rename get_epoch_start_shard(...) to 0.8.0 get_start_shard(...)

beacon_chain/spec/beaconstate.nim

@@ -277,7 +277,7 @@ func get_attestation_data_slot*(state: BeaconState,
     data: AttestationData, committee_count: uint64): Slot =
   let
     offset = (data.crosslink.shard + SHARD_COUNT -
-      get_epoch_start_shard(state, data.target_epoch)) mod SHARD_COUNT
+      get_start_shard(state, data.target_epoch)) mod SHARD_COUNT
 
   compute_start_slot_of_epoch(data.target_epoch) + offset div
     (committee_count div SLOTS_PER_EPOCH)
@@ -595,7 +595,7 @@ proc makeAttestationData*(
     target_epoch: compute_epoch_of_slot(state.slot),
     crosslink: Crosslink(
       # Alternative is to put this offset into all callers
-      shard: shard + get_epoch_start_shard(state, compute_epoch_of_slot(state.slot)),
+      shard: shard + get_start_shard(state, compute_epoch_of_slot(state.slot)),
       parent_root: hash_tree_root(state.current_crosslinks[shard]),
       data_root: Eth2Digest(), # Stub in phase0
     )

beacon_chain/spec/datatypes.nim

@@ -378,7 +378,9 @@ template ethTimeUnit(typ: type) {.dirty.} =
 
   proc `*`*(x: typ, y: uint64): uint64 {.borrow.}
 
+  proc `+=`*(x: var typ, y: typ) {.borrow.}
   proc `+=`*(x: var typ, y: uint64) {.borrow.}
+  proc `-=`*(x: var typ, y: typ) {.borrow.}
   proc `-=`*(x: var typ, y: uint64) {.borrow.}
 
   # Comparison operators

beacon_chain/spec/state_transition_epoch.nim

@@ -221,7 +221,7 @@ func process_crosslinks(state: var BeaconState, stateCache: var StateCache) =
     let epoch = epoch_int.Epoch
     for offset in 0'u64 ..< get_epoch_committee_count(state, epoch):
       let
-        shard = (get_epoch_start_shard(state, epoch) + offset) mod SHARD_COUNT
+        shard = (get_start_shard(state, epoch) + offset) mod SHARD_COUNT
         crosslink_committee =
           get_crosslink_committee(state, epoch, shard, stateCache)
         # In general, it'll loop over the same shards twice, and
@@ -327,7 +327,7 @@ func get_crosslink_deltas(state: BeaconState, cache: var StateCache):
   let epoch = get_previous_epoch(state)
   for offset in 0'u64 ..< get_epoch_committee_count(state, epoch):
     let
-      shard = (get_epoch_start_shard(state, epoch) + offset) mod SHARD_COUNT
+      shard = (get_start_shard(state, epoch) + offset) mod SHARD_COUNT
       crosslink_committee =
         get_crosslink_committee(state, epoch, shard, cache)
       (winning_crosslink, attesting_indices) =

beacon_chain/spec/validator.nim

@@ -96,8 +96,10 @@ func get_shard_delta*(state: BeaconState, epoch: Epoch): uint64 =
   min(get_epoch_committee_count(state, epoch),
     (SHARD_COUNT - SHARD_COUNT div SLOTS_PER_EPOCH).uint64)
 
-# https://github.com/ethereum/eth2.0-specs/blob/v0.7.1/specs/core/0_beacon-chain.md#get_epoch_start_shard
-func get_epoch_start_shard*(state: BeaconState, epoch: Epoch): Shard =
+# https://github.com/ethereum/eth2.0-specs/blob/v0.8.0/specs/core/0_beacon-chain.md#get_start_shard
+func get_start_shard*(state: BeaconState, epoch: Epoch): Shard =
+  # Return the start shard of the 0th committee at ``epoch``.
+
   doAssert epoch <= get_current_epoch(state) + 1
   var
     check_epoch = get_current_epoch(state) + 1
@@ -105,7 +107,7 @@ func get_epoch_start_shard*(state: BeaconState, epoch: Epoch): Shard =
       (state.latest_start_shard +
        get_shard_delta(state, get_current_epoch(state))) mod SHARD_COUNT
   while check_epoch > epoch:
-    check_epoch -= 1
+    check_epoch -= 1.Epoch
     shard = (shard + SHARD_COUNT - get_shard_delta(state, check_epoch)) mod
       SHARD_COUNT
   return shard
@@ -140,7 +142,7 @@ func get_crosslink_committee*(state: BeaconState, epoch: Epoch, shard: Shard,
 
   doAssert shard >= 0'u64
   # This seems to be required, basically, to be true? But I'm not entirely sure
-  #doAssert shard >= get_epoch_start_shard(state, epoch)
+  #doAssert shard >= get_start_shard(state, epoch)
   doAssert shard < SHARD_COUNT
 
   ## This is a somewhat more fragile, but high-ROI, caching setup --
@@ -153,7 +155,7 @@ func get_crosslink_committee*(state: BeaconState, epoch: Epoch, shard: Shard,
   compute_committee(
     stateCache.active_validator_indices_cache[epoch],
     generate_seed(state, epoch),
-    (shard + SHARD_COUNT - get_epoch_start_shard(state, epoch)) mod SHARD_COUNT,
+    (shard + SHARD_COUNT - get_start_shard(state, epoch)) mod SHARD_COUNT,
     get_epoch_committee_count(state, epoch),
     stateCache
   )
@@ -177,7 +179,7 @@ func get_beacon_proposer_index*(state: BeaconState, stateCache: var StateCache):
     committees_per_slot =
       get_epoch_committee_count(state, epoch) div SLOTS_PER_EPOCH
     offset = committees_per_slot * (state.slot mod SLOTS_PER_EPOCH)
-    shard = (get_epoch_start_shard(state, epoch) + offset) mod SHARD_COUNT
+    shard = (get_start_shard(state, epoch) + offset) mod SHARD_COUNT
     first_committee = get_crosslink_committee(state, epoch, shard, stateCache)
     seed = generate_seed(state, epoch)
 

research/state_sim.nim

@@ -106,7 +106,7 @@ cli do(slots = 448,
           mapIt(
             0'u64 .. (get_epoch_committee_count(state, epoch) - 1),
             get_crosslink_committee(state, epoch,
-              (it + get_epoch_start_shard(state, epoch)) mod SHARD_COUNT,
+              (it + get_start_shard(state, epoch)) mod SHARD_COUNT,
               cache))
 
       for scas in scass:

tests/testutil.nim

@@ -147,7 +147,7 @@ proc find_shard_committee(
   var cache = get_empty_per_epoch_cache()
   for shard in 0'u64 ..< get_epoch_committee_count(state, epoch):
     let committee = get_crosslink_committee(state, epoch,
-      (shard + get_epoch_start_shard(state, epoch)) mod SHARD_COUNT, cache)
+      (shard + get_start_shard(state, epoch)) mod SHARD_COUNT, cache)
     if validator_index in committee:
       return (committee, shard)
   doAssert false