)
|
|
|
|
## Caching here for get_beacon_committee(...) can break otherwise, since
|
|
## get_active_validator_indices(...) usually changes.
|
|
clear(per_epoch_cache.beacon_committee_cache)
|
|
|
|
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#slashings
|
|
process_slashings(state)
|
|
|
|
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#final-updates
|
|
process_final_updates(state)
|
|
|
|
# Once per epoch metrics
|
|
beacon_finalized_epoch.set(state.finalized_checkpoint.epoch.int64)
|
|
beacon_finalized_root.set(state.finalized_checkpoint.root.toGaugeValue)
|
|
beacon_current_justified_epoch.set(
|
|
state.current_justified_checkpoint.epoch.int64)
|
|
beacon_current_justified_root.set(
|
|
state.current_justified_checkpoint.root.toGaugeValue)
|
|
beacon_previous_justified_epoch.set(
|
|
state.previous_justified_checkpoint.epoch.int64)
|
|
beacon_previous_justified_root.set(
|
|
state.previous_justified_checkpoint.root.toGaugeValue)
|