Restore per-algo block index tracking

src/chain.cpp

@@ -33,6 +33,18 @@ CBlockIndex::CBlockIndex(const CBlockHeader& block)
 
 }
 
+int CBlockIndex::GetAlgo() const
+{
+    switch (nVersion & BLOCK_VERSION_ALGO) {
+        case BLOCK_VERSION_SHA256D:
+            return ALGO_SHA256D;
+        case BLOCK_VERSION_RANDOMX:
+            return ALGO_RANDOMX;
+        default:
+            return ALGO_UNKNOWN;
+    }
+}
+
 void CChain::SetTip(CBlockIndex *pindex) {
     if (pindex == nullptr) {
         vChain.clear();

src/chain.h

@@ -201,6 +201,9 @@ public:
     //! (memory only) Maximum nTime in the chain up to and including this block.
     unsigned int nTimeMax{0};
 
+    //! (memory only) Most recent block index for each mining algorithm.
+    CBlockIndex* lastAlgoBlocks[NUM_ALGOS_IMPL]{};
+
     /**
      * Default constructor (no header):
      */
@@ -264,6 +267,8 @@ public:
 
     bool HaveTxsDownloaded() const { return nChainTx != 0; }
 
+    int GetAlgo() const;
+
     int64_t GetBlockTime() const
     {
         return (int64_t)nTime;

src/validation.cpp

@@ -3036,9 +3036,18 @@ CBlockIndex* BlockManager::AddToBlockIndex(const CBlockHeader& block)
         pindexNew->nHeight = pindexNew->pprev->nHeight + 1;
         pindexNew->BuildSkip();
     }
-
-    // Use memcpy to copy the entire array at once.
+    // Keep track of the most recent block for each mining algorithm.
     if (pindexNew->pprev) {
+        memcpy(
+            pindexNew->lastAlgoBlocks,
+            pindexNew->pprev->lastAlgoBlocks,
+            sizeof(pindexNew->lastAlgoBlocks)
+        );
+    }
+
+    const int algo = pindexNew->GetAlgo();
+    if (algo >= 0 && algo < NUM_ALGOS_IMPL) {
+        pindexNew->lastAlgoBlocks[algo] = pindexNew;
     }
 
     pindexNew->nTimeMax = (pindexNew->pprev ? std::max(pindexNew->pprev->nTimeMax, pindexNew->nTime) : pindexNew->nTime);
@@ -3822,9 +3831,18 @@ bool BlockManager::LoadBlockIndex(
         }
         if (ShutdownRequested()) return false;
         CBlockIndex* pindex = item.second;
-
-        // Use memcpy to copy the entire array at once.
+        // Rebuild the most recent block pointer for each mining algorithm.
         if (pindex->pprev) {
+            memcpy(
+                pindex->lastAlgoBlocks,
+                pindex->pprev->lastAlgoBlocks,
+                sizeof(pindex->lastAlgoBlocks)
+            );
+        }
+
+        const int algo = pindex->GetAlgo();
+        if (algo >= 0 && algo < NUM_ALGOS_IMPL) {
+            pindex->lastAlgoBlocks[algo] = pindex;
         }
 
         nHeight = pindex-> nHeight;