text: // Copyright (c) 2016-2021 The BIGKEYCOIN Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include <versionbits.h>
  #include <consensus/params.h>
  
  ThresholdState AbstractThresholdConditionChecker::GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const
  {
      int nPeriod = Period(params);
      int nThreshold = Threshold(params);
      int min_activation_height = MinActivationHeight(params);
      int64_t nTimeStart = BeginTime(params);
      int64_t nTimeTimeout = EndTime(params);
  
      // Check if this deployment is always active.
      if (nTimeStart == Consensus::BIP9Deployment::ALWAYS_ACTIVE) {
          return ThresholdState::ACTIVE;
      }
  
      // Check if this deployment is never active.
      if (nTimeStart == Consensus::BIP9Deployment::NEVER_ACTIVE) {
          return ThresholdState::FAILED;
      }
  
      // A block's state is always the same as that of the first of its period, so it is computed based on a pindexPrev whose height equals a multiple of nPeriod - 1.
      if (pindexPrev != nullptr) {
          pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - ((pindexPrev->nHeight + 1) % nPeriod));
      }
  
      // Walk backwards in steps of nPeriod to find a pindexPrev whose information is known
      std::vector<const CBlockIndex*> vToCompute;
      while (cache.count(pindexPrev) == 0) {
          if (pindexPrev == nullptr) {
              // The genesis block is by definition defined.
              cache[pindexPrev] = ThresholdState::DEFINED;
              break;
          }
          if (pindexPrev->GetMedianTimePast() < nTimeStart) {
              // Optimization: don't recompute down further, as we know every earlier block will be before the start time
              cache[pindexPrev] = ThresholdState::DEFINED;
              break;
          }
          vToCompute.push_back(pindexPrev);
          pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
      }
  
      // At this point, cache[pindexPrev] is known
      assert(cache.count(pindexPrev));
      ThresholdState state = cache[pindexPrev];
  
      // Now walk forward and compute the state of descendants of pindexPrev
      while (!vToCompute.empty()) {
          ThresholdState stateNext = state;
          pindexPrev = vToCompute.back();
          vToCompute.pop_back();
  
          switch (state) {
              case ThresholdState::DEFINED: {
                  if (pindexPrev->GetMedianTimePast() >= nTimeStart) {
                      stateNext = ThresholdState::STARTED;
                  }
                  break;
              }
              case ThresholdState::STARTED: {
                  // We need to count
                  const CBlockIndex* pindexCount = pindexPrev;
                  int count = 0;
                  for (int i = 0; i < nPeriod; i++) {
                      if (Condition(pindexCount, params)) {
                          count++;
                      }
                      pindexCount = pindexCount->pprev;
                  }
                  if (count >= nThreshold) {
                      stateNext = ThresholdState::LOCKED_IN;
                  } else if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
                      stateNext = ThresholdState::FAILED;
                  }
                  break;
              }
              case ThresholdState::LOCKED_IN: {
                  // Progresses into ACTIVE provided activation height will have been reached.
                  if (pindexPrev->nHeight + 1 >= min_activation_height) {
                      stateNext = ThresholdState::ACTIVE;
                  }
                  break;
              }
              case ThresholdState::FAILED:
              case ThresholdState::ACTIVE: {
                  // Nothing happens, these are terminal states.
                  break;
              }
          }
          cache[pindexPrev] = state = stateNext;
      }
  
      return state;
  }
  
  BIP9Stats AbstractThresholdConditionChecker::GetStateStatisticsFor(const CBlockIndex* pindex, const Consensus::Params& params, std::vector<bool>* signalling_blocks) const
  {
      BIP9Stats stats = {};
  
      stats.period = Period(params);
      stats.threshold = Threshold(params);
  
      if (pindex == nullptr) return stats;
  
      // Find how many blocks are in the current period
      int blocks_in_period = 1 + (pindex->nHeight % stats.period);
  
      // Reset signalling_blocks
      if (signalling_blocks) {
          signalling_blocks->assign(blocks_in_period, false);
      }
  
