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spec: implement get_epoch_start_shard v0.6.1

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Michael Sproul 2019-05-14 15:37:40 +10:00
parent 79de966d3a
commit 45506ded5d
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GPG Key ID: 77B1309D2E54E914
1 changed files with 18 additions and 4 deletions
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22
eth2/types/src/beacon_state.rs
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@ -301,9 +301,23 @@ impl<T: EthSpec> BeaconState<T> {
)
}
pub fn get_epoch_start_shard(&self, epoch: Epoch, spec: &ChainSpec) -> u64 {
drop((epoch, spec));
unimplemented!("FIXME(sproul) get_epoch_start_shard")
/// Return the start shard for an epoch less than or equal to the next epoch.
///
/// Spec v0.6.1
pub fn get_epoch_start_shard(&self, epoch: Epoch, spec: &ChainSpec) -> Result<u64, Error> {
if epoch > self.current_epoch(spec) + 1 {
return Err(Error::EpochOutOfBounds);
}
let shard_count = T::ShardCount::to_u64();
let mut check_epoch = self.current_epoch(spec) + 1;
let mut shard = (self.latest_start_shard
+ self.get_shard_delta(self.current_epoch(spec), spec))
% shard_count;
while check_epoch > epoch {
check_epoch -= 1;
shard = (shard + shard_count - self.get_shard_delta(check_epoch, spec)) % shard_count;
}
Ok(shard)
}
/// Get the slot of an attestation.
@ -317,7 +331,7 @@ impl<T: EthSpec> BeaconState<T> {
let epoch = attestation_data.target_epoch;
let committee_count = self.get_epoch_committee_count(epoch, spec);
let offset = (attestation_data.shard + spec.shard_count
- self.get_epoch_start_shard(epoch, spec))
- self.get_epoch_start_shard(epoch, spec)?)
% spec.shard_count;
Ok(epoch.start_slot(spec.slots_per_epoch)
+ offset / (committee_count / spec.slots_per_epoch))