text: //------------------------------------------------------------------------------
  /*
      This file is part of rippled: https://github.com/ripple/rippled
      Copyright (c) 2012, 2013 Ripple Labs Inc.
  
      Permission to use, copy, modify, and/or distribute this software for any
      purpose  with  or without fee is hereby granted, provided that the above
      copyright notice and this permission notice appear in all copies.
  
      THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
      WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
      MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
      ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
      WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
      ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
      OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
  //==============================================================================
  
  #include <ripple/basics/contract.h>
  #include <ripple/shamap/SHAMap.h>
  
  namespace ripple {
  
  // This code is used to compare another node's transaction tree
  // to our own. It returns a map containing all items that are different
  // between two SHA maps. It is optimized not to descend down tree
  // branches with the same branch hash. A limit can be passed so
  // that we will abort early if a node sends a map to us that
  // makes no sense at all. (And our sync algorithm will avoid
  // synchronizing matching branches too.)
  
  bool SHAMap::walkBranch (SHAMapAbstractNode* node,
                           std::shared_ptr<SHAMapItem const> const& otherMapItem,
                           bool isFirstMap,Delta& differences, int& maxCount) const
  {
      // Walk a branch of a SHAMap that's matched by an empty branch or single item in the other map
      std::stack <SHAMapAbstractNode*, std::vector<SHAMapAbstractNode*>> nodeStack;
      nodeStack.push (node);
  
      bool emptyBranch = !otherMapItem;
  
      while (!nodeStack.empty ())
      {
          node = nodeStack.top ();
          nodeStack.pop ();
  
          if (node->isInner ())
          {
              // This is an inner node, add all non-empty branches
              auto inner = static_cast<SHAMapInnerNode*>(node);
              for (int i = 0; i < 16; ++i)
                  if (!inner->isEmptyBranch (i))
                      nodeStack.push ({descendThrow (inner, i)});
          }
          else
          {
              // This is a leaf node, process its item
              auto item = static_cast<SHAMapTreeNode*>(node)->peekItem();
  
              if (emptyBranch || (item->key() != otherMapItem->key()))
              {
                  // unmatched
                  if (isFirstMap)
                      differences.insert (std::make_pair (item->key(),
                          DeltaRef (item, std::shared_ptr<SHAMapItem const> ())));
                  else
                      differences.insert (std::make_pair (item->key(),
                          DeltaRef (std::shared_ptr<SHAMapItem const> (), item)));
  
                  if (--maxCount <= 0)
                      return false;
              }
              else if (item->peekData () != otherMapItem->peekData ())
              {
                  // non-matching items with same tag
                  if (isFirstMap)
                      differences.insert (std::make_pair (item->key(),
                                                  DeltaRef (item, otherMapItem)));
                  else
                      differences.insert (std::make_pair (item->key(),
                                                  DeltaRef (otherMapItem, item)));
  
                  if (--maxCount <= 0)
                      return false;
  
                  emptyBranch = true;
              }
              else
              {
                  // exact match
                  emptyBranch = true;
              }
          }
      }
  
      if (!emptyBranch)
      {
          // otherMapItem was unmatched, must add
          if (isFirstMap) // this is first map, so other item is from second
              differences.insert(std::make_pair(otherMapItem->key(),
                                                DeltaRef(std::shared_ptr<SHAMapItem const>(),
                                                         otherMapItem)));
          else
              differences.insert(std::make_pair(otherMapItem->key(),
                  DeltaRef(otherMapItem, std::shared_ptr<SHAMapItem const>())));
  
          if (--maxCount <= 0)
              return false;
      }
  
      return true;
  }
  
  bool
  SHAMap::compare (SHAMap const& otherMap,
                   Delta& differences, int maxCount) const
  {
      // compare two hash trees, add up to maxCount differences to the difference table
      // return value: true=complete table of differences given, false=too many differences
      // throws on corrupt tables or missing nodes
      // CAUTION: otherMap is not locked and must be immutable
  
      assert (isValid () && otherMap.isValid ());
  
      if (getHash () == otherMap.getHash ())
          return true;
  
      using StackEntry = std::pair <SHAMapAbstractNode*, SHAMapAbstractNode*>;
      std::stack <StackEntry, std::vector<StackEntry>> nodeStack; // track nodes we've pushed
  
      nodeStack.push ({root_.get(), otherMap.root_.get()});
      while (!nodeStack.empty ())
      {
          SHAMapAbstractNode* ourNode = nodeStack.top().first;
          SHAMapAbstractNode* otherNode = nodeStack.top().second;
          nodeStack.pop ();
  
