Add cached PTC window to the state

specs/gloas/beacon-chain.md

@@ -54,6 +54,7 @@
     - [New `compute_balance_weighted_selection`](#new-compute_balance_weighted_selection)
     - [New `compute_balance_weighted_acceptance`](#new-compute_balance_weighted_acceptance)
     - [Modified `compute_proposer_indices`](#modified-compute_proposer_indices)
+    - [New `compute_ptc`](#new-compute_ptc)
   - [Beacon state accessors](#beacon-state-accessors)
     - [Modified `get_next_sync_committee_indices`](#modified-get_next_sync_committee_indices)
     - [Modified `get_attestation_participation_flag_indices`](#modified-get_attestation_participation_flag_indices)
@@ -67,6 +68,7 @@
   - [Epoch processing](#epoch-processing)
     - [Modified `process_epoch`](#modified-process_epoch)
     - [New `process_builder_pending_payments`](#new-process_builder_pending_payments)
+    - [New `process_ptc_lookbehind`](#new-process_ptc_lookbehind)
   - [Block processing](#block-processing)
     - [Withdrawals](#withdrawals)
       - [New `get_builder_withdrawals`](#new-get_builder_withdrawals)
@@ -384,6 +386,8 @@ class BeaconState(Container):
     latest_block_hash: Hash32
     # [New in Gloas:EIP7732]
     payload_expected_withdrawals: List[Withdrawal, MAX_WITHDRAWALS_PER_PAYLOAD]
+    # [New in Gloas:EIP7732]
+    ptc_lookbehind: Vector[Vector[ValidatorIndex, PTC_SIZE], (2 + MIN_SEED_LOOKAHEAD)* SLOTS_PER_EPOCH]
 ```
 
 ## Dataclasses
@@ -630,6 +634,26 @@ def compute_proposer_indices(
     ]
 ```
 
+#### New `compute_ptc`
+
+```python
+def compute_ptc(state: BeaconState, slot: Slot) -> Vector[ValidatorIndex, PTC_SIZE]:
+    """
+    Get the payload timeliness committee for the given ``slot``.
+    """
+    epoch = compute_epoch_at_slot(slot)
+    seed = hash(get_seed(state, epoch, DOMAIN_PTC_ATTESTER) + uint_to_bytes(slot))
+    indices: List[ValidatorIndex] = []
+    # Concatenate all committees for this slot in order
+    committees_per_slot = get_committee_count_per_slot(state, epoch)
+    for i in range(committees_per_slot):
+        committee = get_beacon_committee(state, slot, CommitteeIndex(i))
+        indices.extend(committee)
+    return compute_balance_weighted_selection(
+        state, indices, seed, size=PTC_SIZE, shuffle_indices=False
+    )
+```
+
 ### Beacon state accessors
 
 #### Modified `get_next_sync_committee_indices`
@@ -705,22 +729,21 @@ def get_attestation_participation_flag_indices(
 
 #### New `get_ptc`
 
+*Note*: `get_ptc` uses the cached `ptc_lookbehind` for lookups. 
+
 ```python
 def get_ptc(state: BeaconState, slot: Slot) -> Vector[ValidatorIndex, PTC_SIZE]:
     """
     Get the payload timeliness committee for the given ``slot``.
     """
     epoch = compute_epoch_at_slot(slot)
-    seed = hash(get_seed(state, epoch, DOMAIN_PTC_ATTESTER) + uint_to_bytes(slot))
-    indices: List[ValidatorIndex] = []
-    # Concatenate all committees for this slot in order
-    committees_per_slot = get_committee_count_per_slot(state, epoch)
-    for i in range(committees_per_slot):
-        committee = get_beacon_committee(state, slot, CommitteeIndex(i))
-        indices.extend(committee)
-    return compute_balance_weighted_selection(
-        state, indices, seed, size=PTC_SIZE, shuffle_indices=False
-    )
+    state_epoch = get_current_epoch(state)
+    if epoch < state_epoch:
+        assert epoch + 1 == state_epoch
+        return state.ptc_lookbehind[slot % SLOTS_PER_EPOCH]
+    assert epoch <= state_epoch + MIN_SEED_LOOKAHEAD
+    offset = (epoch - state_epoch + 1) * SLOTS_PER_EPOCH
+    return state.ptc_lookbehind[offset + slot % SLOTS_PER_EPOCH]
 ```
 
