feat: add bitlists and bitvectors natively in SSZ nif library (#785)

Co-authored-by: Tomás Grüner <[email protected]>

Author: Arkenan

lib/lambda_ethereum_consensus/p2p/gossip/handler.ex

@@ -7,7 +7,7 @@ defmodule LambdaEthereumConsensus.P2P.Gossip.Handler do
 
   alias LambdaEthereumConsensus.Beacon.BeaconChain
   alias LambdaEthereumConsensus.Beacon.PendingBlocks
-  alias LambdaEthereumConsensus.Utils.BitVector
+  alias LambdaEthereumConsensus.Utils.BitField
   alias Types.{AggregateAndProof, SignedAggregateAndProof, SignedBeaconBlock}
 
   def handle_beacon_block(%SignedBeaconBlock{message: block} = signed_block) do
@@ -25,11 +25,11 @@ defmodule LambdaEthereumConsensus.P2P.Gossip.Handler do
   def handle_beacon_aggregate_and_proof(%SignedAggregateAndProof{
         message: %AggregateAndProof{aggregate: aggregate}
       }) do
-    votes = BitVector.count(aggregate.aggregation_bits)
+    votes = BitField.count(aggregate.aggregation_bits)
     slot = aggregate.data.slot
     root = aggregate.data.beacon_block_root |> Base.encode16()
 
-    # We are getting ~500 attestations in half a second. This is overwheling the store GenServer at the moment.
+    # We are getting ~500 attestations in half a second. This is overwhelming the store GenServer at the moment.
     # Store.on_attestation(aggregate)
 
     Logger.debug(

lib/lambda_ethereum_consensus/state_transition/accessors.ex

@@ -6,6 +6,7 @@ defmodule LambdaEthereumConsensus.StateTransition.Accessors do
   alias LambdaEthereumConsensus.SszEx
   alias LambdaEthereumConsensus.StateTransition.{Cache, Math, Misc, Predicates}
   alias LambdaEthereumConsensus.Utils
+  alias LambdaEthereumConsensus.Utils.BitList
   alias LambdaEthereumConsensus.Utils.Randao
   alias Types.{Attestation, BeaconState, IndexedAttestation, SyncCommittee, Validator}
 
@@ -510,13 +511,7 @@ defmodule LambdaEthereumConsensus.StateTransition.Accessors do
     |> Enum.sort()
   end
 
-  defp participated?(bits, index) do
-    # The bit order inside the byte is reversed (e.g. bits[0] is the 8th bit).
-    # Here we keep the byte index the same, but reverse the bit index.
-    bit_index = index + 7 - 2 * rem(index, 8)
-    <<_::size(bit_index), flag::1, _::bits>> = bits
-    flag == 1
-  end
+  defp participated?(bits, index), do: BitList.set?(bits, index)
 
   @doc """
   Return the combined effective balance of the ``indices``.

lib/lambda_ethereum_consensus/state_transition/epoch_processing.ex

@@ -358,16 +358,10 @@ defmodule LambdaEthereumConsensus.StateTransition.EpochProcessing do
   end
 
   defp update_first_bit(state) do
-    bits =
-      state.justification_bits
-      |> BitVector.new(4)
-      |> BitVector.shift_higher(1)
-      |> BitVector.to_bytes()
-
     %BeaconState{
       state
       | previous_justified_checkpoint: state.current_justified_checkpoint,
-        justification_bits: bits
+        justification_bits: BitVector.shift_higher(state.justification_bits, 1)
     }
   end
 
@@ -377,13 +371,11 @@ defmodule LambdaEthereumConsensus.StateTransition.EpochProcessing do
     with {:ok, block_root} <- Accessors.get_block_root(state, epoch) do
       new_checkpoint = %Types.Checkpoint{epoch: epoch, root: block_root}
 
-      bits =
-        state.justification_bits
-        |> BitVector.new(4)
-        |> BitVector.set(index)
-        |> BitVector.to_bytes()
-
-      %{state | current_justified_checkpoint: new_checkpoint, justification_bits: bits}
+      %{
+        state
+        | current_justified_checkpoint: new_checkpoint,
+          justification_bits: BitVector.set(state.justification_bits, index)
+      }
       |> then(&{:ok, &1})
     end
   end
@@ -395,10 +387,7 @@ defmodule LambdaEthereumConsensus.StateTransition.EpochProcessing do
          range,
          offset
        ) do
-    bits_set =
-      state.justification_bits
-      |> BitVector.new(4)
-      |> BitVector.all?(range)
+    bits_set = BitVector.all?(state.justification_bits, range)
 
     if bits_set and old_justified_checkpoint.epoch + offset == current_epoch do
       %BeaconState{state | finalized_checkpoint: old_justified_checkpoint}

lib/lambda_ethereum_consensus/state_transition/operations.ex

@@ -117,13 +117,10 @@ defmodule LambdaEthereumConsensus.StateTransition.Operations do
     # Verify sync committee aggregate signature signing over the previous slot block root
     committee_pubkeys = state.current_sync_committee.pubkeys
 
