119 lines
3.6 KiB
Rust
119 lines
3.6 KiB
Rust
use std::collections::HashSet;
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use std::iter::FromIterator;
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use types::*;
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#[derive(Clone)]
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pub struct WinningRoot {
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pub crosslink_data_root: Hash256,
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pub attesting_validator_indices: Vec<usize>,
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pub total_attesting_balance: u64,
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}
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impl WinningRoot {
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/// Returns `true` if `self` is a "better" candidate than `other`.
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///
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/// A winning root is "better" than another if it has a higher `total_attesting_balance`. Ties
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/// are broken by favouring the lower `crosslink_data_root` value.
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///
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/// Spec v0.4.0
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pub fn is_better_than(&self, other: &Self) -> bool {
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if self.total_attesting_balance > other.total_attesting_balance {
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true
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} else if self.total_attesting_balance == other.total_attesting_balance {
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self.crosslink_data_root < other.crosslink_data_root
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} else {
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false
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}
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}
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}
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/// Returns the `crosslink_data_root` with the highest total attesting balance for the given shard.
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/// Breaks ties by favouring the smaller `crosslink_data_root` hash.
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///
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/// The `WinningRoot` object also contains additional fields that are useful in later stages of
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/// per-epoch processing.
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///
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/// Spec v0.4.0
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pub fn winning_root(
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state: &BeaconState,
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shard: u64,
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current_epoch_attestations: &[&PendingAttestation],
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previous_epoch_attestations: &[&PendingAttestation],
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spec: &ChainSpec,
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) -> Result<Option<WinningRoot>, BeaconStateError> {
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let mut winning_root: Option<WinningRoot> = None;
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let crosslink_data_roots: HashSet<Hash256> = HashSet::from_iter(
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previous_epoch_attestations
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.iter()
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.chain(current_epoch_attestations.iter())
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.filter_map(|a| {
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if a.data.shard == shard {
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Some(a.data.crosslink_data_root)
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} else {
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None
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}
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}),
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);
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for crosslink_data_root in crosslink_data_roots {
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let attesting_validator_indices = get_attesting_validator_indices(
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state,
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shard,
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current_epoch_attestations,
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previous_epoch_attestations,
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&crosslink_data_root,
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spec,
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)?;
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let total_attesting_balance: u64 = attesting_validator_indices
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.iter()
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.fold(0, |acc, i| acc + state.get_effective_balance(*i, spec));
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let candidate = WinningRoot {
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crosslink_data_root,
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attesting_validator_indices,
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total_attesting_balance,
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};
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if let Some(ref winner) = winning_root {
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if candidate.is_better_than(&winner) {
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winning_root = Some(candidate);
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}
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} else {
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winning_root = Some(candidate);
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}
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}
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Ok(winning_root)
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}
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/// Returns all indices which voted for a given crosslink. May contain duplicates.
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///
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/// Spec v0.4.0
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fn get_attesting_validator_indices(
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state: &BeaconState,
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shard: u64,
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current_epoch_attestations: &[&PendingAttestation],
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previous_epoch_attestations: &[&PendingAttestation],
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crosslink_data_root: &Hash256,
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spec: &ChainSpec,
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) -> Result<Vec<usize>, BeaconStateError> {
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let mut indices = vec![];
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for a in current_epoch_attestations
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.iter()
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.chain(previous_epoch_attestations.iter())
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{
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if (a.data.shard == shard) && (a.data.crosslink_data_root == *crosslink_data_root) {
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indices.append(&mut state.get_attestation_participants(
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&a.data,
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&a.aggregation_bitfield,
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spec,
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)?);
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}
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}
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Ok(indices)
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}
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