add start index back in

configs/mainnet.yaml

@@ -6,7 +6,7 @@
 # Misc
 # ---------------------------------------------------------------
 # 2**5 (= 32)
-COMMITTEES_PER_SLOT: 32
+MAX_COMMITTEES_PER_SLOT: 32
 # 2**7 (= 128)
 TARGET_COMMITTEE_SIZE: 128
 # 2**12 (= 4,096)

configs/minimal.yaml

@@ -5,7 +5,7 @@
 # ---------------------------------------------------------------
 
 # [customized] Just 2 committees for slot for testing purposes
-COMMITTEES_PER_SLOT: 2
+MAX_COMMITTEES_PER_SLOT: 2
 # [customized] unsecure, but fast
 TARGET_COMMITTEE_SIZE: 4
 # 2**12 (= 4,096)

specs/core/0_beacon-chain.md

@@ -168,8 +168,8 @@ The following values are (non-configurable) constants used throughout the specif
 
 | Name | Value |
 | - | - |
-| `COMMITTEES_PER_SLOT` | `2**5` (= 32) |
 | `SHARD_COUNT` | `2**10` (= 1,024) |
+| `MAX_COMMITTEES_PER_SLOT` | `2**5` (= 32) |
 | `TARGET_COMMITTEE_SIZE` | `2**7` (= 128) |
 | `MAX_VALIDATORS_PER_COMMITTEE` | `2**12` (= 4,096) |
 | `MIN_PER_EPOCH_CHURN_LIMIT` | `2**2` (= 4) |
@@ -490,6 +490,7 @@ class BeaconState(Container):
     validators: List[Validator, VALIDATOR_REGISTRY_LIMIT]
     balances: List[Gwei, VALIDATOR_REGISTRY_LIMIT]
     # Shuffling
+    start_index: uint64
     randao_mixes: Vector[Hash, EPOCHS_PER_HISTORICAL_VECTOR]
     # Slashings
     slashings: Vector[Gwei, EPOCHS_PER_SLASHINGS_VECTOR]  # Per-epoch sums of slashed effective balances
@@ -857,6 +858,21 @@ def get_seed(state: BeaconState, epoch: Epoch, domain_type: DomainType) -> Hash:
     return hash(domain_type + int_to_bytes(epoch, length=8) + mix)
 ```
 
+
+#### `get_committee_count`
+
+```python
+def get_committee_count(state: BeaconState, epoch: Epoch) -> uint64:
+    """
+    Return the number of committees at ``epoch``.
+    """
+    committees_per_slot = max(1, min(
+        MAX_COMMITTEES_PER_SLOT,
+        len(get_active_validator_indices(state, epoch)) // SLOTS_PER_EPOCH // TARGET_COMMITTEE_SIZE,
+    ))
+    return committees_per_slot * SLOTS_PER_EPOCH
+```
+
 #### `get_crosslink_committee`
 
