Implement mining slow start with a linear ramp

src/chainparams.cpp

@@ -31,6 +31,7 @@ class CMainParams : public CChainParams {
 public:
     CMainParams() {
         strNetworkID = "main";
+        consensus.nSubsidySlowStartInterval = 5000;
         consensus.nSubsidyHalvingInterval = 210000;
         consensus.nMajorityEnforceBlockUpgrade = 750;
         consensus.nMajorityRejectBlockOutdated = 950;

src/consensus/params.h

@@ -14,6 +14,20 @@ namespace Consensus {
  */
 struct Params {
     uint256 hashGenesisBlock;
+    /** Needs to evenly divide MAX_SUBSIDY to avoid rounding errors. */
+    int nSubsidySlowStartInterval;
+    /**
+     * Shift based on a linear ramp for slow start:
+     *
+     * MAX_SUBSIDY*(t_s/2 + t/r) = MAX_SUBSIDY*t_h  Coin balance
+     *                 t_s + t_r = t_h + t_c        Block balance
+     *
+     * t_s = nSubsidySlowStartInterval
+     * t_r = number of blocks between end of slow start and first halving
+     * t_h = nSubsidyHalvingInterval
+     * t_c = SubsidySlowStartShift()
+     */
+    int SubsidySlowStartShift() const { return nSubsidySlowStartInterval / 2; }
     int nSubsidyHalvingInterval;
     /** Used to check majorities for block version upgrade */
     int nMajorityEnforceBlockUpgrade;

src/main.cpp

@@ -1324,12 +1324,27 @@ bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex)
 
 CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams)
 {
-    int halvings = nHeight / consensusParams.nSubsidyHalvingInterval;
+    CAmount nSubsidy = 50 * COIN;
+
+    // Mining slow start
+    // The subsidy is ramped up linearly, skipping the middle payout of
+    // MAX_SUBSIDY/2 to keep the monetary curve consistent with no slow start.
+    if (nHeight < consensusParams.nSubsidySlowStartInterval / 2) {
+        nSubsidy /= consensusParams.nSubsidySlowStartInterval;
+        nSubsidy *= nHeight;
+        return nSubsidy;
+    } else if (nHeight < consensusParams.nSubsidySlowStartInterval) {
+        nSubsidy /= consensusParams.nSubsidySlowStartInterval;
+        nSubsidy *= (nHeight+1);
+        return nSubsidy;
+    }
+
+    assert(nHeight > consensusParams.SubsidySlowStartShift());
+    int halvings = (nHeight - consensusParams.SubsidySlowStartShift()) / consensusParams.nSubsidyHalvingInterval;
     // Force block reward to zero when right shift is undefined.
     if (halvings >= 64)
         return 0;
 
-    CAmount nSubsidy = 50 * COIN;
     // Subsidy is cut in half every 210,000 blocks which will occur approximately every 4 years.
     nSubsidy >>= halvings;
     return nSubsidy;