miden-crypto/src/merkle/smt/tests.rs

use alloc::{collections::BTreeMap, vec::Vec};

use super::{
    NodeIndex, PairComputations, SmtLeaf, SparseMerkleTree, SubtreeLeaf, SubtreeLeavesIter,
    COLS_PER_SUBTREE, SUBTREE_DEPTH,
};

use crate::{
    hash::rpo::RpoDigest,
    merkle::{Smt, SMT_DEPTH},
    Felt, Word, ONE,
};

fn smtleaf_to_subtree_leaf(leaf: &SmtLeaf) -> SubtreeLeaf {
    SubtreeLeaf {
        col: leaf.index().index.value(),
        hash: leaf.hash(),
    }
}

#[test]
fn test_sorted_pairs_to_leaves() {
    let entries: Vec<(RpoDigest, Word)> = vec![
        // Subtree 0.
        (RpoDigest::new([ONE, ONE, ONE, Felt::new(16)]), [ONE; 4]),
        (RpoDigest::new([ONE, ONE, ONE, Felt::new(17)]), [ONE; 4]),
        // Leaf index collision.
        (RpoDigest::new([ONE, ONE, Felt::new(10), Felt::new(20)]), [ONE; 4]),
        (RpoDigest::new([ONE, ONE, Felt::new(20), Felt::new(20)]), [ONE; 4]),
        // Subtree 1. Normal single leaf again.
        (RpoDigest::new([ONE, ONE, ONE, Felt::new(400)]), [ONE; 4]), // Subtree boundary.
        (RpoDigest::new([ONE, ONE, ONE, Felt::new(401)]), [ONE; 4]),
        // Subtree 2. Another normal leaf.
        (RpoDigest::new([ONE, ONE, ONE, Felt::new(1024)]), [ONE; 4]),
    ];

    let control = Smt::with_entries(entries.clone()).unwrap();

    let control_leaves: Vec<SmtLeaf> = {
        let mut entries_iter = entries.iter().cloned();
        let mut next_entry = || entries_iter.next().unwrap();
        let control_leaves = vec![
            // Subtree 0.
            SmtLeaf::Single(next_entry()),
            SmtLeaf::Single(next_entry()),
            SmtLeaf::new_multiple(vec![next_entry(), next_entry()]).unwrap(),
            // Subtree 1.
            SmtLeaf::Single(next_entry()),
            SmtLeaf::Single(next_entry()),
            // Subtree 2.
            SmtLeaf::Single(next_entry()),
        ];
        assert_eq!(entries_iter.next(), None);
        control_leaves
    };

    let control_subtree_leaves: Vec<Vec<SubtreeLeaf>> = {
        let mut control_leaves_iter = control_leaves.iter();
        let mut next_leaf = || control_leaves_iter.next().unwrap();

        let control_subtree_leaves: Vec<Vec<SubtreeLeaf>> = [
            // Subtree 0.
            vec![next_leaf(), next_leaf(), next_leaf()],
            // Subtree 1.
            vec![next_leaf(), next_leaf()],
            // Subtree 2.
            vec![next_leaf()],
        ]
        .map(|subtree| subtree.into_iter().map(smtleaf_to_subtree_leaf).collect())
        .to_vec();
        assert_eq!(control_leaves_iter.next(), None);
        control_subtree_leaves
    };

    let subtrees: PairComputations<u64, SmtLeaf> = Smt::sorted_pairs_to_leaves(entries);
    // This will check that the hashes, columns, and subtree assignments all match.
    assert_eq!(subtrees.leaves, control_subtree_leaves);

    // Flattening and re-separating out the leaves into subtrees should have the same result.
    let mut all_leaves: Vec<SubtreeLeaf> = subtrees.leaves.clone().into_iter().flatten().collect();
    let re_grouped: Vec<Vec<_>> = SubtreeLeavesIter::from_leaves(&mut all_leaves).collect();
    assert_eq!(subtrees.leaves, re_grouped);

    // Then finally we might as well check the computed leaf nodes too.
    let control_leaves: BTreeMap<u64, SmtLeaf> = control
        .leaves()
        .map(|(index, value)| (index.index.value(), value.clone()))
        .collect();

    for (column, test_leaf) in subtrees.nodes {
        if test_leaf.is_empty() {
            continue;
        }
        let control_leaf = control_leaves
            .get(&column)
            .unwrap_or_else(|| panic!("no leaf node found for column {column}"));
        assert_eq!(control_leaf, &test_leaf);
    }
}

// Helper for the below tests.
fn generate_entries(pair_count: u64) -> Vec<(RpoDigest, Word)> {
    (0..pair_count)
        .map(|i| {
            let leaf_index = ((i as f64 / pair_count as f64) * (pair_count as f64)) as u64;
            let key = RpoDigest::new([ONE, ONE, Felt::new(i), Felt::new(leaf_index)]);
            let value = [ONE, ONE, ONE, Felt::new(i)];
            (key, value)
        })
        .collect()
}

#[test]
fn test_single_subtree() {
    // A single subtree's worth of leaves.
    const PAIR_COUNT: u64 = COLS_PER_SUBTREE;

    let entries = generate_entries(PAIR_COUNT);

    let control = Smt::with_entries(entries.clone()).unwrap();

    // `entries` should already be sorted by nature of how we constructed it.
    let leaves = Smt::sorted_pairs_to_leaves(entries).leaves;
    let leaves = leaves.into_iter().next().unwrap();

    let (first_subtree, next_leaves) = Smt::build_subtree(leaves, SMT_DEPTH);
    assert!(!first_subtree.is_empty());

    // The inner nodes computed from that subtree should match the nodes in our control tree.
    for (index, node) in first_subtree.into_iter() {
        let control = control.get_inner_node(index);
        assert_eq!(
            control, node,
            "subtree-computed node at index {index:?} does not match control",
        );
    }

    // The "next leaves" returned should also have matching hashes from the equivalent nodes in
    // our control tree.
    for SubtreeLeaf { col, hash } in next_leaves {
        let index = NodeIndex::new(SMT_DEPTH - SUBTREE_DEPTH, col).unwrap();
        let control_node = control.get_inner_node(index);
        let control = control_node.hash();
        assert_eq!(
            control, hash,
            "subtree-computed next leaf at index {index:?} does not match control",
        );
    }
}