uint256 CPartialMerkleTree::ExtractMatches(std::vector<uint256> &vMatch, std::vector<unsigned int> &vnIndex) {
vMatch.clear();
// An empty set will not work
if (nTransactions == 0)
return uint256();
// check for excessively high numbers of transactions
if (nTransactions > MAX_BLOCK_WEIGHT / MIN_TRANSACTION_WEIGHT)
return uint256();
// there can never be more hashes provided than one for every txid
if (vHash.size() > nTransactions)
return uint256();
// there must be at least one bit per node in the partial tree, and at least one node per hash
if (vBits.size() < vHash.size())
return uint256();
// calculate height of tree
int nHeight = 0;
while (CalcTreeWidth(nHeight) > 1)
nHeight++;
// traverse the partial tree
unsigned int nBitsUsed = 0, nHashUsed = 0;
uint256 hashMerkleRoot = TraverseAndExtract(nHeight, 0, nBitsUsed, nHashUsed, vMatch, vnIndex);
// verify that no problems occurred during the tree traversal
if (fBad)
return uint256();
// verify that all bits were consumed (except for the padding caused by serializing it as a byte sequence)
if ((nBitsUsed+7)/8 != (vBits.size()+7)/8)
return uint256();
// verify that all hashes were consumed
if (nHashUsed != vHash.size())
return uint256();
return hashMerkleRoot;
}
CPartialMerkleTree::CPartialMerkleTree(const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch) : nTransactions(vTxid.size()), fBad(false) {
// reset state
vBits.clear();
vHash.clear();
// calculate height of tree
int nHeight = 0;
while (CalcTreeWidth(nHeight) > 1)
nHeight++;
// traverse the partial tree
TraverseAndBuild(nHeight, 0, vTxid, vMatch);
}
void CPartialMerkleTree::TraverseAndBuild(int height, unsigned int pos, const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch) {
// determine whether this node is the parent of at least one matched txid
bool fParentOfMatch = false;
for (unsigned int p = pos << height; p < (pos+1) << height && p < nTransactions; p++)
fParentOfMatch |= vMatch[p];
// store as flag bit
vBits.push_back(fParentOfMatch);
if (height==0 || !fParentOfMatch) {
// if at height 0, or nothing interesting below, store hash and stop
vHash.push_back(CalcHash(height, pos, vTxid));
} else {
// otherwise, don't store any hash, but descend into the subtrees
TraverseAndBuild(height-1, pos*2, vTxid, vMatch);
if (pos*2+1 < CalcTreeWidth(height-1))
TraverseAndBuild(height-1, pos*2+1, vTxid, vMatch);
}
}
uint256 CPartialMerkleTree::TraverseAndExtract(
int height, unsigned int pos, unsigned int &nBitsUsed,
unsigned int &nHashUsed, std::vector<uint256> &vMatch,
std::vector<unsigned int> &vnIndex) {
if (nBitsUsed >= vBits.size()) {
// Overflowed the bits array - failure
fBad = true;
return uint256();
}
bool fParentOfMatch = vBits[nBitsUsed++];
if (height == 0 || !fParentOfMatch) {
// If at height 0, or nothing interesting below, use stored hash and do
// not descend.
if (nHashUsed >= vHash.size()) {
// Overflowed the hash array - failure
fBad = true;
return uint256();
}
const uint256 &hash = vHash[nHashUsed++];
// In case of height 0, we have a matched txid.
if (height == 0 && fParentOfMatch) {
vMatch.push_back(hash);
vnIndex.push_back(pos);
}
return hash;
} else {
// Otherwise, descend into the subtrees to extract matched txids and
// hashes.
uint256 left = TraverseAndExtract(height - 1, pos * 2, nBitsUsed,
nHashUsed, vMatch, vnIndex),
right;
if (pos * 2 + 1 < CalcTreeWidth(height - 1)) {
right = TraverseAndExtract(height - 1, pos * 2 + 1, nBitsUsed,
nHashUsed, vMatch, vnIndex);
if (right == left) {
// The left and right branches should never be identical, as the
// transaction hashes covered by them must each be unique.
fBad = true;
}
} else {
right = left;
}
// and combine them before returning.
return Hash(BEGIN(left), END(left), BEGIN(right), END(right));
}
}
uint256 CPartialMerkleTree::CalcHash(int height, unsigned int pos, const std::vector<uint256> &vTxid) {
//we can never have zero txs in a merkle block, we always need the coinbase tx
//if we do not have this assert, we can hit a memory access violation when indexing into vTxid
assert(vTxid.size() != 0);
if (height == 0) {
// hash at height 0 is the txids themself
return vTxid[pos];
} else {
// calculate left hash
uint256 left = CalcHash(height-1, pos*2, vTxid), right;
// calculate right hash if not beyond the end of the array - copy left hash otherwise
if (pos*2+1 < CalcTreeWidth(height-1))
right = CalcHash(height-1, pos*2+1, vTxid);
else
right = left;
// combine subhashes
return Hash(BEGIN(left), END(left), BEGIN(right), END(right));
}
}
uint256 CPartialMerkleTree::CalcHash(int height, unsigned int pos,
const std::vector<uint256> &vTxid) {
if (height == 0) {
// hash at height 0 is the txids themself.
return vTxid[pos];
} else {
// Calculate left hash.
uint256 left = CalcHash(height - 1, pos * 2, vTxid), right;
// Calculate right hash if not beyond the end of the array - copy left
// hash otherwise1.
if (pos * 2 + 1 < CalcTreeWidth(height - 1)) {
right = CalcHash(height - 1, pos * 2 + 1, vTxid);
} else {
right = left;
}
// Combine subhashes.
return Hash(BEGIN(left), END(left), BEGIN(right), END(right));
}
}