Use a uint256 for bnChainWork

Every block index entry currently requires a separately-allocated
CBigNum. By replacing them with uint256, it's just 32 bytes extra
in CBlockIndex itself.

This should save us a few megabytes in RAM, and less allocation
overhead.

5 files changed, 48 insertions, 36 deletions

diff --git a/contrib/test-patches/bitcoind-comparison.patch b/contrib/test-patches/bitcoind-comparison.patch
index 04a8618286..7464349b3c 100644
--- a/contrib/test-patches/bitcoind-comparison.patch
+++ b/contrib/test-patches/bitcoind-comparison.patch
@@ -1,5 +1,5 @@
-diff --git a/src/main.cpp b/src/main.cpp
-index 8c115c2..1e70ff2 100644
+diff --git a/contrib/test-patches/bitcoind-comparison.patch b/contrib/test-patches/bitcoind-comparison.patch
+index 04a8618..519429a 100644
 --- a/src/main.cpp
 +++ b/src/main.cpp
 @@ -31,8 +31,8 @@ CTxMemPool mempool;
@@ -12,7 +12,7 @@ index 8c115c2..1e70ff2 100644
 +static CBigNum bnProofOfWorkLimit(~uint256(0) >> 1);
  CBlockIndex* pindexGenesisBlock = NULL;
  int nBestHeight = -1;
- CBigNum bnBestChainWork = 0;
+ uint256 nBestChainWork = 0;
 @@ -1055,7 +1055,7 @@ int64 static GetBlockValue(int nHeight, int64 nFees)
      int64 nSubsidy = 50 * COIN;
  
@@ -22,7 +22,7 @@ index 8c115c2..1e70ff2 100644
  
      return nSubsidy + nFees;
  }
-@@ -2706,9 +2706,9 @@ bool InitBlockIndex() {
+@@ -2736,9 +2736,9 @@ bool InitBlockIndex() {
          block.hashPrevBlock = 0;
          block.hashMerkleRoot = block.BuildMerkleTree();
          block.nVersion = 1;
@@ -35,7 +35,7 @@ index 8c115c2..1e70ff2 100644
  
          if (fTestNet)
          {
-@@ -3007,7 +3007,7 @@ bool static AlreadyHave(const CInv& inv)
+@@ -3024,7 +3024,7 @@ bool static AlreadyHave(const CInv& inv)
  // 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
  // a large 4-byte int at any alignment.
diff --git a/src/bignum.h b/src/bignum.h
index 1ee7a99934..0881807d70 100644
--- a/src/bignum.h
+++ b/src/bignum.h
@@ -222,7 +222,7 @@ public:
         BN_mpi2bn(pch, p - pch, this);
     }
 
-    uint256 getuint256()
+    uint256 getuint256() const
     {
         unsigned int nSize = BN_bn2mpi(this, NULL);
         if (nSize < 4)
diff --git a/src/main.cpp b/src/main.cpp
index 8284d54c7c..bf13e79151 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -35,8 +35,8 @@ uint256 hashGenesisBlock("0x000000000019d6689c085ae165831e934ff763ae46a2a6c172b3
 static CBigNum bnProofOfWorkLimit(~uint256(0) >> 32);
 CBlockIndex* pindexGenesisBlock = NULL;
 int nBestHeight = -1;
-CBigNum bnBestChainWork = 0;
-CBigNum bnBestInvalidWork = 0;
+uint256 nBestChainWork = 0;
+uint256 nBestInvalidWork = 0;
 uint256 hashBestChain = 0;
 CBlockIndex* pindexBest = NULL;
 set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexValid; // may contain all CBlockIndex*'s that have validness >=BLOCK_VALID_TRANSACTIONS, and must contain those who aren't failed
@@ -1191,20 +1191,20 @@ bool IsInitialBlockDownload()
 
 void static InvalidChainFound(CBlockIndex* pindexNew)
 {
-    if (pindexNew->bnChainWork > bnBestInvalidWork)
+    if (pindexNew->nChainWork > nBestInvalidWork)
     {
-        bnBestInvalidWork = pindexNew->bnChainWork;
-        pblocktree->WriteBestInvalidWork(bnBestInvalidWork);
+        nBestInvalidWork = pindexNew->nChainWork;
+        pblocktree->WriteBestInvalidWork(CBigNum(nBestInvalidWork));
         uiInterface.NotifyBlocksChanged();
     }
-    printf("InvalidChainFound: invalid block=%s  height=%d  work=%s  date=%s\n",
+    printf("InvalidChainFound: invalid block=%s  height=%d  log2_work=%.8g  date=%s\n",
       pindexNew->GetBlockHash().ToString().c_str(), pindexNew->nHeight,
-      pindexNew->bnChainWork.ToString().c_str(), DateTimeStrFormat("%Y-%m-%d %H:%M:%S",
+      log(pindexNew->nChainWork.getdouble())/log(2.0), DateTimeStrFormat("%Y-%m-%d %H:%M:%S",
       pindexNew->GetBlockTime()).c_str());
-    printf("InvalidChainFound:  current best=%s  height=%d  work=%s  date=%s\n",
-      hashBestChain.ToString().c_str(), nBestHeight, bnBestChainWork.ToString().c_str(),
+    printf("InvalidChainFound:  current best=%s  height=%d  log2_work=%.8g  date=%s\n",
+      hashBestChain.ToString().c_str(), nBestHeight, log(nBestChainWork.getdouble())/log(2.0),
       DateTimeStrFormat("%Y-%m-%d %H:%M:%S", pindexBest->GetBlockTime()).c_str());
-    if (pindexBest && bnBestInvalidWork > bnBestChainWork + pindexBest->GetBlockWork() * 6)
+    if (pindexBest && nBestInvalidWork > nBestChainWork + (pindexBest->GetBlockWork() * 6).getuint256())
         printf("InvalidChainFound: Warning: Displayed transactions may not be correct! You may need to upgrade, or other nodes may need to upgrade.\n");
 }
 
