Repository: bitcoin/bitcoin
File: src/consensus/merkle.cpp (C++)

Code before:
}


uint256 BlockMerkleRoot(const CBlock& block, bool* mutated)
{
    std::vector<uint256> leaves;
    leaves.resize(block.vtx.size());
    for (size_t s = 0; s < block.vtx.size(); s++) {
        leaves[s] = block.vtx[s]->GetHash().ToUint256();
    }
    return ComputeMerkleRoot(std::move(leaves), mutated);
}

uint256 BlockWitnessMerkleRoot(const CBlock& block, bool* mutated)
{
    std::vector<uint256> leaves;
    leaves.resize(block.vtx.size());
    leaves[0].SetNull(); // The witness hash of the coinbase is 0.
    for (size_t s = 1; s < block.vtx.size(); s++) {
        leaves[s] = block.vtx[s]->GetWitnessHash().ToUint256();
    }
    return ComputeMerkleRoot(std::move(leaves), mutated);
}

/* This implements a constant-space merkle root/path calculator, limited to 2^32 leaves. */
static void MerkleComputation(const std::vector<uint256>& leaves, uint256* proot, bool* pmutated, uint32_t leaf_pos, std::vector<uint256>* path)
{
    if (path) path->clear();
    Assume(leaves.size() <= UINT32_MAX);
    if (leaves.size() == 0) {
        if (pmutated) *pmutated = false;
        if (proot) *proot = uint256();
        return;
    }
    bool mutated = false;
    // count is the number of leaves processed so far.
    uint32_t count = 0;
    // inner is an array of eagerly computed subtree hashes, indexed by tree
    // level (0 being the leaves).
    // For example, when count is 25 (11001 in binary), inner[4] is the hash of
    // the first 16 leaves, inner[3] of the next 8 leaves, and inner[0] equal to
    // the last leaf. The other inner entries are undefined.
    uint256 inner[32];
    // Which position in inner is a hash that depends on the matching leaf.
    int matchlevel = -1;
    // First process all leaves into 'inner' values.
    while (count < leaves.size()) {
        uint256 h = leaves[count];
        bool matchh = count == leaf_pos;
        count++;
        int level;

Review comment (performance):
meganit: Could declare parameter `const` to decrease cognitive complexity
```suggestion
static void MerkleComputation(const std::vector<uint256>& leaves, const uint32_t leaf_pos, std::vector<uint256>& path)
```

Code after:
}


uint256 BlockMerkleRoot(const CBlock& block, bool* mutated)
{
    std::vector<uint256> leaves;
    leaves.resize(block.vtx.size());
    for (size_t s = 0; s < block.vtx.size(); s++) {
        leaves[s] = block.vtx[s]->GetHash().ToUint256();
    }
    return ComputeMerkleRoot(std::move(leaves), mutated);
}

uint256 BlockWitnessMerkleRoot(const CBlock& block)
{
    std::vector<uint256> leaves;
    leaves.resize(block.vtx.size());
    leaves[0].SetNull(); // The witness hash of the coinbase is 0.
    for (size_t s = 1; s < block.vtx.size(); s++) {
        leaves[s] = block.vtx[s]->GetWitnessHash().ToUint256();
    }
    return ComputeMerkleRoot(std::move(leaves));
}

/* This implements a constant-space merkle path calculator, limited to 2^32 leaves. */
static void MerkleComputation(const std::vector<uint256>& leaves, uint32_t leaf_pos, std::vector<uint256>& path)
{
    path.clear();
    Assume(leaves.size() <= UINT32_MAX);
    if (leaves.size() == 0) {
        return;
    }
    // count is the number of leaves processed so far.
    uint32_t count = 0;
    // inner is an array of eagerly computed subtree hashes, indexed by tree
    // level (0 being the leaves).
    // For example, when count is 25 (11001 in binary), inner[4] is the hash of
    // the first 16 leaves, inner[3] of the next 8 leaves, and inner[0] equal to
    // the last leaf. The other inner entries are undefined.
    uint256 inner[32];
    // Which position in inner is a hash that depends on the matching leaf.
    int matchlevel = -1;
    // First process all leaves into 'inner' values.
    while (count < leaves.size()) {
        uint256 h = leaves[count];
        bool matchh = count == leaf_pos;
        count++;
        int level;
        // For each of the lower bits in count that are 0, do 1 step. Each
        // corresponds to an inner value that existed before processing the
        // current leaf, and each needs a hash to combine it.