1 files changed, 20 insertions, 1 deletions
diff --git a/src/chain.cpp b/src/chain.cpp
index a5b369c4fc..ffd58d471d 100644
--- a/src/chain.cpp
+++ b/src/chain.cpp
@@ -126,7 +126,7 @@ arith_uint256 GetBlockProof(const CBlockIndex& block)
     if (fNegative || fOverflow || bnTarget == 0)
         return 0;
     // We need to compute 2**256 / (bnTarget+1), but we can't represent 2**256
-    // as it's too large for a arith_uint256. However, as 2**256 is at least as large
+    // as it's too large for an arith_uint256. However, as 2**256 is at least as large
     // as bnTarget+1, it is equal to ((2**256 - bnTarget - 1) / (bnTarget+1)) + 1,
     // or ~bnTarget / (nTarget+1) + 1.
     return (~bnTarget / (bnTarget + 1)) + 1;
@@ -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-NULL. */
+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;
+}