1  // Copyright (c) 2009-2010 Satoshi Nakamoto
  2  // Copyright (c) 2009-2022 The Bitcoin Core developers
  3  // Distributed under the MIT software license, see the accompanying
  4  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  5  
  6  #include <chain.h>
  7  #include <tinyformat.h>
  8  #include <util/time.h>
  9  
 10  std::string CBlockFileInfo::ToString() const
 11  {
 12      return strprintf("CBlockFileInfo(blocks=%u, size=%u, heights=%u...%u, time=%s...%s)", nBlocks, nSize, nHeightFirst, nHeightLast, FormatISO8601Date(nTimeFirst), FormatISO8601Date(nTimeLast));
 13  }
 14  
 15  std::string CBlockIndex::ToString() const
 16  {
 17      return strprintf("CBlockIndex(pprev=%p, nHeight=%d, merkle=%s, hashBlock=%s)",
 18                       pprev, nHeight, hashMerkleRoot.ToString(), GetBlockHash().ToString());
 19  }
 20  
 21  void CChain::SetTip(CBlockIndex& block)
 22  {
 23      CBlockIndex* pindex = &block;
 24      vChain.resize(pindex->nHeight + 1);
 25      while (pindex && vChain[pindex->nHeight] != pindex) {
 26          vChain[pindex->nHeight] = pindex;
 27          pindex = pindex->pprev;
 28      }
 29  }
 30  
 31  std::vector<uint256> LocatorEntries(const CBlockIndex* index)
 32  {
 33      int step = 1;
 34      std::vector<uint256> have;
 35      if (index == nullptr) return have;
 36  
 37      have.reserve(32);
 38      while (index) {
 39          have.emplace_back(index->GetBlockHash());
 40          if (index->nHeight == 0) break;
 41          // Exponentially larger steps back, plus the genesis block.
 42          int height = std::max(index->nHeight - step, 0);
 43          // Use skiplist.
 44          index = index->GetAncestor(height);
 45          if (have.size() > 10) step *= 2;
 46      }
 47      return have;
 48  }
 49  
 50  CBlockLocator GetLocator(const CBlockIndex* index)
 51  {
 52      return CBlockLocator{LocatorEntries(index)};
 53  }
 54  
 55  CBlockLocator CChain::GetLocator() const
 56  {
 57      return ::GetLocator(Tip());
 58  }
 59  
 60  const CBlockIndex *CChain::FindFork(const CBlockIndex *pindex) const {
 61      if (pindex == nullptr) {
 62          return nullptr;
 63      }
 64      if (pindex->nHeight > Height())
 65          pindex = pindex->GetAncestor(Height());
 66      while (pindex && !Contains(pindex))
 67          pindex = pindex->pprev;
 68      return pindex;
 69  }
 70  
 71  CBlockIndex* CChain::FindEarliestAtLeast(int64_t nTime, int height) const
 72  {
 73      std::pair<int64_t, int> blockparams = std::make_pair(nTime, height);
 74      std::vector<CBlockIndex*>::const_iterator lower = std::lower_bound(vChain.begin(), vChain.end(), blockparams,
 75          [](CBlockIndex* pBlock, const std::pair<int64_t, int>& blockparams) -> bool { return pBlock->GetBlockTimeMax() < blockparams.first || pBlock->nHeight < blockparams.second; });
 76      return (lower == vChain.end() ? nullptr : *lower);
 77  }
 78  
 79  /** Turn the lowest '1' bit in the binary representation of a number into a '0'. */
 80  int static inline InvertLowestOne(int n) { return n & (n - 1); }
 81  
 82  /** Compute what height to jump back to with the CBlockIndex::pskip pointer. */
 83  int static inline GetSkipHeight(int height) {
 84      if (height < 2)
 85          return 0;
 86  
 87      // Determine which height to jump back to. Any number strictly lower than height is acceptable,
 88      // but the following expression seems to perform well in simulations (max 110 steps to go back
 89      // up to 2**18 blocks).
