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Separate out get_switchover_epoch #868

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merged 2 commits into from
Apr 11, 2019
Merged

Separate out get_switchover_epoch #868

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bb990e9
Separate out get_switchover_epoch
vbuterin Mar 31, 2019
c4321c7
Update 1_shard-data-chains.md
JustinDrake Apr 2, 2019
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17 changes: 12 additions & 5 deletions specs/core/1_shard-data-chains.md
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
- [`ShardAttestation`](#shardattestation)
- [Helper functions](#helper-functions)
- [`get_period_committee`](#get_period_committee)
- [`get_switchover_epoch`](#get_switchover_epoch)
- [`get_persistent_committee`](#get_persistent_committee)
- [`get_shard_proposer_index`](#get_shard_proposer_index)
- [`get_shard_header`](#get_shard_header)
Expand Down Expand Up @@ -137,6 +138,14 @@ def get_period_committee(state: BeaconState,
)
```

### `get_switchover_epoch`

```python
def get_switchover_epoch(state: BeaconState, epoch: Epoch, index: ValidatorIndex):
earlier_start_epoch = epoch - (epoch % PERSISTENT_COMMITTEE_PERIOD) - PERSISTENT_COMMITTEE_PERIOD * 2
return bytes_to_int(hash(generate_seed(state, earlier_start_epoch) + bytes3(index))[0:8]) % PERSISTENT_COMMITTEE_PERIOD
```

### `get_persistent_committee`

```python
Expand All @@ -146,6 +155,7 @@ def get_persistent_committee(state: BeaconState,
"""
Return the persistent committee for the given ``shard`` at the given ``slot``.
"""
epoch = slot_to_epoch(slot)
earlier_start_epoch = epoch - (epoch % PERSISTENT_COMMITTEE_PERIOD) - PERSISTENT_COMMITTEE_PERIOD * 2
later_start_epoch = epoch - (epoch % PERSISTENT_COMMITTEE_PERIOD) - PERSISTENT_COMMITTEE_PERIOD

Expand All @@ -160,14 +170,11 @@ def get_persistent_committee(state: BeaconState,
earlier_committee = get_period_committee(state, shard, earlier_start_epoch, index, committee_count)
later_committee = get_period_committee(state, shard, later_start_epoch, index, committee_count)

def get_switchover_epoch(index):
return bytes_to_int(hash(earlier_seed + bytes3(index))[0:8]) % PERSISTENT_COMMITTEE_PERIOD

# Take not-yet-cycled-out validators from earlier committee and already-cycled-in validators from
# later committee; return a sorted list of the union of the two, deduplicated
return sorted(list(set(
[i for i in earlier_committee if epoch % PERSISTENT_COMMITTEE_PERIOD < get_switchover_epoch(i)] +
[i for i in later_committee if epoch % PERSISTENT_COMMITTEE_PERIOD >= get_switchover_epoch(i)]
[i for i in earlier_committee if epoch % PERSISTENT_COMMITTEE_PERIOD < get_switchover_epoch(state, epoch, i)] +
[i for i in later_committee if epoch % PERSISTENT_COMMITTEE_PERIOD >= get_switchover_epoch(state, epoch, i)]
)))
```

Expand Down