src/checkpoints.cpp

   1 // Copyright (c) 2011 The Bitcoin developers
   2 // Copyright (c) 2011 The PPCoin developers
   3 // Distributed under the MIT/X11 software license, see the accompanying
   4 // file license.txt or http://www.opensource.org/licenses/mit-license.php.
   5
   6 #include <boost/assign/list_of.hpp> // for 'map_list_of()'
   7 #include <boost/foreach.hpp>
   8
   9 #include "headers.h"
  10 #include "checkpoints.h"
  11
  12 namespace Checkpoints
  13 {
  14     typedef std::map<int, uint256> MapCheckpoints;   // hardened checkpoints
  15
  16     //
  17     // What makes a good checkpoint block?
  18     // + Is surrounded by blocks with reasonable timestamps
  19     //   (no blocks before with a timestamp after, none after with
  20     //    timestamp before)
  21     // + Contains no strange transactions
  22     //
  23     static MapCheckpoints mapCheckpoints =
  24         boost::assign::map_list_of
  25         ( 0, hashGenesisBlock )
  26         ; // ppcoin: no checkpoint yet; to be created in future releases
  27
  28     // ppcoin: automatic checkpoint (represented by height of checkpoint)
  29     int nAutoCheckpoint = 0;
  30
  31     bool CheckHardened(int nHeight, const uint256& hash)
  32     {
  33         if (fTestNet) return true; // Testnet has no checkpoints
  34
  35         MapCheckpoints::const_iterator i = mapCheckpoints.find(nHeight);
  36         if (i == mapCheckpoints.end()) return true;
  37         return hash == i->second;
  38     }
  39
  40     // ppcoin: check automatic checkpoint
  41     // To pass the check:
  42     //   - All ancestors (including the block itself) have block index already
  43     //   - The immediate ancestor in main chain must not have height less than
  44     //     checkpoint height
  45     bool CheckAuto(const CBlockIndex *pindex)
  46     {
  47         while (pindex)
  48         {
  49             if (pindex->IsInMainChain())
  50             {
  51                 if (pindex->nHeight >= nAutoCheckpoint)
  52                     return true;
  53                 else
  54                     return error("Checkpoints: new block on alternative branch at height=%d before auto checkpoint at height=%d", pindex->nHeight, nAutoCheckpoint);
  55             }
  56             else
  57                 pindex = pindex->pprev;
  58         }
  59         return error("Checkpoints: failed to find any ancestor on main chain for the new block - internal error");
  60     }
  61
  62     // ppcoin: get next chain checkpoint
  63     int GetNextChainCheckpoint(const CBlockIndex *pindexLast)
  64     {
  65         CBigNum bnTarget;
  66         CBigNum bnTargetMax = 0;  // max target of all blocks since checkpoint
  67         CBigNum bnTargetMin = 0;  // min target of all candidate checkpoints
  68         int nMinTargetHeight = 0; // min target height of candidate checkpoints
  69         int nCheckpointMin = 0;   // minimum candidate checkpoint
  70         int nCheckpointMax = 0;   // maximum candidate checkpoint
  71         int nDepth = pindexLast->nHeight - pindexLast->nCheckpoint;
  72         const CBlockIndex *pindex = pindexLast;
  73         while (nDepth >= 0 && pindex)
  74         {
  75             bnTarget.SetCompact(pindex->nBits);
  76             if (bnTarget > bnTargetMax)
  77                 bnTargetMax = bnTarget;
  78             if (nCheckpointMax > 0 && bnTarget < bnTargetMin)
  79             {
  80                 bnTargetMin = bnTarget;
  81                 nMinTargetHeight = pindex->nHeight;
  82             }
  83             if (nCheckpointMax == 0 && pindexLast->GetBlockTime() - pindex->GetBlockTime() > AUTO_CHECKPOINT_MIN_SPAN)
  84             {
  85                 nCheckpointMax = pindex->nHeight;
  86                 bnTargetMin.SetCompact(pindex->nBits);
  87                 nMinTargetHeight = pindex->nHeight;
  88             }
  89             if (pindexLast->GetBlockTime() - pindex->GetBlockTime() < AUTO_CHECKPOINT_MAX_SPAN)
  90                 nCheckpointMin = pindex->nHeight;
  91             pindex = pindex->pprev;
  92             nDepth--;
  93         }
  94
  95         assert (nDepth == -1);  // arrive at chain checkpoint now
  96
  97         printf("Checkpoints: min=%d max=%d tminheight=%d tmin=0x%08x tmax=0x%08x\n",
  98             nCheckpointMin, nCheckpointMax, nMinTargetHeight,
  99             bnTargetMin.GetCompact(), bnTargetMax.GetCompact());
 100         if (nCheckpointMax == 0) // checkpoint stays if max candidate not found
 101             return pindexLast->nCheckpoint;
 102
 103         if (bnTargetMin * 100 > bnTargetMax * 90)
 104             return nCheckpointMax;
 105         if (bnTarget * 100 > bnTargetMax * 90)
 106             return nMinTargetHeight;
 107         else
 108             return nCheckpointMin;
 109     }
 110
 111     // ppcoin: get next auto checkpoint from the new chain checkpoint
 112     int GetNextAutoCheckpoint(int nCheckpoint)
 113     {
 114         return (std::max(nAutoCheckpoint, nCheckpoint));
 115     }
 116
 117     // ppcoin: advance to next automatic checkpoint
 118     void AdvanceAutoCheckpoint(int nCheckpoint)
 119     {
 120         nAutoCheckpoint = GetNextAutoCheckpoint(nCheckpoint);
 121         printf("Checkpoints: auto checkpoint now at height=%d\n", nAutoCheckpoint);
 122     }
 123
 124     int GetTotalBlocksEstimate()
 125     {
 126         if (fTestNet) return 0;
 127
 128         return mapCheckpoints.rbegin()->first;
 129     }
 130
 131     CBlockIndex* GetLastCheckpoint(const std::map<uint256, CBlockIndex*>& mapBlockIndex)
 132     {
 133         if (fTestNet) return NULL;
 134
 135         int64 nResult;
 136         BOOST_REVERSE_FOREACH(const MapCheckpoints::value_type& i, mapCheckpoints)
 137         {
 138             const uint256& hash = i.second;
 139             std::map<uint256, CBlockIndex*>::const_iterator t = mapBlockIndex.find(hash);
 140             if (t != mapBlockIndex.end())
 141                 return t->second;
 142         }
 143         return NULL;
 144     }
 145 }