313 lines
10 KiB
Rust
313 lines
10 KiB
Rust
use super::types::{ShardAndCommittee, ValidatorRecord, ChainConfig};
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use super::TransitionError;
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use super::shuffle;
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use std::cmp::min;
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type DelegatedCycle = Vec<Vec<ShardAndCommittee>>;
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/// Iterator for the honey_badger_split function
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struct Split<'a, T: 'a> {
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n: usize,
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current_pos: usize,
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list: &'a [T],
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list_length: usize
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}
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impl<'a,T> Iterator for Split<'a, T> {
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type Item = &'a [T];
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fn next(&mut self) -> Option<Self::Item> {
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self.current_pos +=1;
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if self.current_pos <= self.n {
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match self.list.get(self.list_length*(self.current_pos-1)/self.n..self.list_length*self.current_pos/self.n) {
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Some(v) => Some(v),
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None => unreachable!()
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}
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}
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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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/// splits a slice into chunks of size n. All postive n values are applicable,
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/// hence the honey_badger prefix.
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/// Returns an iterator over the original list.
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trait SplitExt<T> {
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fn honey_badger_split(&self, n: usize) -> Split<T>;
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}
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impl<T> SplitExt<T> for [T] {
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fn honey_badger_split(&self, n: usize) -> Split<T> {
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Split {
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n,
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current_pos: 0,
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list: &self,
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list_length: self.len(),
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}
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}
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}
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/* Produce a vector of validators indicies where those validators start and end
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* dynasties are within the supplied `dynasty`.
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*/
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fn active_validator_indicies(
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dynasty: u64,
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validators: &[ValidatorRecord])
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-> Vec<usize>
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{
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validators.iter()
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.enumerate()
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.filter_map(|(i, validator)| {
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if (validator.start_dynasty >= dynasty) &
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(validator.end_dynasty < dynasty)
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{
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Some(i)
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} else {
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None
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}
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})
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.collect()
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}
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/*
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* Delegates active validators into slots for a given cycle, given a random seed.
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* Returns a vector or ShardAndComitte vectors representing the shards and committiees for
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* each slot.
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* References get_new_shuffling (ethereum 2.1 specification)
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*/
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pub fn delegate_validators(
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seed: &[u8],
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validators: &[ValidatorRecord],
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dynasty: u64,
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crosslinking_shard_start: u16,
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config: &ChainConfig)
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-> Result<DelegatedCycle, TransitionError>
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{
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let shuffled_validator_indices = {
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let mut validator_indices = active_validator_indicies(dynasty, validators);
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match shuffle(seed, validator_indices) {
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Ok(shuffled) => shuffled,
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_ => return Err(TransitionError::InvalidInput(
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String::from("Shuffle list length exceed.")))
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}
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};
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let shard_indices: Vec<usize> = (0_usize..config.shard_count as usize).into_iter().collect();
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let crosslinking_shard_start = crosslinking_shard_start as usize;
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let cycle_length = config.cycle_length as usize;
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let min_committee_size = config.min_committee_size as usize;
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generate_cycle(
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&shuffled_validator_indices,
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&shard_indices,
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crosslinking_shard_start,
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cycle_length,
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min_committee_size)
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}
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/*
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* Given the validator list, delegates the validators into slots and comittees for a given cycle.
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*/
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fn generate_cycle(
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validator_indices: &[usize],
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shard_indices: &[usize],
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crosslinking_shard_start: usize,
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cycle_length: usize,
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min_committee_size: usize)
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-> Result<DelegatedCycle, TransitionError>
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{
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let validator_count = validator_indices.len();
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let shard_count = shard_indices.len();
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if shard_count / cycle_length == 0 {
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return Err(TransitionError::InvalidInput(String::from("Number of
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shards needs to be greater than
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cycle length")));
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}
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let (committees_per_slot, slots_per_committee) = {
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if validator_count >= cycle_length * min_committee_size {
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let committees_per_slot = min(validator_count / cycle_length /
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(min_committee_size * 2) + 1, shard_count /
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cycle_length);
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let slots_per_committee = 1;
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(committees_per_slot, slots_per_committee)
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} else {
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let committees_per_slot = 1;
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let mut slots_per_committee = 1;
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while (validator_count * slots_per_committee < cycle_length * min_committee_size) &
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(slots_per_committee < cycle_length) {
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slots_per_committee *= 2;
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}
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(committees_per_slot, slots_per_committee)
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}
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};
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let cycle = validator_indices.honey_badger_split(cycle_length)
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.enumerate()
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.map(|(i, slot_indices)| {
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let shard_id_start = crosslinking_shard_start + i * committees_per_slot / slots_per_committee;
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slot_indices.honey_badger_split(committees_per_slot)
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.enumerate()
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.map(|(j, shard_indices)| {
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ShardAndCommittee{
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shard_id: ((shard_id_start + j) % shard_count) as u16,
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committee: shard_indices.to_vec(),