 #### New `get_indexed_payload_attestation`
@@ -815,6 +838,9 @@ def process_slot(state: BeaconState) -> None:
 
 #### Modified `process_epoch`
 
+*Note*: The function `process_epoch` is modified in Gloas to call the new
+helpers `process_builder_pending_payments` and `process_ptc_lookbehind`.
+
 ```python
 def process_epoch(state: BeaconState) -> None:
     process_justification_and_finalization(state)
@@ -834,6 +860,8 @@ def process_epoch(state: BeaconState) -> None:
     process_participation_flag_updates(state)
     process_sync_committee_updates(state)
     process_proposer_lookahead(state)
+    # [New in Gloas:EIP7732]
+    process_ptc_lookbehind(state)
 ```
 
 #### New `process_builder_pending_payments`
@@ -853,6 +881,25 @@ def process_builder_pending_payments(state: BeaconState) -> None:
     state.builder_pending_payments = old_payments + new_payments
 ```
 
+#### New `process_ptc_lookbehind`
+
+```python
+def process_ptc_lookbehind(state: BeaconState) -> None:
+    """
+    Update the cached PTC window.
+    """
+    # Shift out PTC members in the first epoch
+    last_epoch_start = len(state.ptc_lookbehind) - SLOTS_PER_EPOCH
+    state.ptc_lookbehind[:last_epoch_start] = state.ptc_lookbehind[SLOTS_PER_EPOCH:]
+    # Fill in the last epoch with the PTC for the epoch that starts after this boundary
+    next_epoch = Epoch(get_current_epoch(state) + MIN_SEED_LOOKAHEAD + 1)
+    start_slot = compute_start_slot_at_epoch(next_epoch)
+    last_epoch_committees = [
+        compute_ptc(state, Slot(slot)) for slot in range(start_slot, start_slot + SLOTS_PER_EPOCH)
+    ]
+    state.ptc_lookbehind[last_epoch_start:] = last_epoch_committees
+```
+
 ### Block processing
 
 ```python

specs/gloas/fork.md

@@ -7,6 +7,7 @@
 - [Introduction](#introduction)
 - [Configuration](#configuration)
 - [Helpers](#helpers)
+  - [New `initialize_ptc_lookbehind`](#new-initialize_ptc_lookbehind)
   - [New `onboard_builders_from_pending_deposits`](#new-onboard_builders_from_pending_deposits)
 - [Fork to Gloas](#fork-to-gloas)
   - [Fork trigger](#fork-trigger)
@@ -29,6 +30,26 @@ Warning: this configuration is not definitive.
 
 ## Helpers
 
+### New `initialize_ptc_lookbehind`
+
+```python
+def initialize_ptc_lookbehind(
+    state: BeaconState,
+) -> Vector[Vector[ValidatorIndex, PTC_SIZE], 2 * SLOTS_PER_EPOCH]:
+    """
+    Return the cached PTC window starting from the current epoch.
+    Used to initialize the ``ptc_lookbehind`` field in the beacon state at genesis and after forks.
+    """
+    current_epoch = get_current_epoch(state)
+    start_slot = compute_start_slot_at_epoch(current_epoch)
+    empty_previous_epoch = [
+        Vector[ValidatorIndex, PTC_SIZE]([ValidatorIndex(0) for _ in range(PTC_SIZE)])
+        for _ in range(SLOTS_PER_EPOCH)
+    ]
+    current_epoch_ptc = [compute_ptc(state, Slot(start_slot + i)) for i in range(SLOTS_PER_EPOCH)]
+    return empty_previous_epoch + current_epoch_ptc
+```
+
 ### New `onboard_builders_from_pending_deposits`
 
 ```python
@@ -159,6 +180,8 @@ def upgrade_to_gloas(pre: fulu.BeaconState) -> BeaconState:
         latest_block_hash=pre.latest_execution_payload_header.block_hash,
         # [New in Gloas:EIP7732]
         payload_expected_withdrawals=[],
+        # [New in Gloas:EIP7732]
+        ptc_lookbehind=initialize_ptc_lookbehind(pre),
     )
 
     # [New in Gloas:EIP7732]

specs/heze/beacon-chain.md

@@ -150,6 +150,7 @@ class BeaconState(Container):
     builder_pending_withdrawals: List[BuilderPendingWithdrawal, BUILDER_PENDING_WITHDRAWALS_LIMIT]
     latest_block_hash: Hash32
     payload_expected_withdrawals: List[Withdrawal, MAX_WITHDRAWALS_PER_PAYLOAD]
+    ptc_lookbehind: Vector[Vector[ValidatorIndex, PTC_SIZE], 2 * SLOTS_PER_EPOCH]
 ```
 
