Implement the majority of per-epoch processing

beacon_node/beacon_chain/src/epoch_processing.rs

@@ -0,0 +1,9 @@
+use super::{BeaconChain, ClientDB, DBError, SlotClock};
+
+impl<T, U> BeaconChain<T, U>
+where
+    T: ClientDB,
+    U: SlotClock,
+{
+    pub fn per_epoch_processing(&self) {}
+}

beacon_node/beacon_chain/src/lib.rs

@@ -4,6 +4,7 @@ pub mod block_processing;
 pub mod block_production;
 mod canonical_head;
 pub mod dump;
+pub mod epoch_processing;
 mod finalized_head;
 mod info;
 mod lmd_ghost;

beacon_node/beacon_chain/src/state_transition.rs

@@ -239,12 +239,13 @@ where
             }
             ensure!(
                 attestation.data.justified_block_root
-                    == *get_block_root(
-                        &state,
-                        attestation.data.justified_slot,
-                        self.spec.latest_block_roots_length
-                    )
-                    .ok_or(Error::NoBlockRoot)?,
+                    == *state
+                        .get_block_root(
+                            &state,
+                            attestation.data.justified_slot,
+                            self.spec.latest_block_roots_length
+                        )
+                        .ok_or(Error::NoBlockRoot)?,
                 Error::BadAttestation
             );
             ensure!(
@@ -376,24 +377,10 @@ fn get_attestation_participants(
     _attestation_data: &AttestationData,
     _aggregation_bitfield: &BooleanBitfield,
 ) -> Vec<usize> {
+    // TODO: stubbed out.
     vec![0, 1]
 }
 
-fn get_block_root(
-    state: &BeaconState,
-    slot: u64,
-    latest_block_roots_length: u64,
-) -> Option<&Hash256> {
-    // TODO: test
-    if state.slot <= slot + latest_block_roots_length && slot <= state.slot {
-        state
-            .latest_block_roots
-            .get((slot % latest_block_roots_length) as usize)
-    } else {
-        None
-    }
-}
-
 fn penalize_validator(_state: &BeaconState, _proposer_index: usize) {
     // TODO: stubbed out.
 }

eth2/types/Cargo.toml

@@ -9,6 +9,7 @@ bls = { path = "../utils/bls" }
 boolean-bitfield = { path = "../utils/boolean-bitfield" }
 ethereum-types = "0.4.0"
 hashing = { path = "../utils/hashing" }
+integer-sqrt = "0.1"
 rand = "0.5.5"
 serde = "1.0"
 serde_derive = "1.0"