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}
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})
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.collect()
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})
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.collect();
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Ok(cycle)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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fn generate_cycle_helper(
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validator_count: &usize,
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shard_count: &usize,
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crosslinking_shard_start: usize,
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cycle_length: usize,
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min_committee_size: usize)
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-> (Vec<usize>, Vec<usize>, Result<DelegatedCycle, TransitionError>)
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{
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let validator_indices: Vec<usize> = (0_usize..*validator_count).into_iter().collect();
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let shard_indices: Vec<usize> = (0_usize..*shard_count).into_iter().collect();
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let result = generate_cycle(
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&validator_indices,
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&shard_indices,
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crosslinking_shard_start,
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cycle_length,
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min_committee_size);
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(validator_indices, shard_indices, result)
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}
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#[allow(dead_code)]
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fn print_cycle(cycle: &DelegatedCycle) {
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cycle.iter()
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.enumerate()
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.for_each(|(i, slot)| {
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println!("slot {:?}", &i);
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slot.iter()
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.enumerate()
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.for_each(|(i, sac)| {
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println!("#{:?}\tshard_id={}\tcommittee.len()={}",
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&i, &sac.shard_id, &sac.committee.len())
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})
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});
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}
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fn flatten_validators(cycle: &DelegatedCycle)
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-> Vec<usize>
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{
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let mut flattened = vec![];
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for slot in cycle.iter() {
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for sac in slot.iter() {
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for validator in sac.committee.iter() {
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flattened.push(*validator);
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}
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}
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}
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flattened
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}
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fn flatten_and_dedup_shards(cycle: &DelegatedCycle)
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-> Vec<usize>
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{
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let mut flattened = vec![];
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for slot in cycle.iter() {
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for sac in slot.iter() {
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flattened.push(sac.shard_id as usize);
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}
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}
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flattened.dedup();
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flattened
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}
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fn flatten_shards_in_slots(cycle: &DelegatedCycle)
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-> Vec<Vec<usize>>
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{
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let mut shards_in_slots: Vec<Vec<usize>> = vec![];
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for slot in cycle.iter() {
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let mut shards: Vec<usize> = vec![];
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for sac in slot.iter() {
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shards.push(sac.shard_id as usize);
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}
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shards_in_slots.push(shards);
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}
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shards_in_slots
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}
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// TODO: Improve these tests to check committee lengths
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#[test]
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fn test_generate_cycle() {
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let validator_count: usize = 100;
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let shard_count: usize = 20;
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let crosslinking_shard_start: usize = 0;
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let cycle_length: usize = 20;
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let min_committee_size: usize = 10;
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let (validators, shards, result) = generate_cycle_helper(
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&validator_count,
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&shard_count,
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crosslinking_shard_start,
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cycle_length,
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min_committee_size);
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let cycle = result.unwrap();
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let assigned_validators = flatten_validators(&cycle);
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let assigned_shards = flatten_and_dedup_shards(&cycle);
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let shards_in_slots = flatten_shards_in_slots(&cycle);
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let expected_shards = shards.get(0..10).unwrap();
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assert_eq!(assigned_validators, validators, "Validator assignment incorrect");
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assert_eq!(assigned_shards, expected_shards, "Shard assignment incorrect");
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let expected_shards_in_slots: Vec<Vec<usize>> = vec![
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vec![0], vec![0], // Each line is 2 slots..
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vec![1], vec![1],
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vec![2], vec![2],
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vec![3], vec![3],
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vec![4], vec![4],
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vec![5], vec![5],
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vec![6], vec![6],
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vec![7], vec![7],
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vec![8], vec![8],
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vec![9], vec![9],
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];
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// assert!(compare_shards_in_slots(&cycle, &expected_shards_in_slots));
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assert_eq!(expected_shards_in_slots, shards_in_slots, "Shard assignment incorrect.")
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}
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#[test]
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// Check that the committees per slot is upper bounded by shard count
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fn test_generate_cycle_committees_bounded() {
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let validator_count: usize = 523;
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let shard_count: usize = 31;
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let crosslinking_shard_start: usize = 0;
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let cycle_length: usize = 11;
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let min_committee_size: usize = 5;
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let (validators, shards, result) = generate_cycle_helper(
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&validator_count,
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&shard_count,
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crosslinking_shard_start,
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cycle_length,
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min_committee_size);
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let cycle = result.unwrap();
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let assigned_validators = flatten_validators(&cycle);
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let assigned_shards = flatten_and_dedup_shards(&cycle);
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let shards_in_slots = flatten_shards_in_slots(&cycle);
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let expected_shards = shards.get(0..22).unwrap();
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let expected_shards_in_slots: Vec<Vec<usize>> =
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(0_usize..11_usize) .map(|x| vec![2*x,2*x+1]).collect();
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assert_eq!(assigned_validators, validators, "Validator assignment incorrect");
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assert_eq!(assigned_shards, expected_shards, "Shard assignment incorrect");
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// assert!(compare_shards_in_slots(&cycle, &expected_shards_in_slots));
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assert_eq!(expected_shards_in_slots, shards_in_slots, "Shard assignment incorrect.")
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}
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}
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