@@ -1230,7 +1230,7 @@ bool ConnectBestBlock(CValidationState &state) {
             pindexNewBest = *it;
         }
 
-        if (pindexNewBest == pindexBest || (pindexBest && pindexNewBest->bnChainWork == pindexBest->bnChainWork))
+        if (pindexNewBest == pindexBest || (pindexBest && pindexNewBest->nChainWork == pindexBest->nChainWork))
             return true; // nothing to do
 
         // check ancestry
@@ -1250,7 +1250,7 @@ bool ConnectBestBlock(CValidationState &state) {
                 break;
             }
 
-            if (pindexBest == NULL || pindexTest->bnChainWork > pindexBest->bnChainWork)
+            if (pindexBest == NULL || pindexTest->nChainWork > pindexBest->nChainWork)
                 vAttach.push_back(pindexTest);
 
             if (pindexTest->pprev == NULL || pindexTest->pnext != NULL) {
@@ -1858,11 +1858,11 @@ bool SetBestChain(CValidationState &state, CBlockIndex* pindexNew)
     pindexBest = pindexNew;
     pblockindexFBBHLast = NULL;
     nBestHeight = pindexBest->nHeight;
-    bnBestChainWork = pindexNew->bnChainWork;
+    nBestChainWork = pindexNew->nChainWork;
     nTimeBestReceived = GetTime();
     nTransactionsUpdated++;
-    printf("SetBestChain: new best=%s  height=%d  work=%s  tx=%lu  date=%s  progress=%f\n",
-      hashBestChain.ToString().c_str(), nBestHeight, bnBestChainWork.ToString().c_str(), (unsigned long)pindexNew->nChainTx,
+    printf("SetBestChain: new best=%s  height=%d  log2_work=%.8g  tx=%lu  date=%s progress=%f\n",
+      hashBestChain.ToString().c_str(), nBestHeight, log(nBestChainWork.getdouble())/log(2.0), (unsigned long)pindexNew->nChainTx,
       DateTimeStrFormat("%Y-%m-%d %H:%M:%S", pindexBest->GetBlockTime()).c_str(),
       Checkpoints::GuessVerificationProgress(pindexBest));
 
@@ -1915,7 +1915,7 @@ bool CBlock::AddToBlockIndex(CValidationState &state, const CDiskBlockPos &pos)
         pindexNew->nHeight = pindexNew->pprev->nHeight + 1;
     }
     pindexNew->nTx = vtx.size();
-    pindexNew->bnChainWork = (pindexNew->pprev ? pindexNew->pprev->bnChainWork : 0) + pindexNew->GetBlockWork();
+    pindexNew->nChainWork = (pindexNew->pprev ? pindexNew->pprev->nChainWork : 0) + pindexNew->GetBlockWork().getuint256();
     pindexNew->nChainTx = (pindexNew->pprev ? pindexNew->pprev->nChainTx : 0) + pindexNew->nTx;
     pindexNew->nFile = pos.nFile;
     pindexNew->nDataPos = pos.nPos;
@@ -2537,7 +2537,7 @@ bool static LoadBlockIndexDB()
 
     boost::this_thread::interruption_point();
 
-    // Calculate bnChainWork
+    // Calculate nChainWork
     vector<pair<int, CBlockIndex*> > vSortedByHeight;
     vSortedByHeight.reserve(mapBlockIndex.size());
     BOOST_FOREACH(const PAIRTYPE(uint256, CBlockIndex*)& item, mapBlockIndex)
@@ -2549,7 +2549,7 @@ bool static LoadBlockIndexDB()
     BOOST_FOREACH(const PAIRTYPE(int, CBlockIndex*)& item, vSortedByHeight)
     {
         CBlockIndex* pindex = item.second;
-        pindex->bnChainWork = (pindex->pprev ? pindex->pprev->bnChainWork : 0) + pindex->GetBlockWork();
+        pindex->nChainWork = (pindex->pprev ? pindex->pprev->nChainWork : 0) + pindex->GetBlockWork().getuint256();
         pindex->nChainTx = (pindex->pprev ? pindex->pprev->nChainTx : 0) + pindex->nTx;
         if ((pindex->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_TRANSACTIONS && !(pindex->nStatus & BLOCK_FAILED_MASK))
             setBlockIndexValid.insert(pindex);
@@ -2561,8 +2561,10 @@ bool static LoadBlockIndexDB()
     if (pblocktree->ReadBlockFileInfo(nLastBlockFile, infoLastBlockFile))
         printf("LoadBlockIndexDB(): last block file info: %s\n", infoLastBlockFile.ToString().c_str());
 
