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Move BlockMerkleBranch back to merkle.{h,cpp}
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The Mining interface uses this function in the next commit
to calculate the coinbase merkle path. Stratum v2 uses
this to send a compact work template.

This partially undoes the change in 4defdfa,
but is not a revert, because the implementation changed in the meantime.

This commit also documents the function.
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@Sjors
Sjors committed Sep 26, 2024
1 parent 65f6e70 commit 63d6ad7
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Showing 3 changed files with 113 additions and 104 deletions.
103 changes: 103 additions & 0 deletions src/consensus/merkle.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -83,3 +83,106 @@ uint256 BlockWitnessMerkleRoot(const CBlock& block, bool* mutated)
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 branchpos, std::vector<uint256>* pbranch) {
if (pbranch) pbranch->clear();
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 == branchpos;
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.
for (level = 0; !(count & ((uint32_t{1}) << level)); level++) {
if (pbranch) {
if (matchh) {
pbranch->push_back(inner[level]);
} else if (matchlevel == level) {
pbranch->push_back(h);
matchh = true;
}
}
mutated |= (inner[level] == h);
h = Hash(inner[level], h);
}
// Store the resulting hash at inner position level.
inner[level] = h;
if (matchh) {
matchlevel = level;
}
}
// Do a final 'sweep' over the rightmost branch of the tree to process
// odd levels, and reduce everything to a single top value.
// Level is the level (counted from the bottom) up to which we've sweeped.
int level = 0;
// As long as bit number level in count is zero, skip it. It means there
// is nothing left at this level.
while (!(count & ((uint32_t{1}) << level))) {
level++;
}
uint256 h = inner[level];
bool matchh = matchlevel == level;
while (count != ((uint32_t{1}) << level)) {
// If we reach this point, h is an inner value that is not the top.
// We combine it with itself (Bitcoin's special rule for odd levels in
// the tree) to produce a higher level one.
if (pbranch && matchh) {
pbranch->push_back(h);
}
h = Hash(h, h);
// Increment count to the value it would have if two entries at this
// level had existed.
count += ((uint32_t{1}) << level);
level++;
// And propagate the result upwards accordingly.
while (!(count & ((uint32_t{1}) << level))) {
if (pbranch) {
if (matchh) {
pbranch->push_back(inner[level]);
} else if (matchlevel == level) {
pbranch->push_back(h);
matchh = true;
}
}
h = Hash(inner[level], h);
level++;
}
}
// Return result.
if (pmutated) *pmutated = mutated;
if (proot) *proot = h;
}

static std::vector<uint256> ComputeMerkleBranch(const std::vector<uint256>& leaves, uint32_t position) {
std::vector<uint256> ret;
MerkleComputation(leaves, nullptr, nullptr, position, &ret);
return ret;
}

std::vector<uint256> BlockMerkleBranch(const CBlock& block, uint32_t position)
{
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();
}
return ComputeMerkleBranch(leaves, position);
}
10 changes: 10 additions & 0 deletions src/consensus/merkle.h
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Original file line number Diff line number Diff line change
Expand Up @@ -24,4 +24,14 @@ uint256 BlockMerkleRoot(const CBlock& block, bool* mutated = nullptr);
*/
uint256 BlockWitnessMerkleRoot(const CBlock& block, bool* mutated = nullptr);

/**
* Compute merkle path to the specified transaction
*
* @param[in] block the block
* @param[in] position transaction for which to calculate the merkle path, defaults to coinbase
*
* @return merkle path ordered from the deepest
*/
std::vector<uint256> BlockMerkleBranch(const CBlock& block, uint32_t position = 0);

#endif // BITCOIN_CONSENSUS_MERKLE_H
104 changes: 0 additions & 104 deletions src/test/merkle_tests.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -23,110 +23,6 @@ static uint256 ComputeMerkleRootFromBranch(const uint256& leaf, const std::vecto
return hash;
}

/* 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 branchpos, std::vector<uint256>* pbranch) {
if (pbranch) pbranch->clear();
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 == branchpos;
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.
for (level = 0; !(count & ((uint32_t{1}) << level)); level++) {
if (pbranch) {
if (matchh) {
pbranch->push_back(inner[level]);
} else if (matchlevel == level) {
pbranch->push_back(h);
matchh = true;
}
}
mutated |= (inner[level] == h);
h = Hash(inner[level], h);
}
// Store the resulting hash at inner position level.
inner[level] = h;
if (matchh) {
matchlevel = level;
}
}
// Do a final 'sweep' over the rightmost branch of the tree to process
// odd levels, and reduce everything to a single top value.
// Level is the level (counted from the bottom) up to which we've sweeped.
int level = 0;
// As long as bit number level in count is zero, skip it. It means there
// is nothing left at this level.
while (!(count & ((uint32_t{1}) << level))) {
level++;
}
uint256 h = inner[level];
bool matchh = matchlevel == level;
while (count != ((uint32_t{1}) << level)) {
// If we reach this point, h is an inner value that is not the top.
// We combine it with itself (Bitcoin's special rule for odd levels in
// the tree) to produce a higher level one.
if (pbranch && matchh) {
pbranch->push_back(h);
}
h = Hash(h, h);
// Increment count to the value it would have if two entries at this
// level had existed.
count += ((uint32_t{1}) << level);
level++;
// And propagate the result upwards accordingly.
while (!(count & ((uint32_t{1}) << level))) {
if (pbranch) {
if (matchh) {
pbranch->push_back(inner[level]);
} else if (matchlevel == level) {
pbranch->push_back(h);
matchh = true;
}
}
h = Hash(inner[level], h);
level++;
}
}
// Return result.
if (pmutated) *pmutated = mutated;
if (proot) *proot = h;
}

static std::vector<uint256> ComputeMerkleBranch(const std::vector<uint256>& leaves, uint32_t position) {
std::vector<uint256> ret;
MerkleComputation(leaves, nullptr, nullptr, position, &ret);
return ret;
}

static std::vector<uint256> BlockMerkleBranch(const CBlock& block, uint32_t position)
{
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();
}
return ComputeMerkleBranch(leaves, position);
}

// Older version of the merkle root computation code, for comparison.
static uint256 BlockBuildMerkleTree(const CBlock& block, bool* fMutated, std::vector<uint256>& vMerkleTree)
{
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