-    sync_committee_bits =
-      BitVector.new(aggregate.sync_committee_bits, ChainSpec.get("SYNC_COMMITTEE_SIZE"))
-
     participant_pubkeys =
       committee_pubkeys
       |> Enum.with_index()
-      |> Enum.filter(fn {_, index} -> BitVector.set?(sync_committee_bits, index) end)
+      |> Enum.filter(fn {_, index} -> BitVector.set?(aggregate.sync_committee_bits, index) end)
       |> Enum.map(fn {public_key, _} -> public_key end)
 
     previous_slot = max(state.slot, 1) - 1
@@ -138,15 +135,15 @@ defmodule LambdaEthereumConsensus.StateTransition.Operations do
       # Compute participant and proposer rewards
       {participant_reward, proposer_reward} = compute_sync_aggregate_rewards(state)
 
-      total_proposer_reward = BitVector.count(sync_committee_bits) * proposer_reward
+      total_proposer_reward = BitVector.count(aggregate.sync_committee_bits) * proposer_reward
 
       # PERF: make Map with committee_index by pubkey, then
       # Enum.map validators -> new balance all in place, without map_reduce
       state.validators
       |> get_sync_committee_indices(committee_pubkeys)
       |> Stream.with_index()
       |> Stream.map(fn {validator_index, committee_index} ->
-        if BitVector.set?(sync_committee_bits, committee_index),
+        if BitVector.set?(aggregate.sync_committee_bits, committee_index),
           do: {validator_index, participant_reward},
           else: {validator_index, -participant_reward}
       end)
@@ -845,7 +842,7 @@ defmodule LambdaEthereumConsensus.StateTransition.Operations do
   end
 
   defp check_matching_aggregation_bits_length(attestation, beacon_committee) do
-    if BitList.length_of_bitlist(attestation.aggregation_bits) == length(beacon_committee) do
+    if BitList.length(attestation.aggregation_bits) == length(beacon_committee) do
       :ok
     else
       {:error, "Mismatched aggregation bits length"}

lib/ssz_ex.ex

@@ -300,8 +300,7 @@ defmodule LambdaEthereumConsensus.SszEx do
   end
 
   def pack_bits(value, :bitlist) do
-    len = value |> bit_size()
-    {value, len} |> BitList.to_packed_bytes() |> pack_bytes()
+    value |> BitList.to_packed_bytes() |> pack_bytes()
   end
 
   def chunk_count({:list, type, max_size}) do
@@ -354,7 +353,7 @@ defmodule LambdaEthereumConsensus.SszEx do
     if len > max_size do
       {:error, "excess bits"}
     else
-      {:ok, BitList.to_bytes({bit_list, len})}
+      {:ok, BitList.to_bytes(bit_list)}
     end
   end
 
@@ -407,11 +406,12 @@ defmodule LambdaEthereumConsensus.SszEx do
 
   defp decode_bitlist(bit_list, max_size) when bit_size(bit_list) > 0 do
     num_bytes = byte_size(bit_list)
-    {decoded, len} = BitList.new(bit_list)
+    decoded = BitList.new(bit_list)
+    len = BitList.length(decoded)
 
     cond do
-      len < 0 ->
-        {:error, "missing length information"}
+      match?(<<_::binary-size(num_bytes - 1), 0>>, bit_list) ->
+        {:error, "BitList has no length information."}
 
       div(len, @bits_per_byte) + 1 != num_bytes ->
         {:error, "invalid byte count"}
@@ -652,7 +652,7 @@ defmodule LambdaEthereumConsensus.SszEx do
 
   defp check_first_offset([{offset, _} | _rest], items_index, _binary_size) do
     cond do
-      offset < items_index -> {:error, "OffsetIntoFixedPortion"}
+      offset < items_index -> {:error, "OffsetIntoFixedPortion (#{offset})"}
       offset > items_index -> {:error, "OffsetSkipsVariableBytes"}
       true -> :ok
     end
@@ -738,7 +738,7 @@ defmodule LambdaEthereumConsensus.SszEx do
   defp sanitize_offset(offset, previous_offset, _num_bytes, num_fixed_bytes) do
     cond do
       offset < num_fixed_bytes ->
-        {:error, "OffsetIntoFixedPortion"}
+        {:error, "OffsetIntoFixedPortion #{offset}"}
 
       previous_offset == nil && offset != num_fixed_bytes ->
         {:error, "OffsetSkipsVariableBytes"}

lib/types/beacon_chain/attestation.ex

@@ -3,6 +3,8 @@ defmodule Types.Attestation do
   Struct definition for `AttestationMainnet`.
   Related definitions in `native/ssz_nif/src/types/`.
   """
+  alias LambdaEthereumConsensus.Utils.BitList
+
   @behaviour LambdaEthereumConsensus.Container
 
