Merge pull request #157 from 0xPolygonMiden/tohrnii-digest

refactor: refactor crypto APIs to use RpoDigest instead of Word

benches/store.rs

@@ -409,7 +409,7 @@ fn update_leaf_merkletree(c: &mut Criterion) {
                     // The MerkleTree automatically updates its internal root, the Store maintains
                     // the old root and adds the new one. Here we update the root to have a fair
                     // comparison
-                    store_root = store.set_node(root, index, value).unwrap().root;
+                    store_root = store.set_node(root, index, value.into()).unwrap().root;
                     black_box(store_root)
                 },
                 BatchSize::SmallInput,
@@ -455,7 +455,7 @@ fn update_leaf_simplesmt(c: &mut Criterion) {
                     // The MerkleTree automatically updates its internal root, the Store maintains
                     // the old root and adds the new one. Here we update the root to have a fair
                     // comparison
-                    store_root = store.set_node(root, index, value).unwrap().root;
+                    store_root = store.set_node(root, index, value.into()).unwrap().root;
                     black_box(store_root)
                 },
                 BatchSize::SmallInput,

src/hash/rpo/tests.rs

@@ -2,7 +2,10 @@ use super::{
     Felt, FieldElement, Hasher, Rpo256, RpoDigest, StarkField, ALPHA, INV_ALPHA, ONE, STATE_WIDTH,
     ZERO,
 };
-use crate::utils::collections::{BTreeSet, Vec};
+use crate::{
+    utils::collections::{BTreeSet, Vec},
+    Word,
+};
 use core::convert::TryInto;
 use proptest::prelude::*;
 use rand_utils::rand_value;
@@ -232,7 +235,7 @@ proptest! {
     }
 }
 
-const EXPECTED: [[Felt; 4]; 19] = [
+const EXPECTED: [Word; 19] = [
     [
         Felt::new(1502364727743950833),
         Felt::new(5880949717274681448),

src/merkle/merkle_tree.rs

@@ -1,11 +1,6 @@
-use super::{
-    Felt, InnerNodeInfo, MerkleError, MerklePath, NodeIndex, Rpo256, RpoDigest, Vec, Word,
-};
-use crate::{
-    utils::{string::String, uninit_vector, word_to_hex},
-    FieldElement,
-};
-use core::{fmt, slice};
+use super::{InnerNodeInfo, MerkleError, MerklePath, NodeIndex, Rpo256, RpoDigest, Vec, Word};
+use crate::utils::{string::String, uninit_vector, word_to_hex};
+use core::{fmt, ops::Deref, slice};
 use winter_math::log2;
 
 // MERKLE TREE
@@ -14,7 +9,7 @@ use winter_math::log2;
 /// A fully-balanced binary Merkle tree (i.e., a tree where the number of leaves is a power of two).
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct MerkleTree {
-    nodes: Vec<Word>,
+    nodes: Vec<RpoDigest>,
 }
 
 impl MerkleTree {
@@ -34,10 +29,12 @@ impl MerkleTree {
 
         // create un-initialized vector to hold all tree nodes
         let mut nodes = unsafe { uninit_vector(2 * n) };
-        nodes[0] = [Felt::ZERO; 4];
+        nodes[0] = RpoDigest::default();
 
         // copy leaves into the second part of the nodes vector
-        nodes[n..].copy_from_slice(&leaves);
+        nodes[n..].iter_mut().zip(leaves).for_each(|(node, leaf)| {
+            *node = RpoDigest::from(leaf);
+        });
 
         // re-interpret nodes as an array of two nodes fused together
         // Safety: `nodes` will never move here as it is not bound to an external lifetime (i.e.
@@ -47,7 +44,7 @@ impl MerkleTree {
 
         // calculate all internal tree nodes
         for i in (1..n).rev() {
-            nodes[i] = Rpo256::merge(&pairs[i]).into();
+            nodes[i] = Rpo256::merge(&pairs[i]);
         }
 
         Ok(Self { nodes })
@@ -57,7 +54,7 @@ impl MerkleTree {
     // --------------------------------------------------------------------------------------------
 
     /// Returns the root of this Merkle tree.
-    pub fn root(&self) -> Word {
+    pub fn root(&self) -> RpoDigest {
         self.nodes[1]
     }
 
@@ -74,7 +71,7 @@ impl MerkleTree {
     /// Returns an error if:
     /// * The specified depth is greater than the depth of the tree.
     /// * The specified index is not valid for the specified depth.
-    pub fn get_node(&self, index: NodeIndex) -> Result<Word, MerkleError> {
+    pub fn get_node(&self, index: NodeIndex) -> Result<RpoDigest, MerkleError> {
         if index.is_root() {
             return Err(MerkleError::DepthTooSmall(index.depth()));
         } else if index.depth() > self.depth() {
@@ -120,7 +117,11 @@ impl MerkleTree {
     /// Returns an iterator over the leaves of this [MerkleTree].
     pub fn leaves(&self) -> impl Iterator<Item = (u64, &Word)> {
         let leaves_start = self.nodes.len() / 2;
-        self.nodes.iter().skip(leaves_start).enumerate().map(|(i, v)| (i as u64, v))
+        self.nodes
+            .iter()
+            .skip(leaves_start)
+            .enumerate()
+            .map(|(i, v)| (i as u64, v.deref()))
     }
 
     /// Returns n iterator over every inner node of this [MerkleTree].
@@ -159,13 +160,13 @@ impl MerkleTree {
 
         // update the current node
         let pos = index.to_scalar_index() as usize;
-        self.nodes[pos] = value;
+        self.nodes[pos] = value.into();
 
         // traverse to the root, updating each node with the merged values of its parents
         for _ in 0..index.depth() {
             index.move_up();
             let pos = index.to_scalar_index() as usize;
-            let value = Rpo256::merge(&pairs[pos]).into();
+            let value = Rpo256::merge(&pairs[pos]);
             self.nodes[pos] = value;
         }
 
@@ -180,7 +181,7 @@ impl MerkleTree {
 ///
 /// Use this to extract the data of the tree, there is no guarantee on the order of the elements.
 pub struct InnerNodeIterator<'a> {
-    nodes: &'a Vec<Word>,
+    nodes: &'a Vec<RpoDigest>,
     index: usize,
 }
 
@@ -258,13 +259,17 @@ pub fn path_to_text(path: &MerklePath) -> Result {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::merkle::{int_to_node, InnerNodeInfo};
+    use crate::{
+        merkle::{digests_to_words, int_to_leaf, int_to_node, InnerNodeInfo},
+        Felt, Word, WORD_SIZE,
+    };
     use core::mem::size_of;
     use proptest::prelude::*;
 
-    const LEAVES4: [Word; 4] = [int_to_node(1), int_to_node(2), int_to_node(3), int_to_node(4)];
+    const LEAVES4: [RpoDigest; WORD_SIZE] =
+        [int_to_node(1), int_to_node(2), int_to_node(3), int_to_node(4)];
 
-    const LEAVES8: [Word; 8] = [
+    const LEAVES8: [RpoDigest; 8] = [
         int_to_node(1),
         int_to_node(2),
         int_to_node(3),
@@ -277,12 +282,12 @@ mod tests {
 
     #[test]
     fn build_merkle_tree() {
-        let tree = super::MerkleTree::new(LEAVES4.to_vec()).unwrap();
+        let tree = super::MerkleTree::new(digests_to_words(&LEAVES4)).unwrap();
         assert_eq!(8, tree.nodes.len());
 
         // leaves were copied correctly
         for (a, b) in tree.nodes.iter().skip(4).zip(LEAVES4.iter()) {
-            assert_eq!(a, b);
+            assert_eq!(*a, RpoDigest::from(*b));
         }
 
         let (root, node2, node3) = compute_internal_nodes();
@@ -296,7 +301,7 @@ mod tests {
 
     #[test]
     fn get_leaf() {
-        let tree = super::MerkleTree::new(LEAVES4.to_vec()).unwrap();
+        let tree = super::MerkleTree::new(digests_to_words(&LEAVES4)).unwrap();
 
         // check depth 2
         assert_eq!(LEAVES4[0], tree.get_node(NodeIndex::make(2, 0)).unwrap());
@@ -313,7 +318,7 @@ mod tests {
 
     #[test]
     fn get_path() {
-        let tree = super::MerkleTree::new(LEAVES4.to_vec()).unwrap();
+        let tree = super::MerkleTree::new(digests_to_words(&LEAVES4)).unwrap();
 
         let (_, node2, node3) = compute_internal_nodes();
 
@@ -330,13 +335,13 @@ mod tests {
 
     #[test]
     fn update_leaf() {
-        let mut tree = super::MerkleTree::new(LEAVES8.to_vec()).unwrap();
+        let mut tree = super::MerkleTree::new(digests_to_words(&LEAVES8)).unwrap();
 
         // update one leaf
         let value = 3;
-        let new_node = int_to_node(9);
-        let mut expected_leaves = LEAVES8.to_vec();
-        expected_leaves[value as usize] = new_node;
+        let new_node = int_to_leaf(9);
+        let mut expected_leaves = digests_to_words(&LEAVES8);
+        expected_leaves[value as usize] = new_node.into();
         let expected_tree = super::MerkleTree::new(expected_leaves.clone()).unwrap();
 
         tree.update_leaf(value, new_node).unwrap();
@@ -344,7 +349,7 @@ mod tests {
 
         // update another leaf
         let value = 6;
-        let new_node = int_to_node(10);
+        let new_node = int_to_leaf(10);
         expected_leaves[value as usize] = new_node;
         let expected_tree = super::MerkleTree::new(expected_leaves.clone()).unwrap();
 
@@ -354,7 +359,7 @@ mod tests {
 
     #[test]
     fn nodes() -> Result<(), MerkleError> {
-        let tree = super::MerkleTree::new(LEAVES4.to_vec()).unwrap();
+        let tree = super::MerkleTree::new(digests_to_words(&LEAVES4)).unwrap();
         let root = tree.root();
         let l1n0 = tree.get_node(NodeIndex::make(1, 0))?;
         let l1n1 = tree.get_node(NodeIndex::make(1, 1))?;
@@ -417,11 +422,13 @@ mod tests {
     // HELPER FUNCTIONS
     // --------------------------------------------------------------------------------------------
 
-    fn compute_internal_nodes() -> (Word, Word, Word) {
-        let node2 = Rpo256::hash_elements(&[LEAVES4[0], LEAVES4[1]].concat());
-        let node3 = Rpo256::hash_elements(&[LEAVES4[2], LEAVES4[3]].concat());
+    fn compute_internal_nodes() -> (RpoDigest, RpoDigest, RpoDigest) {
+        let node2 =
+            Rpo256::hash_elements(&[Word::from(LEAVES4[0]), Word::from(LEAVES4[1])].concat());
+        let node3 =
+            Rpo256::hash_elements(&[Word::from(LEAVES4[2]), Word::from(LEAVES4[3])].concat());
         let root = Rpo256::merge(&[node2, node3]);
 
-        (root.into(), node2.into(), node3.into())
+        (root, node2, node3)
     }
 }

src/merkle/mmr/accumulator.rs

@@ -1,4 +1,7 @@
-use super::{super::Vec, super::ZERO, Felt, MmrProof, Rpo256, Word};
+use super::{
+    super::{RpoDigest, Vec, ZERO},
+    Felt, MmrProof, Rpo256, Word,
+};
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct MmrPeaks {
@@ -25,7 +28,7 @@ pub struct MmrPeaks {
     /// leaves, starting from the peak with most children, to the one with least.
     ///
     /// Invariant: The length of `peaks` must be equal to the number of true bits in `num_leaves`.
-    pub peaks: Vec<Word>,
+    pub peaks: Vec<RpoDigest>,
 }
 
 impl MmrPeaks {
@@ -38,7 +41,7 @@ impl MmrPeaks {
         Rpo256::hash_elements(&self.flatten_and_pad_peaks()).into()
     }
 