eth2/types/src/beacon_state/epoch_processing.rs

@@ -0,0 +1,837 @@
+use super::winning_root::WinningRoot;
+use crate::{
+    validator::StatusFlags, validator_registry::get_active_validator_indices, Attestation,
+    AttestationData, BeaconState, Bitfield, ChainSpec, Crosslink, Hash256, PendingAttestation,
+};
+use integer_sqrt::IntegerSquareRoot;
+use std::collections::{HashMap, HashSet};
+use std::iter::FromIterator;
+
+pub enum Error {
+    UnableToDetermineProducer,
+    NoBlockRoots,
+    UnableToGetCrosslinkCommittees,
+    BaseRewardQuotientIsZero,
+}
+
+macro_rules! safe_add_assign {
+    ($a: expr, $b: expr) => {
+        $a = $a.saturating_add($b);
+    };
+}
+macro_rules! safe_sub_assign {
+    ($a: expr, $b: expr) => {
+        $a = $a.saturating_sub($b);
+    };
+}
+
+impl BeaconState {
+    pub fn per_epoch_processing(&mut self, spec: &ChainSpec) -> Result<(), Error> {
+        /*
+         * All Validators
+         */
+        let active_validator_indices =
+            get_active_validator_indices(&self.validator_registry, self.slot);
+        let total_balance: u64 = active_validator_indices
+            .iter()
+            .fold(0, |acc, i| self.get_effective_balance(*i, spec));
+
+        let current_epoch_attestations: Vec<&PendingAttestation> = self
+            .latest_attestations
+            .iter()
+            .filter(|a| (self.slot - spec.epoch_length <= a.data.slot) && (a.data.slot < self.slot))
+            .collect();
+
+        /*
+         * Validators attesting during the current epoch.
+         */
+        if self.latest_block_roots.is_empty() {
+            return Err(Error::NoBlockRoots);
+        }
+
+        let current_epoch_boundary_attestations: Vec<&PendingAttestation> =
+            current_epoch_attestations
+                .iter()
+                // `filter_map` is used to avoid a double borrow (`&&..`).
+                .filter_map(|a| {
+                    // TODO: ensure this saturating sub is correct.
+                    let block_root = match self
+                        .get_block_root(self.slot.saturating_sub(spec.epoch_length), spec)
+                    {
+                        Some(root) => root,
+                        // Protected by a check that latest_block_roots isn't empty.
+                        //
+                        // TODO: provide detailed reasoning.
+                        None => unreachable!(),
+                    };
+
+                    if (a.data.epoch_boundary_root == *block_root)
+                        && (a.data.justified_slot == self.justified_slot)
+                    {
+                        Some(*a)
+                    } else {
+                        None
+                    }
+                })
+                .collect();
+
+        let current_epoch_boundary_attester_indices: Vec<usize> =
+            current_epoch_boundary_attestations
+                .iter()
+                .fold(vec![], |mut acc, a| {
+                    acc.append(
+                        &mut self.get_attestation_participants(&a.data, &a.aggregation_bitfield),
+                    );
+                    acc
+                });
+
+        let current_epoch_boundary_attesting_balance = current_epoch_boundary_attester_indices
+            .iter()
+            .fold(0_u64, |acc, i| acc + self.get_effective_balance(*i, spec));
+
+        /*
+         * Validators attesting during the previous epoch
+         */
+
+        /*
+         * Validators that made an attestation during the previous epoch
+         */
+        let previous_epoch_attestations: Vec<&PendingAttestation> = self
+            .latest_attestations
+            .iter()
+            .filter(|a| {
+                //TODO: ensure these saturating subs are correct.
+                (self.slot.saturating_sub(2 * spec.epoch_length) <= a.data.slot)
+                    && (a.data.slot < self.slot.saturating_sub(spec.epoch_length))
+            })
+            .collect();
+
+        let previous_epoch_attester_indices: Vec<usize> =
+            previous_epoch_attestations
+                .iter()
+                .fold(vec![], |mut acc, a| {
+                    acc.append(
+                        &mut self.get_attestation_participants(&a.data, &a.aggregation_bitfield),
+                    );
+                    acc
+                });
+
+        /*
+         * Validators targetting the previous justified slot
+         */
+        let previous_epoch_justified_attestations: Vec<&PendingAttestation> = {
+            let mut a: Vec<&PendingAttestation> = current_epoch_attestations
+                .iter()
+                // `filter_map` is used to avoid a double borrow (`&&..`).
+                .filter_map(|a| {
+                    if a.data.justified_slot == self.previous_justified_slot {
+                        Some(*a)
+                    } else {
+                        None
+                    }
+                })
+                .collect();
+            let mut b: Vec<&PendingAttestation> = previous_epoch_attestations
+                .iter()
+                // `filter_map` is used to avoid a double borrow (`&&..`).
+                .filter_map(|a| {
+                    if a.data.justified_slot == self.previous_justified_slot {
+                        Some(*a)
+                    } else {
+                        None
+                    }
+                })
+                .collect();
