1  // Copyright (c) 2009-2010 Satoshi Nakamoto
  2  // Copyright (c) 2009-present 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/check.h>
  9  
 10  std::string CBlockIndex::ToString() const
 11  {
 12      return strprintf("CBlockIndex(pprev=%p, nHeight=%d, merkle=%s, hashBlock=%s)",
 13                       pprev, nHeight, hashMerkleRoot.ToString(), GetBlockHash().ToString());
 14  }
 15  
 16  void CChain::SetTip(CBlockIndex& block)
 17  {
 18      CBlockIndex* pindex = &block;
 19      vChain.resize(pindex->nHeight + 1);
 20      while (pindex && vChain[pindex->nHeight] != pindex) {
 21          vChain[pindex->nHeight] = pindex;
 22          pindex = pindex->pprev;
 23      }
 24  }
 25  
 26  std::vector<uint256> LocatorEntries(const CBlockIndex* index)
 27  {
 28      int step = 1;
 29      std::vector<uint256> have;
 30      if (index == nullptr) return have;
 31  
 32      have.reserve(32);
 33      while (index) {
 34          have.emplace_back(index->GetBlockHash());
 35          if (index->nHeight == 0) break;
 36          // Exponentially larger steps back, plus the genesis block.
 37          int height = std::max(index->nHeight - step, 0);
 38          // Use skiplist.
 39          index = index->GetAncestor(height);
 40          if (have.size() > 10) step *= 2;
 41      }
 42      return have;
 43  }
 44  
 45  CBlockLocator GetLocator(const CBlockIndex* index)
 46  {
 47      return CBlockLocator{LocatorEntries(index)};
 48  }
 49  
 50  const CBlockIndex* CChain::FindFork(const CBlockIndex& index) const
 51  {
 52      const auto* pindex{&index};
 53      if (pindex->nHeight > Height())
 54          pindex = pindex->GetAncestor(Height());
 55      while (pindex && !Contains(*pindex))
 56          pindex = pindex->pprev;
 57      return pindex;
 58  }
 59  
 60  CBlockIndex* CChain::FindEarliestAtLeast(int64_t nTime, int height) const
 61  {
 62      std::pair<int64_t, int> blockparams = std::make_pair(nTime, height);
 63      std::vector<CBlockIndex*>::const_iterator lower = std::lower_bound(vChain.begin(), vChain.end(), blockparams,
 64          [](CBlockIndex* pBlock, const std::pair<int64_t, int>& blockparams) -> bool { return pBlock->GetBlockTimeMax() < blockparams.first || pBlock->nHeight < blockparams.second; });
 65      return (lower == vChain.end() ? nullptr : *lower);
 66  }
 67  
 68  /** Turn the lowest '1' bit in the binary representation of a number into a '0'. */
 69  int static inline InvertLowestOne(int n) { return n & (n - 1); }
 70  
 71  /** Compute what height to jump back to with the CBlockIndex::pskip pointer. */
 72  int static inline GetSkipHeight(int height) {
 73      if (height < 2)
 74          return 0;
 75  
 76      // Determine which height to jump back to. Any number strictly lower than height is acceptable,
 77      // but the following expression seems to perform well in simulations (max 110 steps to go back
 78      // up to 2**18 blocks).
 79      return (height & 1) ? InvertLowestOne(InvertLowestOne(height - 1)) + 1 : InvertLowestOne(height);
 80  }
 81  
 82  const CBlockIndex* CBlockIndex::GetAncestor(int height) const
 83  {
 84      if (height > nHeight || height < 0) {
 85          return nullptr;
 86      }
 87  
 88      const CBlockIndex* pindexWalk = this;
 89      int heightWalk = nHeight;
 90      while (heightWalk > height) {
 91          int heightSkip = GetSkipHeight(heightWalk);
 92          int heightSkipPrev = GetSkipHeight(heightWalk - 1);
 93          if (pindexWalk->pskip != nullptr &&
 94              (heightSkip == height ||
 95               (heightSkip > height && !(heightSkipPrev < heightSkip - 2 &&
 96                                         heightSkipPrev >= height)))) {
 97              // Only follow pskip if pprev->pskip isn't better than pskip->pprev.
 98              pindexWalk = pindexWalk->pskip;
 99              heightWalk = heightSkip;
100          } else {
101              assert(pindexWalk->pprev);
102              pindexWalk = pindexWalk->pprev;
103              heightWalk--;
104          }
105      }
106      return pindexWalk;
107  }
108  
109  CBlockIndex* CBlockIndex::GetAncestor(int height)
110  {
111      return const_cast<CBlockIndex*>(static_cast<const CBlockIndex*>(this)->GetAncestor(height));
112  }
113  
114  void CBlockIndex::BuildSkip()
115  {
116      if (pprev)
117          pskip = pprev->GetAncestor(GetSkipHeight(nHeight));
118  }
119  
120  arith_uint256 GetBitsProof(uint32_t bits)
121  {
122      arith_uint256 bnTarget;
123      bool fNegative;
124      bool fOverflow;
125      bnTarget.SetCompact(bits, &fNegative, &fOverflow);
126      if (fNegative || fOverflow || bnTarget == 0)
127          return 0;
128      // We need to compute 2**256 / (bnTarget+1), but we can't represent 2**256
129      // as it's too large for an arith_uint256. However, as 2**256 is at least as large
130      // as bnTarget+1, it is equal to ((2**256 - bnTarget - 1) / (bnTarget+1)) + 1,
131      // or ~bnTarget / (bnTarget+1) + 1.
132      return (~bnTarget / (bnTarget + 1)) + 1;
133  }
134  
135  int64_t GetBlockProofEquivalentTime(const CBlockIndex& to, const CBlockIndex& from, const CBlockIndex& tip, const Consensus::Params& params)
136  {
137      arith_uint256 r;
138      int sign = 1;
139      if (to.nChainWork > from.nChainWork) {
140          r = to.nChainWork - from.nChainWork;
141      } else {
142          r = from.nChainWork - to.nChainWork;
143          sign = -1;
144      }
145      r = r * arith_uint256(params.nPowTargetSpacing) / GetBlockProof(tip);
146      if (r.bits() > 63) {
147          return sign * std::numeric_limits<int64_t>::max();
148      }
149      return sign * int64_t(r.GetLow64());
150  }
151  
152  /** Find the last common ancestor two blocks have.
153   *  Both pa and pb must be non-nullptr. */
154  const CBlockIndex* LastCommonAncestor(const CBlockIndex* pa, const CBlockIndex* pb) {
155      // First rewind to the last common height (the forking point cannot be past one of the two).
156      if (pa->nHeight > pb->nHeight) {
157          pa = pa->GetAncestor(pb->nHeight);
158      } else if (pb->nHeight > pa->nHeight) {
159          pb = pb->GetAncestor(pa->nHeight);
160      }
161      while (pa != pb) {
162          // Jump back until pa and pb have a common "skip" ancestor.
163          while (pa->pskip != pb->pskip) {
164              // This logic relies on the property that equal-height blocks have equal-height skip
165              // pointers.
166              Assume(pa->nHeight == pb->nHeight);
167              Assume(pa->pskip->nHeight == pb->pskip->nHeight);
168              pa = pa->pskip;
169              pb = pb->pskip;
170          }
171          // At this point, pa and pb are different, but have equal pskip. The forking point lies in
172          // between pa/pb on the one end, and pa->pskip/pb->pskip on the other end.
173          pa = pa->pprev;
174          pb = pb->pprev;
175      }
176      return pa;
177  }