-    pub fn verify(&self, value: Word, opening: MmrProof) -> bool {
+    pub fn verify(&self, value: RpoDigest, opening: MmrProof) -> bool {
         let root = &self.peaks[opening.peak_index()];
         opening.merkle_path.verify(opening.relative_pos() as u64, value, root)
     }
@@ -72,7 +75,15 @@ impl MmrPeaks {
         };
 
         let mut elements = Vec::with_capacity(len);
-        elements.extend_from_slice(&self.peaks.as_slice().concat());
+        elements.extend_from_slice(
+            &self
+                .peaks
+                .as_slice()
+                .iter()
+                .map(|digest| digest.into())
+                .collect::<Vec<Word>>()
+                .concat(),
+        );
         elements.resize(len, ZERO);
         elements
     }

src/merkle/mmr/full.rs

@@ -10,10 +10,10 @@
 //! depths, i.e. as part of adding adding a new element to the forest the trees with same depth are
 //! merged, creating a new tree with depth d+1, this process is continued until the property is
 //! restabilished.
-use super::bit::TrueBitPositionIterator;
 use super::{
-    super::{InnerNodeInfo, MerklePath, Vec},
-    MmrPeaks, MmrProof, Rpo256, Word,
+    super::{InnerNodeInfo, MerklePath, RpoDigest, Vec},
+    bit::TrueBitPositionIterator,
+    MmrPeaks, MmrProof, Rpo256,
 };
 use core::fmt::{Display, Formatter};
 
@@ -38,7 +38,7 @@ pub struct Mmr {
     /// the elements of every tree in the forest to be stored in the same sequential buffer. It
     /// also means new elements can be added to the forest, and merging of trees is very cheap with
     /// no need to copy elements.
-    pub(super) nodes: Vec<Word>,
+    pub(super) nodes: Vec<RpoDigest>,
 }
 
 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
@@ -129,7 +129,7 @@ impl Mmr {
     /// Note: The leaf position is the 0-indexed number corresponding to the order the leaves were
     /// added, this corresponds to the MMR size _prior_ to adding the element. So the 1st element
     /// has position 0, the second position 1, and so on.
-    pub fn get(&self, pos: usize) -> Result<Word, MmrError> {
+    pub fn get(&self, pos: usize) -> Result<RpoDigest, MmrError> {
         // find the target tree responsible for the MMR position
         let tree_bit =
             leaf_to_corresponding_tree(pos, self.forest).ok_or(MmrError::InvalidPosition(pos))?;
@@ -153,7 +153,7 @@ impl Mmr {
     }
 
     /// Adds a new element to the MMR.
-    pub fn add(&mut self, el: Word) {
+    pub fn add(&mut self, el: RpoDigest) {
         // Note: every node is also a tree of size 1, adding an element to the forest creates a new
         // rooted-tree of size 1. This may temporarily break the invariant that every tree in the
         // forest has different sizes, the loop below will eagerly merge trees of same size and
@@ -164,7 +164,7 @@ impl Mmr {
         let mut right = el;
         let mut left_tree = 1;
         while self.forest & left_tree != 0 {
-            right = *Rpo256::merge(&[self.nodes[left_offset].into(), right.into()]);
+            right = Rpo256::merge(&[self.nodes[left_offset], right]);
             self.nodes.push(right);
 
             left_offset = left_offset.saturating_sub(nodes_in_forest(left_tree));
@@ -176,7 +176,7 @@ impl Mmr {
 
     /// Returns an accumulator representing the current state of the MMR.
     pub fn accumulator(&self) -> MmrPeaks {
-        let peaks: Vec<Word> = TrueBitPositionIterator::new(self.forest)
+        let peaks: Vec<RpoDigest> = TrueBitPositionIterator::new(self.forest)
             .rev()
             .map(|bit| nodes_in_forest(1 << bit))
             .scan(0, |offset, el| {
@@ -212,7 +212,7 @@ impl Mmr {
         relative_pos: usize,
         index_offset: usize,
         mut index: usize,
-    ) -> (Word, Vec<Word>) {
+    ) -> (RpoDigest, Vec<RpoDigest>) {
         // collect the Merkle path
         let mut tree_depth = tree_bit as usize;
         let mut path = Vec::with_capacity(tree_depth + 1);
@@ -247,7 +247,7 @@ impl Mmr {
 
 impl<T> From<T> for Mmr
 where
-    T: IntoIterator<Item = Word>,
+    T: IntoIterator<Item = RpoDigest>,
 {
     fn from(values: T) -> Self {
         let mut mmr = Mmr::new();

src/merkle/mmr/tests.rs

@@ -1,10 +1,14 @@
-use super::bit::TrueBitPositionIterator;
-use super::full::{high_bitmask, leaf_to_corresponding_tree, nodes_in_forest};
 use super::{
-    super::{InnerNodeInfo, Vec, WORD_SIZE, ZERO},
-    Mmr, MmrPeaks, Rpo256, Word,
+    super::{InnerNodeInfo, Vec},
+    bit::TrueBitPositionIterator,
+    full::{high_bitmask, leaf_to_corresponding_tree, nodes_in_forest},
+    Mmr, MmrPeaks, Rpo256,
+};
+use crate::{
+    hash::rpo::RpoDigest,
+    merkle::{int_to_node, MerklePath},
+    Felt, Word,
 };
-use crate::merkle::{int_to_node, MerklePath};
 
 #[test]
 fn test_position_equal_or_higher_than_leafs_is_never_contained() {
@@ -99,7 +103,7 @@ fn test_nodes_in_forest_single_bit() {
     }
 }
 
-const LEAVES: [Word; 7] = [
+const LEAVES: [RpoDigest; 7] = [
     int_to_node(0),
     int_to_node(1),
     int_to_node(2),
@@ -114,14 +118,14 @@ fn test_mmr_simple() {
     let mut postorder = Vec::new();
     postorder.push(LEAVES[0]);
     postorder.push(LEAVES[1]);
-    postorder.push(*Rpo256::hash_elements(&[LEAVES[0], LEAVES[1]].concat()));
+    postorder.push(Rpo256::merge(&[LEAVES[0], LEAVES[1]]));
     postorder.push(LEAVES[2]);
     postorder.push(LEAVES[3]);
-    postorder.push(*Rpo256::hash_elements(&[LEAVES[2], LEAVES[3]].concat()));
-    postorder.push(*Rpo256::hash_elements(&[postorder[2], postorder[5]].concat()));
+    postorder.push(Rpo256::merge(&[LEAVES[2], LEAVES[3]]));
+    postorder.push(Rpo256::merge(&[postorder[2], postorder[5]]));
     postorder.push(LEAVES[4]);
     postorder.push(LEAVES[5]);
-    postorder.push(*Rpo256::hash_elements(&[LEAVES[4], LEAVES[5]].concat()));
+    postorder.push(Rpo256::merge(&[LEAVES[4], LEAVES[5]]));
     postorder.push(LEAVES[6]);
 
     let mut mmr = Mmr::new();
@@ -195,8 +199,8 @@ fn test_mmr_simple() {
 #[test]
 fn test_mmr_open() {
     let mmr: Mmr = LEAVES.into();
-    let h01: Word = Rpo256::hash_elements(&LEAVES[0..2].concat()).into();
-    let h23: Word = Rpo256::hash_elements(&LEAVES[2..4].concat()).into();
+    let h01 = Rpo256::merge(&[LEAVES[0], LEAVES[1]]);
+    let h23 = Rpo256::merge(&[LEAVES[2], LEAVES[3]]);
 
     // node at pos 7 is the root
     assert!(mmr.open(7).is_err(), "Element 7 is not in the tree, result should be None");
@@ -214,7 +218,7 @@ fn test_mmr_open() {
         "MmrProof should be valid for the current accumulator."
     );
 
-    // nodes 4,5 are detph 1
+    // nodes 4,5 are depth 1
     let root_to_path = MerklePath::new(vec![LEAVES[4]]);
     let opening = mmr
         .open(5)
@@ -361,10 +365,10 @@ fn test_mmr_inner_nodes() {
     let mmr: Mmr = LEAVES.into();
     let nodes: Vec<InnerNodeInfo> = mmr.inner_nodes().collect();
 
-    let h01 = *Rpo256::hash_elements(&[LEAVES[0], LEAVES[1]].concat());
-    let h23 = *Rpo256::hash_elements(&[LEAVES[2], LEAVES[3]].concat());
-    let h0123 = *Rpo256::hash_elements(&[h01, h23].concat());
-    let h45 = *Rpo256::hash_elements(&[LEAVES[4], LEAVES[5]].concat());
+    let h01 = Rpo256::merge(&[LEAVES[0], LEAVES[1]]);
+    let h23 = Rpo256::merge(&[LEAVES[2], LEAVES[3]]);
+    let h0123 = Rpo256::merge(&[h01, h23]);
+    let h45 = Rpo256::merge(&[LEAVES[4], LEAVES[5]]);
     let postorder = vec![
         InnerNodeInfo {
             value: h01,
@@ -396,17 +400,20 @@ fn test_mmr_hash_peaks() {
     let mmr: Mmr = LEAVES.into();
     let peaks = mmr.accumulator();
 
-    let first_peak = *Rpo256::merge(&[
-        Rpo256::hash_elements(&[LEAVES[0], LEAVES[1]].concat()),
-        Rpo256::hash_elements(&[LEAVES[2], LEAVES[3]].concat()),
+    let first_peak = Rpo256::merge(&[
+        Rpo256::merge(&[LEAVES[0], LEAVES[1]]),
+        Rpo256::merge(&[LEAVES[2], LEAVES[3]]),
     ]);
-    let second_peak = *Rpo256::hash_elements(&[LEAVES[4], LEAVES[5]].concat());
+    let second_peak = Rpo256::merge(&[LEAVES[4], LEAVES[5]]);
     let third_peak = LEAVES[6];
 
     // minimum length is 16
     let mut expected_peaks = [first_peak, second_peak, third_peak].to_vec();
-    expected_peaks.resize(16, [ZERO; WORD_SIZE]);
-    assert_eq!(peaks.hash_peaks(), *Rpo256::hash_elements(&expected_peaks.as_slice().concat()));
+    expected_peaks.resize(16, RpoDigest::default());
+    assert_eq!(
+        peaks.hash_peaks(),
+        *Rpo256::hash_elements(&digests_to_elements(&expected_peaks))
+    );
 }
 
 #[test]
@@ -422,10 +429,10 @@ fn test_mmr_peaks_hash_less_than_16() {
 
         // minimum length is 16
         let mut expected_peaks = peaks.clone();
-        expected_peaks.resize(16, [ZERO; WORD_SIZE]);
+        expected_peaks.resize(16, RpoDigest::default());
         assert_eq!(
             accumulator.hash_peaks(),
-            *Rpo256::hash_elements(&expected_peaks.as_slice().concat())
+            *Rpo256::hash_elements(&digests_to_elements(&expected_peaks))
         );
     }
 }
@@ -441,10 +448,10 @@ fn test_mmr_peaks_hash_odd() {
 
     // odd length bigger than 16 is padded to the next even nubmer
     let mut expected_peaks = peaks.clone();
-    expected_peaks.resize(18, [ZERO; WORD_SIZE]);
+    expected_peaks.resize(18, RpoDigest::default());
     assert_eq!(
         accumulator.hash_peaks(),
-        *Rpo256::hash_elements(&expected_peaks.as_slice().concat())
+        *Rpo256::hash_elements(&digests_to_elements(&expected_peaks))
     );
 }
 
