ProjectFactor · ReverseControl · Jul 10, 2025 · Jul 1, 2025 · Jul 1, 2025 · Jul 1, 2025
diff --git a/configure.ac b/configure.ac
@@ -1,7 +1,7 @@
 AC_PREREQ([2.69])
-define(_CLIENT_VERSION_MAJOR, 5)    
-define(_CLIENT_VERSION_MINOR, 0)
-define(_CLIENT_VERSION_BUILD, 70 )
+define(_CLIENT_VERSION_MAJOR, 5)
+define(_CLIENT_VERSION_MINOR, 1)
+define(_CLIENT_VERSION_BUILD, 42)
 define(_CLIENT_VERSION_RC, 0)
 define(_CLIENT_VERSION_IS_RELEASE, true )
 define(_COPYRIGHT_YEAR, 2025)

diff --git a/src/chainparams.cpp b/src/chainparams.cpp
@@ -129,6 +129,12 @@ class CMainParams : public CChainParams {
         consensus.nDeadpoolAnnounceValidity = 672;
         consensus.nDeadpoolAnnounceMinBurn = 1000000; // 0.01 COIN
 
+        // Hard diff removal hardfork
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].bit = 26;
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].nStartTime = 1743465600LL; // 2025-04-01
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].nTimeout = 1775001600LL; // 2026-04-01
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].min_activation_height = 160000; // no delay
+
         /**
          * The message start string is designed to be unlikely to occur in normal data.
          * The characters are rarely used upper ASCII, not valid as UTF-8, and produce
@@ -232,6 +238,12 @@ class CTestNetParams : public CChainParams {
         consensus.nDeadpoolAnnounceValidity = 100;
         consensus.nDeadpoolAnnounceMinBurn = 1000000; // 0.01 COIN
 
+        // Hard diff removal hardfork
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].bit = 26;
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].nStartTime = 0;
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].nTimeout = Consensus::BIP9Deployment::NO_TIMEOUT;
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].min_activation_height = (4 * consensus.nMinerConfirmationWindow);
+
 	    //Number of rounds for gHash to generate random Ws around which to search for semiprimes.
 	    consensus.hashRounds = 1;
 
@@ -389,6 +401,12 @@ class SigNetParams : public CChainParams {
         consensus.nDeadpoolAnnounceValidity = 100;
         consensus.nDeadpoolAnnounceMinBurn = 1000000; // 0.01 COIN
 
+        // Hard diff removal hardfork
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].bit = 26;
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].nStartTime = 1743465600LL; // 2025-04-01
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].nTimeout = 1775001600LL; // 2026-04-01
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].min_activation_height = 160000; // no delay
+
         vFixedSeeds.clear();
         base58Prefixes[PUBKEY_ADDRESS] = std::vector<unsigned char>(1,111);
         base58Prefixes[SCRIPT_ADDRESS] = std::vector<unsigned char>(1,196);
@@ -467,6 +485,12 @@ class CRegTestParams : public CChainParams {
         consensus.nDeadpoolAnnounceValidity = 100;
         consensus.nDeadpoolAnnounceMinBurn = 1000000; // 0.01 COIN
 
+        // Hard diff removal hardfork
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].bit = 26;
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].nStartTime = 1743465600LL; // 2025-04-01
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].nTimeout = 1775001600LL; // 2026-04-01
+        consensus.vDeployments[Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL].min_activation_height = 160000; // no delay
+
         UpdateActivationParametersFromArgs(args);
 
         vFixedSeeds.clear(); //!< Regtest mode doesn't have any fixed seeds.

diff --git a/src/consensus/params.h b/src/consensus/params.h
@@ -29,6 +29,7 @@ constexpr bool ValidDeployment(BuriedDeployment dep) { return dep <= DEPLOYMENT_
 enum DeploymentPos : uint16_t {
     DEPLOYMENT_TESTDUMMY,
     DEPLOYMENT_DEADPOOL,
+    DEPLOYMENT_HARD_DIFF_REMOVAL,
     // NOTE: Also add new deployments to VersionBitsDeploymentInfo in deploymentinfo.cpp
     MAX_VERSION_BITS_DEPLOYMENTS
 };

diff --git a/src/deploymentinfo.cpp b/src/deploymentinfo.cpp
@@ -15,6 +15,10 @@ const struct VBDeploymentInfo VersionBitsDeploymentInfo[Consensus::MAX_VERSION_B
         /*.name =*/ "deadpool",
         /*.gbt_force =*/ true,
     },
+    {
+        /*.name =*/ "hard_diff_removal",
+        /*.gbt_force =*/ true,
+    },
 };
 
 std::string DeploymentName(Consensus::BuriedDeployment dep)

diff --git a/src/pow.cpp b/src/pow.cpp
@@ -28,6 +28,9 @@
 //Fancy popcount implementation
 #include <libpopcnt.h>
 
+// DeploymentActiveAfter
+#include <deploymentstatus.h>
+
 uint16_t GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader* pblock, const Consensus::Params& params)
 {
     assert(pindexLast != nullptr);
@@ -62,6 +65,73 @@ uint16_t GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader*
     return CalculateNextWorkRequired(pindexLast, pindexFirst->GetBlockTime(), params);
 }
 
