add get_value() to SparseMerkleTree trait

src/merkle/smt/full/mod.rs

@@ -249,6 +249,15 @@ impl SparseMerkleTree<SMT_DEPTH> for Smt {
         }
     }
 
+    fn get_value(&self, key: &RpoDigest) -> Word {
+        let leaf_pos = LeafIndex::<SMT_DEPTH>::from(*key).value();
+
+        self.leaves
+            .get(&leaf_pos)
+            .map(|leaf| leaf.get_value(key).unwrap_or_default())
+            .unwrap_or_default()
+    }
+
     fn get_leaf(&self, key: &RpoDigest) -> Self::Leaf {
         let leaf_pos = LeafIndex::<SMT_DEPTH>::from(*key).value();
 

src/merkle/smt/mod.rs

@@ -157,6 +157,9 @@ pub(crate) trait SparseMerkleTree<const DEPTH: u8> {
     /// Inserts a leaf node, and returns the value at the key if already exists
     fn insert_value(&mut self, key: Self::Key, value: Self::Value) -> Option<Self::Value>;
 
+    /// Returns the value at the specified key, without modifying the tree.
+    fn get_value(&self, key: &Self::Key) -> Self::Value;
+
     /// Returns the leaf at the specified index.
     fn get_leaf(&self, key: &Self::Key) -> Self::Leaf;
 

src/merkle/smt/simple/mod.rs

@@ -288,6 +288,13 @@ impl<const DEPTH: u8> SparseMerkleTree<DEPTH> for SimpleSmt<DEPTH> {
         }
     }
 
+    fn get_value(&self, key: &LeafIndex<DEPTH>) -> Word {
+        let leaf_pos = key.value();
+
+        *self.leaves.get(&leaf_pos)
+            .unwrap_or(&Self::EMPTY_VALUE)
+    }
+
     fn get_leaf(&self, key: &LeafIndex<DEPTH>) -> Word {
         let leaf_pos = key.value();
         match self.leaves.get(&leaf_pos) {