text: // Copyright (c) 2015 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 "consensus/merkle.h"
  #include "test/test_whatcoin.h"
  
  #include <boost/test/unit_test.hpp>
  
  BOOST_FIXTURE_TEST_SUITE(merkle_tests, TestingSetup)
  
  static uint256 ComputeMerkleRootFromBranch(const uint256& leaf, const std::vector<uint256>& vMerkleBranch, uint32_t nIndex) {
      uint256 hash = leaf;
      for (std::vector<uint256>::const_iterator it = vMerkleBranch.begin(); it != vMerkleBranch.end(); ++it) {
          if (nIndex & 1) {
              hash = Hash(BEGIN(*it), END(*it), BEGIN(hash), END(hash));
          } else {
              hash = Hash(BEGIN(hash), END(hash), BEGIN(*it), END(*it));
          }
          nIndex >>= 1;
      }
      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);
              CHash256().Write(inner[level].begin(), 32).Write(h.begin(), 32).Finalize(h.begin());
          }
          // 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);
          }
          CHash256().Write(h.begin(), 32).Write(h.begin(), 32).Finalize(h.begin());
          // 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;
                  }
              }
              CHash256().Write(inner[level].begin(), 32).Write(h.begin(), 32).Finalize(h.begin());
              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)
  {
      vMerkleTree.clear();
      vMerkleTree.reserve(block.vtx.size() * 2 + 16); // Safe upper bound for the number of total nodes.
      for (std::vector<CTransactionRef>::const_iterator it(block.vtx.begin()); it != block.vtx.end(); ++it)
          vMerkleTree.push_back((*it)->GetHash());
      int j = 0;
      bool mutated = false;
      for (int nSize = block.vtx.size(); nSize > 1; nSize = (nSize + 1) / 2)
      {
          for (int i = 0; i < nSize; i += 2)
          {
              int i2 = std::min(i+1, nSize-1);
              if (i2 == i + 1 && i2 + 1 == nSize && vMerkleTree[j+i] == vMerkleTree[j+i2]) {
                  // Two identical hashes at the end of the list at a particular level.
                  mutated = true;
              }
              vMerkleTree.push_back(Hash(vMerkleTree[j+i].begin(), vMerkleTree[j+i].end(),
                                         vMerkleTree[j+i2].begin(), vMerkleTree[j+i2].end()));
          }
          j += nSize;
      }
      if (fMutated) {
          *fMutated = mutated;
      }
      return (vMerkleTree.empty() ? uint256() : vMerkleTree.back());
  }
  
  // Older version of the merkle branch computation code, for comparison.
  static std::vector<uint256> BlockGetMerkleBranch(const CBlock& block, const std::vector<uint256>& vMerkleTree, int nIndex)
  {
      std::vector<uint256> vMerkleBranch;
      int j = 0;
      for (int nSize = block.vtx.size(); nSize > 1; nSize = (nSize + 1) / 2)
      {
          int i = std::min(nIndex^1, nSize-1);
          vMerkleBranch.push_back(vMerkleTree[j+i]);
          nIndex >>= 1;
          j += nSize;
      }
      return vMerkleBranch;
  }
  
  static inline int ctz(uint32_t i) {
      if (i == 0) return 0;
      int j = 0;
      while (!(i & 1)) {
          j++;
          i >>= 1;
      }
      return j;
  }
  
  BOOST_AUTO_TEST_CASE(merkle_test)
  {
      for (int i = 0; i < 32; i++) {
          // Try 32 block sizes: all sizes from 0 to 16 inclusive, and then 15 random sizes.
          int ntx = (i <= 16) ? i : 17 + (InsecureRandRange(4000));
          // Try up to 3 mutations.
          for (int mutate = 0; mutate <= 3; mutate++) {
              int duplicate1 = mutate >= 1 ? 1 << ctz(ntx) : 0; // The last how many transactions to duplicate first.
              if (duplicate1 >= ntx) break; // Duplication of the entire tree results in a different root (it adds a level).
              int ntx1 = ntx + duplicate1; // The resulting number of transactions after the first duplication.
              int duplicate2 = mutate >= 2 ? 1 << ctz(ntx1) : 0; // Likewise for the second mutation.
              if (duplicate2 >= ntx1) break;
              int ntx2 = ntx1 + duplicate2;
              int duplicate3 = mutate >= 3 ? 1 << ctz(ntx2) : 0; // And for the third mutation.
              if (duplicate3 >= ntx2) break;
              int ntx3 = ntx2 + duplicate3;
              // Build a block with ntx different transactions.
              CBlock block;
              block.vtx.resize(ntx);
              for (int j = 0; j < ntx; j++) {
                  CMutableTransaction mtx;
                  mtx.nLockTime = j;
                  block.vtx[j] = MakeTransactionRef(std::move(mtx));
              }
              // Compute the root of the block before mutating it.
              bool unmutatedMutated = false;
              uint256 unmutatedRoot = BlockMerkleRoot(block, &unmutatedMutated);
              BOOST_CHECK(unmutatedMutated == false);
              // Optionally mutate by duplicating the last transactions, resulting in the same merkle root.
              block.vtx.resize(ntx3);
              for (int j = 0; j < duplicate1; j++) {
                  block.vtx[ntx + j] = block.vtx[ntx + j - duplicate1];
              }
              for (int j = 0; j < duplicate2; j++) {
                  block.vtx[ntx1 + j] = block.vtx[ntx1 + j - duplicate2];
              }
              for (int j = 0; j < duplicate3; j++) {
                  block.vtx[ntx2 + j] = block.vtx[ntx2 + j - duplicate3];
              }
              // Compute the merkle root and merkle tree using the old mechanism.
              bool oldMutated = false;
              std::vector<uint256> merkleTree;
              uint256 oldRoot = BlockBuildMerkleTree(block, &oldMutated, merkleTree);
              // Compute the merkle root using the new mechanism.
              bool newMutated = false;
              uint256 newRoot = BlockMerkleRoot(block, &newMutated);
              BOOST_CHECK(oldRoot == newRoot);
              BOOST_CHECK(newRoot == unmutatedRoot);
              BOOST_CHECK((newRoot == uint256()) == (ntx == 0));
              BOOST_CHECK(oldMutated == newMutated);
              BOOST_CHECK(newMutated == !!mutate);
              // If no mutation was done (once for every ntx value), try up to 16 branches.
              if (mutate == 0) {
                  for (int loop = 0; loop < std::min(ntx, 16); loop++) {
                      // If ntx <= 16, try all branches. Otherwise, try 16 random ones.
                      int mtx = loop;
                      if (ntx > 16) {
                          mtx = InsecureRandRange(ntx);
                      }
                      std::vector<uint256> newBranch = BlockMerkleBranch(block, mtx);
                      std::vector<uint256> oldBranch = BlockGetMerkleBranch(block, merkleTree, mtx);
                      BOOST_CHECK(oldBranch == newBranch);
                      BOOST_CHECK(ComputeMerkleRootFromBranch(block.vtx[mtx]->GetHash(), newBranch, mtx) == oldRoot);
                  }
              }
          }
      }
  }
  
  BOOST_AUTO_TEST_SUITE_END()
  