 90      return (height & 1) ? InvertLowestOne(InvertLowestOne(height - 1)) + 1 : InvertLowestOne(height);
 91  }
 92  
 93  const CBlockIndex* CBlockIndex::GetAncestor(int height) const
 94  {
 95      if (height > nHeight || height < 0) {
 96          return nullptr;
 97      }
 98  
 99      const CBlockIndex* pindexWalk = this;
100      int heightWalk = nHeight;
101      while (heightWalk > height) {
102          int heightSkip = GetSkipHeight(heightWalk);
103          int heightSkipPrev = GetSkipHeight(heightWalk - 1);
104          if (pindexWalk->pskip != nullptr &&
105              (heightSkip == height ||
106               (heightSkip > height && !(heightSkipPrev < heightSkip - 2 &&
107                                         heightSkipPrev >= height)))) {
108              // Only follow pskip if pprev->pskip isn't better than pskip->pprev.
109              pindexWalk = pindexWalk->pskip;
110              heightWalk = heightSkip;
111          } else {
112              assert(pindexWalk->pprev);
113              pindexWalk = pindexWalk->pprev;
114              heightWalk--;
115          }
116      }
117      return pindexWalk;
118  }
119  
120  CBlockIndex* CBlockIndex::GetAncestor(int height)
121  {
122      return const_cast<CBlockIndex*>(static_cast<const CBlockIndex*>(this)->GetAncestor(height));
123  }
124  
125  void CBlockIndex::BuildSkip()
126  {
127      if (pprev)
128          pskip = pprev->GetAncestor(GetSkipHeight(nHeight));
129  }
130  
131  arith_uint256 GetBlockProof(const CBlockIndex& block)
132  {
133      arith_uint256 bnTarget;
134      bool fNegative;
135      bool fOverflow;
136      bnTarget.SetCompact(block.nBits, &fNegative, &fOverflow);
137      if (fNegative || fOverflow || bnTarget == 0)
138          return 0;
139      // We need to compute 2**256 / (bnTarget+1), but we can't represent 2**256
140      // as it's too large for an arith_uint256. However, as 2**256 is at least as large
141      // as bnTarget+1, it is equal to ((2**256 - bnTarget - 1) / (bnTarget+1)) + 1,
142      // or ~bnTarget / (bnTarget+1) + 1.
143      return (~bnTarget / (bnTarget + 1)) + 1;
144  }
145  
146  int64_t GetBlockProofEquivalentTime(const CBlockIndex& to, const CBlockIndex& from, const CBlockIndex& tip, const Consensus::Params& params)
147  {
148      arith_uint256 r;
149      int sign = 1;
150      if (to.nChainWork > from.nChainWork) {
151          r = to.nChainWork - from.nChainWork;
152      } else {
153          r = from.nChainWork - to.nChainWork;
154          sign = -1;
155      }
156      r = r * arith_uint256(params.nPowTargetSpacing) / GetBlockProof(tip);
157      if (r.bits() > 63) {
158          return sign * std::numeric_limits<int64_t>::max();
159      }
160      return sign * int64_t(r.GetLow64());
161  }
162  
163  /** Find the last common ancestor two blocks have.
164   *  Both pa and pb must be non-nullptr. */
165  const CBlockIndex* LastCommonAncestor(const CBlockIndex* pa, const CBlockIndex* pb) {
166      if (pa->nHeight > pb->nHeight) {
167          pa = pa->GetAncestor(pb->nHeight);
168      } else if (pb->nHeight > pa->nHeight) {
169          pb = pb->GetAncestor(pa->nHeight);
170      }
171  
172      while (pa != pb && pa && pb) {
173          pa = pa->pprev;
174          pb = pb->pprev;
175      }
176  
177      // Eventually all chain branches meet at the genesis block.
178      assert(pa == pb);
179      return pa;
180  }