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bitfield for PTC votes

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This commit is contained in:
hopinheimer
2026-03-16 02:30:35 -04:00
parent d89e7f78bb
commit f747696113
7 changed files with 235 additions and 236 deletions
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193
consensus/proto_array/src/proto_array.rs
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@@ -129,9 +129,16 @@ pub struct ProtoNode {
pub full_payload_weight: u64,
#[superstruct(only(V29), partial_getter(copy))]
pub execution_payload_block_hash: ExecutionBlockHash,
/// Tiebreaker for payload preference when full_payload_weight == empty_payload_weight.
#[superstruct(only(V29), partial_getter(copy))]
pub payload_tiebreak: PayloadTiebreak,
/// PTC timeliness vote bitfield, indexed by PTC committee position.
/// Bit i set means PTC member i voted `payload_present = true`.
/// Tiebreak derived as: `count_ones() > ptc_size / 2`.
#[superstruct(only(V29))]
pub payload_timeliness_votes: Vec<u8>,
/// PTC data availability vote bitfield, indexed by PTC committee position.
/// Bit i set means PTC member i voted `blob_data_available = true`.
/// Tiebreak derived as: `count_ones() > ptc_size / 2`.
#[superstruct(only(V29))]
pub payload_data_availability_votes: Vec<u8>,
}
#[derive(PartialEq, Debug, Encode, Decode, Serialize, Deserialize, Copy, Clone)]
@@ -154,7 +161,6 @@ pub struct NodeDelta {
pub delta: i64,
pub empty_delta: i64,
pub full_delta: i64,
pub payload_tiebreaker: Option<PayloadTiebreak>,
}
impl NodeDelta {
@@ -192,6 +198,15 @@ impl NodeDelta {
Ok(())
}
/// Create a delta that only affects the aggregate `delta` field.
pub fn from_delta(delta: i64) -> Self {
Self {
delta,
empty_delta: 0,
full_delta: 0,
}
}
/// Subtract a balance from the appropriate payload status.
pub fn sub_payload_delta(
&mut self,
@@ -211,21 +226,14 @@ impl NodeDelta {
}
}
/// Compare NodeDelta with i64 by comparing the aggregate `delta` field.
/// This is used by tests that only care about the total weight delta.
impl PartialEq<i64> for NodeDelta {
fn eq(&self, other: &i64) -> bool {
self.delta == *other
&& self.empty_delta == 0
&& self.full_delta == 0
&& self.payload_tiebreaker.is_none()
}
}
#[derive(Clone, Copy, PartialEq, Eq, Debug, Default, Encode, Decode, Serialize, Deserialize)]
pub struct PayloadTiebreak {
pub is_timely: bool,
pub is_data_available: bool,
}
#[derive(PartialEq, Debug, Serialize, Deserialize, Clone)]
pub struct ProtoArray {
/// Do not attempt to prune the tree unless it has at least this many nodes. Small prunes
@@ -363,9 +371,6 @@ impl ProtoArray {
apply_delta(node.empty_payload_weight, node_empty_delta, node_index)?;
node.full_payload_weight =
apply_delta(node.full_payload_weight, node_full_delta, node_index)?;
if let Some(payload_tiebreaker) = node_delta.payload_tiebreaker {
node.payload_tiebreak = payload_tiebreaker;
}
}
// Update the parent delta (if any).
@@ -535,7 +540,8 @@ impl ProtoArray {
empty_payload_weight: 0,
full_payload_weight: 0,
execution_payload_block_hash,
payload_tiebreak: PayloadTiebreak::default(),
payload_timeliness_votes: empty_ptc_bitfield(E::ptc_size()),
payload_data_availability_votes: empty_ptc_bitfield(E::ptc_size()),
})
};
@@ -593,10 +599,10 @@ impl ProtoArray {
let v29 = node
.as_v29_mut()
.map_err(|_| Error::InvalidNodeVariant { block_root })?;
v29.payload_tiebreak = PayloadTiebreak {
is_timely: true,
is_data_available: true,
};
// A valid execution payload means the payload is timely and data is available.
// Set all bits to ensure the threshold is met regardless of PTC size.
v29.payload_timeliness_votes.fill(0xFF);
v29.payload_data_availability_votes.fill(0xFF);
Ok(())
}
@@ -1062,72 +1068,79 @@ impl ProtoArray {
);
let no_change = (parent.best_child(), parent.best_descendant());
let (new_best_child, new_best_descendant) = if let Some(best_child_index) =
parent.best_child()
{
if best_child_index == child_index && !child_leads_to_viable_head {
// If the child is already the best-child of the parent but it's not viable for
// the head, remove it.
change_to_none
} else if best_child_index == child_index {
// If the child is the best-child already, set it again to ensure that the
// best-descendant of the parent is updated.
change_to_child
} else {
let best_child = self
.nodes
.get(best_child_index)
.ok_or(Error::InvalidBestDescendant(best_child_index))?;
let best_child_leads_to_viable_head = self.node_leads_to_viable_head::<E>(
best_child,
current_slot,
best_justified_checkpoint,
best_finalized_checkpoint,
)?;
if child_leads_to_viable_head && !best_child_leads_to_viable_head {
// The child leads to a viable head, but the current best-child doesn't.
