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merkleblock.cpp
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merkleblock.cpp
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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2014 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include "merkleblock.h"
#include "hash.h"
#include "consensus/consensus.h"
#include "utilstrencodings.h"
using namespace std;
CMerkleBlock::CMerkleBlock(const CBlock& block, CBloomFilter& filter)
{
header = block.GetBlockHeader();
vector<bool> vMatch;
vector<uint256> vHashes;
vMatch.reserve(block.vtx.size());
vHashes.reserve(block.vtx.size());
for (unsigned int i = 0; i < block.vtx.size(); i++)
{
const uint256& hash = block.vtx[i].GetHash();
if (filter.IsRelevantAndUpdate(block.vtx[i]))
{
vMatch.push_back(true);
vMatchedTxn.push_back(make_pair(i, hash));
}
else
vMatch.push_back(false);
vHashes.push_back(hash);
}
txn = CPartialMerkleTree(vHashes, vMatch);
}
CMerkleBlock::CMerkleBlock(const CBlock& block, const std::set<uint256>& txids)
{
header = block.GetBlockHeader();
vector<bool> vMatch;
vector<uint256> vHashes;
vMatch.reserve(block.vtx.size());
vHashes.reserve(block.vtx.size());
for (unsigned int i = 0; i < block.vtx.size(); i++)
{
const uint256& hash = block.vtx[i].GetHash();
if (txids.count(hash))
vMatch.push_back(true);
else
vMatch.push_back(false);
vHashes.push_back(hash);
}
txn = CPartialMerkleTree(vHashes, vMatch);
}
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));
}
}
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) {
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++];
if (height==0 && fParentOfMatch) // in case of height 0, we have a matched txid
vMatch.push_back(hash);
return hash;
} else {
// otherwise, descend into the subtrees to extract matched txids and hashes
uint256 left = TraverseAndExtract(height-1, pos*2, nBitsUsed, nHashUsed, vMatch), right;
if (pos*2+1 < CalcTreeWidth(height-1)) {
right = TraverseAndExtract(height-1, pos*2+1, nBitsUsed, nHashUsed, vMatch);
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));
}
}
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);
}
CPartialMerkleTree::CPartialMerkleTree() : nTransactions(0), fBad(true) {}
uint256 CPartialMerkleTree::ExtractMatches(std::vector<uint256> &vMatch) {
vMatch.clear();
// An empty set will not work
if (nTransactions == 0)
return uint256();
// check for excessively high numbers of transactions
if (nTransactions > MAX_BLOCK_SIZE / 60) // 60 is the lower bound for the size of a serialized CTransaction
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);
// verify that no problems occured 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;
}

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