+            a.append(&mut b);
+            a
+        };
+
+        let previous_epoch_justified_attester_indices: Vec<usize> =
+            previous_epoch_justified_attestations
+                .iter()
+                .fold(vec![], |mut acc, a| {
+                    acc.append(
+                        &mut self.get_attestation_participants(&a.data, &a.aggregation_bitfield),
+                    );
+                    acc
+                });
+
+        let previous_epoch_justified_attesting_balance = previous_epoch_justified_attester_indices
+            .iter()
+            .fold(0, |acc, i| acc + self.get_effective_balance(*i, spec));
+
+        /*
+         * Validators justifying the epoch boundary block at the start of the previous epoch
+         */
+        let previous_epoch_boundary_attestations: Vec<&PendingAttestation> =
+            previous_epoch_justified_attestations
+                .iter()
+                // `filter_map` is used to avoid a double borrow (`&&..`).
+                .filter_map(|a| {
+                    // TODO: ensure this saturating sub is correct.
+                    let block_root = match self
+                        .get_block_root(self.slot.saturating_sub(2 * spec.epoch_length), spec)
+                    {
+                        Some(root) => root,
+                        // Protected by a check that latest_block_roots isn't empty.
+                        //
+                        // TODO: provide detailed reasoning.
+                        None => unreachable!(),
+                    };
+
+                    if a.data.epoch_boundary_root == *block_root {
+                        Some(*a)
+                    } else {
+                        None
+                    }
+                })
+                .collect();
+
+        let previous_epoch_boundary_attester_indices: Vec<usize> =
+            previous_epoch_boundary_attestations
+                .iter()
+                .fold(vec![], |mut acc, a| {
+                    acc.append(
+                        &mut self.get_attestation_participants(&a.data, &a.aggregation_bitfield),
+                    );
+                    acc
+                });
+
+        let previous_epoch_boundary_attesting_balance: u64 =
+            previous_epoch_boundary_attester_indices
+                .iter()
+                .fold(0, |acc, i| acc + self.get_effective_balance(*i, spec));
+
+        /*
+         * Validators attesting to the expected beacon chain head during the previous epoch.
+         */
+        let previous_epoch_head_attestations: Vec<&PendingAttestation> =
+            previous_epoch_attestations
+                .iter()
+                .filter_map(|a| {
+                    let block_root = match self
+                        .get_block_root(self.slot.saturating_sub(2 * spec.epoch_length), spec)
+                    {
+                        Some(root) => root,
+                        // Protected by a check that latest_block_roots isn't empty.
+                        //
+                        // TODO: provide detailed reasoning.
+                        None => unreachable!(),
+                    };
+
+                    if a.data.beacon_block_root == *block_root {
+                        Some(*a)
+                    } else {
+                        None
+                    }
+                })
+                .collect();
+
+        let previous_epoch_head_attester_indices: Vec<usize> = previous_epoch_head_attestations
+            .iter()
+            .fold(vec![], |mut acc, a| {
+                acc.append(
+                    &mut self.get_attestation_participants(&a.data, &a.aggregation_bitfield),
+                );
+                acc
+            });
+
+        let previous_epoch_head_attesting_balance: u64 = previous_epoch_head_attester_indices
+            .iter()
+            .fold(0, |acc, i| acc + self.get_effective_balance(*i, spec));
+
+        let all_crosslink_committees: Vec<CrosslinkCommittees> = {
+            // TODO: check staturating sub is correct
+            let start_slot = self.slot.saturating_sub(2 * spec.epoch_length);
+
+            // Sub is safe due to previous line.
+            //
+            // TODO: provide detailed reasoning.
+            let mut committees = Vec::with_capacity((self.slot - start_slot) as usize);
+            for slot in start_slot..self.slot {
+                match self.get_crosslink_committees_at_slot(slot) {
+                    Some(c) => committees.push(c),
+                    None => return Err(Error::UnableToGetCrosslinkCommittees),
+                }
+            }
+            committees
+        };
+
+        // TODO: I didn't include the `winning_balance` stuff.. Not sure why it's there.
+
+        /*
+         * Eth1 Data
+         */
+        if self.slot % spec.eth1_data_voting_period == 0 {
+            for eth1_data_vote in &self.eth1_data_votes {
+                if eth1_data_vote.vote_count * 2 > spec.eth1_data_voting_period {
+                    self.latest_eth1_data = eth1_data_vote.eth1_data.clone();
+                }
+            }
+            self.eth1_data_votes = vec![];
+        }
+
+        /*
+         * Justification
+         */
+        self.previous_justified_slot = self.justified_slot;
+        self.justification_bitfield = (self.justification_bitfield * 2) % u64::pow(2, 64);
+
+        // If >= 2/3 of validators voted for the previous epoch boundary
