From 2fd45e093ca066326de6a7e2ec09991274d6eadc Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Mon, 20 May 2019 14:00:47 +1000
Subject: [PATCH] Remove shard_count from ChainSpec

---
 .../src/beacon_state/beacon_state_types.rs     | 17 +++++++++++++++++
 eth2/types/src/beacon_state/epoch_cache.rs     |  9 ++++-----
 eth2/types/src/beacon_state/tests.rs           |  2 +-
 eth2/types/src/chain_spec.rs                   | 18 +-----------------
 4 files changed, 23 insertions(+), 23 deletions(-)

diff --git a/eth2/types/src/beacon_state/beacon_state_types.rs b/eth2/types/src/beacon_state/beacon_state_types.rs
index e76ea9253..07eda2435 100644
--- a/eth2/types/src/beacon_state/beacon_state_types.rs
+++ b/eth2/types/src/beacon_state/beacon_state_types.rs
@@ -14,6 +14,23 @@ pub trait EthSpec:
 
     fn spec() -> ChainSpec;
 
+    /// Return the number of committees in one epoch.
+    ///
+    /// Spec v0.6.1
+    fn get_epoch_committee_count(active_validator_count: usize) -> usize {
+        let target_committee_size = Self::spec().target_committee_size;
+        let shard_count = Self::shard_count();
+        let slots_per_epoch = Self::slots_per_epoch() as usize;
+
+        std::cmp::max(
+            1,
+            std::cmp::min(
+                shard_count / slots_per_epoch,
+                active_validator_count / slots_per_epoch / target_committee_size,
+            ),
+        ) * slots_per_epoch
+    }
+
     /// Returns the minimum number of validators required for this spec.
     ///
     /// This is the _absolute_ minimum, the number required to make the chain operate in the most
diff --git a/eth2/types/src/beacon_state/epoch_cache.rs b/eth2/types/src/beacon_state/epoch_cache.rs
index 8e1593f14..3c4cb6c05 100644
--- a/eth2/types/src/beacon_state/epoch_cache.rs
+++ b/eth2/types/src/beacon_state/epoch_cache.rs
@@ -43,14 +43,13 @@ impl EpochCache {
             return Err(BeaconStateError::InsufficientValidators);
         }
 
-        let committee_count =
-            spec.get_epoch_committee_count(active_validator_indices.len()) as usize;
+        let committee_count = T::get_epoch_committee_count(active_validator_indices.len()) as usize;
 
         let shuffling_start_shard = match relative_epoch {
             RelativeEpoch::Current => state.latest_start_shard,
             RelativeEpoch::Previous => {
                 let committees_in_previous_epoch =
-                    spec.get_epoch_committee_count(active_validator_indices.len());
+                    T::get_epoch_committee_count(active_validator_indices.len()) as u64;
 
                 (state.latest_start_shard + T::shard_count() as u64 - committees_in_previous_epoch)
                     % T::shard_count() as u64
@@ -59,9 +58,9 @@ impl EpochCache {
                 let current_active_validators =
                     get_active_validator_count(&state.validator_registry, state.current_epoch());
                 let committees_in_current_epoch =
-                    spec.get_epoch_committee_count(current_active_validators);
+                    T::get_epoch_committee_count(current_active_validators) as u64;
 
-                (state.latest_start_shard + committees_in_current_epoch) % T::shard_count as u64
+                (state.latest_start_shard + committees_in_current_epoch) % T::shard_count() as u64
             }
         };
 
diff --git a/eth2/types/src/beacon_state/tests.rs b/eth2/types/src/beacon_state/tests.rs
index 93391fc2b..753f8bf8e 100644
--- a/eth2/types/src/beacon_state/tests.rs
+++ b/eth2/types/src/beacon_state/tests.rs
@@ -266,7 +266,7 @@ mod committees {
     fn committee_consistency_test_suite<T: EthSpec>(cached_epoch: RelativeEpoch) {
         let spec = T::spec();
 
-        let validator_count = (spec.shard_count * spec.target_committee_size) + 1;
+        let validator_count = (T::shard_count() * spec.target_committee_size) + 1;
 
         committee_consistency_test::<T>(validator_count as usize, Epoch::new(0), cached_epoch);
 
diff --git a/eth2/types/src/chain_spec.rs b/eth2/types/src/chain_spec.rs
index a2ee15d07..20aa6fcdb 100644
--- a/eth2/types/src/chain_spec.rs
+++ b/eth2/types/src/chain_spec.rs
@@ -24,8 +24,7 @@ pub struct ChainSpec {
     /*
      * Misc
      */
-    pub shard_count: u64,
-    pub target_committee_size: u64,
+    pub target_committee_size: usize,
     pub max_indices_per_attestation: u64,
     pub min_per_epoch_churn_limit: u64,
     pub churn_limit_quotient: u64,
@@ -113,19 +112,6 @@ pub struct ChainSpec {
 }
 
 impl ChainSpec {
-    /// Return the number of committees in one epoch.
-    ///
-    /// Spec v0.6.1
-    pub fn get_epoch_committee_count(&self, active_validator_count: usize) -> u64 {
-        std::cmp::max(
-            1,
-            std::cmp::min(
-                self.shard_count / self.slots_per_epoch,
-                active_validator_count as u64 / self.slots_per_epoch / self.target_committee_size,
-            ),
-        ) * self.slots_per_epoch
-    }
-
     /// Get the domain number that represents the fork meta and signature domain.
     ///
     /// Spec v0.6.1
@@ -156,7 +142,6 @@ impl ChainSpec {
             /*
              * Misc
              */
-            shard_count: 1_024,
             target_committee_size: 128,
             max_indices_per_attestation: 4096,
             min_per_epoch_churn_limit: 4,
@@ -263,7 +248,6 @@ impl ChainSpec {
         let genesis_epoch = genesis_slot.epoch(slots_per_epoch);
 
         Self {
-            shard_count: 8,
             target_committee_size: 1,
             genesis_slot,
             genesis_epoch,