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Speed up compute_ptc #5044

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Merged
jtraglia merged 4 commits into from
Mar 26, 2026
+7 −8
Merged

Speed up compute_ptc #5044

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1cf4c69
Pre-fetch effective balances in `compute_balance_weighted_selection`
jtraglia Mar 26, 2026
9190a03
Add caching for expensive balance-weighted selection functions
jtraglia Mar 26, 2026
56f6134
Revert non-Gloas specific changes
jtraglia Mar 26, 2026
c6ef15d
Remove compute_ptc cache
jtraglia Mar 26, 2026
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12 changes: 5 additions & 7 deletions specs/gloas/beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -581,14 +581,15 @@ def compute_balance_weighted_selection(
"""
total = uint64(len(indices))
assert total > 0
effective_balances = [state.validators[index].effective_balance for index in indices]
selected: List[ValidatorIndex] = []
i = uint64(0)
while len(selected) < size:
next_index = i % total
if shuffle_indices:
next_index = compute_shuffled_index(next_index, total, seed)
candidate_index = indices[next_index]
if compute_balance_weighted_acceptance(state, candidate_index, seed, i):
if compute_balance_weighted_acceptance(effective_balances[next_index], seed, i):
selected.append(candidate_index)
i += 1
return selected
Expand All @@ -597,18 +598,15 @@ def compute_balance_weighted_selection(
#### New `compute_balance_weighted_acceptance`

```python
def compute_balance_weighted_acceptance(
state: BeaconState, index: ValidatorIndex, seed: Bytes32, i: uint64
) -> bool:
def compute_balance_weighted_acceptance(effective_balance: Gwei, seed: Bytes32, i: uint64) -> bool:
"""
Return whether to accept the selection of the validator ``index``, with probability
proportional to its ``effective_balance``, and randomness given by ``seed`` and ``i``.
Return whether to accept the selection of a validator with the given ``effective_balance``,
with probability proportional to its balance, and randomness given by ``seed`` and ``i``.
"""
MAX_RANDOM_VALUE = 2**16 - 1
random_bytes = hash(seed + uint_to_bytes(i // 16))
offset = i % 16 * 2
random_value = bytes_to_uint64(random_bytes[offset : offset + 2])
effective_balance = state.validators[index].effective_balance
return effective_balance * MAX_RANDOM_VALUE >= MAX_EFFECTIVE_BALANCE_ELECTRA * random_value
```

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3 changes: 2 additions & 1 deletion ...yspec/eth_consensus_specs/test/gloas/block_processing/test_process_payload_attestation.py
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Expand Up @@ -126,7 +126,8 @@ def _compute_selection_with_acceptance_iterations(spec, state, indices, seed, si
i = 0
while len(selected) < size:
candidate_index = indices[i % total]
if spec.compute_balance_weighted_acceptance(state, candidate_index, seed, spec.uint64(i)):
effective_balance = state.validators[candidate_index].effective_balance
if spec.compute_balance_weighted_acceptance(effective_balance, seed, spec.uint64(i)):
selected.append(candidate_index)
accepted_at.append(i)
i += 1
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