From a7cbb8475f96621d554df600fdf244ca2464c6fa Mon Sep 17 00:00:00 2001
From: Sean Bowe <ewillbefull@gmail.com>
Date: Thu, 12 Apr 2018 17:10:04 -0600
Subject: [PATCH] Abstract `uncommitted` and depth personalization for
 IncrementalMerkleTree.

---
 src/zcash/IncrementalMerkleTree.cpp | 18 +++++++++++-------
 src/zcash/IncrementalMerkleTree.hpp | 14 +++++++++++---
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/src/zcash/IncrementalMerkleTree.cpp b/src/zcash/IncrementalMerkleTree.cpp
index f8fafb31a..3101cf3f3 100644
--- a/src/zcash/IncrementalMerkleTree.cpp
+++ b/src/zcash/IncrementalMerkleTree.cpp
@@ -8,7 +8,11 @@
 
 namespace libzcash {
 
-SHA256Compress SHA256Compress::combine(const SHA256Compress& a, const SHA256Compress& b)
+SHA256Compress SHA256Compress::combine(
+    const SHA256Compress& a,
+    const SHA256Compress& b,
+    size_t depth
+)
 {
     SHA256Compress res = SHA256Compress();
 
@@ -111,7 +115,7 @@ void IncrementalMerkleTree<Depth, Hash>::append(Hash obj) {
         right = obj;
     } else {
         // Combine the leaves and propagate it up the tree
-        boost::optional<Hash> combined = Hash::combine(*left, *right);
+        boost::optional<Hash> combined = Hash::combine(*left, *right, 0);
 
         // Set the "left" leaf to the object and make the "right" leaf none
         left = obj;
@@ -120,7 +124,7 @@ void IncrementalMerkleTree<Depth, Hash>::append(Hash obj) {
         for (size_t i = 0; i < Depth; i++) {
             if (i < parents.size()) {
                 if (parents[i]) {
-                    combined = Hash::combine(*parents[i], *combined);
+                    combined = Hash::combine(*parents[i], *combined, i+1);
                     parents[i] = boost::none;
                 } else {
                     parents[i] = *combined;
@@ -202,15 +206,15 @@ Hash IncrementalMerkleTree<Depth, Hash>::root(size_t depth,
     Hash combine_left =  left  ? *left  : filler.next(0);
     Hash combine_right = right ? *right : filler.next(0);
 
-    Hash root = Hash::combine(combine_left, combine_right);
+    Hash root = Hash::combine(combine_left, combine_right, 0);
 
     size_t d = 1;
 
     BOOST_FOREACH(const boost::optional<Hash>& parent, parents) {
         if (parent) {
-            root = Hash::combine(*parent, root);
+            root = Hash::combine(*parent, root, d);
         } else {
-            root = Hash::combine(root, filler.next(d));
+            root = Hash::combine(root, filler.next(d), d);
         }
 
         d++;
@@ -219,7 +223,7 @@ Hash IncrementalMerkleTree<Depth, Hash>::root(size_t depth,
     // We may not have parents for ancestor trees, so we fill
     // the rest in here.
     while (d < depth) {
-        root = Hash::combine(root, filler.next(d));
+        root = Hash::combine(root, filler.next(d), d);
         d++;
     }
 
diff --git a/src/zcash/IncrementalMerkleTree.hpp b/src/zcash/IncrementalMerkleTree.hpp
index c4cf9d675..ce536fec4 100644
--- a/src/zcash/IncrementalMerkleTree.hpp
+++ b/src/zcash/IncrementalMerkleTree.hpp
@@ -57,9 +57,9 @@ template<size_t Depth, typename Hash>
 class EmptyMerkleRoots {
 public:
     EmptyMerkleRoots() {
-        empty_roots.at(0) = Hash();
+        empty_roots.at(0) = Hash::uncommitted();
         for (size_t d = 1; d <= Depth; d++) {
-            empty_roots.at(d) = Hash::combine(empty_roots.at(d-1), empty_roots.at(d-1));
+            empty_roots.at(d) = Hash::combine(empty_roots.at(d-1), empty_roots.at(d-1), d-1);
         }
     }
     Hash empty_root(size_t depth) {
@@ -213,7 +213,15 @@ public:
     SHA256Compress() : uint256() {}
     SHA256Compress(uint256 contents) : uint256(contents) { }
 
-    static SHA256Compress combine(const SHA256Compress& a, const SHA256Compress& b);
+    static SHA256Compress combine(
+        const SHA256Compress& a,
+        const SHA256Compress& b,
+        size_t depth
+    );
+
+    static SHA256Compress uncommitted() {
+        return SHA256Compress();
+    }
 };
 
 template<size_t Depth, typename Hash>