feat: Allow merkle trees of 1 node (its root) (#919)

* feat: change is_power_of_two to allow merkle trees of 1 node (its root) * fix: unit tests * chore: cargo fmt * Update crypto/src/merkle_tree/proof.rs Co-authored-by: Mario Rugiero <[email protected]> --------- Co-authored-by: Diego K <[email protected]> Co-authored-by: Mario Rugiero <[email protected]>
lambdaclass · Sep 27, 2024 · efd46f0 · efd46f0
1 parent 0103cee
commit efd46f0
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Showing 3 changed files with 9 additions and 11 deletions.
diff --git a/crypto/src/merkle_tree/merkle.rs b/crypto/src/merkle_tree/merkle.rs
@@ -123,7 +123,7 @@ mod tests {
 
         let values: Vec<FE> = vec![FE::new(1)]; // Single element
         let merkle_tree = MerkleTree::<TestBackend<U64PF>>::build(&values).unwrap();
-        assert_eq!(merkle_tree.root, FE::new(4)); // Adjusted expected value
+        assert_eq!(merkle_tree.root, FE::new(2)); // Adjusted expected value
     }
 
     #[test]

diff --git a/crypto/src/merkle_tree/proof.rs b/crypto/src/merkle_tree/proof.rs
@@ -163,8 +163,8 @@ mod tests {
         let merkle_tree = MerkleTree::<TestBackend<U64PF>>::build(&values).unwrap();
 
         // Update the expected root value based on the actual logic of TestBackend
-        // For example, if combining two `1`s results in `4`, update this accordingly
-        let expected_root = FE::new(4); // Assuming combining two `1`s results in `4`
+        // For example, in this case hashing a single `1` results in `2`
+        let expected_root = FE::new(2); // Assuming hashing a `1`s results in `2`
         assert_eq!(
             merkle_tree.root, expected_root,
             "The root of the Merkle tree does not match the expected value."

diff --git a/crypto/src/merkle_tree/utils.rs b/crypto/src/merkle_tree/utils.rs
@@ -29,13 +29,12 @@ pub fn complete_until_power_of_two<T: Clone>(mut values: Vec<T>) -> Vec<T> {
 }
 
 // ! NOTE !
-// We in this function we  say 2^0 = 1 is not a power of two when it is infact true. We
-// need this to maintain that the smallest tree at two leaves counts and we could not find
-// a name that wasn't overly verbose. In the case of a single value being present in a leaf node
-// this indicates we pad to next power of two (i.e. 2). The function is private and is only used
-// to ensure the tree has a power of 2 number of leaves.
+// In this function we say 2^0 = 1 is a power of two.
+// In turn, this makes the smallest tree of one leaf, possible.
+// The function is private and is only used to ensure the tree
+// has a power of 2 number of leaves.
 fn is_power_of_two(x: usize) -> bool {
-    (x > 1) && ((x & (x - 1)) == 0)
+    (x & (x - 1)) == 0
 }
 
 // ! CAUTION !
@@ -124,9 +123,8 @@ mod tests {
 
         let mut expected_leaves = vec![FE::new(2)];
         expected_leaves.extend([FE::new(2)]);
-        assert_eq!(hashed_leaves.len(), 2);
+        assert_eq!(hashed_leaves.len(), 1);
         assert_eq!(hashed_leaves[0], expected_leaves[0]);
-        assert_eq!(hashed_leaves[1], expected_leaves[1]);
     }
 
     const ROOT: usize = 0;