Add get_shuffling to state

eth2/types/Cargo.toml

@@ -9,9 +9,11 @@ bls = { path = "../utils/bls" }
 boolean-bitfield = { path = "../utils/boolean-bitfield" }
 ethereum-types = "0.4.0"
 hashing = { path = "../utils/hashing" }
+honey-badger-split =  { path = "../utils/honey-badger-split" }
 integer-sqrt = "0.1"
 rand = "0.5.5"
 serde = "1.0"
 serde_derive = "1.0"
 serde_json = "1.0"
 ssz = { path = "../utils/ssz" }
+vec_shuffle = { path = "../utils/vec_shuffle" }

eth2/types/src/beacon_state/epoch_processing.rs

@@ -717,22 +717,6 @@ impl BeaconState {
         self.get_committee_count_per_slot(current_active_validators.len(), spec)
     }
 
-    fn get_committee_count_per_slot(
-        &self,
-        active_validator_count: usize,
-        spec: &ChainSpec,
-    ) -> usize {
-        std::cmp::max(
-            1,
-            std::cmp::min(
-                spec.shard_count as usize / spec.epoch_length as usize,
-                active_validator_count
-                    / spec.epoch_length as usize
-                    / spec.target_committee_size as usize,
-            ),
-        )
-    }
-
     fn process_ejections(&self) {
         //TODO: stubbed out.
     }
@@ -784,10 +768,6 @@ impl BeaconState {
         self.get_effective_balance(validator_index, spec) / base_reward_quotient / 5
     }
 
-    pub fn get_crosslink_committees_at_slot(&self, _slot: u64) -> Option<CrosslinkCommittees> {
-        Some(vec![(vec![0], 0)])
-    }
-
     pub fn get_effective_balance(&self, validator_index: usize, spec: &ChainSpec) -> u64 {
         std::cmp::min(self.validator_balances[validator_index], spec.max_deposit)
     }
@@ -810,6 +790,3 @@ impl BeaconState {
         vec![0, 1]
     }
 }
-
-type CrosslinkCommittee = (Vec<usize>, usize);
-type CrosslinkCommittees = Vec<CrosslinkCommittee>;

eth2/types/src/beacon_state/mod.rs

@@ -12,6 +12,7 @@ use ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 
 mod attestation_validation;
 mod epoch_processing;
+mod shuffling;
 mod slot_processing;
 mod winning_root;
 

eth2/types/src/beacon_state/shuffling.rs

@@ -0,0 +1,47 @@
+use crate::{validator_registry::get_active_validator_indices, BeaconState, ChainSpec, Hash256};
+use honey_badger_split::SplitExt;
+use vec_shuffle::shuffle;
+
+type CrosslinkCommittee = (Vec<usize>, usize);
+type CrosslinkCommittees = Vec<CrosslinkCommittee>;
+
+impl BeaconState {
+    pub fn get_shuffling(&self, seed: Hash256, slot: u64, spec: &ChainSpec) -> Vec<Vec<usize>> {
+        let slot = slot - (slot % spec.epoch_length);
+
+        let active_validator_indices = get_active_validator_indices(&self.validator_registry, slot);
+
+        let committees_per_slot =
+            self.get_committee_count_per_slot(active_validator_indices.len(), spec);
+
+        // TODO: check that Hash256 matches 'int_to_bytes32'.
+        let seed = seed ^ Hash256::from(slot);
+        let shuffled_active_validator_indices =
+            shuffle(&seed, active_validator_indices).expect("Max validator count exceed!");
+
+        shuffled_active_validator_indices
+            .honey_badger_split(committees_per_slot * spec.epoch_length as usize)
+            .filter_map(|slice: &[usize]| Some(slice.to_vec()))
+            .collect()
+    }
+
+    pub fn get_committee_count_per_slot(
+        &self,
+        active_validator_count: usize,
+        spec: &ChainSpec,
+    ) -> usize {
+        std::cmp::max(
+            1,
+            std::cmp::min(
+                spec.shard_count as usize / spec.epoch_length as usize,
+                active_validator_count
+                    / spec.epoch_length as usize
+                    / spec.target_committee_size as usize,
+            ),
+        )
+    }
+
+    pub fn get_crosslink_committees_at_slot(&self, _slot: u64) -> Option<CrosslinkCommittees> {
+        Some(vec![(vec![0], 0)])
+    }
+}