 ```python
@@ -865,14 +881,60 @@ def get_crosslink_committee(state: BeaconState, slot: Slot, index: uint64) -> Se
     Return the crosslink committee at ``epoch`` for ``index``.
     """
     epoch = compute_epoch_of_slot(slot)
+    committees_per_slot = get_committee_count(state, epoch) // SLOTS_PER_EPOCH
+    slot_start_index = get_slot_start_index(state, slot)
+    slot_offset = (index + MAX_COMMITTEES_PER_SLOT - slot_start_index) % MAX_COMMITTEES_PER_SLOT
+    epoch_offset = slot_offset + (slot % SLOTS_PER_EPOCH) * committees_per_slot
+    print(epoch_offset)
+
     return compute_committee(
         indices=get_active_validator_indices(state, epoch),
         seed=get_seed(state, epoch, DOMAIN_BEACON_ATTESTER),
-        index=(slot % SLOTS_PER_EPOCH) * COMMITTEES_PER_SLOT + index,
+        index=epoch_offset,
-        count=COMMITTEES_PER_SLOT * SLOTS_PER_EPOCH,
+        count=get_committee_count(state, epoch),
     )
 ```
 
+#### `get_slot_start_index`
+
+```python
+def get_slot_start_index(state: BeaconState, slot: Slot) -> uint64:
+    """
+    Return the start index of the 0th committee at ``slot``.
+    """
+    epoch = compute_epoch_of_slot(slot)
+    committees_per_slot = get_committee_count(state, epoch) // SLOTS_PER_EPOCH
+    slot_start_index = ((slot % SLOTS_PER_EPOCH) * committees_per_slot + get_start_index(state, epoch)) % MAX_COMMITTEES_PER_SLOT
+    return slot_start_index
+```
+
+#### `get_start_index`
+
+```python
+def get_start_index(state: BeaconState, epoch: Epoch) -> uint64:
+    """
+    Return the start index of the 0th committee at ``epoch``.
+    """
+    assert epoch <= get_current_epoch(state) + 1
+    check_epoch = Epoch(get_current_epoch(state) + 1)
+    index = (state.start_index + get_index_delta(state, get_current_epoch(state))) % MAX_COMMITTEES_PER_SLOT
+    MAX_COMMITTEES_PER_EPOCH = MAX_COMMITTEES_PER_SLOT * SLOTS_PER_EPOCH
+    while check_epoch > epoch:
+        check_epoch -= Epoch(1)
+        index = (index + MAX_COMMITTEES_PER_EPOCH - get_index_delta(state, check_epoch)) % MAX_COMMITTEES_PER_SLOT
+    return index
+```
+
+#### `get_index_delta`
+
+```python
+def get_index_delta(state: BeaconState, epoch: Epoch) -> uint64:
+    """
+    Return the amount to increase ``state.start_index`` at ``epoch``.
+    """
+    return get_committee_count(state, epoch)
+```
+
 #### `get_beacon_proposer_index`
 
