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Decouple justification and finalization processing (#925)

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Justin 2019-04-16 14:59:35 +10:00 committed by GitHub
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specs/core/0_beacon-chain.md
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@ -1726,47 +1726,42 @@ Run the following function:
```python
def update_justification_and_finalization(state: BeaconState) -> None:
new_justified_epoch = state.current_justified_epoch
new_finalized_epoch = state.finalized_epoch
antepenultimate_justified_epoch = state.previous_justified_epoch
# Rotate the justification bitfield up one epoch to make room for the current epoch (and limit to 64 bits)
# Process justifications
state.previous_justified_epoch = state.current_justified_epoch
state.previous_justified_root = state.current_justified_root
state.justification_bitfield = (state.justification_bitfield << 1) % 2**64
# If the previous epoch gets justified, fill the second last bit
previous_boundary_attesting_balance = get_attesting_balance(state, get_previous_epoch_boundary_attestations(state))
if previous_boundary_attesting_balance * 3 >= get_previous_total_balance(state) * 2:
new_justified_epoch = get_current_epoch(state) - 1
state.justification_bitfield |= 2
# If the current epoch gets justified, fill the last bit
state.current_justified_epoch = get_previous_epoch(state)
state.current_justified_root = get_block_root(state, get_epoch_start_slot(state.current_justified_epoch))
state.justification_bitfield |= (1 << 1)
current_boundary_attesting_balance = get_attesting_balance(state, get_current_epoch_boundary_attestations(state))
if current_boundary_attesting_balance * 3 >= get_current_total_balance(state) * 2:
new_justified_epoch = get_current_epoch(state)
state.justification_bitfield |= 1
state.current_justified_epoch = get_current_epoch(state)
state.current_justified_root = get_block_root(state, get_epoch_start_slot(state.current_justified_epoch))
state.justification_bitfield |= (1 << 0)
# Process finalizations
bitfield = state.justification_bitfield
current_epoch = get_current_epoch(state)
# The 2nd/3rd/4th most recent epochs are all justified, the 2nd using the 4th as source
if (bitfield >> 1) % 8 == 0b111 and state.previous_justified_epoch == current_epoch - 3:
new_finalized_epoch = state.previous_justified_epoch
# The 2nd/3rd most recent epochs are both justified, the 2nd using the 3rd as source
if (bitfield >> 1) % 4 == 0b11 and state.previous_justified_epoch == current_epoch - 2:
new_finalized_epoch = state.previous_justified_epoch
# The 1st/2nd/3rd most recent epochs are all justified, the 1st using the 3rd as source
if (bitfield >> 0) % 8 == 0b111 and state.current_justified_epoch == current_epoch - 2:
new_finalized_epoch = state.current_justified_epoch
# The 1st/2nd most recent epochs are both justified, the 1st using the 2nd as source
if (bitfield >> 0) % 4 == 0b11 and state.current_justified_epoch == current_epoch - 1:
new_finalized_epoch = state.current_justified_epoch
# Update state jusification/finality fields
state.previous_justified_epoch = state.current_justified_epoch
state.previous_justified_root = state.current_justified_root
if new_justified_epoch != state.current_justified_epoch:
state.current_justified_epoch = new_justified_epoch
state.current_justified_root = get_block_root(state, get_epoch_start_slot(new_justified_epoch))
if new_finalized_epoch != state.finalized_epoch:
state.finalized_epoch = new_finalized_epoch
state.finalized_root = get_block_root(state, get_epoch_start_slot(new_finalized_epoch))
# The 2nd/3rd/4th most recent epochs are justified, the 2nd using the 4th as source
if (bitfield >> 1) % 8 == 0b111 and antepenultimate_justified_epoch == current_epoch - 3:
state.finalized_epoch = antepenultimate_justified_epoch
state.finalized_root = get_block_root(state, get_epoch_start_slot(state.finalized_epoch))
# The 2nd/3rd most recent epochs are justified, the 2nd using the 3rd as source
if (bitfield >> 1) % 4 == 0b11 and antepenultimate_justified_epoch == current_epoch - 2:
state.finalized_epoch = antepenultimate_justified_epoch
state.finalized_root = get_block_root(state, get_epoch_start_slot(state.finalized_epoch))
# The 1st/2nd/3rd most recent epochs are justified, the 1st using the 3rd as source
if (bitfield >> 0) % 8 == 0b111 and state.previous_justified_root == current_epoch - 2:
state.finalized_epoch = state.previous_justified_root
state.finalized_root = get_block_root(state, get_epoch_start_slot(state.finalized_epoch))
# The 1st/2nd most recent epochs are justified, the 1st using the 2nd as source
if (bitfield >> 0) % 4 == 0b11 and state.previous_justified_root == current_epoch - 1:
state.finalized_epoch = state.previous_justified_root
state.finalized_root = get_block_root(state, get_epoch_start_slot(state.finalized_epoch))
```
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