 ## Helpers

specs/heze/fork.md

@@ -103,6 +103,7 @@ def upgrade_to_heze(pre: gloas.BeaconState) -> BeaconState:
         builder_pending_withdrawals=pre.builder_pending_withdrawals,
         latest_block_hash=pre.latest_block_hash,
         payload_expected_withdrawals=pre.payload_expected_withdrawals,
+        ptc_lookbehind=pre.ptc_lookbehind,
     )
 
     return post

tests/core/pyspec/eth_consensus_specs/test/gloas/block_processing/test_process_payload_attestation.py

@@ -375,6 +375,8 @@ def test_process_payload_attestation_sampling_not_capped(spec, state):
     low_balance = spec.EFFECTIVE_BALANCE_INCREMENT
     for validator in state.validators:
         validator.effective_balance = low_balance
+    # Direct balance mutations bypass epoch processing, so refresh the cached current-epoch PTC.
+    state.ptc_lookbehind = spec.initialize_ptc_lookbehind(state)
 
     chosen_slot = None
     chosen_index = None

tests/core/pyspec/eth_consensus_specs/test/gloas/epoch_processing/test_process_ptc_lookbehind.py

@@ -0,0 +1,40 @@
+from eth_consensus_specs.test.context import (
+    single_phase,
+    spec_state_test,
+    with_phases,
+)
+from eth_consensus_specs.test.helpers.constants import GLOAS
+from eth_consensus_specs.test.helpers.epoch_processing import run_epoch_processing_with
+
+
+def _compute_epoch_ptc(spec, state, epoch):
+    start_slot = spec.compute_start_slot_at_epoch(epoch)
+    return [
+        spec.compute_ptc(state, spec.Slot(slot))
+        for slot in range(start_slot, start_slot + spec.SLOTS_PER_EPOCH)
+    ]
+
+
+@with_phases([GLOAS])
+@spec_state_test
+@single_phase
+def test_process_ptc_lookbehind_rotates_to_next_epoch(spec, state):
+    spec.process_slots(state, state.slot + spec.SLOTS_PER_EPOCH - 1)
+
+    current_epoch = spec.get_current_epoch(state)
+    current_epoch_ptc = _compute_epoch_ptc(spec, state, current_epoch)
+    state.ptc_lookbehind = current_epoch_ptc + current_epoch_ptc
+
+    next_epoch = spec.Epoch(current_epoch + 1)
+    next_epoch_ptc = _compute_epoch_ptc(spec, state, next_epoch)
+
+    yield from run_epoch_processing_with(spec, state, "process_ptc_lookbehind")
+
+    assert list(state.ptc_lookbehind[: spec.SLOTS_PER_EPOCH]) == current_epoch_ptc
+    assert list(state.ptc_lookbehind[spec.SLOTS_PER_EPOCH :]) == next_epoch_ptc
+
+    # run_epoch_processing_with does not increment the slot
+    state.slot += 1
+
+    assert spec.get_ptc(state, spec.Slot(state.slot - 1)) == current_epoch_ptc[-1]
+    assert spec.get_ptc(state, state.slot) == next_epoch_ptc[0]

tests/core/pyspec/eth_consensus_specs/test/gloas/unittests/validator/__init__.py

@@ -0,0 +1 @@
+

tests/core/pyspec/eth_consensus_specs/test/gloas/unittests/validator/test_validator.py

@@ -0,0 +1,102 @@
+from eth_consensus_specs.test.context import (
+    expect_assertion_error,
+    single_phase,
+    spec_test,
+    with_phases,
+    with_state,
+)
+from eth_consensus_specs.test.helpers.constants import GLOAS
+from eth_consensus_specs.test.helpers.state import next_epoch
+
+
+def _compute_first_ptc_assignments(spec, state, epoch):
+    assignments = {}
+    start_slot = spec.compute_start_slot_at_epoch(epoch)
+    for slot in range(start_slot, start_slot + spec.SLOTS_PER_EPOCH):
+        for validator_index in spec.compute_ptc(state, spec.Slot(slot)):
+            assignments.setdefault(validator_index, spec.Slot(slot))
+    return assignments
+
+
+def _run_get_ptc_assignments(spec, state, epoch, valid=True, assignments=None):
+    if not valid:
+        expect_assertion_error(
+            lambda: spec.get_ptc_assignment(state, epoch, spec.ValidatorIndex(0))
+        )
+        return
+
+    if assignments is None:
+        assignments = _compute_first_ptc_assignments(spec, state, epoch)
+    _assert_get_ptc_assignments(spec, state, epoch, assignments)
+
+
+def _assert_get_ptc_assignments(spec, state, epoch, assignments):
+    assert len(assignments) > 0
+
+    for validator_index, expected_slot in assignments.items():
+        assert spec.get_ptc_assignment(state, epoch, validator_index) == expected_slot
+
+    unassigned_validator = next(
+        (spec.ValidatorIndex(i) for i in range(len(state.validators)) if i not in assignments),
+        None,
+    )
+    if unassigned_validator is not None:
+        assert spec.get_ptc_assignment(state, epoch, unassigned_validator) is None
+
+
+@with_phases([GLOAS])
+@spec_test
+@with_state
+@single_phase
+def test_get_ptc_assignment__current_epoch_minus_2(spec, state):
+    next_epoch(spec, state)
+    next_epoch(spec, state)
+
+    epoch = spec.Epoch(spec.get_current_epoch(state) - 2)
+    _run_get_ptc_assignments(spec, state, epoch, valid=False)
+
+
+@with_phases([GLOAS])
+@spec_test
+@with_state
+@single_phase
+def test_get_ptc_assignment__current_epoch_minus_1(spec, state):
+    previous_epoch = spec.get_current_epoch(state)
+    previous_assignments = _compute_first_ptc_assignments(spec, state, previous_epoch)
+
+    next_epoch(spec, state)
+
+    _run_get_ptc_assignments(
+        spec,
+        state,
+        previous_epoch,
+        valid=True,
+        assignments=previous_assignments,
+    )
+
+
+@with_phases([GLOAS])
+@spec_test
+@with_state
+@single_phase
+def test_get_ptc_assignment__current_epoch(spec, state):
+    epoch = spec.get_current_epoch(state)
+    _run_get_ptc_assignments(spec, state, epoch, valid=True)
+
+
+@with_phases([GLOAS])
+@spec_test
+@with_state
+@single_phase
+def test_get_ptc_assignment__current_epoch_plus_1(spec, state):
+    epoch = spec.Epoch(spec.get_current_epoch(state) + 1)
+    _run_get_ptc_assignments(spec, state, epoch, valid=True)
+
+
+@with_phases([GLOAS])
+@spec_test
+@with_state
+@single_phase
+def test_get_ptc_assignment__current_epoch_plus_2(spec, state):
+    epoch = spec.Epoch(spec.get_current_epoch(state) + 2)
+    _run_get_ptc_assignments(spec, state, epoch, valid=False)

tests/core/pyspec/eth_consensus_specs/test/helpers/genesis.py

@@ -252,6 +252,7 @@ def create_genesis_state(spec, validator_balances, activation_threshold):
             spec.BuilderPendingPayment() for _ in range(2 * spec.SLOTS_PER_EPOCH)
         ]
         state.builder_pending_withdrawals = []
+        state.ptc_lookbehind = spec.initialize_ptc_lookbehind(state)
 
     if is_post_fulu(spec):
         # Initialize proposer lookahead list