106 lines
3.5 KiB
Rust
106 lines
3.5 KiB
Rust
/// The representation of a single Merkle path.
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use super::super::MerklePath;
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use super::{full::high_bitmask, leaf_to_corresponding_tree};
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// MMR PROOF
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// ================================================================================================
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#[derive(Debug, Clone, PartialEq)]
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#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
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pub struct MmrProof {
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/// The state of the MMR when the MmrProof was created.
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pub forest: usize,
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/// The position of the leaf value on this MmrProof.
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pub position: usize,
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/// The Merkle opening, starting from the value's sibling up to and excluding the root of the
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/// responsible tree.
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pub merkle_path: MerklePath,
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}
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impl MmrProof {
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/// Converts the leaf global position into a local position that can be used to verify the
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/// merkle_path.
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pub fn relative_pos(&self) -> usize {
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let tree_bit = leaf_to_corresponding_tree(self.position, self.forest)
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.expect("position must be part of the forest");
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let forest_before = self.forest & high_bitmask(tree_bit + 1);
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self.position - forest_before
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}
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/// Returns index of the MMR peak against which the Merkle path in this proof can be verified.
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pub fn peak_index(&self) -> usize {
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let root = leaf_to_corresponding_tree(self.position, self.forest)
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.expect("position must be part of the forest");
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let smaller_peak_mask = 2_usize.pow(root) as usize - 1;
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let num_smaller_peaks = (self.forest & smaller_peak_mask).count_ones();
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(self.forest.count_ones() - num_smaller_peaks - 1) as usize
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}
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}
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// TESTS
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// ================================================================================================
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#[cfg(test)]
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mod tests {
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use super::{MerklePath, MmrProof};
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#[test]
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fn test_peak_index() {
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// --- single peak forest ---------------------------------------------
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let forest = 11;
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// the first 4 leaves belong to peak 0
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for position in 0..8 {
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let proof = make_dummy_proof(forest, position);
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assert_eq!(proof.peak_index(), 0);
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}
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// --- forest with non-consecutive peaks ------------------------------
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let forest = 11;
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// the first 8 leaves belong to peak 0
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for position in 0..8 {
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let proof = make_dummy_proof(forest, position);
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assert_eq!(proof.peak_index(), 0);
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}
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// the next 2 leaves belong to peak 1
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for position in 8..10 {
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let proof = make_dummy_proof(forest, position);
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assert_eq!(proof.peak_index(), 1);
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}
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// the last leaf is the peak 2
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let proof = make_dummy_proof(forest, 10);
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assert_eq!(proof.peak_index(), 2);
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// --- forest with consecutive peaks ----------------------------------
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let forest = 7;
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// the first 4 leaves belong to peak 0
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for position in 0..4 {
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let proof = make_dummy_proof(forest, position);
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assert_eq!(proof.peak_index(), 0);
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}
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// the next 2 leaves belong to peak 1
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for position in 4..6 {
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let proof = make_dummy_proof(forest, position);
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assert_eq!(proof.peak_index(), 1);
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}
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// the last leaf is the peak 2
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let proof = make_dummy_proof(forest, 6);
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assert_eq!(proof.peak_index(), 2);
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}
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fn make_dummy_proof(forest: usize, position: usize) -> MmrProof {
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MmrProof {
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forest,
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position,
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merkle_path: MerklePath::default(),
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}
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}
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}
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