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reduce justification and finalization Altair diff
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@protolambda
protolambda committed Mar 21, 2021
1 parent a69ad6c commit 493dd17
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42 changes: 7 additions & 35 deletions specs/altair/beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -575,48 +575,20 @@ def process_epoch(state: BeaconState) -> None:

#### Justification and finalization

*Note*: The function `process_justification_and_finalization` is modified with `matching_target_attestations` replaced by `matching_target_indices`.
*Note*: The function `process_justification_and_finalization` is modified to adapt to the new participation records.

```python
def process_justification_and_finalization(state: BeaconState) -> None:
# Initial FFG checkpoint values have a `0x00` stub for `root`.
# Skip FFG updates in the first two epochs to avoid corner cases that might result in modifying this stub.
if get_current_epoch(state) <= GENESIS_EPOCH + 1:
return
previous_epoch = get_previous_epoch(state)
current_epoch = get_current_epoch(state)
old_previous_justified_checkpoint = state.previous_justified_checkpoint
old_current_justified_checkpoint = state.current_justified_checkpoint

# Process justifications
state.previous_justified_checkpoint = state.current_justified_checkpoint
state.justification_bits[1:] = state.justification_bits[:JUSTIFICATION_BITS_LENGTH - 1]
state.justification_bits[0] = 0b0
matching_target_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, previous_epoch)
if get_total_balance(state, matching_target_indices) * 3 >= get_total_active_balance(state) * 2:
state.current_justified_checkpoint = Checkpoint(epoch=previous_epoch,
root=get_block_root(state, previous_epoch))
state.justification_bits[1] = 0b1
matching_target_indices = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, current_epoch)
if get_total_balance(state, matching_target_indices) * 3 >= get_total_active_balance(state) * 2:
state.current_justified_checkpoint = Checkpoint(epoch=current_epoch,
root=get_block_root(state, current_epoch))
state.justification_bits[0] = 0b1

# Process finalizations
bits = state.justification_bits
# The 2nd/3rd/4th most recent epochs are justified, the 2nd using the 4th as source
if all(bits[1:4]) and old_previous_justified_checkpoint.epoch + 3 == current_epoch:
state.finalized_checkpoint = old_previous_justified_checkpoint
# The 2nd/3rd most recent epochs are justified, the 2nd using the 3rd as source
if all(bits[1:3]) and old_previous_justified_checkpoint.epoch + 2 == current_epoch:
state.finalized_checkpoint = old_previous_justified_checkpoint
# The 1st/2nd/3rd most recent epochs are justified, the 1st using the 3rd as source
if all(bits[0:3]) and old_current_justified_checkpoint.epoch + 2 == current_epoch:
state.finalized_checkpoint = old_current_justified_checkpoint
# The 1st/2nd most recent epochs are justified, the 1st using the 2nd as source
if all(bits[0:2]) and old_current_justified_checkpoint.epoch + 1 == current_epoch:
state.finalized_checkpoint = old_current_justified_checkpoint
previous = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_previous_epoch(state))
current = get_unslashed_participating_indices(state, TIMELY_TARGET_FLAG_INDEX, get_current_epoch(state))
weigh_justification_and_finalization(
state, get_total_active_balance(state),
get_total_balance(state, previous),
get_total_balance(state, current))
```

#### Inactivity scores
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17 changes: 13 additions & 4 deletions specs/phase0/beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -1320,7 +1320,18 @@ def process_justification_and_finalization(state: BeaconState) -> None:
# Skip FFG updates in the first two epochs to avoid corner cases that might result in modifying this stub.
if get_current_epoch(state) <= GENESIS_EPOCH + 1:
return
previous = get_matching_target_attestations(state, get_previous_epoch(state))
current = get_matching_target_attestations(state, get_current_epoch(state))
weigh_justification_and_finalization(
state, get_total_active_balance(state),
get_attesting_balance(state, previous),
get_attesting_balance(state, current))
```

```python
def weigh_justification_and_finalization(state: BeaconState, total_active_balance: Gwei,
previous_epoch_target_balance: Gwei,
current_epoch_target_balance: Gwei) -> None:
previous_epoch = get_previous_epoch(state)
current_epoch = get_current_epoch(state)
old_previous_justified_checkpoint = state.previous_justified_checkpoint
Expand All @@ -1330,13 +1341,11 @@ def process_justification_and_finalization(state: BeaconState) -> None:
state.previous_justified_checkpoint = state.current_justified_checkpoint
state.justification_bits[1:] = state.justification_bits[:JUSTIFICATION_BITS_LENGTH - 1]
state.justification_bits[0] = 0b0
matching_target_attestations = get_matching_target_attestations(state, previous_epoch) # Previous epoch
if get_attesting_balance(state, matching_target_attestations) * 3 >= get_total_active_balance(state) * 2:
if previous_epoch_target_balance * 3 >= total_active_balance * 2:
state.current_justified_checkpoint = Checkpoint(epoch=previous_epoch,
root=get_block_root(state, previous_epoch))
state.justification_bits[1] = 0b1
matching_target_attestations = get_matching_target_attestations(state, current_epoch) # Current epoch
if get_attesting_balance(state, matching_target_attestations) * 3 >= get_total_active_balance(state) * 2:
if current_epoch_target_balance * 3 >= total_active_balance * 2:
state.current_justified_checkpoint = Checkpoint(epoch=current_epoch,
root=get_block_root(state, current_epoch))
state.justification_bits[0] = 0b1
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