@@ -476,3 +483,10 @@ mod property_tests {
         }
     }
 }
+
+// HELPER FUNCTIONS
+// ================================================================================================
+
+fn digests_to_elements(digests: &[RpoDigest]) -> Vec<Felt> {
+    digests.iter().flat_map(|v| Word::from(v)).collect()
+}

src/merkle/mod.rs

@@ -10,7 +10,6 @@ use core::fmt;
 
 mod empty_roots;
 pub use empty_roots::EmptySubtreeRoots;
-use empty_roots::EMPTY_WORD;
 
 mod index;
 pub use index::NodeIndex;
@@ -44,7 +43,7 @@ pub use node::InnerNodeInfo;
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum MerkleError {
-    ConflictingRoots(Vec<Word>),
+    ConflictingRoots(Vec<RpoDigest>),
     DepthTooSmall(u8),
     DepthTooBig(u64),
     DuplicateValuesForIndex(u64),
@@ -54,9 +53,9 @@ pub enum MerkleError {
     InvalidPath(MerklePath),
     InvalidNumEntries(usize, usize),
     NodeNotInSet(NodeIndex),
-    NodeNotInStore(Word, NodeIndex),
+    NodeNotInStore(RpoDigest, NodeIndex),
     NumLeavesNotPowerOfTwo(usize),
-    RootNotInStore(Word),
+    RootNotInStore(RpoDigest),
 }
 
 impl fmt::Display for MerkleError {
@@ -95,6 +94,16 @@ impl std::error::Error for MerkleError {}
 // ================================================================================================
 
 #[cfg(test)]
-const fn int_to_node(value: u64) -> Word {
+const fn int_to_node(value: u64) -> RpoDigest {
+    RpoDigest::new([Felt::new(value), ZERO, ZERO, ZERO])
+}
+
+#[cfg(test)]
+const fn int_to_leaf(value: u64) -> Word {
     [Felt::new(value), ZERO, ZERO, ZERO]
 }
+
+#[cfg(test)]
+fn digests_to_words(digests: &[RpoDigest]) -> Vec<Word> {
+    digests.iter().map(|d| d.into()).collect()
+}

src/merkle/node.rs

@@ -1,9 +1,9 @@
-use super::Word;
+use crate::hash::rpo::RpoDigest;
 
 /// Representation of a node with two children used for iterating over containers.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct InnerNodeInfo {
-    pub value: Word,
-    pub left: Word,
-    pub right: Word,
+    pub value: RpoDigest,
+    pub left: RpoDigest,
+    pub right: RpoDigest,
 }

src/merkle/path.rs

@@ -1,4 +1,4 @@
-use super::{vec, InnerNodeInfo, MerkleError, NodeIndex, Rpo256, Vec, Word};
+use super::{vec, InnerNodeInfo, MerkleError, NodeIndex, Rpo256, RpoDigest, Vec};
 use core::ops::{Deref, DerefMut};
 
 // MERKLE PATH
@@ -7,7 +7,7 @@ use core::ops::{Deref, DerefMut};
 /// A merkle path container, composed of a sequence of nodes of a Merkle tree.
 #[derive(Clone, Debug, Default, PartialEq, Eq)]
 pub struct MerklePath {
-    nodes: Vec<Word>,
+    nodes: Vec<RpoDigest>,
 }
 
 impl MerklePath {
@@ -15,7 +15,7 @@ impl MerklePath {
     // --------------------------------------------------------------------------------------------
 
     /// Creates a new Merkle path from a list of nodes.
-    pub fn new(nodes: Vec<Word>) -> Self {
+    pub fn new(nodes: Vec<RpoDigest>) -> Self {
         Self { nodes }
     }
 
@@ -28,13 +28,13 @@ impl MerklePath {
     }
 
     /// Computes the merkle root for this opening.
-    pub fn compute_root(&self, index: u64, node: Word) -> Result<Word, MerkleError> {
+    pub fn compute_root(&self, index: u64, node: RpoDigest) -> Result<RpoDigest, MerkleError> {
         let mut index = NodeIndex::new(self.depth(), index)?;
         let root = self.nodes.iter().copied().fold(node, |node, sibling| {
             // compute the node and move to the next iteration.
-            let input = index.build_node(node.into(), sibling.into());
+            let input = index.build_node(node, sibling);
             index.move_up();
-            Rpo256::merge(&input).into()
+            Rpo256::merge(&input)
         });
         Ok(root)
     }
@@ -42,7 +42,7 @@ impl MerklePath {
     /// Verifies the Merkle opening proof towards the provided root.
     ///
     /// Returns `true` if `node` exists at `index` in a Merkle tree with `root`.
-    pub fn verify(&self, index: u64, node: Word, root: &Word) -> bool {
+    pub fn verify(&self, index: u64, node: RpoDigest, root: &RpoDigest) -> bool {
         match self.compute_root(index, node) {
             Ok(computed_root) => root == &computed_root,
             Err(_) => false,
@@ -55,7 +55,11 @@ impl MerklePath {
     ///
     /// # Errors
     /// Returns an error if the specified index is not valid for this path.
-    pub fn inner_nodes(&self, index: u64, node: Word) -> Result<InnerNodeIterator, MerkleError> {
+    pub fn inner_nodes(
+        &self,
+        index: u64,
+        node: RpoDigest,
+    ) -> Result<InnerNodeIterator, MerkleError> {
         Ok(InnerNodeIterator {
             nodes: &self.nodes,
             index: NodeIndex::new(self.depth(), index)?,
@@ -64,8 +68,8 @@ impl MerklePath {
     }
 }
 
-impl From<Vec<Word>> for MerklePath {
-    fn from(path: Vec<Word>) -> Self {
+impl From<Vec<RpoDigest>> for MerklePath {
+    fn from(path: Vec<RpoDigest>) -> Self {
         Self::new(path)
     }
 }
@@ -73,7 +77,7 @@ impl From> for MerklePath {
 impl Deref for MerklePath {
     // we use `Vec` here instead of slice so we can call vector mutation methods directly from the
     // merkle path (example: `Vec::remove`).
-    type Target = Vec<Word>;
+    type Target = Vec<RpoDigest>;
 
     fn deref(&self) -> &Self::Target {
         &self.nodes
@@ -89,15 +93,15 @@ impl DerefMut for MerklePath {
 // ITERATORS
 // ================================================================================================
 
-impl FromIterator<Word> for MerklePath {
-    fn from_iter<T: IntoIterator<Item = Word>>(iter: T) -> Self {
+impl FromIterator<RpoDigest> for MerklePath {
+    fn from_iter<T: IntoIterator<Item = RpoDigest>>(iter: T) -> Self {
         Self::new(iter.into_iter().collect())
     }
 }
 
 impl IntoIterator for MerklePath {
-    type Item = Word;
-    type IntoIter = vec::IntoIter<Word>;
+    type Item = RpoDigest;
+    type IntoIter = vec::IntoIter<RpoDigest>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.nodes.into_iter()
@@ -106,9 +110,9 @@ impl IntoIterator for MerklePath {
 
 /// An iterator over internal nodes of a [MerklePath].
 pub struct InnerNodeIterator<'a> {
-    nodes: &'a Vec<Word>,
+    nodes: &'a Vec<RpoDigest>,
     index: NodeIndex,
-    value: Word,
+    value: RpoDigest,
 }
 
 impl<'a> Iterator for InnerNodeIterator<'a> {
@@ -123,7 +127,7 @@ impl<'a> Iterator for InnerNodeIterator<'a> {
                 (self.value, self.nodes[sibling_pos])
             };
 
-            self.value = Rpo256::merge(&[left.into(), right.into()]).into();
+            self.value = Rpo256::merge(&[left, right]);
             self.index.move_up();
 
             Some(InnerNodeInfo {
@@ -144,7 +148,7 @@ impl<'a> Iterator for InnerNodeIterator<'a> {
 #[derive(Clone, Debug, Default, PartialEq, Eq)]
 pub struct ValuePath {
     /// The node value opening for `path`.
-    pub value: Word,
+    pub value: RpoDigest,
     /// The path from `value` to `root` (exclusive).
     pub path: MerklePath,
 }
@@ -156,7 +160,7 @@ pub struct ValuePath {
 #[derive(Clone, Debug, Default, PartialEq, Eq)]
 pub struct RootPath {
     /// The node value opening for `path`.
-    pub root: Word,
+    pub root: RpoDigest,
     /// The path from `value` to `root` (exclusive).
     pub path: MerklePath,
 }

src/merkle/path_set.rs

@@ -1,4 +1,5 @@
-use super::{BTreeMap, MerkleError, MerklePath, NodeIndex, Rpo256, ValuePath, Vec, Word, ZERO};
+use super::{BTreeMap, MerkleError, MerklePath, NodeIndex, Rpo256, ValuePath, Vec};
+use crate::{hash::rpo::RpoDigest, Word};
 
 // MERKLE PATH SET
 // ================================================================================================
@@ -6,7 +7,7 @@ use super::{BTreeMap, MerkleError, MerklePath, NodeIndex, Rpo256, ValuePath, Vec
 /// A set of Merkle paths.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct MerklePathSet {
-    root: Word,
+    root: RpoDigest,
     total_depth: u8,
     paths: BTreeMap<u64, MerklePath>,
 }
@@ -17,7 +18,7 @@ impl MerklePathSet {
 
     /// Returns an empty MerklePathSet.
     pub fn new(depth: u8) -> Self {
-        let root = [ZERO; 4];
+        let root = RpoDigest::default();
         let paths = BTreeMap::new();
 
         Self {
@@ -32,10 +33,10 @@ impl MerklePathSet {
     /// Analogous to `[Self::add_path]`.
     pub fn with_paths<I>(self, paths: I) -> Result<Self, MerkleError>
     where
-        I: IntoIterator<Item = (u64, Word, MerklePath)>,
+        I: IntoIterator<Item = (u64, RpoDigest, MerklePath)>,
     {
         paths.into_iter().try_fold(self, |mut set, (index, value, path)| {
-            set.add_path(index, value, path)?;
+            set.add_path(index, value.into(), path)?;
             Ok(set)
         })
     }
@@ -44,7 +45,7 @@ impl MerklePathSet {
     // --------------------------------------------------------------------------------------------
 
     /// Returns the root to which all paths in this set resolve.
-    pub const fn root(&self) -> Word {
+    pub const fn root(&self) -> RpoDigest {
         self.root
     }
 
@@ -61,7 +62,7 @@ impl MerklePathSet {
     /// Returns an error if:
     /// * The specified index is not valid for the depth of structure.
     /// * Requested node does not exist in the set.
-    pub fn get_node(&self, index: NodeIndex) -> Result<Word, MerkleError> {
+    pub fn get_node(&self, index: NodeIndex) -> Result<RpoDigest, MerkleError> {
         if index.depth() != self.total_depth {
             return Err(MerkleError::InvalidDepth {
                 expected: self.total_depth,
@@ -84,7 +85,7 @@ impl MerklePathSet {
     /// * Leaf with the requested path does not exist in the set.
     pub fn get_leaf(&self, index: u64) -> Result<Word, MerkleError> {
         let index = NodeIndex::new(self.depth(), index)?;
-        self.get_node(index)
+        Ok(self.get_node(index)?.into())
     }
 
     /// Returns a Merkle path to the node at the specified index. The node itself is
@@ -163,18 +164,18 @@ impl MerklePathSet {
 
         // update the current path
         let parity = index_value & 1;
-        path.insert(parity as usize, value);
+        path.insert(parity as usize, value.into());
 
         // traverse to the root, updating the nodes
-        let root: Word = Rpo256::merge(&[path[0].into(), path[1].into()]).into();
+        let root = Rpo256::merge(&[path[0], path[1]]);
         let root = path.iter().skip(2).copied().fold(root, |root, hash| {
             index.move_up();
-            Rpo256::merge(&index.build_node(root.into(), hash.into())).into()
+            Rpo256::merge(&index.build_node(root, hash))
         });
 
         // if the path set is empty (the root is all ZEROs), set the root to the root of the added
         // path; otherwise, the root of the added path must be identical to the current root
-        if self.root == [ZERO; 4] {
+        if self.root == RpoDigest::default() {
             self.root = root;
         } else if self.root != root {
             return Err(MerkleError::ConflictingRoots([self.root, root].to_vec()));
@@ -203,24 +204,24 @@ impl MerklePathSet {
         // Fill old_hashes vector -----------------------------------------------------------------
         let mut current_index = index;
         let mut old_hashes = Vec::with_capacity(path.len().saturating_sub(2));
-        let mut root: Word = Rpo256::merge(&[path[0].into(), path[1].into()]).into();
+        let mut root = Rpo256::merge(&[path[0], path[1]]);
         for hash in path.iter().skip(2).copied() {
             old_hashes.push(root);
             current_index.move_up();
-            let input = current_index.build_node(hash.into(), root.into());
-            root = Rpo256::merge(&input).into();
+            let input = current_index.build_node(hash, root);
+            root = Rpo256::merge(&input);
         }
 
         // Fill new_hashes vector -----------------------------------------------------------------
-        path[index.is_value_odd() as usize] = value;
+        path[index.is_value_odd() as usize] = value.into();
 
         let mut new_hashes = Vec::with_capacity(path.len().saturating_sub(2));
-        let mut new_root: Word = Rpo256::merge(&[path[0].into(), path[1].into()]).into();
+        let mut new_root = Rpo256::merge(&[path[0], path[1]]);
         for path_hash in path.iter().skip(2).copied() {
             new_hashes.push(new_root);
             index.move_up();
-            let input = current_index.build_node(path_hash.into(), new_root.into());
-            new_root = Rpo256::merge(&input).into();
+            let input = current_index.build_node(path_hash, new_root);
+            new_root = Rpo256::merge(&input);
         }
 
         self.root = new_root;
@@ -245,7 +246,7 @@ impl MerklePathSet {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::merkle::int_to_node;
+    use crate::merkle::{int_to_leaf, int_to_node};
 
     #[test]
     fn get_root() {
@@ -318,20 +319,20 @@ mod tests {
             ])
             .unwrap();
 
-        let new_hash_6 = int_to_node(100);
-        let new_hash_5 = int_to_node(55);
+        let new_hash_6 = int_to_leaf(100);
+        let new_hash_5 = int_to_leaf(55);
 
         set.update_leaf(index_6, new_hash_6).unwrap();
         let new_path_4 = set.get_path(NodeIndex::make(depth, index_4)).unwrap();
-        let new_hash_67 = calculate_parent_hash(new_hash_6, 14_u64, hash_7);
+        let new_hash_67 = calculate_parent_hash(new_hash_6.into(), 14_u64, hash_7);
         assert_eq!(new_hash_67, new_path_4[1]);
 
         set.update_leaf(index_5, new_hash_5).unwrap();
         let new_path_4 = set.get_path(NodeIndex::make(depth, index_4)).unwrap();
         let new_path_6 = set.get_path(NodeIndex::make(depth, index_6)).unwrap();
-        let new_hash_45 = calculate_parent_hash(new_hash_5, 13_u64, hash_4);
+        let new_hash_45 = calculate_parent_hash(new_hash_5.into(), 13_u64, hash_4);
         assert_eq!(new_hash_45, new_path_6[1]);
-        assert_eq!(new_hash_5, new_path_4[0]);
+        assert_eq!(RpoDigest::from(new_hash_5), new_path_4[0]);
     }
 
     #[test]
@@ -345,13 +346,13 @@ mod tests {
         let g = int_to_node(7);
         let h = int_to_node(8);
 
-        let i = Rpo256::merge(&[a.into(), b.into()]);
-        let j = Rpo256::merge(&[c.into(), d.into()]);
-        let k = Rpo256::merge(&[e.into(), f.into()]);
-        let l = Rpo256::merge(&[g.into(), h.into()]);
+        let i = Rpo256::merge(&[a, b]);
+        let j = Rpo256::merge(&[c, d]);
+        let k = Rpo256::merge(&[e, f]);
+        let l = Rpo256::merge(&[g, h]);
 
-        let m = Rpo256::merge(&[i.into(), j.into()]);
-        let n = Rpo256::merge(&[k.into(), l.into()]);
+        let m = Rpo256::merge(&[i, j]);
+        let n = Rpo256::merge(&[k, l]);
 
         let root = Rpo256::merge(&[m.into(), n.into()]);
 
@@ -359,31 +360,31 @@ mod tests {
 
         let value = b;
         let index = 1;
-        let path = MerklePath::new([a.into(), j.into(), n.into()].to_vec());
-        set.add_path(index, value, path.clone()).unwrap();
-        assert_eq!(value, set.get_leaf(index).unwrap());
-        assert_eq!(Word::from(root), set.root());
+        let path = MerklePath::new([a, j, n].to_vec());
+        set.add_path(index, value.into(), path.clone()).unwrap();
+        assert_eq!(*value, set.get_leaf(index).unwrap());
+        assert_eq!(root, set.root());
 
         let value = e;
         let index = 4;
         let path = MerklePath::new([f.into(), l.into(), m.into()].to_vec());
-        set.add_path(index, value, path.clone()).unwrap();
-        assert_eq!(value, set.get_leaf(index).unwrap());
-        assert_eq!(Word::from(root), set.root());
+        set.add_path(index, value.into(), path.clone()).unwrap();
+        assert_eq!(*value, set.get_leaf(index).unwrap());
+        assert_eq!(root, set.root());
 
         let value = a;
         let index = 0;
         let path = MerklePath::new([b.into(), j.into(), n.into()].to_vec());
-        set.add_path(index, value, path.clone()).unwrap();
-        assert_eq!(value, set.get_leaf(index).unwrap());
-        assert_eq!(Word::from(root), set.root());
+        set.add_path(index, value.into(), path.clone()).unwrap();
+        assert_eq!(*value, set.get_leaf(index).unwrap());
+        assert_eq!(root, set.root());
 
         let value = h;
         let index = 7;
         let path = MerklePath::new([g.into(), k.into(), m.into()].to_vec());
-        set.add_path(index, value, path.clone()).unwrap();
-        assert_eq!(value, set.get_leaf(index).unwrap());
-        assert_eq!(Word::from(root), set.root());
+        set.add_path(index, value.into(), path.clone()).unwrap();
+        assert_eq!(*value, set.get_leaf(index).unwrap());
+        assert_eq!(root, set.root());
     }
 
     // HELPER FUNCTIONS
@@ -397,11 +398,11 @@ mod tests {
     /// - node — current node
     /// - node_pos — position of the current node
     /// - sibling — neighboring vertex in the tree
-    fn calculate_parent_hash(node: Word, node_pos: u64, sibling: Word) -> Word {
+    fn calculate_parent_hash(node: RpoDigest, node_pos: u64, sibling: RpoDigest) -> RpoDigest {
         if is_even(node_pos) {
-            Rpo256::merge(&[node.into(), sibling.into()]).into()
+            Rpo256::merge(&[node, sibling])
         } else {
-            Rpo256::merge(&[sibling.into(), node.into()]).into()
+            Rpo256::merge(&[sibling, node])
         }
     }
 }

src/merkle/simple_smt/mod.rs

@@ -1,6 +1,6 @@
 use super::{
-    BTreeMap, BTreeSet, EmptySubtreeRoots, InnerNodeInfo, MerkleError, MerklePath, NodeIndex,
-    Rpo256, RpoDigest, Vec, Word, EMPTY_WORD,
+    empty_roots::EMPTY_WORD, BTreeMap, BTreeSet, EmptySubtreeRoots, InnerNodeInfo, MerkleError,
+    MerklePath, NodeIndex, Rpo256, RpoDigest, Vec, Word,
 };
 
 #[cfg(test)]
@@ -15,7 +15,7 @@ mod tests;
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct SimpleSmt {
     depth: u8,
-    root: Word,
+    root: RpoDigest,
     leaves: BTreeMap<u64, Word>,
     branches: BTreeMap<NodeIndex, BranchNode>,
     empty_hashes: Vec<RpoDigest>,
@@ -49,7 +49,7 @@ impl SimpleSmt {
         }
 
         let empty_hashes = EmptySubtreeRoots::empty_hashes(depth).to_vec();
-        let root = empty_hashes[0].into();
+        let root = empty_hashes[0];
 
         Ok(Self {
             root,
@@ -107,7 +107,7 @@ impl SimpleSmt {
     // --------------------------------------------------------------------------------------------
 
     /// Returns the root of this Merkle tree.
-    pub const fn root(&self) -> Word {
+    pub const fn root(&self) -> RpoDigest {
         self.root
     }
 
@@ -121,7 +121,7 @@ impl SimpleSmt {
     /// # Errors
     /// Returns an error if the specified index has depth set to 0 or the depth is greater than
     /// the depth of this Merkle tree.
-    pub fn get_node(&self, index: NodeIndex) -> Result<Word, MerkleError> {
+    pub fn get_node(&self, index: NodeIndex) -> Result<RpoDigest, MerkleError> {
         if index.is_root() {
             Err(MerkleError::DepthTooSmall(index.depth()))
         } else if index.depth() > self.depth() {
@@ -129,11 +129,12 @@ impl SimpleSmt {
         } else if index.depth() == self.depth() {
             // the lookup in empty_hashes could fail only if empty_hashes were not built correctly
             // by the constructor as we check the depth of the lookup above.
-            Ok(self
-                .get_leaf_node(index.value())
-                .unwrap_or_else(|| self.empty_hashes[index.depth() as usize].into()))
+            Ok(RpoDigest::from(
+                self.get_leaf_node(index.value())
+                    .unwrap_or_else(|| *self.empty_hashes[index.depth() as usize]),
+            ))
         } else {
-            Ok(self.get_branch_node(&index).parent().into())
+            Ok(self.get_branch_node(&index).parent())
         }
     }
 
@@ -143,7 +144,7 @@ impl SimpleSmt {
     /// Returns an error if the index is greater than the maximum tree capacity, that is 2^{depth}.
     pub fn get_leaf(&self, index: u64) -> Result<Word, MerkleError> {
         let index = NodeIndex::new(self.depth, index)?;
-        self.get_node(index)
+        Ok(self.get_node(index)?.into())
     }
 
     /// Returns a Merkle path from the node at the specified index to the root.
@@ -166,9 +167,9 @@ impl SimpleSmt {
             index.move_up();
             let BranchNode { left, right } = self.get_branch_node(&index);
             let value = if is_right { left } else { right };
-            path.push(*value);
+            path.push(value);
         }
-        Ok(path.into())
+        Ok(MerklePath::new(path))
     }
 
     /// Return a Merkle path from the leaf at the specified index to the root.
@@ -193,9 +194,9 @@ impl SimpleSmt {
     /// Returns an iterator over the inner nodes of this Merkle tree.
     pub fn inner_nodes(&self) -> impl Iterator<Item = InnerNodeInfo> + '_ {
         self.branches.values().map(|e| InnerNodeInfo {
-            value: e.parent().into(),
-            left: e.left.into(),
-            right: e.right.into(),
+            value: e.parent(),
+            left: e.left,
+            right: e.right,
         })
     }
 
@@ -226,7 +227,7 @@ impl SimpleSmt {
             self.insert_branch_node(index, left, right);
             value = Rpo256::merge(&[left, right]);
         }
-        self.root = value.into();
+        self.root = value;
         Ok(old_value)
     }
 

src/merkle/simple_smt/tests.rs

@@ -1,6 +1,10 @@
 use super::{
-    super::{int_to_node, InnerNodeInfo, MerkleError, MerkleTree, RpoDigest, SimpleSmt},
-    NodeIndex, Rpo256, Vec, Word, EMPTY_WORD,
+    super::{InnerNodeInfo, MerkleError, MerkleTree, RpoDigest, SimpleSmt},
+    NodeIndex, Rpo256, Vec,
+};
+use crate::{
+    merkle::{digests_to_words, empty_roots::EMPTY_WORD, int_to_leaf, int_to_node},
+    Word,
 };
 
 // TEST DATA
@@ -9,9 +13,9 @@ use super::{
 const KEYS4: [u64; 4] = [0, 1, 2, 3];
 const KEYS8: [u64; 8] = [0, 1, 2, 3, 4, 5, 6, 7];
 
-const VALUES4: [Word; 4] = [int_to_node(1), int_to_node(2), int_to_node(3), int_to_node(4)];
+const VALUES4: [RpoDigest; 4] = [int_to_node(1), int_to_node(2), int_to_node(3), int_to_node(4)];
 
-const VALUES8: [Word; 8] = [
+const VALUES8: [RpoDigest; 8] = [
     int_to_node(1),
     int_to_node(2),
     int_to_node(3),
@@ -22,7 +26,7 @@ const VALUES8: [Word; 8] = [
     int_to_node(8),
 ];
 
-const ZERO_VALUES8: [Word; 8] = [int_to_node(0); 8];
+const ZERO_VALUES8: [Word; 8] = [int_to_leaf(0); 8];
 
 // TESTS
 // ================================================================================================
@@ -42,7 +46,7 @@ fn build_sparse_tree() {
 
     // insert single value
     let key = 6;
-    let new_node = int_to_node(7);
+    let new_node = int_to_leaf(7);
     values[key as usize] = new_node;
     let old_value = smt.update_leaf(key, new_node).expect("Failed to update leaf");
     let mt2 = MerkleTree::new(values.clone()).unwrap();
@@ -55,7 +59,7 @@ fn build_sparse_tree() {
 
     // insert second value at distinct leaf branch
     let key = 2;
-    let new_node = int_to_node(3);
+    let new_node = int_to_leaf(3);
     values[key as usize] = new_node;
     let old_value = smt.update_leaf(key, new_node).expect("Failed to update leaf");
     let mt3 = MerkleTree::new(values).unwrap();
@@ -69,7 +73,9 @@ fn build_sparse_tree() {
 
 #[test]
 fn test_depth2_tree() {
-    let tree = SimpleSmt::with_leaves(2, KEYS4.into_iter().zip(VALUES4.into_iter())).unwrap();
+    let tree =
+        SimpleSmt::with_leaves(2, KEYS4.into_iter().zip(digests_to_words(&VALUES4).into_iter()))
+            .unwrap();
 
     // check internal structure
     let (root, node2, node3) = compute_internal_nodes();
@@ -96,7 +102,9 @@ fn test_depth2_tree() {
 
 #[test]
 fn test_inner_node_iterator() -> Result<(), MerkleError> {
-    let tree = SimpleSmt::with_leaves(2, KEYS4.into_iter().zip(VALUES4.into_iter())).unwrap();
+    let tree =
+        SimpleSmt::with_leaves(2, KEYS4.into_iter().zip(digests_to_words(&VALUES4).into_iter()))
+            .unwrap();
 
     // check depth 2
     assert_eq!(VALUES4[0], tree.get_node(NodeIndex::make(2, 0)).unwrap());
@@ -116,19 +124,19 @@ fn test_inner_node_iterator() -> Result<(), MerkleError> {
     let nodes: Vec<InnerNodeInfo> = tree.inner_nodes().collect();
     let expected = vec![
         InnerNodeInfo {
-            value: root.into(),
-            left: l1n0.into(),
-            right: l1n1.into(),
+            value: root,
+            left: l1n0,
+            right: l1n1,
         },
         InnerNodeInfo {
-            value: l1n0.into(),
-            left: l2n0.into(),
-            right: l2n1.into(),
+            value: l1n0,
+            left: l2n0,
+            right: l2n1,
         },
         InnerNodeInfo {
-            value: l1n1.into(),
-            left: l2n2.into(),
-            right: l2n3.into(),
+            value: l1n1,
+            left: l2n2,
+            right: l2n3,
         },
     ];
     assert_eq!(nodes, expected);
@@ -138,28 +146,30 @@ fn test_inner_node_iterator() -> Result<(), MerkleError> {
 
 #[test]
 fn update_leaf() {
-    let mut tree = SimpleSmt::with_leaves(3, KEYS8.into_iter().zip(VALUES8.into_iter())).unwrap();
+    let mut tree =
+        SimpleSmt::with_leaves(3, KEYS8.into_iter().zip(digests_to_words(&VALUES8).into_iter()))
+            .unwrap();
 
     // update one value
     let key = 3;
-    let new_node = int_to_node(9);
-    let mut expected_values = VALUES8.to_vec();
+    let new_node = int_to_leaf(9);
+    let mut expected_values = digests_to_words(&VALUES8);
     expected_values[key] = new_node;
     let expected_tree = MerkleTree::new(expected_values.clone()).unwrap();
 
     let old_leaf = tree.update_leaf(key as u64, new_node).unwrap();
     assert_eq!(expected_tree.root(), tree.root);
-    assert_eq!(old_leaf, VALUES8[key]);
+    assert_eq!(old_leaf, *VALUES8[key]);
 
     // update another value
     let key = 6;
-    let new_node = int_to_node(10);
+    let new_node = int_to_leaf(10);
     expected_values[key] = new_node;
     let expected_tree = MerkleTree::new(expected_values.clone()).unwrap();
 
     let old_leaf = tree.update_leaf(key as u64, new_node).unwrap();
     assert_eq!(expected_tree.root(), tree.root);
-    assert_eq!(old_leaf, VALUES8[key]);
+    assert_eq!(old_leaf, *VALUES8[key]);
 }
 
 #[test]
@@ -172,34 +182,34 @@ fn small_tree_opening_is_consistent() {
     //  / \   / \   / \   / \
     // a   b 0   0 c   0 0   d
 
-    let z = Word::from(RpoDigest::default());
+    let z = EMPTY_WORD;
 
     let a = Word::from(Rpo256::merge(&[z.into(); 2]));
     let b = Word::from(Rpo256::merge(&[a.into(); 2]));
     let c = Word::from(Rpo256::merge(&[b.into(); 2]));
     let d = Word::from(Rpo256::merge(&[c.into(); 2]));
 
-    let e = Word::from(Rpo256::merge(&[a.into(), b.into()]));
-    let f = Word::from(Rpo256::merge(&[z.into(), z.into()]));
-    let g = Word::from(Rpo256::merge(&[c.into(), z.into()]));
-    let h = Word::from(Rpo256::merge(&[z.into(), d.into()]));
+    let e = Rpo256::merge(&[a.into(), b.into()]);
+    let f = Rpo256::merge(&[z.into(), z.into()]);
+    let g = Rpo256::merge(&[c.into(), z.into()]);
+    let h = Rpo256::merge(&[z.into(), d.into()]);
 
-    let i = Word::from(Rpo256::merge(&[e.into(), f.into()]));
-    let j = Word::from(Rpo256::merge(&[g.into(), h.into()]));
+    let i = Rpo256::merge(&[e, f]);
+    let j = Rpo256::merge(&[g, h]);
 
-    let k = Word::from(Rpo256::merge(&[i.into(), j.into()]));
+    let k = Rpo256::merge(&[i, j]);
 
     let depth = 3;
     let entries = vec![(0, a), (1, b), (4, c), (7, d)];
     let tree = SimpleSmt::with_leaves(depth, entries).unwrap();
 
-    assert_eq!(tree.root(), Word::from(k));
+    assert_eq!(tree.root(), RpoDigest::from(k));
 
-    let cases: Vec<(u8, u64, Vec<Word>)> = vec![
-        (3, 0, vec![b, f, j]),
-        (3, 1, vec![a, f, j]),
-        (3, 4, vec![z, h, i]),
-        (3, 7, vec![z, g, i]),
+    let cases: Vec<(u8, u64, Vec<RpoDigest>)> = vec![
+        (3, 0, vec![b.into(), f, j]),
+        (3, 1, vec![a.into(), f, j]),
+        (3, 4, vec![z.into(), h, i]),
+        (3, 7, vec![z.into(), g, i]),
         (2, 0, vec![f, j]),
         (2, 1, vec![e, j]),
         (2, 2, vec![h, i]),
@@ -217,26 +227,26 @@ fn small_tree_opening_is_consistent() {
 
 #[test]
 fn fail_on_duplicates() {
-    let entries = [(1_u64, int_to_node(1)), (5, int_to_node(2)), (1_u64, int_to_node(3))];
+    let entries = [(1_u64, int_to_leaf(1)), (5, int_to_leaf(2)), (1_u64, int_to_leaf(3))];
     let smt = SimpleSmt::with_leaves(64, entries);
     assert!(smt.is_err());
 
-    let entries = [(1_u64, int_to_node(0)), (5, int_to_node(2)), (1_u64, int_to_node(0))];
+    let entries = [(1_u64, int_to_leaf(0)), (5, int_to_leaf(2)), (1_u64, int_to_leaf(0))];
     let smt = SimpleSmt::with_leaves(64, entries);
     assert!(smt.is_err());
 
-    let entries = [(1_u64, int_to_node(0)), (5, int_to_node(2)), (1_u64, int_to_node(1))];
+    let entries = [(1_u64, int_to_leaf(0)), (5, int_to_leaf(2)), (1_u64, int_to_leaf(1))];
     let smt = SimpleSmt::with_leaves(64, entries);
     assert!(smt.is_err());
 
-    let entries = [(1_u64, int_to_node(1)), (5, int_to_node(2)), (1_u64, int_to_node(0))];
+    let entries = [(1_u64, int_to_leaf(1)), (5, int_to_leaf(2)), (1_u64, int_to_leaf(0))];
     let smt = SimpleSmt::with_leaves(64, entries);
     assert!(smt.is_err());
 }
 
 #[test]
 fn with_no_duplicates_empty_node() {
-    let entries = [(1_u64, int_to_node(0)), (5, int_to_node(2))];
+    let entries = [(1_u64, int_to_leaf(0)), (5, int_to_leaf(2))];
     let smt = SimpleSmt::with_leaves(64, entries);
     assert!(smt.is_ok());
 }
@@ -244,10 +254,10 @@ fn with_no_duplicates_empty_node() {
 // HELPER FUNCTIONS
 // --------------------------------------------------------------------------------------------
 
-fn compute_internal_nodes() -> (Word, Word, Word) {
-    let node2 = Rpo256::hash_elements(&[VALUES4[0], VALUES4[1]].concat());
-    let node3 = Rpo256::hash_elements(&[VALUES4[2], VALUES4[3]].concat());
+fn compute_internal_nodes() -> (RpoDigest, RpoDigest, RpoDigest) {
+    let node2 = Rpo256::merge(&[VALUES4[0], VALUES4[1]]);
+    let node3 = Rpo256::merge(&[VALUES4[2], VALUES4[3]]);
     let root = Rpo256::merge(&[node2, node3]);
 
-    (root.into(), node2.into(), node3.into())
+    (root, node2, node3)
 }

src/merkle/store/mod.rs

@@ -1,6 +1,6 @@
 use super::{
     mmr::Mmr, BTreeMap, EmptySubtreeRoots, InnerNodeInfo, MerkleError, MerklePath, MerklePathSet,
-    MerkleTree, NodeIndex, RootPath, Rpo256, RpoDigest, SimpleSmt, TieredSmt, ValuePath, Vec, Word,
+    MerkleTree, NodeIndex, RootPath, Rpo256, RpoDigest, SimpleSmt, TieredSmt, ValuePath, Vec,
 };
 use crate::utils::{ByteReader, ByteWriter, Deserializable, DeserializationError, Serializable};
 use core::borrow::Borrow;
@@ -130,21 +130,20 @@ impl MerkleStore {
     /// This method can return the following errors:
     /// - `RootNotInStore` if the `root` is not present in the store.
     /// - `NodeNotInStore` if a node needed to traverse from `root` to `index` is not present in the store.
-    pub fn get_node(&self, root: Word, index: NodeIndex) -> Result<Word, MerkleError> {
-        let mut hash: RpoDigest = root.into();
+    pub fn get_node(&self, root: RpoDigest, index: NodeIndex) -> Result<RpoDigest, MerkleError> {
+        let mut hash = root;
 
         // corner case: check the root is in the store when called with index `NodeIndex::root()`
-        self.nodes.get(&hash).ok_or(MerkleError::RootNotInStore(hash.into()))?;
+        self.nodes.get(&hash).ok_or(MerkleError::RootNotInStore(hash))?;
 
         for i in (0..index.depth()).rev() {
-            let node =
-                self.nodes.get(&hash).ok_or(MerkleError::NodeNotInStore(hash.into(), index))?;
+            let node = self.nodes.get(&hash).ok_or(MerkleError::NodeNotInStore(hash, index))?;
 
             let bit = (index.value() >> i) & 1;
             hash = if bit == 0 { node.left } else { node.right }
         }
 
-        Ok(hash.into())
+        Ok(hash)
     }
 
     /// Returns the node at the specified `index` and its opening to the `root`.
@@ -155,23 +154,22 @@ impl MerkleStore {
     /// This method can return the following errors:
     /// - `RootNotInStore` if the `root` is not present in the store.
     /// - `NodeNotInStore` if a node needed to traverse from `root` to `index` is not present in the store.
-    pub fn get_path(&self, root: Word, index: NodeIndex) -> Result<ValuePath, MerkleError> {
-        let mut hash: RpoDigest = root.into();
+    pub fn get_path(&self, root: RpoDigest, index: NodeIndex) -> Result<ValuePath, MerkleError> {
+        let mut hash = root;
         let mut path = Vec::with_capacity(index.depth().into());
 
         // corner case: check the root is in the store when called with index `NodeIndex::root()`
-        self.nodes.get(&hash).ok_or(MerkleError::RootNotInStore(hash.into()))?;
+        self.nodes.get(&hash).ok_or(MerkleError::RootNotInStore(hash))?;
 
         for i in (0..index.depth()).rev() {
-            let node =
-                self.nodes.get(&hash).ok_or(MerkleError::NodeNotInStore(hash.into(), index))?;
+            let node = self.nodes.get(&hash).ok_or(MerkleError::NodeNotInStore(hash, index))?;
 
             let bit = (index.value() >> i) & 1;
             hash = if bit == 0 {
-                path.push(node.right.into());
+                path.push(node.right);
                 node.left
             } else {
-                path.push(node.left.into());
+                path.push(node.left);
                 node.right
             }
         }
@@ -180,7 +178,7 @@ impl MerkleStore {
         path.reverse();
 
         Ok(ValuePath {
-            value: hash.into(),
+            value: hash,
             path: MerklePath::new(path),
         })
     }
@@ -202,7 +200,7 @@ impl MerkleStore {
     /// information, check [NodeIndex::new].
     pub fn get_leaf_depth(
         &self,
-        root: Word,
+        root: RpoDigest,
         tree_depth: u8,
         index: u64,
     ) -> Result<u8, MerkleError> {
@@ -221,9 +219,9 @@ impl MerkleStore {
 
         // check if the root exists, providing the proper error report if it doesn't
         let empty = EmptySubtreeRoots::empty_hashes(tree_depth);
-        let mut hash: RpoDigest = root.into();
+        let mut hash = root;
         if !self.nodes.contains_key(&hash) {
-            return Err(MerkleError::RootNotInStore(hash.into()));
+            return Err(MerkleError::RootNotInStore(hash));
         }
 
         // we traverse from root to leaf, so the path is reversed
@@ -266,11 +264,11 @@ impl MerkleStore {
     pub fn subset<I, R>(&self, roots: I) -> MerkleStore
     where
         I: Iterator<Item = R>,
-        R: Borrow<Word>,
+        R: Borrow<RpoDigest>,
     {
         let mut store = MerkleStore::new();
         for root in roots {
-            let root = RpoDigest::from(*root.borrow());
+            let root = *root.borrow();
             store.clone_tree_from(root, self);
         }
         store
@@ -279,9 +277,9 @@ impl MerkleStore {
     /// Iterator over the inner nodes of the [MerkleStore].
     pub fn inner_nodes(&self) -> impl Iterator<Item = InnerNodeInfo> + '_ {
         self.nodes.iter().map(|(r, n)| InnerNodeInfo {
-            value: r.into(),
-            left: n.left.into(),
-            right: n.right.into(),
+            value: *r,
+            left: n.left,
+            right: n.right,
         })
     }
 
@@ -294,9 +292,9 @@ impl MerkleStore {
         I: Iterator<Item = InnerNodeInfo>,
     {
         for node in iter {
-            let value: RpoDigest = node.value.into();
-            let left: RpoDigest = node.left.into();
-            let right: RpoDigest = node.right.into();
+            let value: RpoDigest = node.value;
+            let left: RpoDigest = node.left;
+            let right: RpoDigest = node.right;
 
             debug_assert_eq!(Rpo256::merge(&[left, right]), value);
             self.nodes.insert(value, Node { left, right });
@@ -313,13 +311,13 @@ impl MerkleStore {
     pub fn add_merkle_path(
         &mut self,
         index: u64,
-        node: Word,
+        node: RpoDigest,
         path: MerklePath,
-    ) -> Result<Word, MerkleError> {
-        let root = path.inner_nodes(index, node)?.fold(Word::default(), |_, node| {
-            let value: RpoDigest = node.value.into();
-            let left: RpoDigest = node.left.into();
-            let right: RpoDigest = node.right.into();
+    ) -> Result<RpoDigest, MerkleError> {
+        let root = path.inner_nodes(index, node)?.fold(RpoDigest::default(), |_, node| {
+            let value: RpoDigest = node.value;
+            let left: RpoDigest = node.left;
+            let right: RpoDigest = node.right;
 
             debug_assert_eq!(Rpo256::merge(&[left, right]), value);
             self.nodes.insert(value, Node { left, right });
@@ -337,7 +335,7 @@ impl MerkleStore {
     /// For further reference, check [MerkleStore::add_merkle_path].
     pub fn add_merkle_paths<I>(&mut self, paths: I) -> Result<(), MerkleError>
     where
-        I: IntoIterator<Item = (u64, Word, MerklePath)>,
+        I: IntoIterator<Item = (u64, RpoDigest, MerklePath)>,
     {
         for (index_value, node, path) in paths.into_iter() {
             self.add_merkle_path(index_value, node, path)?;
@@ -348,7 +346,10 @@ impl MerkleStore {
     /// Appends the provided [MerklePathSet] into the store.
     ///
     /// For further reference, check [MerkleStore::add_merkle_path].
-    pub fn add_merkle_path_set(&mut self, path_set: &MerklePathSet) -> Result<Word, MerkleError> {
+    pub fn add_merkle_path_set(
+        &mut self,
+        path_set: &MerklePathSet,
+    ) -> Result<RpoDigest, MerkleError> {
         let root = path_set.root();
         for (index, path) in path_set.to_paths() {
             self.add_merkle_path(index, path.value, path.path)?;
@@ -365,9 +366,9 @@ impl MerkleStore {
     /// - `NodeNotInStore` if a node needed to traverse from `root` to `index` is not present in the store.
     pub fn set_node(
         &mut self,
-        mut root: Word,
+        mut root: RpoDigest,
         index: NodeIndex,
-        value: Word,
+        value: RpoDigest,
     ) -> Result<RootPath, MerkleError> {
         let node = value;
         let ValuePath { value, path } = self.get_path(root, index)?;
@@ -383,14 +384,21 @@ impl MerkleStore {
     /// Merges two elements and adds the resulting node into the store.
     ///
     /// Merges arbitrary values. They may be leafs, nodes, or a mixture of both.
-    pub fn merge_roots(&mut self, root1: Word, root2: Word) -> Result<Word, MerkleError> {
-        let left: RpoDigest = root1.into();
-        let right: RpoDigest = root2.into();
-
-        let parent = Rpo256::merge(&[left, right]);
-        self.nodes.insert(parent, Node { left, right });
-
-        Ok(parent.into())
+    pub fn merge_roots(
+        &mut self,
+        left_root: RpoDigest,
+        right_root: RpoDigest,
+    ) -> Result<RpoDigest, MerkleError> {
+        let parent = Rpo256::merge(&[left_root, right_root]);
+        self.nodes.insert(
+            parent,
+            Node {
+                left: left_root,
+                right: right_root,
+            },
+        );
+
+        Ok(parent)
     }
 
     // HELPER METHODS
@@ -404,7 +412,7 @@ impl MerkleStore {
         if let Some(node) = source.nodes.get(&root) {
             // if the node has already been inserted, no need to process it further as all of its
             // descendants should be already cloned from the source store
-            if matches!(self.nodes.insert(root, *node), None) {
+            if self.nodes.insert(root, *node).is_none() {
                 self.clone_tree_from(node.left, source);
                 self.clone_tree_from(node.right, source);
             }

src/merkle/store/tests.rs

@@ -1,10 +1,10 @@
 use super::{
-    super::EMPTY_WORD, Deserializable, EmptySubtreeRoots, MerkleError, MerklePath, MerkleStore,
-    NodeIndex, RpoDigest, Serializable,
+    Deserializable, EmptySubtreeRoots, MerkleError, MerklePath, MerkleStore, NodeIndex, RpoDigest,
+    Serializable,
 };
 use crate::{
     hash::rpo::Rpo256,
-    merkle::{int_to_node, MerklePathSet, MerkleTree, SimpleSmt},
+    merkle::{digests_to_words, int_to_leaf, int_to_node, MerklePathSet, MerkleTree, SimpleSmt},
     Felt, Word, WORD_SIZE,
 };
 
@@ -15,9 +15,9 @@ use std::error::Error;
 // ================================================================================================
 
 const KEYS4: [u64; 4] = [0, 1, 2, 3];
-const VALUES4: [Word; 4] = [int_to_node(1), int_to_node(2), int_to_node(3), int_to_node(4)];
+const VALUES4: [RpoDigest; 4] = [int_to_node(1), int_to_node(2), int_to_node(3), int_to_node(4)];
 
-const VALUES8: [Word; 8] = [
+const VALUES8: [RpoDigest; 8] = [
     int_to_node(1),
     int_to_node(2),
     int_to_node(3),
@@ -33,7 +33,7 @@ const VALUES8: [Word; 8] = [
 
 #[test]
 fn test_root_not_in_store() -> Result<(), MerkleError> {
-    let mtree = MerkleTree::new(VALUES4.to_vec())?;
+    let mtree = MerkleTree::new(digests_to_words(&VALUES4))?;
     let store = MerkleStore::from(&mtree);
     assert_eq!(
         store.get_node(VALUES4[0], NodeIndex::make(mtree.depth(), 0)),
@@ -51,7 +51,7 @@ fn test_root_not_in_store() -> Result<(), MerkleError> {
 
 #[test]
 fn test_merkle_tree() -> Result<(), MerkleError> {
-    let mtree = MerkleTree::new(VALUES4.to_vec())?;
+    let mtree = MerkleTree::new(digests_to_words(&VALUES4))?;
     let store = MerkleStore::from(&mtree);
 
     // STORE LEAVES ARE CORRECT -------------------------------------------------------------------
@@ -152,12 +152,12 @@ fn test_merkle_tree() -> Result<(), MerkleError> {
 #[test]
 fn test_empty_roots() {
     let store = MerkleStore::default();
-    let mut root = RpoDigest::new(EMPTY_WORD);
+    let mut root = RpoDigest::default();
 
     for depth in 0..255 {
         root = Rpo256::merge(&[root; 2]);
         assert!(
-            store.get_node(root.into(), NodeIndex::make(0, 0)).is_ok(),
+            store.get_node(root, NodeIndex::make(0, 0)).is_ok(),
             "The root of the empty tree of depth {depth} must be registered"
         );
     }
@@ -176,13 +176,17 @@ fn test_leaf_paths_for_empty_trees() -> Result<(), MerkleError> {
         let index = NodeIndex::make(depth, 0);
         let store_path = store.get_path(smt.root(), index)?;
         let smt_path = smt.get_path(index)?;
-        assert_eq!(store_path.value, EMPTY_WORD, "the leaf of an empty tree is always ZERO");
+        assert_eq!(
+            store_path.value,
+            RpoDigest::default(),
+            "the leaf of an empty tree is always ZERO"
+        );
         assert_eq!(
             store_path.path, smt_path,
             "the returned merkle path does not match the computed values"
         );
         assert_eq!(
-            store_path.path.compute_root(depth.into(), EMPTY_WORD).unwrap(),
+            store_path.path.compute_root(depth.into(), RpoDigest::default()).unwrap(),
             smt.root(),
             "computed root from the path must match the empty tree root"
         );
@@ -193,7 +197,8 @@ fn test_leaf_paths_for_empty_trees() -> Result<(), MerkleError> {
 