   fields = [
@@ -29,4 +31,12 @@ defmodule Types.Attestation do
       {:signature, TypeAliases.bls_signature()}
     ]
   end
+
+  def encode(%__MODULE__{} = map) do
+    Map.update!(map, :aggregation_bits, &BitList.to_bytes/1)
+  end
+
+  def decode(%__MODULE__{} = map) do
+    Map.update!(map, :aggregation_bits, &BitList.new/1)
+  end
 end

lib/types/beacon_chain/beacon_state.ex

@@ -3,9 +3,10 @@ defmodule Types.BeaconState do
   Struct definition for `BeaconState`.
   Related definitions in `native/ssz_nif/src/types/`.
   """
-  @behaviour LambdaEthereumConsensus.Container
   alias LambdaEthereumConsensus.Utils.BitVector
 
+  @behaviour LambdaEthereumConsensus.Container
+
   fields = [
     :genesis_time,
     :genesis_validators_root,
@@ -114,6 +115,7 @@ defmodule Types.BeaconState do
     |> Map.update!(:previous_epoch_participation, &Aja.Vector.to_list/1)
     |> Map.update!(:current_epoch_participation, &Aja.Vector.to_list/1)
     |> Map.update!(:latest_execution_payload_header, &Types.ExecutionPayloadHeader.encode/1)
+    |> Map.update!(:justification_bits, &BitVector.to_bytes/1)
   end
 
   def decode(%__MODULE__{} = map) do
@@ -124,6 +126,9 @@ defmodule Types.BeaconState do
     |> Map.update!(:previous_epoch_participation, &Aja.Vector.new/1)
     |> Map.update!(:current_epoch_participation, &Aja.Vector.new/1)
     |> Map.update!(:latest_execution_payload_header, &Types.ExecutionPayloadHeader.decode/1)
+    |> Map.update!(:justification_bits, fn bits ->
+      BitVector.new(bits, Constants.justification_bits_length())
+    end)
   end
 
   @doc """
@@ -261,7 +266,7 @@ defmodule Types.BeaconState do
        {:list, TypeAliases.participation_flags(), ChainSpec.get("VALIDATOR_REGISTRY_LIMIT")}},
       {:current_epoch_participation,
        {:list, TypeAliases.participation_flags(), ChainSpec.get("VALIDATOR_REGISTRY_LIMIT")}},
-      {:justification_bits, {:bitvector, ChainSpec.get("JUSTIFICATION_BITS_LENGTH")}},
+      {:justification_bits, {:bitvector, Constants.justification_bits_length()}},
       {:previous_justified_checkpoint, Types.Checkpoint},
       {:current_justified_checkpoint, Types.Checkpoint},
       {:finalized_checkpoint, Types.Checkpoint},

lib/types/beacon_chain/pending_attestation.ex

@@ -3,6 +3,8 @@ defmodule Types.PendingAttestation do
   Struct definition for `PendingAttestation`.
   Related definitions in `native/ssz_nif/src/types/`.
   """
+  alias LambdaEthereumConsensus.Utils.BitList
+
   @behaviour LambdaEthereumConsensus.Container
 
   fields = [
@@ -32,4 +34,12 @@ defmodule Types.PendingAttestation do
       {:proposer_index, TypeAliases.validator_index()}
     ]
   end
+
+  def encode(%__MODULE__{} = map) do
+    Map.update!(map, :aggregation_bits, &BitList.to_bytes/1)
+  end
+
+  def decode(%__MODULE__{} = map) do
+    Map.update!(map, :aggregation_bits, &BitList.new/1)
+  end
 end

lib/types/beacon_chain/sync_aggregate.ex

@@ -3,6 +3,8 @@ defmodule Types.SyncAggregate do
   Struct definition for `SyncAggregate`.
   Related definitions in `native/ssz_nif/src/types/`.
   """
+  alias LambdaEthereumConsensus.Utils.BitVector
+
   @behaviour LambdaEthereumConsensus.Container
 
   fields = [
@@ -15,7 +17,7 @@ defmodule Types.SyncAggregate do
 
   @type t :: %__MODULE__{
           # max size SYNC_COMMITTEE_SIZE
-          sync_committee_bits: Types.bitvector(),
+          sync_committee_bits: BitVector.t(),
           sync_committee_signature: Types.bls_signature()
         }
 
@@ -26,4 +28,14 @@ defmodule Types.SyncAggregate do
       {:sync_committee_signature, TypeAliases.bls_signature()}
     ]
   end
+
+  def encode(%__MODULE__{} = map) do
+    Map.update!(map, :sync_committee_bits, &BitVector.to_bytes/1)
+  end
+
+  def decode(%__MODULE__{} = map) do
+    Map.update!(map, :sync_committee_bits, fn bits ->
+      BitVector.new(bits, ChainSpec.get("SYNC_COMMITTEE_SIZE"))
+    end)
+  end
 end