zec
/
incrementalmerkletree
mirror of https://github.com/zcash/incrementalmerkletree.git
1
0
Fork 0
Code Issues Projects Releases Wiki Activity

incrementalmerkletree: Refactor `Address::common_ancestor`

This commit is contained in:
Jack Grigg 2023-07-06 12:37:33 +00:00
parent 1292d478b6
commit 0eff26f313
1 changed files with 16 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
incrementalmerkletree/src/lib.rs
View File

@ -384,22 +384,23 @@ impl Address {
/// Returns the common ancestor of `self` and `other` having the smallest level value.
pub fn common_ancestor(&self, other: &Self) -> Self {
if self.level >= other.level {
let other_ancestor_idx = other.index >> (self.level.0 - other.level.0);
let index_delta = self.index ^ other_ancestor_idx;
let level_delta = (u64::BITS - index_delta.leading_zeros()) as u8;
Address {
level: self.level + level_delta,
index: std::cmp::max(self.index, other_ancestor_idx) >> level_delta,
}
// We can leverage the symmetry of a binary tree to share the calculation logic,
// by ordering the nodes.
let (higher, lower) = if self.level >= other.level {
(self, other)
} else {
let self_ancestor_idx = self.index >> (other.level.0 - self.level.0);
let index_delta = other.index ^ self_ancestor_idx;
let level_delta = (u64::BITS - index_delta.leading_zeros()) as u8;
Address {
level: other.level + level_delta,
index: std::cmp::max(other.index, self_ancestor_idx) >> level_delta,
}
(other, self)
};
// We follow the lower node's subtree up to the same level as the higher node, and
// then use their XOR distance to determine how many levels of the tree their
// Merkle paths differ on.
let lower_ancestor_idx = lower.index >> (higher.level.0 - lower.level.0);
let index_delta = higher.index ^ lower_ancestor_idx;
let level_delta = (u64::BITS - index_delta.leading_zeros()) as u8;
Address {
level: higher.level + level_delta,
index: std::cmp::max(higher.index, lower_ancestor_idx) >> level_delta,
}
}