Allow to use low difficulty and higher block rewards for devnet (#2369)

* Allow to use low difficulty and higher block rewards for devnet

Configurable through -minimumdifficultyblocks, -highsubsidyblocks and -highsubsidyfactor

* Fix review comments

* Handle review comments

src/chainparams.cpp

@@ -554,6 +554,13 @@ class CDevNetParams : public CChainParams {
             0.01                          // * estimated number of transactions per second
         };
     }
+
+    void UpdateSubsidyAndDiffParams(int nMinimumDifficultyBlocks, int nHighSubsidyBlocks, int nHighSubsidyFactor)
+    {
+        consensus.nMinimumDifficultyBlocks = nMinimumDifficultyBlocks;
+        consensus.nHighSubsidyBlocks = nHighSubsidyBlocks;
+        consensus.nHighSubsidyFactor = nHighSubsidyFactor;
+    }
 };
 static CDevNetParams *devNetParams;
 
@@ -731,3 +738,9 @@ void UpdateRegtestBudgetParameters(int nMasternodePaymentsStartBlock, int nBudge
 {
     regTestParams.UpdateBudgetParameters(nMasternodePaymentsStartBlock, nBudgetPaymentsStartBlock, nSuperblockStartBlock);
 }
+
+void UpdateDevnetSubsidyAndDiffParams(int nMinimumDifficultyBlocks, int nHighSubsidyBlocks, int nHighSubsidyFactor)
+{
+    assert(devNetParams);
+    devNetParams->UpdateSubsidyAndDiffParams(nMinimumDifficultyBlocks, nHighSubsidyBlocks, nHighSubsidyFactor);
+}

src/chainparams.h

@@ -148,4 +148,9 @@ void UpdateRegtestBIP9Parameters(Consensus::DeploymentPos d, int64_t nStartTime,
  */
 void UpdateRegtestBudgetParameters(int nMasternodePaymentsStartBlock, int nBudgetPaymentsStartBlock, int nSuperblockStartBlock);
 
+/**
+ * Allows modifying the subsidy and difficulty devnet parameters.
+ */
+void UpdateDevnetSubsidyAndDiffParams(int nMinimumDifficultyBlocks, int nHighSubsidyBlocks, int nHighSubsidyFactor);
+
 #endif // BITCOIN_CHAINPARAMS_H

src/consensus/params.h

@@ -91,6 +91,11 @@ struct Params {
     int64_t DifficultyAdjustmentInterval() const { return nPowTargetTimespan / nPowTargetSpacing; }
     uint256 nMinimumChainWork;
     uint256 defaultAssumeValid;
+
+    /** these parameters are only used on devnet and can be configured from the outside */
+    int nMinimumDifficultyBlocks{0};
+    int nHighSubsidyBlocks{0};
+    int nHighSubsidyFactor{1};
 };
 } // namespace Consensus
 

src/init.cpp

@@ -1323,6 +1323,15 @@ bool AppInitParameterInteraction()
         UpdateRegtestBudgetParameters(nMasternodePaymentsStartBlock, nBudgetPaymentsStartBlock, nSuperblockStartBlock);
     }
 
+    if (chainparams.NetworkIDString() == CBaseChainParams::DEVNET) {
+        int nMinimumDifficultyBlocks = GetArg("-minimumdifficultyblocks", chainparams.GetConsensus().nMinimumDifficultyBlocks);
+        int nHighSubsidyBlocks = GetArg("-highsubsidyblocks", chainparams.GetConsensus().nHighSubsidyBlocks);
+        int nHighSubsidyFactor = GetArg("-highsubsidyfactor", chainparams.GetConsensus().nHighSubsidyFactor);
+        UpdateDevnetSubsidyAndDiffParams(nMinimumDifficultyBlocks, nHighSubsidyBlocks, nHighSubsidyFactor);
+    } else if (IsArgSet("-minimumdifficultyblocks") || IsArgSet("-highsubsidyblocks") || IsArgSet("-highsubsidyfactor")) {
+        return InitError("Difficulty and subsidy parameters may only be overridden on devnet.");
+    }
+
     return true;
 }
 

src/pow.cpp

@@ -210,6 +210,12 @@ unsigned int GetNextWorkRequiredBTC(const CBlockIndex* pindexLast, const CBlockH
 
 unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params)
 {
+    // this is only active on devnets
+    if (pindexLast->nHeight < params.nMinimumDifficultyBlocks) {
+        unsigned int nProofOfWorkLimit = UintToArith256(params.powLimit).GetCompact();
+        return nProofOfWorkLimit;
+    }
+
     // Most recent algo first
     if (pindexLast->nHeight + 1 >= params.nPowDGWHeight) {
         return DarkGravityWave(pindexLast, pblock, params);

src/validation.cpp

@@ -1171,6 +1171,11 @@ CAmount GetBlockSubsidy(int nPrevBits, int nPrevHeight, const Consensus::Params&
         nSubsidy -= nSubsidy/14;
     }
 
+    // this is only active on devnets
+    if (nPrevHeight < consensusParams.nHighSubsidyBlocks) {
+        nSubsidy *= consensusParams.nHighSubsidyFactor;
+    }
+
     // Hard fork to reduce the block reward by 10 extra percent (allowing budget/superblocks)
     CAmount nSuperblockPart = (nPrevHeight > consensusParams.nBudgetPaymentsStartBlock) ? nSubsidy/10 : 0;