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mmr: support arbitrary from/to delta updates

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This commit is contained in:
Augusto F. Hack
2023-10-27 19:53:50 +02:00
committed by Bobbin Threadbare
parent 5f2d170435
commit a8acc0b39d
2 changed files with 68 additions and 26 deletions
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30
src/merkle/mmr/full.rs
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@@ -164,32 +164,32 @@ impl Mmr {
///
/// The result is a packed sequence of the authentication elements required to update the trees
/// that have been merged together, followed by the new peaks of the [Mmr].
pub fn get_delta(&self, original_forest: usize) -> Result<MmrDelta, MmrError> {
if original_forest > self.forest {
pub fn get_delta(&self, from_forest: usize, to_forest: usize) -> Result<MmrDelta, MmrError> {
if to_forest > self.forest || from_forest > to_forest {
return Err(MmrError::InvalidPeaks);
}
if original_forest == self.forest {
return Ok(MmrDelta { forest: self.forest, data: Vec::new() });
if from_forest == to_forest {
return Ok(MmrDelta { forest: to_forest, data: Vec::new() });
}
let mut result = Vec::new();
// Find the largest tree in this [Mmr] which is new to `original_forest`.
let candidate_trees = self.forest ^ original_forest;
// Find the largest tree in this [Mmr] which is new to `from_forest`.
let candidate_trees = to_forest ^ from_forest;
let mut new_high = 1 << candidate_trees.ilog2();
// Collect authentication nodes used for tree merges
// ----------------------------------------------------------------------------------------
// Find the trees from `original_forest` that have been merged into `new_high`.
let mut merges = original_forest & (new_high - 1);
// Find the trees from `from_forest` that have been merged into `new_high`.
let mut merges = from_forest & (new_high - 1);
// Find the peaks that are common to `original_forest` and this [Mmr]
let common_trees = original_forest ^ merges;
// Find the peaks that are common to `from_forest` and this [Mmr]
let common_trees = from_forest ^ merges;
if merges != 0 {
// Skip the smallest trees unknown to `original_forest`.
// Skip the smallest trees unknown to `from_forest`.
let mut target = 1 << merges.trailing_zeros();
// Collect siblings required to computed the merged tree's peak
@@ -214,15 +214,15 @@ impl Mmr {
}
} else {
// The new high tree may not be the result of any merges, if it is smaller than all the
// trees of `original_forest`.
// trees of `from_forest`.
new_high = 0;
}
// Collect the new [Mmr] peaks
// ----------------------------------------------------------------------------------------
let mut new_peaks = self.forest ^ common_trees ^ new_high;
let old_peaks = self.forest ^ new_peaks;
let mut new_peaks = to_forest ^ common_trees ^ new_high;
let old_peaks = to_forest ^ new_peaks;
let mut offset = nodes_in_forest(old_peaks);
while new_peaks != 0 {
let target = 1 << new_peaks.ilog2();
@@ -231,7 +231,7 @@ impl Mmr {
new_peaks ^= target;
}
Ok(MmrDelta { forest: self.forest, data: result })
Ok(MmrDelta { forest: to_forest, data: result })
}
/// An iterator over inner nodes in the MMR. The order of iteration is unspecified.