add some helper functions, change epoch processing, add some new constants

beacon_chain/spec/beaconstate.nim

@@ -267,6 +267,13 @@ func get_block_root*(state: BeaconState,
   doAssert slot < state.slot
   state.latest_block_roots[slot mod LATEST_BLOCK_ROOTS_LENGTH]
 
+func get_randao_mix*(state: BeaconState,
+                    slot: uint64): Eth2Digest =
+    ## Returns the randao mix at a recent ``slot``.
+    assert state.slot < slot + LATEST_RANDAO_MIXES_LENGTH
+    assert slot <= state.slot
+    state.latest_randao_mixes[slot mod LATEST_RANDAO_MIXES_LENGTH]
+
 func get_attestation_participants*(state: BeaconState,
                                    attestation_data: AttestationData,
                                    participation_bitfield: seq[byte]): seq[Uint24] =
@@ -356,6 +363,18 @@ func update_validator_registry*(state: var BeaconState) =
         get_effective_balance(state, index.Uint24) *
           min(total_penalties * 3, total_balance) div total_balance
 
+  # Perform additional updates
+  state.previous_epoch_calculation_slot = state.current_epoch_calculation_slot
+  state.previous_epoch_start_shard = state.current_epoch_start_shard
+  state.previous_epoch_randao_mix = state.current_epoch_randao_mix
+  state.current_epoch_calculation_slot = state.slot
+  state.current_epoch_start_shard = (state.current_epoch_start_shard + get_current_epoch_committee_count_per_slot(state) * EPOCH_LENGTH) mod SHARD_COUNT
+  state.current_epoch_randao_mix = get_randao_mix(state, state.current_epoch_calculation_slot - SEED_LOOKAHEAD)
+
+  # TODO "If a validator registry update does not happen do the following: ..."
+
+  #process_penalties_and_exits(state)
+
 proc checkAttestation*(
     state: BeaconState, attestation: Attestation, flags: UpdateFlags): bool =
   ## Check that an attestation follows the rules of being included in the state

beacon_chain/spec/datatypes.nim

@@ -135,6 +135,12 @@ const
   ZERO_BALANCE_VALIDATOR_TTL* = 2'u64^22 ##\
   ## slots (~291 days)
 
+  DEPOSIT_ROOT_VOTING_PERIOD* = 2'u64^10 ##\
+  ## slots (~1.7 hours)
+
+  MIN_VALIDATOR_WITHDRAWAL_TIME* = 2'u64^14 ##\
+  ## slots (~27 hours)
+
   # Quotients
   BASE_REWARD_QUOTIENT* = 2'u64^10 ##\
   ## The `BASE_REWARD_QUOTIENT` parameter dictates the per-epoch reward. It
@@ -414,7 +420,7 @@ type
     ## When
 
   DepositRootVote* = object
-    deposit_root*: Eth2Digest       # Candidate PoW receipt root
+    deposit_root*: Eth2Digest
     vote_count*: uint64                           # Vote count
 
   PendingAttestationRecord* = object

beacon_chain/spec/helpers.nim

@@ -180,3 +180,29 @@ proc is_surround_vote*(attestation_data_1: AttestationData,
     (attestation_data_1.justified_slot + 1 == attestation_data_2.slot) and
     (attestation_data_2.slot < attestation_data_1.slot)
   )
+
+#func is_active_validator*(validator: ValidatorRecord, slot: uint64): bool =
+#  ### Checks if validator is active
+#  validator.activation_slot <= slot and slot < validator.exit_slot
+
+func is_active_validator*(validator: ValidatorRecord): bool =
+  validator.status in {ACTIVE, ACTIVE_PENDING_EXIT}
+
+func get_active_validator_indices*(validators: openArray[ValidatorRecord], slot: uint64): seq[Uint24] =
+  ## Gets indices of active validators from validators
+  for idx, val in validators:
+    #if is_active_validator(val, slot):
+    if is_active_validator(val):
+      result.add idx.Uint24
+
+func get_committee_count_per_slot*(active_validator_count: int): uint64 =
+  clamp(
+    active_validator_count div EPOCH_LENGTH div TARGET_COMMITTEE_SIZE,
+    1, SHARD_COUNT div EPOCH_LENGTH).uint64
+
+func get_current_epoch_committee_count_per_slot*(state: BeaconState): uint64 =
+  let current_active_validators = get_active_validator_indices(
+    state.validator_registry,
+    state.current_epoch_calculation_slot,
+  )
+  return get_committee_count_per_slot(len(current_active_validators))

beacon_chain/spec/validator.nim

@@ -12,9 +12,6 @@ import
   ../ssz,
   ./crypto, ./datatypes, ./digest, ./helpers
 
-func is_active_validator*(validator: ValidatorRecord): bool =
-  validator.status in {ACTIVE, ACTIVE_PENDING_EXIT}
-
 func min_empty_validator_index*(
     validators: seq[ValidatorRecord],
     validator_balances: seq[uint64],