feat: add beacon committee indices getter method

consensus/types/src/beacon_state.rs

@@ -809,6 +809,60 @@ impl<E: EthSpec> BeaconState<E> {
         cache.get_all_beacon_committees()
     }
 
+    /// Returns the inclusion list committee for the given `slot` in the current or next epoch.
+    ///
+    /// Spec v0.12.1
+    pub fn get_inclusion_list_commitee(
+        &self,
+        slot: Slot,
+        spec: &ChainSpec,
+    ) -> Result<Vec<usize>, Error> {
+        let epoch = slot.epoch(E::slots_per_epoch());
+        let current_epoch = self.current_epoch();
+        let next_epoch = current_epoch + 1;
+        if epoch != current_epoch || epoch != next_epoch {
+            return Err(Error::SlotOutOfBounds);
+        }
+
+        let seed = self.get_inclusion_list_seed(slot, spec)?;
+        let indices = self.get_active_validator_indices(epoch, spec)?;
+
+        let start =
+            (slot % E::slots_per_epoch()).as_usize() * E::InclusionListCommitteeSize::to_usize();
+        let end = start + E::InclusionListCommitteeSize::to_usize();
+
+        let mut i = start;
+        let mut il_committee_indices =
+            Vec::with_capacity(E::InclusionListCommitteeSize::to_usize());
+        while i < end {
+            let shuffled_index = compute_shuffled_index(
+                i.safe_rem(indices.len())?,
+                indices.len(),
+                &seed,
+                spec.shuffle_round_count,
+            )
+            .ok_or(Error::UnableToShuffle)?;
+            il_committee_indices.push(shuffled_index);
+            i.safe_add_assign(1)?;
+        }
+
+        Ok(il_committee_indices)
+    }
+
+    /// Compute the seed to use for the beacon inclusion list committee selection at the given
+    /// `slot`.
+    ///
+    /// Spec v0.12.1
+    pub fn get_inclusion_list_seed(&self, slot: Slot, spec: &ChainSpec) -> Result<Vec<u8>, Error> {
+        let epoch = slot.epoch(E::slots_per_epoch());
+        let mut preimage = self
+            .get_seed(epoch, Domain::InclusionListCommittee, spec)?
+            .as_slice()
+            .to_vec();
+        preimage.append(&mut int_to_bytes8(slot.as_u64()));
+        Ok(hash(&preimage))
+    }
+
     /// Returns the block root which decided the proposer shuffling for the epoch passed in parameter. This root
     /// can be used to key this proposer shuffling.
     ///

consensus/types/src/chain_spec.rs

@@ -192,6 +192,7 @@ pub struct ChainSpec {
      * FOCIL params
      */
     pub domain_inclusion_list_committee: u32,
+    pub inclusion_list_committee_size: u64,
 
     /*
      * DAS params
@@ -808,6 +809,7 @@ impl ChainSpec {
              * FOCIL params
              */
             domain_inclusion_list_committee: 13,
+            inclusion_list_committee_size: 16,
 
             /*
              * DAS params
@@ -1131,6 +1133,7 @@ impl ChainSpec {
              * FOCIL params
              */
             domain_inclusion_list_committee: 13,
+            inclusion_list_committee_size: 16,
 
             /*
              * DAS params

consensus/types/src/eth_spec.rs

@@ -163,6 +163,7 @@ pub trait EthSpec:
     /*
      * FOCIL
      */
+    type InclusionListCommitteeSize: Unsigned + Clone + Sync + Send + Debug + PartialEq;
     type MaxTransactionsPerInclusionList: Unsigned + Clone + Sync + Send + Debug + PartialEq;
 
     fn default_spec() -> ChainSpec;
@@ -380,6 +381,11 @@ pub trait EthSpec:
         Self::KzgCommitmentsInclusionProofDepth::to_usize()
     }
 
+    /// Returns the `IL_COMMITTEE_SIZE` constant for this specification.
+    fn inclusion_list_committee_size() -> usize {
+        Self::InclusionListCommitteeSize::to_usize()
+    }
+
     /// Returns the `MAX_TRANSACTIONS_PER_INCLUSION_LIST` constant for this specification.
     fn max_transactions_per_inclusion_list() -> usize {
         Self::MaxTransactionsPerInclusionList::to_usize()
@@ -448,6 +454,7 @@ impl EthSpec for MainnetEthSpec {
     type MaxAttesterSlashingsElectra = U1;
     type MaxAttestationsElectra = U8;
     type MaxWithdrawalRequestsPerPayload = U16;
+    type InclusionListCommitteeSize = U16;
     type MaxTransactionsPerInclusionList = U16;
 
     fn default_spec() -> ChainSpec {
@@ -515,6 +522,7 @@ impl EthSpec for MinimalEthSpec {
         MaxConsolidationRequestsPerPayload,
         MaxAttesterSlashingsElectra,
         MaxAttestationsElectra,
+        InclusionListCommitteeSize,
         MaxTransactionsPerInclusionList
     });
 
@@ -581,6 +589,7 @@ impl EthSpec for GnosisEthSpec {
     type FieldElementsPerExtBlob = U8192;
     type BytesPerCell = U2048;
     type KzgCommitmentsInclusionProofDepth = U4;
+    type InclusionListCommitteeSize = U16;
     type MaxTransactionsPerInclusionList = U16;
 
     fn default_spec() -> ChainSpec {