+        if (3 * previous_epoch_boundary_attesting_balance) >= (2 * total_balance) {
+            // TODO: check saturating_sub is correct.
+            self.justification_bitfield |= 2;
+            self.justified_slot = self.slot.saturating_sub(2 * spec.epoch_length);
+        }
+
+        // If >= 2/3 of validators voted for the current epoch boundary
+        if (3 * current_epoch_boundary_attesting_balance) >= (2 * total_balance) {
+            // TODO: check saturating_sub is correct.
+            self.justification_bitfield |= 1;
+            self.justified_slot = self.slot.saturating_sub(1 * spec.epoch_length);
+        }
+
+        if (self.previous_justified_slot == self.slot.saturating_sub(2 * spec.epoch_length))
+            && (self.justification_bitfield % 4 == 3)
+        {
+            self.finalized_slot = self.previous_justified_slot;
+        }
+        if (self.previous_justified_slot == self.slot.saturating_sub(3 * spec.epoch_length))
+            && (self.justification_bitfield % 8 == 7)
+        {
+            self.finalized_slot = self.previous_justified_slot;
+        }
+        if (self.previous_justified_slot == self.slot.saturating_sub(4 * spec.epoch_length))
+            && (self.justification_bitfield % 16 == 14)
+        {
+            self.finalized_slot = self.previous_justified_slot;
+        }
+        if (self.previous_justified_slot == self.slot.saturating_sub(4 * spec.epoch_length))
+            && (self.justification_bitfield % 16 == 15)
+        {
+            self.finalized_slot = self.previous_justified_slot;
+        }
+
+        /*
+         * Crosslinks
+         */
+
+        // Cached for later lookups.
+        let mut winning_root_for_shards: HashMap<u64, WinningRoot> = HashMap::new();
+
+        for slot in self.slot.saturating_sub(2 * spec.epoch_length)..self.slot {
+            let crosslink_committees_at_slot = self
+                .get_crosslink_committees_at_slot(slot)
+                .ok_or_else(|| Error::UnableToGetCrosslinkCommittees)?;
+
+            for (crosslink_committee, shard) in crosslink_committees_at_slot {
+                let shard = shard as u64;
+
+                let winning_root = self.winning_root(
+                    shard,
+                    &current_epoch_attestations,
+                    &previous_epoch_attestations,
+                    spec,
+                );
+
+                if let Some(winning_root) = winning_root {
+                    let total_committee_balance: u64 = crosslink_committee
+                        .iter()
+                        .fold(0, |acc, i| self.get_effective_balance(*i, spec));
+
+                    winning_root_for_shards.insert(shard, winning_root.clone());
+
+                    if (3 * winning_root.total_attesting_balance) >= (2 * total_committee_balance) {
+                        self.latest_crosslinks[shard as usize] = Crosslink {
+                            slot: self.slot,
+                            shard_block_root: winning_root.shard_block_root,
+                        }
+                    }
+                }
+            }
+        }
+
+        /*
+         * Rewards and Penalities
+         */
+        let base_reward_quotient = total_balance.integer_sqrt();
+        if base_reward_quotient == 0 {
+            return Err(Error::BaseRewardQuotientIsZero);
+        }
+
+        /*
+        let base_reward = |i| match self.get_effective_balance(i, spec) {
+            Some(effective_balance) => effective_balance / base_reward_quotient / 5,
+            None => unreachable!(),
+        };
+        */
+
+        /*
+         * Justification and finalization
+         */
+        let epochs_since_finality = (self.slot - self.finalized_slot) / spec.epoch_length;
+
+        // TODO: fix this extra map
+        let previous_epoch_justified_attester_indices_hashset: HashSet<usize> =
+            HashSet::from_iter(previous_epoch_justified_attester_indices.iter().map(|i| *i));
+        let previous_epoch_boundary_attester_indices_hashset: HashSet<usize> =
+            HashSet::from_iter(previous_epoch_boundary_attester_indices.iter().map(|i| *i));
+        let previous_epoch_head_attester_indices_hashset: HashSet<usize> =
+            HashSet::from_iter(previous_epoch_head_attester_indices.iter().map(|i| *i));
+        let previous_epoch_attester_indices_hashset: HashSet<usize> =
+            HashSet::from_iter(previous_epoch_attester_indices.iter().map(|i| *i));
+
+        if epochs_since_finality <= 4 {
+            for index in 0..self.validator_balances.len() {
+                let base_reward = self.base_reward(index, base_reward_quotient, spec);
+
+                if previous_epoch_justified_attester_indices_hashset.contains(&index) {
+                    safe_add_assign!(
+                        self.validator_balances[index],
+                        base_reward * previous_epoch_justified_attesting_balance / total_balance
+                    );
+                } else {
+                    safe_sub_assign!(self.validator_balances[index], base_reward);
+                }
+
+                if previous_epoch_boundary_attester_indices_hashset.contains(&index) {
+                    safe_add_assign!(
+                        self.validator_balances[index],
+                        base_reward * previous_epoch_boundary_attesting_balance / total_balance
+                    );