 ```python
@@ -1356,6 +1418,8 @@ def process_final_updates(state: BeaconState) -> None:
     if next_epoch % (SLOTS_PER_HISTORICAL_ROOT // SLOTS_PER_EPOCH) == 0:
         historical_batch = HistoricalBatch(block_roots=state.block_roots, state_roots=state.state_roots)
         state.historical_roots.append(hash_tree_root(historical_batch))
+    # Update start shard
+    state.start_index = (state.start_index + get_index_delta(state, current_epoch)) % MAX_COMMITTEES_PER_SLOT
     # Rotate current/previous epoch attestations
     state.previous_epoch_attestations = state.current_epoch_attestations
     state.current_epoch_attestations = []
@@ -1482,7 +1546,7 @@ def process_attester_slashing(state: BeaconState, attester_slashing: AttesterSla
 ```python
 def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     data = attestation.data
-    assert data.index < COMMITTEES_PER_SLOT
+    assert data.index < MAX_COMMITTEES_PER_SLOT
     assert data.target.epoch in (get_previous_epoch(state), get_current_epoch(state))
 
     assert data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot <= data.slot + SLOTS_PER_EPOCH

specs/validator/0_beacon-chain-validator.md

@@ -149,7 +149,9 @@ def get_committee_assignment(state: BeaconState,
 
     start_slot = compute_start_slot_of_epoch(epoch)
     for slot in range(start_slot, start_slot + SLOTS_PER_EPOCH):
-        for index in range(COMMITTEES_PER_SLOT):
+        slot_start_index = get_slot_start_index(state, Slot(slot))
+        for i in range(get_committee_count(state, epoch) // SLOTS_PER_EPOCH):
+            index = (slot_start_index + i) % MAX_COMMITTEES_PER_SLOT
             committee = get_crosslink_committee(state, Slot(slot), index)
             if validator_index in committee:
                 return committee, index, Slot(slot)

test_libs/pyspec/eth2spec/test/helpers/attestations.py

@@ -42,7 +42,10 @@ def get_valid_attestation(spec, state, slot=None, index=None, signed=False):
     if slot is None:
         slot = state.slot
     if index is None:
-        index = 0
+        index = spec.get_slot_start_index(state, slot)
+    print(slot)
+    print(index)
+    print(spec.get_committee_count(state, spec.compute_epoch_of_slot(slot)))
 
     attestation_data = build_attestation_data(spec, state, slot, index)
 

test_libs/pyspec/eth2spec/test/helpers/state.py

@@ -51,15 +51,21 @@ def next_epoch_with_attestations(spec,
     for _ in range(spec.SLOTS_PER_EPOCH):
         block = build_empty_block_for_next_slot(spec, post_state)
         if fill_cur_epoch and post_state.slot >= spec.MIN_ATTESTATION_INCLUSION_DELAY:
+            committees_per_slot = spec.get_committee_count(state, spec.get_current_epoch(state)) // spec.SLOTS_PER_EPOCH
             slot_to_attest = post_state.slot - spec.MIN_ATTESTATION_INCLUSION_DELAY + 1
             if slot_to_attest >= spec.compute_start_slot_of_epoch(spec.get_current_epoch(post_state)):
-                for index in range(spec.COMMITTEES_PER_SLOT):
+                slot_start_index = spec.get_slot_start_index(state, slot_to_attest)
+                for i in range(committees_per_slot):
+                    index = (slot_start_index + i) % spec.MAX_COMMITTEES_PER_SLOT
                     cur_attestation = get_valid_attestation(spec, post_state, slot_to_attest, index=index)
                     block.body.attestations.append(cur_attestation)
 
         if fill_prev_epoch:
+            committees_per_slot = spec.get_committee_count(state, spec.get_previous_epoch(state)) // spec.SLOTS_PER_EPOCH
             slot_to_attest = post_state.slot - spec.SLOTS_PER_EPOCH + 1
-            for index in range(spec.COMMITTEES_PER_SLOT):
+            slot_start_index = spec.get_slot_start_index(state, slot_to_attest)
+            for i in range(committees_per_slot):
+                index = (slot_start_index + i) % spec.MAX_COMMITTEES_PER_SLOT
                 prev_attestation = get_valid_attestation(spec, post_state, slot_to_attest, index=index)
                 block.body.attestations.append(prev_attestation)
 

test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py

@@ -122,6 +122,12 @@ def test_old_source_epoch(spec, state):
     yield from run_attestation_processing(spec, state, attestation, False)
 
 
+@with_all_phases
+@spec_state_test
+def test_wrong_index(spec, state):
+    pass
+
+
 @with_all_phases
 @spec_state_test
 @never_bls
@@ -130,7 +136,7 @@ def test_invalid_index(spec, state):
     state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
 
     # off by one (with respect to valid range) on purpose
-    attestation.data.index = spec.COMMITTEES_PER_SLOT
+    attestation.data.index = spec.MAX_COMMITTEES_PER_SLOT
 
     yield from run_attestation_processing(spec, state, attestation, False)
 

test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_justification_and_finalization.py

@@ -26,8 +26,11 @@ def add_mock_attestations(spec, state, epoch, source, target, sufficient_support
     remaining_balance = total_balance * 2 // 3
 
     start_slot = spec.compute_start_slot_of_epoch(epoch)
+    committees_per_slot = spec.get_committee_count(state, epoch) // spec.SLOTS_PER_EPOCH
     for slot in range(start_slot, start_slot + spec.SLOTS_PER_EPOCH):
-        for index in range(spec.COMMITTEES_PER_SLOT):
+        slot_start_index = spec.get_slot_start_index(state, slot)
+        for i in range(committees_per_slot):
+            index = (slot_start_index + i) % spec.MAX_COMMITTEES_PER_SLOT
             # Check if we already have had sufficient balance. (and undone if we don't want it).
             # If so, do not create more attestations. (we do not have empty pending attestations normally anyway)
             if remaining_balance < 0: