Struct PositionalLineageHash 

pub struct PositionalLineageHash(/* private fields */);

A 128-bit positional lineage hash encoding parental lineage for tree traversal.

Layout (using full 128 bits):

• Mode (2 bits): Determines position field size
• Position (8/16/24 bits): Block position in sequence
• Current Sequence Hash (64 bits): Full u64 sequence hash for this block
• Parent Fragment (variable bits): Truncated lower bits of the parent’s sequence hash

Modes (automatically selected based on position):

• Mode 00: 8-bit position (max 255) + 64-bit current + 54-bit parent fragment
• Mode 01: 16-bit position (max 65,535) + 64-bit current + 46-bit parent fragment
• Mode 10: 24-bit position (max 16,777,215) + 64-bit current + 38-bit parent fragment

Carrying the full 64-bit current sequence hash inline makes PLH self-contained for chain extension: a child PLH can be derived from a parent PLH plus the child’s BlockHash alone, with no out-of-band state. The parent fragment shrinks as position grows, but radix backward-traversal always matches on (position, parent_fragment), and the probability of a shared parent at high positions decreases faster than the fragment-collision bound rises.

Implementations

impl PositionalLineageHash

pub fn new( current_seq_hash: SequenceHash, parent_seq_hash: Option<SequenceHash>, position: u64, ) -> Self

Creates a new PositionalLineageHash from components.

The mode is automatically selected based on the position value to use the minimal representation that can fit the position.

Arguments

• current_seq_hash - The full u64 sequence hash of the current block
• parent_seq_hash - The full u64 sequence hash of the parent block (None for root). Will be truncated to this position’s parent-fragment width.
• position - The block position in the sequence

Panics

Panics if position >= 2^24 (16,777,216).

pub fn root(block_hash: BlockHash) -> Self

Creates a root PositionalLineageHash (position 0).

At the root, the sequence hash equals the block hash and there is no parent.

pub fn extend(&self, child_block_hash: BlockHash) -> Self

Extends this lineage by one block, producing the child PLH.

The chain recurrence is compute_next_sequence_hash. Salt does not seed the per-step xxh3: BlockHash is already xxh3(tokens, salt_hash), so salt is mixed into seq_hash[0] and propagates through every parent. Re-feeding it at each step would be redundant.

Panics

Panics if self.position() + 1 >= 2^24.

pub fn position(&self) -> u64

Returns the block position.

pub fn current_sequence_hash(&self) -> SequenceHash

Returns the full 64-bit sequence hash of the current block.

Unlike the legacy current_hash_fragment (now removed), this is the complete SequenceHash and is what extend feeds into the chain.

pub fn parent_hash_fragment(&self) -> u64

Returns the parent sequence hash fragment as stored in this PLH.

Width depends on this PLH’s mode (54/46/38 bits). Backward radix lookup must always combine (position, parent_fragment) — the fragment alone is not unique.

pub fn parent_fragment_for_child_position(&self, child_position: u64) -> u64

Truncates this PLH’s current_sequence_hash to the parent-fragment width that a child at child_position would store.

Useful when an external builder wants to construct a child PLH or verify a parent/child edge: child.parent_hash_fragment() == parent.parent_fragment_for_child_position(child.position()).

pub fn mode(&self) -> u8

Returns the mode used for encoding (0, 1, or 2).

pub fn as_u128(&self) -> u128

Returns the inner 128-bit value.

Trait Implementations

impl Clone for PositionalLineageHash

fn clone(&self) -> PositionalLineageHash

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for PositionalLineageHash

impl Debug for PositionalLineageHash

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for PositionalLineageHash

fn default() -> PositionalLineageHash

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for PositionalLineageHash

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Display for PositionalLineageHash

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for PositionalLineageHash

impl Hash for PositionalLineageHash

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for PositionalLineageHash

fn cmp(&self, other: &Self) -> Ordering

Lexicographic order: Self::position, then Self::current_sequence_hash, then the full packed Self::as_u128 so the order is total and consistent with Eq.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for PositionalLineageHash

fn eq(&self, other: &PositionalLineageHash) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl PartialOrd for PositionalLineageHash

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl PositionalHash for PositionalLineageHash

fn position(&self) -> u64

Returns the position associated with the hash.

impl Serialize for PositionalLineageHash

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for PositionalLineageHash