+                } else {
+                    safe_sub_assign!(self.validator_balances[index], base_reward);
+                }
+
+                if previous_epoch_head_attester_indices_hashset.contains(&index) {
+                    safe_add_assign!(
+                        self.validator_balances[index],
+                        base_reward * previous_epoch_head_attesting_balance / total_balance
+                    );
+                } else {
+                    safe_sub_assign!(self.validator_balances[index], base_reward);
+                }
+            }
+
+            for index in previous_epoch_attester_indices {
+                let base_reward = self.base_reward(index, base_reward_quotient, spec);
+                let inclusion_distance = match self.inclusion_distance(index) {
+                    Some(distance) => distance,
+                    None => unreachable!(),
+                };
+
+                safe_add_assign!(
+                    self.validator_balances[index],
+                    base_reward * spec.min_attestation_inclusion_delay / inclusion_distance
+                )
+            }
+        } else {
+            for index in 0..self.validator_balances.len() {
+                let inactivity_penalty = self.inactivity_penalty(
+                    index,
+                    epochs_since_finality,
+                    base_reward_quotient,
+                    spec,
+                );
+
+                if !previous_epoch_justified_attester_indices_hashset.contains(&index) {
+                    safe_sub_assign!(self.validator_balances[index], inactivity_penalty);
+                }
+
+                if !previous_epoch_boundary_attester_indices_hashset.contains(&index) {
+                    safe_sub_assign!(self.validator_balances[index], inactivity_penalty);
+                }
+
+                if !previous_epoch_head_attester_indices_hashset.contains(&index) {
+                    safe_sub_assign!(self.validator_balances[index], inactivity_penalty);
+                }
+            }
+
+            for index in previous_epoch_attester_indices {
+                let base_reward = self.base_reward(index, base_reward_quotient, spec);
+                let inclusion_distance = match self.inclusion_distance(index) {
+                    Some(distance) => distance,
+                    None => unreachable!(),
+                };
+
+                safe_sub_assign!(
+                    self.validator_balances[index],
+                    base_reward
+                        - base_reward * spec.min_attestation_inclusion_delay / inclusion_distance
+                );
+            }
+        }
+
+        /*
+         * Attestation inclusion
+         */
+        for index in previous_epoch_attester_indices_hashset {
+            let inclusion_slot = match self.inclusion_slot(index) {
+                Some(slot) => slot,
+                None => unreachable!(),
+            };
+            let proposer_index = self
+                .get_beacon_proposer_index(inclusion_slot, spec)
+                .ok_or_else(|| Error::UnableToDetermineProducer)?;
+            let base_reward = self.base_reward(proposer_index, base_reward_quotient, spec);
+            safe_add_assign!(
+                self.validator_balances[proposer_index],
+                base_reward / spec.includer_reward_quotient
+            );
+        }
+
+        /*
+         * Crosslinks
+         */
+        for slot in self.slot.saturating_sub(2 * spec.epoch_length)..self.slot {
+            let crosslink_committees_at_slot = self
+                .get_crosslink_committees_at_slot(slot)
+                .ok_or_else(|| Error::UnableToGetCrosslinkCommittees)?;
+
+            for (_crosslink_committee, shard) in crosslink_committees_at_slot {
+                let shard = shard as u64;
+
+                let winning_root = winning_root_for_shards.get(&shard).expect("unreachable");
+
+                // TODO: remove the map.
+                let attesting_validator_indices: HashSet<usize> =
+                    HashSet::from_iter(winning_root.attesting_validator_indices.iter().map(|i| *i));
+
+                for index in 0..self.validator_balances.len() {
+                    let base_reward = self.base_reward(index, base_reward_quotient, spec);
+
+                    if attesting_validator_indices.contains(&index) {
+                        safe_add_assign!(
+                            self.validator_balances[index],
+                            base_reward * winning_root.total_attesting_balance
+                                / winning_root.total_balance
+                        );
+                    } else {
+                        safe_sub_assign!(self.validator_balances[index], base_reward);
+                    }
+                }
+
+                for index in &winning_root.attesting_validator_indices {
+                    let base_reward = self.base_reward(*index, base_reward_quotient, spec);
+                    safe_add_assign!(
+                        self.validator_balances[*index],
+                        base_reward * winning_root.total_attesting_balance
+                            / winning_root.total_balance
+                    );
+                }
+            }
+        }
+
+        /*
+         * Ejections
+         */
+        self.process_ejections();
+
+        /*
+         * Validator Registry
+         */