 #[test]
 fn test_get_invalid_node() {
-    let mtree = MerkleTree::new(VALUES4.to_vec()).expect("creating a merkle tree must work");
+    let mtree =
+        MerkleTree::new(digests_to_words(&VALUES4)).expect("creating a merkle tree must work");
     let store = MerkleStore::from(&mtree);
     let _ = store.get_node(mtree.root(), NodeIndex::make(mtree.depth(), 3));
 }
@@ -201,16 +206,16 @@ fn test_get_invalid_node() {
 #[test]
 fn test_add_sparse_merkle_tree_one_level() -> Result<(), MerkleError> {
     let keys2: [u64; 2] = [0, 1];
-    let leaves2: [Word; 2] = [int_to_node(1), int_to_node(2)];
+    let leaves2: [Word; 2] = [int_to_leaf(1), int_to_leaf(2)];
     let smt = SimpleSmt::with_leaves(1, keys2.into_iter().zip(leaves2.into_iter())).unwrap();
     let store = MerkleStore::from(&smt);
 
     let idx = NodeIndex::make(1, 0);
-    assert_eq!(smt.get_node(idx).unwrap(), leaves2[0]);
+    assert_eq!(smt.get_node(idx).unwrap(), leaves2[0].into());
     assert_eq!(store.get_node(smt.root(), idx).unwrap(), smt.get_node(idx).unwrap());
 
     let idx = NodeIndex::make(1, 1);
-    assert_eq!(smt.get_node(idx).unwrap(), leaves2[1]);
+    assert_eq!(smt.get_node(idx).unwrap(), leaves2[1].into());
     assert_eq!(store.get_node(smt.root(), idx).unwrap(), smt.get_node(idx).unwrap());
 
     Ok(())
@@ -218,9 +223,11 @@ fn test_add_sparse_merkle_tree_one_level() -> Result<(), MerkleError> {
 
 #[test]
 fn test_sparse_merkle_tree() -> Result<(), MerkleError> {
-    let smt =
-        SimpleSmt::with_leaves(SimpleSmt::MAX_DEPTH, KEYS4.into_iter().zip(VALUES4.into_iter()))
-            .unwrap();
+    let smt = SimpleSmt::with_leaves(
+        SimpleSmt::MAX_DEPTH,
+        KEYS4.into_iter().zip(digests_to_words(&VALUES4).into_iter()),
+    )
+    .unwrap();
 
     let store = MerkleStore::from(&smt);
 
@@ -248,7 +255,7 @@ fn test_sparse_merkle_tree() -> Result<(), MerkleError> {
     );
     assert_eq!(
         store.get_node(smt.root(), NodeIndex::make(smt.depth(), 4)),
-        Ok(EMPTY_WORD),
+        Ok(RpoDigest::default()),
         "unmodified node 4 must be ZERO"
     );
 
@@ -328,7 +335,8 @@ fn test_sparse_merkle_tree() -> Result<(), MerkleError> {
 
     let result = store.get_path(smt.root(), NodeIndex::make(smt.depth(), 4)).unwrap();
     assert_eq!(
-        EMPTY_WORD, result.value,
+        RpoDigest::default(),
+        result.value,
         "Value for merkle path at index 4 must match leaf value"
     );
     assert_eq!(
@@ -342,7 +350,7 @@ fn test_sparse_merkle_tree() -> Result<(), MerkleError> {
 
 #[test]
 fn test_add_merkle_paths() -> Result<(), MerkleError> {
-    let mtree = MerkleTree::new(VALUES4.to_vec())?;
+    let mtree = MerkleTree::new(digests_to_words(&VALUES4))?;
 
     let i0 = 0;
     let p0 = mtree.get_path(NodeIndex::make(2, i0)).unwrap();
@@ -477,7 +485,6 @@ fn wont_open_to_different_depth_root() {
     for depth in (1..=63).rev() {
         root = Rpo256::merge(&[root, empty[depth]]);
     }
-    let root = Word::from(root);
 
     // For this example, the depth of the Merkle tree is 1, as we have only two leaves. Here we
     // attempt to fetch a node on the maximum depth, and it should fail because the root shouldn't
@@ -505,22 +512,22 @@ fn store_path_opens_from_leaf() {
     let k = Rpo256::merge(&[e.into(), f.into()]);
     let l = Rpo256::merge(&[g.into(), h.into()]);
 
-    let m = Rpo256::merge(&[i.into(), j.into()]);
-    let n = Rpo256::merge(&[k.into(), l.into()]);
+    let m = Rpo256::merge(&[i, j]);
+    let n = Rpo256::merge(&[k, l]);
 
-    let root = Rpo256::merge(&[m.into(), n.into()]);
+    let root = Rpo256::merge(&[m, n]);
 
     let mtree = MerkleTree::new(vec![a, b, c, d, e, f, g, h]).unwrap();
     let store = MerkleStore::from(&mtree);
-    let path = store.get_path(root.into(), NodeIndex::make(3, 1)).unwrap().path;
+    let path = store.get_path(root, NodeIndex::make(3, 1)).unwrap().path;
 
-    let expected = MerklePath::new([a.into(), j.into(), n.into()].to_vec());
+    let expected = MerklePath::new([a.into(), j, n].to_vec());
     assert_eq!(path, expected);
 }
 
 #[test]
 fn test_set_node() -> Result<(), MerkleError> {
-    let mtree = MerkleTree::new(VALUES4.to_vec())?;
+    let mtree = MerkleTree::new(digests_to_words(&VALUES4))?;
     let mut store = MerkleStore::from(&mtree);
     let value = int_to_node(42);
     let index = NodeIndex::make(mtree.depth(), 0);
@@ -532,7 +539,7 @@ fn test_set_node() -> Result<(), MerkleError> {
 
 #[test]
 fn test_constructors() -> Result<(), MerkleError> {
-    let mtree = MerkleTree::new(VALUES4.to_vec())?;
+    let mtree = MerkleTree::new(digests_to_words(&VALUES4))?;
     let store = MerkleStore::from(&mtree);
 
     let depth = mtree.depth();
@@ -544,7 +551,11 @@ fn test_constructors() -> Result<(), MerkleError> {
     }
 
     let depth = 32;
-    let smt = SimpleSmt::with_leaves(depth, KEYS4.into_iter().zip(VALUES4.into_iter())).unwrap();
+    let smt = SimpleSmt::with_leaves(
+        depth,
+        KEYS4.into_iter().zip(digests_to_words(&VALUES4).into_iter()),
+    )
+    .unwrap();
     let store = MerkleStore::from(&smt);
     let depth = smt.depth();
 
@@ -590,11 +601,11 @@ fn node_path_should_be_truncated_by_midtier_insert() {
     let key = 0b11010010_11001100_11001100_11001100_11001100_11001100_11001100_11001100_u64;
 
     let mut store = MerkleStore::new();
-    let root: Word = EmptySubtreeRoots::empty_hashes(64)[0].into();
+    let root: RpoDigest = EmptySubtreeRoots::empty_hashes(64)[0];
 
     // insert first node - works as expected
     let depth = 64;
-    let node = [Felt::new(key); WORD_SIZE];
+    let node = RpoDigest::from([Felt::new(key); WORD_SIZE]);
     let index = NodeIndex::new(depth, key).unwrap();
     let root = store.set_node(root, index, node).unwrap().root;
     let result = store.get_node(root, index).unwrap();
@@ -607,7 +618,7 @@ fn node_path_should_be_truncated_by_midtier_insert() {
     let key = key ^ (1 << 63);
     let key = key >> 8;
     let depth = 56;
-    let node = [Felt::new(key); WORD_SIZE];
+    let node = RpoDigest::from([Felt::new(key); WORD_SIZE]);
     let index = NodeIndex::new(depth, key).unwrap();
     let root = store.set_node(root, index, node).unwrap().root;
     let result = store.get_node(root, index).unwrap();
@@ -626,13 +637,13 @@ fn node_path_should_be_truncated_by_midtier_insert() {
 #[test]
 fn get_leaf_depth_works_depth_64() {
     let mut store = MerkleStore::new();
-    let mut root: Word = EmptySubtreeRoots::empty_hashes(64)[0].into();
+    let mut root: RpoDigest = EmptySubtreeRoots::empty_hashes(64)[0];
     let key = u64::MAX;
 
     // this will create a rainbow tree and test all opening to depth 64
     for d in 0..64 {
         let k = key & (u64::MAX >> d);
-        let node = [Felt::new(k); WORD_SIZE];
+        let node = RpoDigest::from([Felt::new(k); WORD_SIZE]);
         let index = NodeIndex::new(64, k).unwrap();
 
         // assert the leaf doesn't exist before the insert. the returned depth should always
@@ -649,14 +660,14 @@ fn get_leaf_depth_works_depth_64() {
 #[test]
 fn get_leaf_depth_works_with_incremental_depth() {
     let mut store = MerkleStore::new();
-    let mut root: Word = EmptySubtreeRoots::empty_hashes(64)[0].into();
+    let mut root: RpoDigest = EmptySubtreeRoots::empty_hashes(64)[0];
 
     // insert some path to the left of the root and assert it
     let key = 0b01001011_10110110_00001101_01110100_00111011_10101101_00000100_01000001_u64;
     assert_eq!(0, store.get_leaf_depth(root, 64, key).unwrap());
     let depth = 64;
     let index = NodeIndex::new(depth, key).unwrap();
-    let node = [Felt::new(key); WORD_SIZE];
+    let node = RpoDigest::from([Felt::new(key); WORD_SIZE]);
     root = store.set_node(root, index, node).unwrap().root;
     assert_eq!(depth, store.get_leaf_depth(root, 64, key).unwrap());
 
@@ -665,7 +676,7 @@ fn get_leaf_depth_works_with_incremental_depth() {
     assert_eq!(1, store.get_leaf_depth(root, 64, key).unwrap());
     let depth = 16;
     let index = NodeIndex::new(depth, key >> (64 - depth)).unwrap();
-    let node = [Felt::new(key); WORD_SIZE];
+    let node = RpoDigest::from([Felt::new(key); WORD_SIZE]);
     root = store.set_node(root, index, node).unwrap().root;
     assert_eq!(depth, store.get_leaf_depth(root, 64, key).unwrap());
 
@@ -673,7 +684,7 @@ fn get_leaf_depth_works_with_incremental_depth() {
     let key = 0b11001011_10110111_00000000_00000000_00000000_00000000_00000000_00000000_u64;
     assert_eq!(16, store.get_leaf_depth(root, 64, key).unwrap());
     let index = NodeIndex::new(depth, key >> (64 - depth)).unwrap();
-    let node = [Felt::new(key); WORD_SIZE];
+    let node = RpoDigest::from([Felt::new(key); WORD_SIZE]);
     root = store.set_node(root, index, node).unwrap().root;
     assert_eq!(depth, store.get_leaf_depth(root, 64, key).unwrap());
 
@@ -682,7 +693,7 @@ fn get_leaf_depth_works_with_incremental_depth() {
     assert_eq!(15, store.get_leaf_depth(root, 64, key).unwrap());
     let depth = 17;
     let index = NodeIndex::new(depth, key >> (64 - depth)).unwrap();
-    let node = [Felt::new(key); WORD_SIZE];
+    let node = RpoDigest::from([Felt::new(key); WORD_SIZE]);
     root = store.set_node(root, index, node).unwrap().root;
     assert_eq!(depth, store.get_leaf_depth(root, 64, key).unwrap());
 }
@@ -690,7 +701,7 @@ fn get_leaf_depth_works_with_incremental_depth() {
 #[test]
 fn get_leaf_depth_works_with_depth_8() {
     let mut store = MerkleStore::new();
-    let mut root: Word = EmptySubtreeRoots::empty_hashes(8)[0].into();
+    let mut root: RpoDigest = EmptySubtreeRoots::empty_hashes(8)[0];
 