-    // Load bnBestInvalidWork, OK if it doesn't exist
+    // Load nBestInvalidWork, OK if it doesn't exist
+    CBigNum bnBestInvalidWork;
     pblocktree->ReadBestInvalidWork(bnBestInvalidWork);
+    nBestInvalidWork = bnBestInvalidWork.getuint256();
 
     // Check whether we need to continue reindexing
     bool fReindexing = false;
@@ -2579,7 +2581,7 @@ bool static LoadBlockIndexDB()
         return true;
     hashBestChain = pindexBest->GetBlockHash();
     nBestHeight = pindexBest->nHeight;
-    bnBestChainWork = pindexBest->bnChainWork;
+    nBestChainWork = pindexBest->nChainWork;
 
     // set 'next' pointers in best chain
     CBlockIndex *pindex = pindexBest;
@@ -2675,8 +2677,8 @@ void UnloadBlockIndex()
     setBlockIndexValid.clear();
     pindexGenesisBlock = NULL;
     nBestHeight = 0;
-    bnBestChainWork = 0;
-    bnBestInvalidWork = 0;
+    nBestChainWork = 0;
+    nBestInvalidWork = 0;
     hashBestChain = 0;
     pindexBest = NULL;
 }
@@ -2953,7 +2955,7 @@ string GetWarnings(string strFor)
     }
 
     // Longer invalid proof-of-work chain
-    if (pindexBest && bnBestInvalidWork > bnBestChainWork + pindexBest->GetBlockWork() * 6)
+    if (pindexBest && nBestInvalidWork > nBestChainWork + (pindexBest->GetBlockWork() * 6).getuint256())
     {
         nPriority = 2000;
         strStatusBar = strRPC = _("Warning: Displayed transactions may not be correct! You may need to upgrade, or other nodes may need to upgrade.");
diff --git a/src/main.h b/src/main.h
index 9a3664a437..24b2cb2aa6 100644
--- a/src/main.h
+++ b/src/main.h
@@ -77,8 +77,8 @@ extern std::set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexValid;
 extern uint256 hashGenesisBlock;
 extern CBlockIndex* pindexGenesisBlock;
 extern int nBestHeight;
-extern CBigNum bnBestChainWork;
-extern CBigNum bnBestInvalidWork;
+extern uint256 nBestChainWork;
+extern uint256 nBestInvalidWork;
 extern uint256 hashBestChain;
 extern CBlockIndex* pindexBest;
 extern unsigned int nTransactionsUpdated;
@@ -1619,7 +1619,7 @@ public:
     unsigned int nUndoPos;
 
     // (memory only) Total amount of work (expected number of hashes) in the chain up to and including this block
-    CBigNum bnChainWork;
+    uint256 nChainWork;
 
     // Number of transactions in this block.
     // Note: in a potential headers-first mode, this number cannot be relied upon
@@ -1648,7 +1648,7 @@ public:
         nFile = 0;
         nDataPos = 0;
         nUndoPos = 0;
-        bnChainWork = 0;
+        nChainWork = 0;
         nTx = 0;
         nChainTx = 0;
         nStatus = 0;
@@ -1669,7 +1669,7 @@ public:
         nFile = 0;
         nDataPos = 0;
         nUndoPos = 0;
-        bnChainWork = 0;
+        nChainWork = 0;
         nTx = 0;
         nChainTx = 0;
         nStatus = 0;
@@ -1793,8 +1793,8 @@ public:
 struct CBlockIndexWorkComparator
 {
     bool operator()(CBlockIndex *pa, CBlockIndex *pb) {
-        if (pa->bnChainWork > pb->bnChainWork) return false;
-        if (pa->bnChainWork < pb->bnChainWork) return true;
+        if (pa->nChainWork > pb->nChainWork) return false;
+        if (pa->nChainWork < pb->nChainWork) return true;
 
         if (pa->GetBlockHash() < pb->GetBlockHash()) return false;
         if (pa->GetBlockHash() > pb->GetBlockHash()) return true;
diff --git a/src/uint256.h b/src/uint256.h
index eb0066fa27..8a9af8ba04 100644
--- a/src/uint256.h
+++ b/src/uint256.h
@@ -55,6 +55,16 @@ public:
         return ret;
     }
 
+    double getdouble() const
+    {
+        double ret = 0.0;
+        double fact = 1.0;
+        for (int i = 0; i < WIDTH; i++) {
+            ret += fact * pn[i];
+            fact *= 4294967296.0;
+        }
+        return ret;
+    }
 
     base_uint& operator=(uint64 b)
     {