+        self.previous_epoch_calculation_slot = self.current_epoch_calculation_slot;
+        self.previous_epoch_start_shard = self.current_epoch_start_shard;
+        self.previous_epoch_randao_mix = self.current_epoch_randao_mix;
+
+        let should_update_validator_registy = if self.finalized_slot
+            > self.validator_registry_update_slot
+        {
+            (0..self.get_current_epoch_committee_count_per_slot(spec)).all(|i| {
+                let shard = (self.current_epoch_start_shard + i as u64) % spec.shard_count;
+                self.latest_crosslinks[shard as usize].slot > self.validator_registry_update_slot
+            })
+        } else {
+            false
+        };
+
+        if should_update_validator_registy {
+            self.update_validator_registry(total_balance, spec);
+
+            self.current_epoch_calculation_slot = self.slot;
+            self.current_epoch_start_shard = (self.current_epoch_start_shard
+                + self.get_current_epoch_committee_count_per_slot(spec) as u64 * spec.epoch_length)
+                % spec.shard_count;
+            self.current_epoch_randao_mix = self.get_randao_mix(
+                self.current_epoch_calculation_slot
+                    .saturating_sub(spec.seed_lookahead),
+                spec,
+            );
+        } else {
+            let epochs_since_last_registry_change =
+                (self.slot - self.validator_registry_update_slot) / spec.epoch_length;
+            if epochs_since_last_registry_change.is_power_of_two() {
+                self.current_epoch_calculation_slot = self.slot;
+                self.current_epoch_randao_mix = self.get_randao_mix(
+                    self.current_epoch_calculation_slot
+                        .saturating_sub(spec.seed_lookahead),
+                    spec,
+                );
+            }
+        }
+
+        self.process_penalties_and_exits(spec);
+
+        let e = self.slot / spec.epoch_length;
+        self.latest_penalized_balances[((e + 1) % spec.latest_penalized_exit_length) as usize] =
+            self.latest_penalized_balances[(e % spec.latest_penalized_exit_length) as usize];
+
+        self.latest_attestations = self
+            .latest_attestations
+            .iter()
+            .filter_map(|a| {
+                if a.data.slot < self.slot - spec.epoch_length {
+                    Some(a.clone())
+                } else {
+                    None
+                }
+            })
+            .collect();
+
+        Ok(())
+    }
+
+    fn process_penalties_and_exits(&mut self, spec: &ChainSpec) {
+        let active_validator_indices =
+            get_active_validator_indices(&self.validator_registry, self.slot);
+        let total_balance = active_validator_indices
+            .iter()
+            .fold(0, |acc, i| self.get_effective_balance(*i, spec));
+
+        for index in 0..self.validator_balances.len() {
+            let validator = &self.validator_registry[index];
+
+            if (self.slot / spec.epoch_length)
+                == (validator.penalized_slot / spec.epoch_length)
+                    + spec.latest_penalized_exit_length / 2
+            {
+                let e = (self.slot / spec.epoch_length) % spec.latest_penalized_exit_length;
+                let total_at_start = self.latest_penalized_balances
+                    [((e + 1) % spec.latest_penalized_exit_length) as usize];
+                let total_at_end = self.latest_penalized_balances[e as usize];
+                let total_penalities = total_at_end.saturating_sub(total_at_end);
+                let penalty = self.get_effective_balance(index, spec)
+                    * std::cmp::min(total_penalities * 3, total_balance)
+                    / total_balance;
+                safe_sub_assign!(self.validator_balances[index], penalty);
+            }
+        }
+
+        let eligible = |index: usize| {
+            let validator = &self.validator_registry[index];
+
+            if validator.penalized_slot <= self.slot {
+                let penalized_withdrawal_time =
+                    spec.latest_penalized_exit_length * spec.epoch_length / 2;
+                self.slot >= validator.penalized_slot + penalized_withdrawal_time
+            } else {
+                self.slot >= validator.exit_slot + spec.min_validator_withdrawal_time
+            }
+        };
+
+        let mut eligable_indices: Vec<usize> = (0..self.validator_registry.len())
+            .filter(|i| eligible(*i))
+            .collect();
+        eligable_indices.sort_by_key(|i| self.validator_registry[*i].exit_count);
+        let mut withdrawn_so_far = 0;
+        for index in eligable_indices {
+            self.prepare_validator_for_withdrawal(index);
+            withdrawn_so_far += 1;
+            if withdrawn_so_far >= spec.max_withdrawals_per_epoch {
+                break;
+            }
+        }
+    }
+
+    fn prepare_validator_for_withdrawal(&mut self, index: usize) {
+        //TODO: we're not ANDing here, we're setting. Potentially wrong.
+        self.validator_registry[index].status_flags = Some(StatusFlags::Withdrawable);
+    }
+
+    fn get_randao_mix(&mut self, slot: u64, spec: &ChainSpec) -> Hash256 {
+        assert!(self.slot < slot + spec.latest_randao_mixes_length);
+        assert!(slot <= self.slot);
+        self.latest_randao_mixes[(slot & spec.latest_randao_mixes_length) as usize]
+    }
+