          if (!ourNode || !otherNode)
          {
              assert (false);
              Throw<SHAMapMissingNode> (type_, uint256 ());
          }
  
          if (ourNode->isLeaf () && otherNode->isLeaf ())
          {
              // two leaves
              auto ours = static_cast<SHAMapTreeNode*>(ourNode);
              auto other = static_cast<SHAMapTreeNode*>(otherNode);
              if (ours->peekItem()->key() == other->peekItem()->key())
              {
                  if (ours->peekItem()->peekData () != other->peekItem()->peekData ())
                  {
                      differences.insert (std::make_pair (ours->peekItem()->key(),
                                                   DeltaRef (ours->peekItem (),
                                                   other->peekItem ())));
                      if (--maxCount <= 0)
                          return false;
                  }
              }
              else
              {
                  differences.insert (std::make_pair(ours->peekItem()->key(),
                                                     DeltaRef(ours->peekItem(),
                                                     std::shared_ptr<SHAMapItem const>())));
                  if (--maxCount <= 0)
                      return false;
  
                  differences.insert(std::make_pair(other->peekItem()->key(),
                      DeltaRef(std::shared_ptr<SHAMapItem const>(), other->peekItem ())));
                  if (--maxCount <= 0)
                      return false;
              }
          }
          else if (ourNode->isInner () && otherNode->isLeaf ())
          {
              auto ours = static_cast<SHAMapInnerNode*>(ourNode);
              auto other = static_cast<SHAMapTreeNode*>(otherNode);
              if (!walkBranch (ours, other->peekItem (),
                      true, differences, maxCount))
                  return false;
          }
          else if (ourNode->isLeaf () && otherNode->isInner ())
          {
              auto ours = static_cast<SHAMapTreeNode*>(ourNode);
              auto other = static_cast<SHAMapInnerNode*>(otherNode);
              if (!otherMap.walkBranch (other, ours->peekItem (),
                                         false, differences, maxCount))
                  return false;
          }
          else if (ourNode->isInner () && otherNode->isInner ())
          {
              auto ours = static_cast<SHAMapInnerNode*>(ourNode);
              auto other = static_cast<SHAMapInnerNode*>(otherNode);
              for (int i = 0; i < 16; ++i)
                  if (ours->getChildHash (i) != other->getChildHash (i))
                  {
                      if (other->isEmptyBranch (i))
                      {
                          // We have a branch, the other tree does not
                          SHAMapAbstractNode* iNode = descendThrow (ours, i);
                          if (!walkBranch (iNode,
                                           std::shared_ptr<SHAMapItem const> (), true,
                                           differences, maxCount))
                              return false;
                      }
                      else if (ours->isEmptyBranch (i))
                      {
                          // The other tree has a branch, we do not
                          SHAMapAbstractNode* iNode =
                              otherMap.descendThrow(other, i);
                          if (!otherMap.walkBranch (iNode,
                                                     std::shared_ptr<SHAMapItem const>(),
                                                     false, differences, maxCount))
                              return false;
                      }
                      else // The two trees have different non-empty branches
                          nodeStack.push ({descendThrow (ours, i),
                                          otherMap.descendThrow (other, i)});
                  }
          }
          else
              assert (false);
      }
  
      return true;
  }
  
  void SHAMap::walkMap (std::vector<SHAMapMissingNode>& missingNodes, int maxMissing) const
  {
      if (!root_->isInner ())  // root_ is only node, and we have it
          return;
  
      using StackEntry = std::shared_ptr<SHAMapInnerNode>;
      std::stack <StackEntry, std::vector <StackEntry>> nodeStack;
  
      nodeStack.push (std::static_pointer_cast<SHAMapInnerNode>(root_));
  
      while (!nodeStack.empty ())
      {
          std::shared_ptr<SHAMapInnerNode> node = std::move (nodeStack.top());
          nodeStack.pop ();
  
          for (int i = 0; i < 16; ++i)
          {
              if (!node->isEmptyBranch (i))
              {
                  std::shared_ptr<SHAMapAbstractNode> nextNode = descendNoStore (node, i);
  
                  if (nextNode)
                  {
                      if (nextNode->isInner ())
                          nodeStack.push(
                              std::static_pointer_cast<SHAMapInnerNode>(nextNode));
                  }
                  else
                  {
                      missingNodes.emplace_back (type_, node->getChildHash (i));
                      if (--maxMissing <= 0)
                          return;
                  }
              }
          }
      }
  }
  
  } // ripple
  