+int32_t CalculateDifficultyDelta(const int32_t nBits, const double nPeriodTimeProportionConsumed, const bool isHardDiffRemoved) {
+    if (!isHardDiffRemoved) {
+        // Original difficulty adjustment algorithm
+
+        //Note for mainnet:
+        //If it takes more than 1 minute over the target blocktime, reduce difficulty.
+        if (nPeriodTimeProportionConsumed > 1.0333f)
+            return -1;
+
+        //Note for mainnet:
+        //To increase difficulty the network must be able to move the blocktime
+        //3 minutes under target blocktime. This is to avoid the difficulty becoming
+        //too much work for the network to handle. Based on heuristics.
+        if (nPeriodTimeProportionConsumed < 0.90f)
+            return 1;
+    } else {
+        // Difficulty adjustment algorithm that skips over odd aka. hard diffs (2025)
+
+        // If block time is too long, decrease to the previous even diff
+        if (nPeriodTimeProportionConsumed > 1.0333f) {
+            int32_t nRetarget = 0;
+            if (nBits % 2 == 0) {
+                // Even diff to even diff
+                nRetarget = -2;
+            } else {
+                // Odd diff to even diff
+                nRetarget = -1;
+            }
+
+            // If block time is way too long (>60 min on mainnet), decrease by 4 or 3 instead of by 2 or 1
+            if (nPeriodTimeProportionConsumed > 2.0f) {
+                nRetarget -= 2;
+            }
+
+            return nRetarget;
+        }
+
+        // If block time is too short, increase to the next even diff
+        if (nPeriodTimeProportionConsumed < 0.90f) {
+            int32_t nRetarget = 0;
+            if (nBits % 2 == 0) {
+                // Even diff to even diff
+                nRetarget = 2;
+            } else {
+                // Odd diff to even diff
+                nRetarget = 1;
+            }
+
+            // If block time is way too short (<15 min on mainnet), increase by 4 or 3 instead of by 2 or 1
+            if (nPeriodTimeProportionConsumed < 0.5f) {
+                nRetarget += 2;
+            }
+
+            return nRetarget;
+        }
+
+        // The block time is just right. See if we should move away from an odd diff
+        if (nBits % 2 == 0) {
+            // Already even diff. Don't change difficulty
+            return 0;
+        } else {
+            // Currently odd diff. Decrease diff by 1 to reach an even difficulty
+            return -1;
+        }
+    }
+}
+
 uint16_t CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime, const Consensus::Params& params)
 {
     if (params.fPowNoRetargeting)
@@ -70,22 +140,10 @@ uint16_t CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirst
     // Compute constants
     const int64_t nActualTimespan = pindexLast->GetBlockTime() - nFirstBlockTime;
     const double nPeriodTimeProportionConsumed = (double)nActualTimespan / (double)params.nPowTargetTimespan;
+    const bool isHardDiffRemoved = DeploymentActiveAfter(pindexLast, params, Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL);
 
     //Variable to set difficulty delta
-    int32_t nRetarget = 0;
-
-    //Note for mainnet:
-    //If it takes more than 1 minute over the target blocktime, reduce difficulty.
-    if (nPeriodTimeProportionConsumed > 1.0333f)
-        nRetarget = -1;
-
-    //Note for mainnet:
-    //To increase difficulty the network must be able to move the blocktime
-    //3 minutes under target blocktime. This is to avoid the difficulty becoming
-    //too much work for the network to handle. Based on heuristics.
-    if (nPeriodTimeProportionConsumed < 0.90f)
-        nRetarget = 1;
-
+    int32_t nRetarget = CalculateDifficultyDelta(pindexLast->nBits, nPeriodTimeProportionConsumed, isHardDiffRemoved);
 
     return (int32_t)pindexLast->nBits + nRetarget;
 }

diff --git a/src/pow.h b/src/pow.h
@@ -16,6 +16,7 @@ class CBlockIndex;
 class uint256;
 
 uint16_t GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params&);
+int32_t CalculateDifficultyDelta(const int32_t nBits, const double nPeriodTimeProportionConsumed, const bool isHardDiffRemoved);
 uint16_t CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime, const Consensus::Params&);
 
 /** Check whether a block hash satisfies the proof-of-work requirement specified by nBits */

diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
@@ -1501,6 +1501,7 @@ RPCHelpMan getblockchaininfo()
     SoftForkDescPushBack(tip, softforks, consensusParams, Consensus::DEPLOYMENT_TESTDUMMY);
     SoftForkDescPushBack(tip, softforks, consensusParams, Consensus::DEPLOYMENT_TAPROOT);
     SoftForkDescPushBack(tip, softforks, consensusParams, Consensus::DEPLOYMENT_DEADPOOL);
+    SoftForkDescPushBack(tip, softforks, consensusParams, Consensus::DEPLOYMENT_HARD_DIFF_REMOVAL);
     obj.pushKV("softforks", softforks);
 
     obj.pushKV("warnings", GetWarnings(false).original);