+    fn update_validator_registry(&mut self, total_balance: u64, spec: &ChainSpec) {
+        let active_validator_indices =
+            get_active_validator_indices(&self.validator_registry, self.slot);
+        let total_balance = active_validator_indices
+            .iter()
+            .fold(0, |acc, i| self.get_effective_balance(*i, spec));
+
+        let max_balance_churn = std::cmp::max(
+            spec.max_deposit,
+            total_balance / (2 * spec.max_balance_churn_quotient),
+        );
+
+        let mut balance_churn = 0;
+        for index in 0..self.validator_registry.len() {
+            let validator = &self.validator_registry[index];
+
+            if (validator.activation_slot > self.slot + spec.entry_exit_delay)
+                && self.validator_balances[index] >= spec.max_deposit
+            {
+                balance_churn += self.get_effective_balance(index, spec);
+                if balance_churn > max_balance_churn {
+                    break;
+                }
+
+                self.activate_validator(index, false, spec);
+            }
+        }
+
+        let mut balance_churn = 0;
+        for index in 0..self.validator_registry.len() {
+            let validator = &self.validator_registry[index];
+
+            if (validator.exit_slot > self.slot + spec.entry_exit_delay)
+                && validator.status_flags == Some(StatusFlags::InitiatedExit)
+            {
+                balance_churn += self.get_effective_balance(index, spec);
+                if balance_churn > max_balance_churn {
+                    break;
+                }
+
+                self.exit_validator(index, spec);
+            }
+        }
+
+        self.validator_registry_update_slot = self.slot;
+    }
+
+    fn exit_validator(&mut self, validator_index: usize, spec: &ChainSpec) {
+        if self.validator_registry[validator_index].exit_slot
+            <= self.entry_exit_effect_slot(self.slot, spec)
+        {
+            return;
+        }
+
+        self.validator_registry[validator_index].exit_slot =
+            self.entry_exit_effect_slot(self.slot, spec);
+
+        self.validator_registry_exit_count += 1;
+        self.validator_registry[validator_index].exit_count = self.validator_registry_exit_count;
+    }
+
+    fn activate_validator(&mut self, validator_index: usize, is_genesis: bool, spec: &ChainSpec) {
+        self.validator_registry[validator_index].activation_slot = if is_genesis {
+            spec.genesis_slot
+        } else {
+            self.entry_exit_effect_slot(self.slot, spec)
+        }
+    }
+
+    fn entry_exit_effect_slot(&self, slot: u64, spec: &ChainSpec) -> u64 {
+        (slot - slot % spec.epoch_length) + spec.epoch_length + spec.entry_exit_delay
+    }
+
+    fn get_current_epoch_committee_count_per_slot(&self, spec: &ChainSpec) -> usize {
+        let current_active_validators = get_active_validator_indices(
+            &self.validator_registry,
+            self.current_epoch_calculation_slot,
+        );
+        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.
+    }
+
+    fn inactivity_penalty(
+        &self,
+        validator_index: usize,
+        epochs_since_finality: u64,
+        base_reward_quotient: u64,
+        spec: &ChainSpec,
+    ) -> u64 {
+        let effective_balance = self.get_effective_balance(validator_index, spec);
+        self.base_reward(validator_index, base_reward_quotient, spec)
+            + effective_balance * epochs_since_finality / spec.inactivity_penalty_quotient / 2
+    }
+
+    fn inclusion_distance(&self, validator_index: usize) -> Option<u64> {
+        let attestation = self.earliest_included_attestation(validator_index)?;
+        Some(
+            attestation
+                .slot_included
+                .saturating_sub(attestation.data.slot),
+        )
+    }
+
+    fn inclusion_slot(&self, validator_index: usize) -> Option<u64> {
+        let attestation = self.earliest_included_attestation(validator_index)?;
+        Some(attestation.slot_included)
+    }
+
+    fn earliest_included_attestation(&self, validator_index: usize) -> Option<&PendingAttestation> {
+        self.latest_attestations
+            .iter()
+            .filter(|a| {
+                self.get_attestation_participants(&a.data, &a.aggregation_bitfield)
+                    .iter()
+                    .find(|i| **i == validator_index)
+                    .is_some()
+            })
+            .min_by_key(|a| a.slot_included)
+    }
+
+    fn base_reward(
+        &self,
+        validator_index: usize,
+        base_reward_quotient: u64,
+        spec: &ChainSpec,
+    ) -> u64 {
+        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)
+    }
+
+    pub fn get_block_root(&self, slot: u64, spec: &ChainSpec) -> Option<&Hash256> {
+        if self.slot <= slot + spec.latest_block_roots_length && slot <= self.slot {
+            self.latest_block_roots
+                .get((slot % spec.latest_block_roots_length) as usize)
+        } else {
+            None
+        }
+    }
+
+    pub fn get_attestation_participants(
+        &self,
+        _attestation_data: &AttestationData,
+        _aggregation_bitfield: &Bitfield,
+    ) -> Vec<usize> {
+        // TODO: stubbed out.
+        vec![0, 1]
+    }
+}
+
+type CrosslinkCommittee = (Vec<usize>, usize);
+type CrosslinkCommittees = Vec<CrosslinkCommittee>;
+
+fn merkle_root(_input: &[Hash256]) -> Hash256 {
+    Hash256::zero()
+}

eth2/types/src/beacon_state/mod.rs

@@ -10,9 +10,12 @@ use rand::RngCore;
 use serde_derive::Serialize;
 use ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 
-mod slot_advance;
+mod epoch_processing;
+mod slot_processing;
+mod winning_root;
 
-pub use self::slot_advance::Error as SlotProcessingError;
+pub use self::epoch_processing::Error as EpochProcessingError;
+pub use self::slot_processing::Error as SlotProcessingError;
 
 // Custody will not be added to the specs until Phase 1 (Sharding Phase) so dummy class used.
 type CustodyChallenge = usize;
@@ -53,7 +56,7 @@ pub struct BeaconState {
     // Recent state
     pub latest_crosslinks: Vec<Crosslink>,
     pub latest_block_roots: Vec<Hash256>,
-    pub latest_penalized_exit_balances: Vec<u64>,
+    pub latest_penalized_balances: Vec<u64>,
     pub latest_attestations: Vec<PendingAttestation>,
     pub batched_block_roots: Vec<Hash256>,
 
@@ -93,7 +96,7 @@ impl Encodable for BeaconState {
         s.append(&self.finalized_slot);
         s.append(&self.latest_crosslinks);
         s.append(&self.latest_block_roots);
-        s.append(&self.latest_penalized_exit_balances);
+        s.append(&self.latest_penalized_balances);
         s.append(&self.latest_attestations);
         s.append(&self.batched_block_roots);
         s.append(&self.latest_eth1_data);
@@ -126,7 +129,7 @@ impl Decodable for BeaconState {
         let (finalized_slot, i) = <_>::ssz_decode(bytes, i)?;
         let (latest_crosslinks, i) = <_>::ssz_decode(bytes, i)?;
         let (latest_block_roots, i) = <_>::ssz_decode(bytes, i)?;
-        let (latest_penalized_exit_balances, i) = <_>::ssz_decode(bytes, i)?;
+        let (latest_penalized_balances, i) = <_>::ssz_decode(bytes, i)?;
         let (latest_attestations, i) = <_>::ssz_decode(bytes, i)?;
         let (batched_block_roots, i) = <_>::ssz_decode(bytes, i)?;
         let (latest_eth1_data, i) = <_>::ssz_decode(bytes, i)?;
@@ -157,7 +160,7 @@ impl Decodable for BeaconState {
                 finalized_slot,
                 latest_crosslinks,
                 latest_block_roots,
-                latest_penalized_exit_balances,
+                latest_penalized_balances,
                 latest_attestations,
                 batched_block_roots,
                 latest_eth1_data,
@@ -194,7 +197,7 @@ impl TreeHash for BeaconState {
         result.append(&mut self.finalized_slot.hash_tree_root());
         result.append(&mut self.latest_crosslinks.hash_tree_root());
         result.append(&mut self.latest_block_roots.hash_tree_root());
-        result.append(&mut self.latest_penalized_exit_balances.hash_tree_root());
+        result.append(&mut self.latest_penalized_balances.hash_tree_root());
         result.append(&mut self.latest_attestations.hash_tree_root());
         result.append(&mut self.batched_block_roots.hash_tree_root());
         result.append(&mut self.latest_eth1_data.hash_tree_root());
@@ -229,7 +232,7 @@ impl<T: RngCore> TestRandom<T> for BeaconState {
             finalized_slot: <_>::random_for_test(rng),
             latest_crosslinks: <_>::random_for_test(rng),
             latest_block_roots: <_>::random_for_test(rng),
-            latest_penalized_exit_balances: <_>::random_for_test(rng),
+            latest_penalized_balances: <_>::random_for_test(rng),
             latest_attestations: <_>::random_for_test(rng),
             batched_block_roots: <_>::random_for_test(rng),
             latest_eth1_data: <_>::random_for_test(rng),

eth2/types/src/beacon_state/winning_root.rs

@@ -0,0 +1,92 @@
+use crate::{BeaconState, ChainSpec, Hash256, PendingAttestation};
+use std::collections::HashMap;
+
+pub enum Error {
+    UnableToDetermineProducer,
+    NoBlockRoots,
+    UnableToGetCrosslinkCommittees,
+    BaseRewardQuotientIsZero,
+}
+
+#[derive(Clone)]
+pub struct WinningRoot {
+    pub shard_block_root: Hash256,
+    pub attesting_validator_indices: Vec<usize>,
+    pub total_balance: u64,
+    pub total_attesting_balance: u64,
+}
+
+impl BeaconState {
+    pub(crate) fn winning_root(
+        &self,
+        shard: u64,
+        current_epoch_attestations: &[&PendingAttestation],
+        previous_epoch_attestations: &[&PendingAttestation],
+        spec: &ChainSpec,
+    ) -> Option<WinningRoot> {
+        let mut attestations = current_epoch_attestations.to_vec();
+        attestations.append(&mut previous_epoch_attestations.to_vec());
+
+        let mut candidates: HashMap<Hash256, WinningRoot> = HashMap::new();
+
+        let mut highest_seen_balance = 0;
+
+        for a in &attestations {
+            if a.data.shard != shard {
+                continue;
+            }
+
+            let shard_block_root = &a.data.shard_block_root;
+
+            if candidates.contains_key(shard_block_root) {
+                continue;
+            }
+
+            let attesting_validator_indices = attestations.iter().fold(vec![], |mut acc, a| {
+                if (a.data.shard == shard) && (a.data.shard_block_root == *shard_block_root) {
+                    acc.append(
+                        &mut self.get_attestation_participants(&a.data, &a.aggregation_bitfield),
+                    );
+                }
+                acc
+            });
+
+            let total_balance: u64 = attesting_validator_indices
+                .iter()
+                .fold(0, |acc, i| acc + self.get_effective_balance(*i, spec));
+
+            let total_attesting_balance: u64 = attesting_validator_indices
+                .iter()
+                .fold(0, |acc, i| acc + self.get_effective_balance(*i, spec));
+
+            if total_attesting_balance > highest_seen_balance {
+                highest_seen_balance = total_attesting_balance;
+            }
+
+            let candidate_root = WinningRoot {
+                shard_block_root: shard_block_root.clone(),
+                attesting_validator_indices,
+                total_attesting_balance,
+                total_balance,
+            };
+
+            candidates.insert(*shard_block_root, candidate_root);
+        }
+
+        let winner = candidates
+            .iter()
+            .filter_map(|(_hash, candidate)| {
+                if candidate.total_attesting_balance == highest_seen_balance {
+                    Some(candidate)
+                } else {
+                    None
+                }
+            })
+            .min_by_key(|candidate| candidate.shard_block_root);
+
+        match winner {
+            Some(winner) => Some(winner.clone()),
+            None => None,
+        }
+    }
+}