     // insert some random, 8 depth keys. `a` diverges from the first bit
     let a = 0b01101001_u64;
@@ -700,7 +711,7 @@ fn get_leaf_depth_works_with_depth_8() {
 
     for k in [a, b, c, d] {
         let index = NodeIndex::new(8, k).unwrap();
-        let node = [Felt::new(k); WORD_SIZE];
+        let node = RpoDigest::from([Felt::new(k); WORD_SIZE]);
         root = store.set_node(root, index, node).unwrap().root;
     }
 
@@ -739,16 +750,16 @@ fn get_leaf_depth_works_with_depth_8() {
 #[test]
 fn mstore_subset() {
     // add a Merkle tree of depth 3 to the store
-    let mtree = MerkleTree::new(VALUES8.to_vec()).unwrap();
+    let mtree = MerkleTree::new(digests_to_words(&VALUES8)).unwrap();
     let mut store = MerkleStore::default();
     let empty_store_num_nodes = store.nodes.len();
     store.extend(mtree.inner_nodes());
 
     // build 3 subtrees contained within the above Merkle tree; note that subtree2 is a subset
     // of subtree1
-    let subtree1 = MerkleTree::new(VALUES8[..4].to_vec()).unwrap();
-    let subtree2 = MerkleTree::new(VALUES8[2..4].to_vec()).unwrap();
-    let subtree3 = MerkleTree::new(VALUES8[6..].to_vec()).unwrap();
+    let subtree1 = MerkleTree::new(digests_to_words(&VALUES8[..4])).unwrap();
+    let subtree2 = MerkleTree::new(digests_to_words(&VALUES8[2..4])).unwrap();
+    let subtree3 = MerkleTree::new(digests_to_words(&VALUES8[6..])).unwrap();
 
     // --- extract all 3 subtrees ---------------------------------------------
 
@@ -780,7 +791,7 @@ fn check_mstore_subtree(store: &MerkleStore, subtree: &MerkleTree) {
     for (i, value) in subtree.leaves() {
         let index = NodeIndex::new(subtree.depth(), i).unwrap();
         let path1 = store.get_path(subtree.root(), index).unwrap();
-        assert_eq!(&path1.value, value);
+        assert_eq!(*path1.value, *value);
 
         let path2 = subtree.get_path(index).unwrap();
         assert_eq!(path1.path, path2);
@@ -793,7 +804,7 @@ fn check_mstore_subtree(store: &MerkleStore, subtree: &MerkleTree) {
 #[cfg(feature = "std")]
 #[test]
 fn test_serialization() -> Result<(), Box<dyn Error>> {
-    let mtree = MerkleTree::new(VALUES4.to_vec())?;
+    let mtree = MerkleTree::new(digests_to_words(&VALUES4))?;
     let store = MerkleStore::from(&mtree);
     let decoded = MerkleStore::read_from_bytes(&store.to_bytes()).expect("deserialization failed");
     assert_eq!(store, decoded);

src/merkle/tiered_smt/mod.rs

@@ -1,6 +1,6 @@
 use super::{
-    BTreeMap, BTreeSet, EmptySubtreeRoots, Felt, InnerNodeInfo, MerkleError, MerklePath, NodeIndex,
-    Rpo256, RpoDigest, StarkField, Vec, Word, EMPTY_WORD, ZERO,
+    empty_roots::EMPTY_WORD, BTreeMap, BTreeSet, EmptySubtreeRoots, Felt, InnerNodeInfo,
+    MerkleError, MerklePath, NodeIndex, Rpo256, RpoDigest, StarkField, Vec, Word, ZERO,
 };
 use core::cmp;
 
@@ -123,7 +123,7 @@ impl TieredSmt {
         let mut path = Vec::with_capacity(index.depth() as usize);
         for _ in 0..index.depth() {
             let node = self.get_node_unchecked(&index.sibling());
-            path.push(node.into());
+            path.push(node);
             index.move_up();
         }
 
@@ -200,9 +200,9 @@ impl TieredSmt {
         self.nodes.iter().filter_map(|(index, node)| {
             if is_inner_node(index) {
                 Some(InnerNodeInfo {
-                    value: node.into(),
-                    left: self.get_node_unchecked(&index.left_child()).into(),
-                    right: self.get_node_unchecked(&index.right_child()).into(),
+                    value: *node,
+                    left: self.get_node_unchecked(&index.left_child()),
+                    right: self.get_node_unchecked(&index.right_child()),
                 })
             } else {
                 None
@@ -456,7 +456,7 @@ impl BottomLeaf {
         let mut elements = Vec::with_capacity(self.values.len() * 2);
         for (key, val) in self.values.iter() {
             key.iter().for_each(|&v| elements.push(Felt::new(v)));
-            elements.extend_from_slice(val);
+            elements.extend_from_slice(val.as_slice());
         }
         // TODO: hash in domain
         Rpo256::hash_elements(&elements)

src/merkle/tiered_smt/tests.rs

@@ -17,11 +17,11 @@ fn tsmt_insert_one() {
     // 16 most significant bits of the key
     let index = NodeIndex::make(16, raw >> 48);
     let leaf_node = build_leaf_node(key, value, 16);
-    let tree_root = store.set_node(smt.root().into(), index, leaf_node.into()).unwrap().root;
+    let tree_root = store.set_node(smt.root(), index, leaf_node).unwrap().root;
 
     smt.insert(key, value);
 
-    assert_eq!(smt.root(), tree_root.into());
+    assert_eq!(smt.root(), tree_root);
 
     // make sure the value was inserted, and the node is at the expected index
     assert_eq!(smt.get_value(key), value);
@@ -66,15 +66,15 @@ fn tsmt_insert_two_16() {
     let mut tree_root = get_init_root();
     let index_a = NodeIndex::make(32, raw_a >> 32);
     let leaf_node_a = build_leaf_node(key_a, val_a, 32);
-    tree_root = store.set_node(tree_root, index_a, leaf_node_a.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index_a, leaf_node_a).unwrap().root;
 
     let index_b = NodeIndex::make(32, raw_b >> 32);
     let leaf_node_b = build_leaf_node(key_b, val_b, 32);
-    tree_root = store.set_node(tree_root, index_b, leaf_node_b.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index_b, leaf_node_b).unwrap().root;
 
     // --- verify that data is consistent between store and tree --------------
 
-    assert_eq!(smt.root(), tree_root.into());
+    assert_eq!(smt.root(), tree_root);
 
     assert_eq!(smt.get_value(key_a), val_a);
     assert_eq!(smt.get_node(index_a).unwrap(), leaf_node_a);
@@ -122,15 +122,15 @@ fn tsmt_insert_two_32() {
     let mut tree_root = get_init_root();
     let index_a = NodeIndex::make(48, raw_a >> 16);
     let leaf_node_a = build_leaf_node(key_a, val_a, 48);
-    tree_root = store.set_node(tree_root, index_a, leaf_node_a.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index_a, leaf_node_a).unwrap().root;
 
     let index_b = NodeIndex::make(48, raw_b >> 16);
     let leaf_node_b = build_leaf_node(key_b, val_b, 48);
-    tree_root = store.set_node(tree_root, index_b, leaf_node_b.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index_b, leaf_node_b).unwrap().root;
 
     // --- verify that data is consistent between store and tree --------------
 
-    assert_eq!(smt.root(), tree_root.into());
+    assert_eq!(smt.root(), tree_root);
 
     assert_eq!(smt.get_value(key_a), val_a);
     assert_eq!(smt.get_node(index_a).unwrap(), leaf_node_a);
@@ -181,19 +181,19 @@ fn tsmt_insert_three() {
     let mut tree_root = get_init_root();
     let index_a = NodeIndex::make(32, raw_a >> 32);
     let leaf_node_a = build_leaf_node(key_a, val_a, 32);
-    tree_root = store.set_node(tree_root, index_a, leaf_node_a.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index_a, leaf_node_a).unwrap().root;
 
     let index_b = NodeIndex::make(32, raw_b >> 32);
     let leaf_node_b = build_leaf_node(key_b, val_b, 32);
-    tree_root = store.set_node(tree_root, index_b, leaf_node_b.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index_b, leaf_node_b).unwrap().root;
 
     let index_c = NodeIndex::make(32, raw_c >> 32);
     let leaf_node_c = build_leaf_node(key_c, val_c, 32);
-    tree_root = store.set_node(tree_root, index_c, leaf_node_c.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index_c, leaf_node_c).unwrap().root;
 
     // --- verify that data is consistent between store and tree --------------
 
-    assert_eq!(smt.root(), tree_root.into());
+    assert_eq!(smt.root(), tree_root);
 
     assert_eq!(smt.get_value(key_a), val_a);
     assert_eq!(smt.get_node(index_a).unwrap(), leaf_node_a);
@@ -236,9 +236,9 @@ fn tsmt_update() {
     let mut tree_root = get_init_root();
     let index = NodeIndex::make(16, raw >> 48);
     let leaf_node = build_leaf_node(key, value_b, 16);
-    tree_root = store.set_node(tree_root, index, leaf_node.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index, leaf_node).unwrap().root;
 
-    assert_eq!(smt.root(), tree_root.into());
+    assert_eq!(smt.root(), tree_root);
 
     assert_eq!(smt.get_value(key), value_b);
     assert_eq!(smt.get_node(index).unwrap(), leaf_node);
@@ -281,11 +281,11 @@ fn tsmt_bottom_tier() {
     // key_b is smaller than key_a.
     let leaf_node = build_bottom_leaf_node(&[key_b, key_a], &[val_b, val_a]);
     let mut tree_root = get_init_root();
-    tree_root = store.set_node(tree_root, index, leaf_node.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index, leaf_node).unwrap().root;
 
     // --- verify that data is consistent between store and tree --------------
 
-    assert_eq!(smt.root(), tree_root.into());
+    assert_eq!(smt.root(), tree_root);
 
     assert_eq!(smt.get_value(key_a), val_a);
     assert_eq!(smt.get_value(key_b), val_b);
@@ -329,15 +329,15 @@ fn tsmt_bottom_tier_two() {
     let mut tree_root = get_init_root();
     let index_a = NodeIndex::make(64, raw_a);
     let leaf_node_a = build_bottom_leaf_node(&[key_a], &[val_a]);
-    tree_root = store.set_node(tree_root, index_a, leaf_node_a.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index_a, leaf_node_a).unwrap().root;
 
     let index_b = NodeIndex::make(64, raw_b);
     let leaf_node_b = build_bottom_leaf_node(&[key_b], &[val_b]);
-    tree_root = store.set_node(tree_root, index_b, leaf_node_b.into()).unwrap().root;
+    tree_root = store.set_node(tree_root, index_b, leaf_node_b).unwrap().root;
 
     // --- verify that data is consistent between store and tree --------------
 
-    assert_eq!(smt.root(), tree_root.into());
+    assert_eq!(smt.root(), tree_root);
 
     assert_eq!(smt.get_value(key_a), val_a);
     assert_eq!(smt.get_node(index_a).unwrap(), leaf_node_a);
@@ -406,8 +406,8 @@ fn tsmt_node_not_available() {
 // HELPER FUNCTIONS
 // ================================================================================================
 
-fn get_init_root() -> Word {
-    EmptySubtreeRoots::empty_hashes(64)[0].into()
+fn get_init_root() -> RpoDigest {
+    EmptySubtreeRoots::empty_hashes(64)[0]
 }
 
 fn build_leaf_node(key: RpoDigest, value: Word, depth: u8) -> RpoDigest {
@@ -423,7 +423,7 @@ fn build_bottom_leaf_node(keys: &[RpoDigest], values: &[Word]) -> RpoDigest {
         let mut key = Word::from(key);
         key[3] = ZERO;
         elements.extend_from_slice(&key);
-        elements.extend_from_slice(val);
+        elements.extend_from_slice(val.as_slice());
     }
 
     Rpo256::hash_elements(&elements)