let (new_best_child, new_best_descendant) =
if let Some(best_child_index) = parent.best_child() {
if best_child_index == child_index && !child_leads_to_viable_head {
// If the child is already the best-child of the parent but it's not viable for
// the head, remove it.
change_to_none
} else if best_child_index == child_index {
// If the child is the best-child already, set it again to ensure that the
// best-descendant of the parent is updated.
change_to_child
} else if !child_leads_to_viable_head && best_child_leads_to_viable_head {
// The best child leads to a viable head, but the child doesn't.
no_change
} else if child.weight() > best_child.weight() {
// Weight is the primary ordering criterion.
change_to_child
} else if child.weight() < best_child.weight() {
no_change
} else {
// Equal weights: for V29 parents, prefer the child whose
// parent_payload_status matches the parent's payload preference
// (full vs empty). This corresponds to the spec's
// `get_payload_status_tiebreaker` ordering in `get_head`.
let child_matches =
child_matches_parent_payload_preference(parent, child, current_slot);
let best_child_matches =
child_matches_parent_payload_preference(parent, best_child, current_slot);
let best_child = self
.nodes
.get(best_child_index)
.ok_or(Error::InvalidBestDescendant(best_child_index))?;
if child_matches && !best_child_matches {
// Child extends the preferred payload chain, best_child doesn't.
let best_child_leads_to_viable_head = self.node_leads_to_viable_head::<E>(
best_child,
current_slot,
best_justified_checkpoint,
best_finalized_checkpoint,
)?;
if child_leads_to_viable_head && !best_child_leads_to_viable_head {
// The child leads to a viable head, but the current best-child doesn't.
change_to_child
} else if !child_matches && best_child_matches {
// Best child extends the preferred payload chain, child doesn't.
} else if !child_leads_to_viable_head && best_child_leads_to_viable_head {
// The best child leads to a viable head, but the child doesn't.
no_change
} else if *child.root() >= *best_child.root() {
// Final tie-breaker: both match or both don't, break by root.
} else if child.weight() > best_child.weight() {
// Weight is the primary ordering criterion.
change_to_child
} else if child.weight() < best_child.weight() {
no_change
} else {
no_change
// Equal weights: for V29 parents, prefer the child whose
// parent_payload_status matches the parent's payload preference
// (full vs empty). This corresponds to the spec's
// `get_payload_status_tiebreaker` ordering in `get_head`.
let child_matches = child_matches_parent_payload_preference(
parent,
child,
current_slot,
E::ptc_size(),
);
let best_child_matches = child_matches_parent_payload_preference(
parent,
best_child,
current_slot,
E::ptc_size(),
);
if child_matches && !best_child_matches {
// Child extends the preferred payload chain, best_child doesn't.
change_to_child
} else if !child_matches && best_child_matches {
// Best child extends the preferred payload chain, child doesn't.
no_change
} else if *child.root() >= *best_child.root() {
// Final tie-breaker: both match or both don't, break by root.
change_to_child
} else {
no_change
}
}
}
}
} else if child_leads_to_viable_head {
// There is no current best-child and the child is viable.
change_to_child
} else {
// There is no current best-child but the child is not viable.
no_change
};
} else if child_leads_to_viable_head {
// There is no current best-child and the child is viable.
change_to_child
} else {
// There is no current best-child but the child is not viable.
no_change
};
let parent = self
.nodes
@@ -1393,6 +1406,7 @@ fn child_matches_parent_payload_preference(
parent: &ProtoNode,
child: &ProtoNode,
current_slot: Slot,
ptc_size: usize,
) -> bool {
let (Ok(parent_v29), Ok(child_v29)) = (parent.as_v29(), child.as_v29()) else {
return true;
@@ -1410,7 +1424,8 @@ fn child_matches_parent_payload_preference(
false
} else {
// Equal weights (or current-slot parent): tiebreaker per spec.
parent_v29.payload_tiebreak.is_timely && parent_v29.payload_tiebreak.is_data_available
is_payload_timely(&parent_v29.payload_timeliness_votes, ptc_size)
&& is_payload_data_available(&parent_v29.payload_data_availability_votes, ptc_size)
};
if prefers_full {
child_v29.parent_payload_status == PayloadStatus::Full
@@ -1419,6 +1434,26 @@ fn child_matches_parent_payload_preference(
}
}
/// Count the number of set bits in a byte-slice bitfield.
pub fn count_set_bits(bitfield: &[u8]) -> usize {
bitfield.iter().map(|b| b.count_ones() as usize).sum()
}
/// Create a zero-initialized bitfield for the given PTC size.
pub fn empty_ptc_bitfield(ptc_size: usize) -> Vec<u8> {
vec![0u8; ptc_size.div_ceil(8)]
}
/// Derive `is_payload_timely` from the timeliness vote bitfield.
pub fn is_payload_timely(timeliness_votes: &[u8], ptc_size: usize) -> bool {
count_set_bits(timeliness_votes) > ptc_size / 2
}
/// Derive `is_payload_data_available` from the data availability vote bitfield.
pub fn is_payload_data_available(availability_votes: &[u8], ptc_size: usize) -> bool {
count_set_bits(availability_votes) > ptc_size / 2
}
/// A helper method to calculate the proposer boost based on the given `justified_balances`.
///
/// https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/fork-choice.md#get_latest_attesting_balance