state_processing: get_attesting_indices in common

eth2/state_processing/src/common/get_attesting_indices.rs

@@ -0,0 +1,46 @@
+use crate::common::verify_bitfield_length;
+use types::*;
+
+/// Returns validator indices which participated in the attestation, sorted by increasing index.
+///
+/// Spec v0.6.1
+pub fn get_attesting_indices<T: EthSpec>(
+    state: &BeaconState<T>,
+    attestation_data: &AttestationData,
+    bitfield: &Bitfield,
+) -> Result<Vec<usize>, BeaconStateError> {
+    get_attesting_indices_unsorted(state, attestation_data, bitfield).map(|mut indices| {
+        // Fast unstable sort is safe because validator indices are unique
+        indices.sort_unstable();
+        indices
+    })
+}
+
+/// Returns validator indices which participated in the attestation, unsorted.
+///
+/// Spec v0.6.1
+pub fn get_attesting_indices_unsorted<T: EthSpec>(
+    state: &BeaconState<T>,
+    attestation_data: &AttestationData,
+    bitfield: &Bitfield,
+) -> Result<Vec<usize>, BeaconStateError> {
+    let target_relative_epoch =
+        RelativeEpoch::from_epoch(state.current_epoch(), attestation_data.target_epoch)?;
+
+    let committee =
+        state.get_crosslink_committee_for_shard(attestation_data.shard, target_relative_epoch)?;
+
+    if !verify_bitfield_length(&bitfield, committee.committee.len()) {
+        return Err(BeaconStateError::InvalidBitfield);
+    }
+
+    Ok(committee
+        .committee
+        .iter()
+        .enumerate()
+        .filter_map(|(i, validator_index)| match bitfield.get(i) {
+            Ok(true) => Some(*validator_index),
+            _ => None,
+        })
+        .collect())
+}

eth2/state_processing/src/common/mod.rs

@@ -1,7 +1,9 @@
 mod exit;
+mod get_attesting_indices;
 mod slash_validator;
 mod verify_bitfield;
 
 pub use exit::initiate_validator_exit;
+pub use get_attesting_indices::{get_attesting_indices, get_attesting_indices_unsorted};
 pub use slash_validator::slash_validator;
 pub use verify_bitfield::verify_bitfield_length;