diff --git a/SHAMapDiff.cpp b/SHAMapDiff.cpp
new file mode 100644
index 0000000000..eb63b031af
--- /dev/null
+++ b/SHAMapDiff.cpp
@@ -0,0 +1,139 @@
+#include "SHAMap.h"
+
+#include <stack>
+
+class SHAMapDiffNode
+{
+	public:
+	SHAMapNode mNodeID;
+	uint256 mOurHash, mOtherHash;
+	
+	SHAMapDiffNode(SHAMapNode id, const uint256& ourHash, const uint256& otherHash) :
+		mNodeID(id), mOurHash(ourHash), mOtherHash(otherHash) { ; }
+};
+
+bool SHAMap::compare(SHAMap::pointer otherMap, SHAMapDiff& differences, int maxCount)
+{ // 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
+
+	std::stack<SHAMapDiffNode> nodeStack; // track nodes we've pushed
+	nodeStack.push(SHAMapDiffNode(SHAMapNode(), getHash(), otherMap->getHash()));
+
+	ScopedLock sl(Lock());
+ 	while(nodeStack.size())
+ 	{
+ 		SHAMapDiffNode node(nodeStack.top());
+ 		nodeStack.pop();
+ 		if(node.mOurHash!=node.mOtherHash)
+ 		{
+		 	if(node.mNodeID.isLeaf())
+		 	{
+		 		if(!node.mOurHash)
+		 		{ // leaf only in our tree
+			 		SHAMapLeafNode::pointer thisNode=getLeaf(node.mNodeID, node.mOurHash, false);
+			 		for(SHAMapItem::pointer item=thisNode->firstItem(); item; item=thisNode->nextItem(item->getTag()))
+			 		{ // items in leaf only in our tree
+			 			differences[item->getTag()]=
+			 				std::pair<SHAMapItem::pointer, SHAMapItem::pointer>(item, SHAMapItem::pointer());
+						if((--maxCount)<=0) return false;
+			 		}
+		 		}
+		 		else if(!node.mOtherHash)
+		 		{ // leaf only in other tree
+			 		SHAMapLeafNode::pointer otherNode=otherMap->getLeaf(node.mNodeID, node.mOtherHash, false);
+			 		for(SHAMapItem::pointer item=otherNode->firstItem(); item; item=otherNode->nextItem(item->getTag()))
+			 		{ // items in leaf only in our tree
+			 			differences[item->getTag()]=
+			 				std::pair<SHAMapItem::pointer, SHAMapItem::pointer>(SHAMapItem::pointer(), item);
+						if((--maxCount)<=0) return false;
+			 		}
+		 		}
+		 		else
+		 		{ // leaf in both trees, but differs
+			 		SHAMapLeafNode::pointer thisNode=getLeaf(node.mNodeID, node.mOurHash, false);
+			 		SHAMapLeafNode::pointer otherNode=otherMap->getLeaf(node.mNodeID, node.mOtherHash, false);
+			 		SHAMapItem::pointer ourItem=thisNode->firstItem();
+			 		SHAMapItem::pointer otherItem=otherNode->firstItem();
+			 		while(ourItem || otherItem)
+			 		{
+			 			if(!otherItem)
+			 			{ // we have items, other tree does not
+			 				differences[otherItem->getTag()]=
+			 					std::pair<SHAMapItem::pointer, SHAMapItem::pointer>(ourItem, otherItem);
+							if((--maxCount)<=0) return false;
+							otherItem=otherNode->nextItem(otherItem->getTag());
+			 			}
+			 			else if(!ourItem)
+			 			{ // we have no items, other tree does
+			 				differences[ourItem->getTag()]=
+			 					std::pair<SHAMapItem::pointer, SHAMapItem::pointer>(ourItem, otherItem);
+							if((--maxCount)<=0) return false;
+							ourItem=thisNode->nextItem(ourItem->getTag());
+			 			}
+			 			else if(ourItem->getTag()==otherItem->getTag())
+			 			{ // we have items with the same tag
+			 				if(ourItem->getData()!=otherItem->getData())
+			 				{ // different data
+				 				differences[ourItem->getTag()]=
+				 					std::pair<SHAMapItem::pointer, SHAMapItem::pointer>(ourItem, otherItem);
+								if((--maxCount)<=0) return false;
+			 				}
+							ourItem=thisNode->nextItem(ourItem->getTag());
+							otherItem=otherNode->nextItem(otherItem->getTag());
+			 			}
+			 			else if(ourItem->getTag()<otherItem->getTag())
+			 			{ // our item comes first
+			 				differences[ourItem->getTag()]=
+			 					std::pair<SHAMapItem::pointer, SHAMapItem::pointer>(ourItem, SHAMapItem::pointer());
+							if((--maxCount)<=0) return false;
+							ourItem=thisNode->nextItem(ourItem->getTag());
+			 			}
+			 			else
+			 			{ // other item comes first
+			 				differences[otherItem->getTag()]=
+			 					std::pair<SHAMapItem::pointer, SHAMapItem::pointer>(SHAMapItem::pointer(), otherItem);
+							if((--maxCount)<=0) return false;
+							otherItem=otherNode->nextItem(otherItem->getTag());
+			 			}
+			 		}
+				}
+			}
+		 	else
+		 	{ // inner node different in two trees
+		 		if(!node.mOurHash)
+		 		{ // node only exist in our tree
+			 		SHAMapInnerNode::pointer thisNode=getInner(node.mNodeID, node.mOurHash, false);
+			 		for(int i=0; i<32; i++)
+			 		{ // push all existing branches onto the stack
+			 			if(!!thisNode->getChildHash(i))
+			 				nodeStack.push(SHAMapDiffNode(thisNode->getChildNodeID(i),
+			 					thisNode->getChildHash(i), uint256()));
+			 		}
+		 		}
+		 		else if(!node.mOtherHash)
+		 		{ // node only exists in other tree
+			 		SHAMapInnerNode::pointer otherNode=otherMap->getInner(node.mNodeID, node.mOtherHash, false);
+			 		for(int i=0; i<32; i++)
+			 		{ // push all existing branches onto the stack
+			 			if(!!otherNode->getChildHash(i))
+			 				nodeStack.push(SHAMapDiffNode(otherNode->getChildNodeID(i),
+			 					uint256(), otherNode->getChildHash(i)));
+			 		}
+		 		}
+		 		else
+		 		{ // node in both trees, but differs
+			 		SHAMapInnerNode::pointer thisNode=getInner(node.mNodeID, node.mOurHash, false);
+			 		SHAMapInnerNode::pointer otherNode=otherMap->getInner(node.mNodeID, node.mOtherHash, false);
+			 		for(int i=0; i<32; i++)
+			 		{ // push all differing branches onto the stack
+			 			if(thisNode->getChildHash(i)!=otherNode->getChildHash(i))
+			 				nodeStack.push(SHAMapDiffNode(thisNode->getChildNodeID(i),
+			 					thisNode->getChildHash(i), otherNode->getChildHash(i)));
+			 		}
+				}
+			}
+		}
+	}
+	return true;
+}