text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2014 The Bitcoin developers
  // Copyright (c) 2015-2017 The PIVX 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 "primitives/block.h" // for MAX_BLOCK_SIZE
  #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);
  }
  
  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 0;
      }
      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 0;
          }
          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);
          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 0;
      // check for excessively high numbers of transactions
      if (nTransactions > MAX_BLOCK_SIZE_CURRENT / 60) // 60 is the lower bound for the size of a serialized CTransaction
          return 0;
      // there can never be more hashes provided than one for every txid
      if (vHash.size() > nTransactions)
          return 0;
      // 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 0;
      // 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 0;
      // 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 0;
      // verify that all hashes were consumed
      if (nHashUsed != vHash.size())
          return 0;
      return hashMerkleRoot;
  }