beacon: justification and finalization

beacon/src/executive/transition/per_epoch/justification.rs

+use crate::types::*;
+use crate::{Config, BeaconState, Error};
+
+impl<C: Config> BeaconState<C> {
+	/// Update casper justification and finalization.
+	pub fn process_justification_and_finalization(&mut self) -> Result<(), Error> {
+		if self.current_epoch() <= C::genesis_epoch() + 1 {
+			return Ok(())
+		}
+
+		let previous_epoch = self.previous_epoch();
+		let current_epoch = self.current_epoch();
+		let old_previous_justified_checkpoint = self.previous_justified_checkpoint.clone();
+		let old_current_justified_checkpoint = self.current_justified_checkpoint.clone();;
+
+		// Process justifications
+		self.previous_justified_checkpoint = self.current_justified_checkpoint.clone();
+		let old_justification_bits = self.justification_bits.clone();
+		let justification_bits_len = self.justification_bits.len();
+		self.justification_bits[1..].copy_from_slice(
+			&old_justification_bits[0..(justification_bits_len - 1)]
+		);
+		self.justification_bits[0] = false;
+		let matching_target_attestations =
+			self.matching_target_attestations(previous_epoch)?;
+		if self.attesting_balance(&matching_target_attestations)? * 3 >=
+			self.total_active_balance() * 2
+		{
+			self.current_justified_checkpoint = Checkpoint {
+				epoch: previous_epoch,
+				root: self.block_root(previous_epoch)?
+			};
+			self.justification_bits[1] = true;
+		}
+		let matching_target_attestations =
+			self.matching_target_attestations(current_epoch)?;
+		if self.attesting_balance(&matching_target_attestations)? * 3 >=
+			self.total_active_balance() * 2
+		{
+			self.current_justified_checkpoint = Checkpoint {
+				epoch: current_epoch,
+				root: self.block_root(current_epoch)?
+			};
+			self.justification_bits[0] = true;
+		}
+
+		// Process finalizations
+		let bits = self.justification_bits.clone();
+		// The 2nd/3rd/4th most recent epochs are justified,
+		// the 2nd using the 4th as source
+		if bits[1..4].iter().all(|v| *v) &&
+			old_previous_justified_checkpoint.epoch + 3 == current_epoch
+		{
+			self.finalized_checkpoint = old_previous_justified_checkpoint.clone();
+		}
+		// The 2nd/3rd most recent epochs are justified,
+		// the 2nd using the 3rd as source
+		if bits[1..3].iter().all(|v| *v) &&
+			old_previous_justified_checkpoint.epoch + 2 == current_epoch
+		{
+			self.finalized_checkpoint = old_previous_justified_checkpoint.clone();
+		}
+		// The 1st/2nd/3rd most recent epochs are justified,
+		// the 1st using the 3rd as source
+		if bits[0..3].iter().all(|v| *v) &&
+			old_current_justified_checkpoint.epoch + 2 == current_epoch
+		{
+			self.finalized_checkpoint = old_current_justified_checkpoint.clone();
+		}
+		// The 1st/2nd most recent epochs are justified,
+		// the 1st using the 2nd as source
+		if bits[0..2].iter().all(|v| *v) &&
+			old_current_justified_checkpoint.epoch + 1 == current_epoch
+		{
+			self.finalized_checkpoint = old_current_justified_checkpoint.clone();
+		}
+
+		Ok(())
+	}
+}

beacon/src/executive/transition/per_epoch/mod.rs

 mod helpers;
+mod justification;