1 files changed, 25 insertions, 6 deletions

diff --git a/src/chain.cpp b/src/chain.cpp
index 8d4c4e7dea..47acde882e 100644
--- a/src/chain.cpp
+++ b/src/chain.cpp
@@ -9,7 +9,7 @@
  * CChain implementation
  */
 void CChain::SetTip(CBlockIndex *pindex) {
-    if (pindex == NULL) {
+    if (pindex == nullptr) {
         vChain.clear();
         return;
     }
@@ -49,8 +49,8 @@ CBlockLocator CChain::GetLocator(const CBlockIndex *pindex) const {
 }
 
 const CBlockIndex *CChain::FindFork(const CBlockIndex *pindex) const {
-    if (pindex == NULL) {
-        return NULL;
+    if (pindex == nullptr) {
+        return nullptr;
     }
     if (pindex->nHeight > Height())
         pindex = pindex->GetAncestor(Height());
@@ -63,7 +63,7 @@ CBlockIndex* CChain::FindEarliestAtLeast(int64_t nTime) const
 {
     std::vector<CBlockIndex*>::const_iterator lower = std::lower_bound(vChain.begin(), vChain.end(), nTime,
         [](CBlockIndex* pBlock, const int64_t& time) -> bool { return pBlock->GetBlockTimeMax() < time; });
-    return (lower == vChain.end() ? NULL : *lower);
+    return (lower == vChain.end() ? nullptr : *lower);
 }
 
 /** Turn the lowest '1' bit in the binary representation of a number into a '0'. */
@@ -83,14 +83,14 @@ int static inline GetSkipHeight(int height) {
 CBlockIndex* CBlockIndex::GetAncestor(int height)
 {
     if (height > nHeight || height < 0)
-        return NULL;
+        return nullptr;
 
     CBlockIndex* pindexWalk = this;
     int heightWalk = nHeight;
     while (heightWalk > height) {
         int heightSkip = GetSkipHeight(heightWalk);
         int heightSkipPrev = GetSkipHeight(heightWalk - 1);
-        if (pindexWalk->pskip != NULL &&
+        if (pindexWalk->pskip != nullptr &&
             (heightSkip == height ||
              (heightSkip > height && !(heightSkipPrev < heightSkip - 2 &&
                                        heightSkipPrev >= height)))) {
@@ -148,3 +148,22 @@ int64_t GetBlockProofEquivalentTime(const CBlockIndex& to, const CBlockIndex& fr
     }
     return sign * r.GetLow64();
 }
+
+/** Find the last common ancestor two blocks have.
+ *  Both pa and pb must be non-nullptr. */
+const CBlockIndex* LastCommonAncestor(const CBlockIndex* pa, const CBlockIndex* pb) {
+    if (pa->nHeight > pb->nHeight) {
+        pa = pa->GetAncestor(pb->nHeight);
+    } else if (pb->nHeight > pa->nHeight) {
+        pb = pb->GetAncestor(pa->nHeight);
+    }
+
+    while (pa != pb && pa && pb) {
+        pa = pa->pprev;
+        pb = pb->pprev;
+    }
+
+    // Eventually all chain branches meet at the genesis block.
+    assert(pa == pb);
+    return pa;
+}