Merge pull request #1392 from rnicoll/1.14-digishield-retarget

Introduce Digishield retarget code to 1.14

src/dogecoin.cpp

@@ -16,6 +16,24 @@ int static generateMTRandom(unsigned int s, int range)
     return dist(gen);
 }
 
+// Dogecoin: Normally minimum difficulty blocks can only occur in between
+// retarget blocks. However, once we introduce Digishield every block is
+// a retarget, so we need to handle minimum difficulty on all blocks.
+bool AllowDigishieldMinDifficultyForBlock(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params)
+{
+    // check if the chain allows minimum difficulty blocks
+    if (!params.fPowAllowMinDifficultyBlocks)
+        return false;
+
+    // check if the chain allows minimum difficulty blocks on recalc blocks
+    if (pindexLast->nHeight < 157500)
+    // if (!params.fPowAllowDigishieldMinDifficultyBlocks)
+        return false;
+
+    // Allow for a minimum block time if the elapsed time > 2*nTargetSpacing
+    return (pblock->GetBlockTime() > pindexLast->GetBlockTime() + params.nPowTargetSpacing*2);
+}
+
 unsigned int CalculateDogecoinNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime, const Consensus::Params& params)
 {
     int nHeight = pindexLast->nHeight + 1;
@@ -88,8 +106,7 @@ bool CheckAuxPowProofOfWork(const CBlockHeader& block, const Consensus::Params&
                      params.nAuxpowChainId, block.nVersion);
 
     /* If there is no auxpow, just check the block hash.  */
-    if (!block.auxpow)
-    {
+    if (!block.auxpow) {
         if (block.IsAuxpow())
             return error("%s : no auxpow on block with auxpow version",
                          __func__);

src/dogecoin.h

@@ -6,6 +6,7 @@
 #include "chain.h"
 #include "chainparams.h"
 
+bool AllowDigishieldMinDifficultyForBlock(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params);
 CAmount GetDogecoinBlockSubsidy(int nHeight, const Consensus::Params& consensusParams, uint256 prevHash);
 unsigned int CalculateDogecoinNextWorkRequired(const CBlockIndex* pindexLast, int64_t nLastRetargetTime, const Consensus::Params& params);
 

src/pow.cpp

@@ -21,8 +21,21 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
     if (pindexLast == NULL)
         return nProofOfWorkLimit;
 
+    // Dogecoin: Special rules for minimum difficulty blocks with Digishield
+    if (AllowDigishieldMinDifficultyForBlock(pindexLast, pblock, params))
+    {
+        // Special difficulty rule for testnet:
+        // If the new block's timestamp is more than 2* nTargetSpacing minutes
+        // then allow mining of a min-difficulty block.
+        return nProofOfWorkLimit;
+    }
+
     // Only change once per difficulty adjustment interval
-    if ((pindexLast->nHeight+1) % params.DifficultyAdjustmentInterval() != 0)
+    bool fNewDifficultyProtocol = (pindexLast->nHeight >= 145000);
+    const int64_t difficultyAdjustmentInterval = fNewDifficultyProtocol
+                                                 ? 1
+                                                 : params.DifficultyAdjustmentInterval();
+    if ((pindexLast->nHeight+1) % difficultyAdjustmentInterval != 0)
     {
         if (params.fPowAllowMinDifficultyBlocks)
         {
@@ -45,9 +58,9 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
 
     // Litecoin: This fixes an issue where a 51% attack can change difficulty at will.
     // Go back the full period unless it's the first retarget after genesis. Code courtesy of Art Forz
-    int blockstogoback = params.DifficultyAdjustmentInterval()-1;
-    if ((pindexLast->nHeight+1) != params.DifficultyAdjustmentInterval())
-        blockstogoback = params.DifficultyAdjustmentInterval();
+    int blockstogoback = difficultyAdjustmentInterval-1;
+    if ((pindexLast->nHeight+1) != difficultyAdjustmentInterval)
+        blockstogoback = difficultyAdjustmentInterval;
 
     // Go back by what we want to be 14 days worth of blocks
     int nHeightFirst = pindexLast->nHeight - blockstogoback;

src/primitives/pureheader.h

@@ -149,7 +149,9 @@ public:
      */
     inline bool IsLegacy() const
     {
-        return nVersion == 1;
+        return nVersion == 1
+            // Dogecoin: We have a random v2 block with no AuxPoW, treat as legacy
+            || (nVersion == 2 && GetChainId() == 0);
     }
 };
 

src/test/auxpow_tests.cpp

@@ -362,7 +362,9 @@ BOOST_AUTO_TEST_CASE(auxpow_pow)
     mineBlock(block, true);
     BOOST_CHECK(CheckAuxPowProofOfWork(block, params));
 
-    block.nVersion = 2;
+    // Dogecoin block version 2 can be both AuxPoW and regular, so test 3
+
+    block.nVersion = 3;
     mineBlock(block, true);
     BOOST_CHECK(!CheckAuxPowProofOfWork(block, params));