some comment changes noting further 0.4.0-spec-update progress, but no meaningful semantic changes (#161)

beacon_chain/spec/beaconstate.nim

@@ -249,7 +249,7 @@ func get_initial_beacon_block*(state: BeaconState): BeaconBlock =
     state_root: Eth2Digest(data: hash_tree_root(state))
   )
 
-# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_block_root
+# https://github.com/ethereum/eth2.0-specs/blob/0.4.0/specs/core/0_beacon-chain.md#get_block_root
 func get_block_root*(state: BeaconState,
                      slot: Slot): Eth2Digest =
   # Return the block root at a recent ``slot``.
@@ -306,7 +306,7 @@ func process_ejections*(state: var BeaconState) =
     if state.validator_balances[index] < EJECTION_BALANCE:
       exit_validator(state, index)
 
-# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_total_balance
+# https://github.com/ethereum/eth2.0-specs/blob/0.4.0/specs/core/0_beacon-chain.md#get_total_balance
 func get_total_balance*(state: BeaconState, validators: auto): Gwei =
   # Return the combined effective balance of an array of validators.
   foldl(validators, a + get_effective_balance(state, b), 0'u64)

beacon_chain/spec/datatypes.nim

@@ -464,7 +464,7 @@ type
     crosslink_data_root*: Eth2Digest ##\
     ## Shard data since the previous crosslink
 
-  # https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#pendingattestation
+  # https://github.com/ethereum/eth2.0-specs/blob/0.4.0/specs/core/0_beacon-chain.md#pendingattestation
   PendingAttestation* = object
     aggregation_bitfield*: seq[byte]          # Attester participation bitfield
     data*: AttestationData                    # Attestation data

beacon_chain/spec/helpers.nim

@@ -155,7 +155,7 @@ func is_active_validator*(validator: Validator, epoch: Epoch): bool =
   ### Checks if validator is active
   validator.activation_epoch <= epoch and epoch < validator.exit_epoch
 
-# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_active_validator_indices
+# https://github.com/ethereum/eth2.0-specs/blob/0.4.0/specs/core/0_beacon-chain.md#get_active_validator_indices
 func get_active_validator_indices*(validators: openArray[Validator], epoch: Epoch): seq[ValidatorIndex] =
   ## Gets indices of active validators from validators
   for idx, val in validators:

beacon_chain/spec/validator.nim

@@ -119,15 +119,10 @@ func get_next_epoch_committee_count(state: BeaconState): uint64 =
   )
   get_epoch_committee_count(len(next_active_validators))
 
-# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_previous_epoch
-func get_previous_epoch(state: BeaconState): Epoch =
+# https://github.com/ethereum/eth2.0-specs/blob/0.4.0/specs/core/0_beacon-chain.md#get_previous_epoch
+func get_previous_epoch*(state: BeaconState): Epoch =
   ## Return the previous epoch of the given ``state``.
-  ## If the current epoch is  ``GENESIS_EPOCH``, return ``GENESIS_EPOCH``.
-  let current_epoch = get_current_epoch(state)
-  if current_epoch == GENESIS_EPOCH:
-    GENESIS_EPOCH
-  else:
-    current_epoch - 1
+  max(get_current_epoch(state) - 1, GENESIS_EPOCH)
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_crosslink_committees_at_slot
 func get_crosslink_committees_at_slot*(state: BeaconState, slot: Slot,

beacon_chain/state_transition.nim

@@ -546,21 +546,17 @@ func process_exit_queue(state: var BeaconState) =
         break
       prepare_validator_for_withdrawal(state, index)
 
-# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#per-epoch-processing
 func processEpoch(state: var BeaconState) =
   if (state.slot + 1) mod SLOTS_PER_EPOCH != 0:
     return
 
-  # https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#helper-variables
+  # https://github.com/ethereum/eth2.0-specs/blob/0.4.0/specs/core/0_beacon-chain.md#helper-variables
   let
     current_epoch = get_current_epoch(state)
-    previous_epoch =
-      if current_epoch > GENESIS_EPOCH:
-        current_epoch - 1
-      else:
-        current_epoch
+    previous_epoch = get_previous_epoch(state)
     next_epoch = (current_epoch + 1).Epoch
 
+    # Spec grabs this later, but it's part of current_total_balance
     active_validator_indices =
       get_active_validator_indices(state.validator_registry, current_epoch)
 
@@ -678,6 +674,9 @@ func processEpoch(state: var BeaconState) =
     get_total_balance(
       statePtr[], attesting_validator_indices(crosslink_committee))
 
+  ## Regarding inclusion_slot and inclusion_distance, as defined they result in
+  ## O(n^2) behavior, so implement slightly differently.
+
   # https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#eth1-data-1
   block:
     if next_epoch mod EPOCHS_PER_ETH1_VOTING_PERIOD == 0:
@@ -872,7 +871,7 @@ func processEpoch(state: var BeaconState) =
       state.validator_balances[proposer_index] +=
         base_reward(state, v) div ATTESTATION_INCLUSION_REWARD_QUOTIENT
 
-  # https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#crosslinks-1
+  # https://github.com/ethereum/eth2.0-specs/blob/0.4.0/specs/core/0_beacon-chain.md#crosslinks-1
   block:
     for slot in get_epoch_start_slot(previous_epoch) ..< get_epoch_start_slot(current_epoch):
       let crosslink_committees_at_slot = get_crosslink_committees_at_slot(state, slot)