PPCoin: Limit the merging of coins into coinstake (to about 10K)

        Help promote proof-of-stake generation in early stages

src/main.cpp

@@ -822,7 +822,7 @@ uint256 WantedByOrphan(const CBlock* pblockOrphan)
 
 int64 static GetProofOfWorkReward(unsigned int nBits)
 {
-    CBigNum bnSubsidyLimit = 9999 * COIN; // subsidy amount for difficulty 1
+    CBigNum bnSubsidyLimit = MAX_MINT_PROOF_OF_WORK;
     CBigNum bnTarget;
     bnTarget.SetCompact(nBits);
     CBigNum bnTargetLimit = bnProofOfWorkLimit;

src/main.h

@@ -35,6 +35,7 @@ static const unsigned int MAX_ORPHAN_TRANSACTIONS = MAX_BLOCK_SIZE/100;
 static const int64 MIN_TX_FEE = 10000;
 static const int64 MIN_RELAY_TX_FEE = 10000;
 static const int64 MAX_MONEY = 2000000000 * COIN;
+static const int64 MAX_MINT_PROOF_OF_WORK = 9999 * COIN;
 inline bool MoneyRange(int64 nValue) { return (nValue >= 0 && nValue <= MAX_MONEY); }
 static const int COINBASE_MATURITY = 100;
 // Threshold for nLockTime: below this value it is interpreted as block number, otherwise as UNIX timestamp.

src/wallet.cpp

@@ -1256,10 +1256,18 @@ bool CWallet::CreateCoinStake(unsigned int nBits, CTransaction& txNew)
         return false;
     BOOST_FOREACH(PAIRTYPE(const CWalletTx*, unsigned int) pcoin, setCoins)
     {
+        // Attempt to add more inputs of the same key
         if (pcoin.first->vout[pcoin.second].scriptPubKey == txNew.vout[1].scriptPubKey && pcoin.first->GetHash() != txNew.vin[0].prevout.hash)
         {
+            // Stop adding more inputs if value is already pretty significant
+            if (nCredit > MAX_MINT_PROOF_OF_WORK)
+                break;
+            // Stop adding inputs if reached reserve limit
             if (nCredit + pcoin.first->vout[pcoin.second].nValue > nBalance - nReserveBalance)
                 break;
+            // Do not add additional significant input
+            if (pcoin.first->vout[pcoin.second].nValue > MAX_MINT_PROOF_OF_WORK)
+                continue;
             txNew.vin.push_back(CTxIn(pcoin.first->GetHash(), pcoin.second));
             nCredit += pcoin.first->vout[pcoin.second].nValue;
             vwtxPrev.push_back(pcoin.first);
@@ -1283,6 +1291,13 @@ bool CWallet::CreateCoinStake(unsigned int nBits, CTransaction& txNew)
         if (!SignSignature(*this, *pcoin, txNew, nIn++))
             return error("CreateCoinStake : failed to sign coinstake");
     }
+
+    // Limit size
+    unsigned int nBytes = ::GetSerializeSize(txNew, SER_NETWORK, PROTOCOL_VERSION);
+    if (nBytes >= MAX_BLOCK_SIZE_GEN/5)
+        return false;
+
+    // Successfully generated coinstake
     return true;
 }