      // Count from current block to beginning of period
      int elapsed = 0;
      int count = 0;
      const CBlockIndex* currentIndex = pindex;
      do {
          ++elapsed;
          --blocks_in_period;
          if (Condition(currentIndex, params)) {
              ++count;
              if (signalling_blocks) signalling_blocks->at(blocks_in_period) = true;
          }
          currentIndex = currentIndex->pprev;
      } while(blocks_in_period > 0);
  
      stats.elapsed = elapsed;
      stats.count = count;
      stats.possible = (stats.period - stats.threshold ) >= (stats.elapsed - count);
  
      return stats;
  }
  
  int AbstractThresholdConditionChecker::GetStateSinceHeightFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const
  {
      int64_t start_time = BeginTime(params);
      if (start_time == Consensus::BIP9Deployment::ALWAYS_ACTIVE || start_time == Consensus::BIP9Deployment::NEVER_ACTIVE) {
          return 0;
      }
  
      const ThresholdState initialState = GetStateFor(pindexPrev, params, cache);
  
      // BIP 9 about state DEFINED: "The genesis block is by definition in this state for each deployment."
      if (initialState == ThresholdState::DEFINED) {
          return 0;
      }
  
      const int nPeriod = Period(params);
  
      // A block's state is always the same as that of the first of its period, so it is computed based on a pindexPrev whose height equals a multiple of nPeriod - 1.
      // To ease understanding of the following height calculation, it helps to remember that
      // right now pindexPrev points to the block prior to the block that we are computing for, thus:
      // if we are computing for the last block of a period, then pindexPrev points to the second to last block of the period, and
      // if we are computing for the first block of a period, then pindexPrev points to the last block of the previous period.
      // The parent of the genesis block is represented by nullptr.
      pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - ((pindexPrev->nHeight + 1) % nPeriod));
  
      const CBlockIndex* previousPeriodParent = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
  
      while (previousPeriodParent != nullptr && GetStateFor(previousPeriodParent, params, cache) == initialState) {
          pindexPrev = previousPeriodParent;
          previousPeriodParent = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
      }
  
      // Adjust the result because right now we point to the parent block.
      return pindexPrev->nHeight + 1;
  }
  
  namespace
  {
  /**
   * Class to implement versionbits logic.
   */
  class VersionBitsConditionChecker : public AbstractThresholdConditionChecker {
  private:
      const Consensus::DeploymentPos id;
  
  protected:
      int64_t BeginTime(const Consensus::Params& params) const override { return params.vDeployments[id].nStartTime; }
      int64_t EndTime(const Consensus::Params& params) const override { return params.vDeployments[id].nTimeout; }
      int MinActivationHeight(const Consensus::Params& params) const override { return params.vDeployments[id].min_activation_height; }
      int Period(const Consensus::Params& params) const override { return params.nMinerConfirmationWindow; }
      int Threshold(const Consensus::Params& params) const override { return params.nRuleChangeActivationThreshold; }
  
      bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const override
      {
          return (((pindex->nVersion & VERSIONBITS_TOP_MASK) == VERSIONBITS_TOP_BITS) && (pindex->nVersion & Mask(params)) != 0);
      }
  
  public:
      explicit VersionBitsConditionChecker(Consensus::DeploymentPos id_) : id(id_) {}
      uint32_t Mask(const Consensus::Params& params) const { return ((uint32_t)1) << params.vDeployments[id].bit; }
  };
  
  } // namespace
  
  ThresholdState VersionBitsCache::State(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos)
  {
      LOCK(m_mutex);
      return VersionBitsConditionChecker(pos).GetStateFor(pindexPrev, params, m_caches[pos]);
  }
  
  BIP9Stats VersionBitsCache::Statistics(const CBlockIndex* pindex, const Consensus::Params& params, Consensus::DeploymentPos pos, std::vector<bool>* signalling_blocks)
  {
      return VersionBitsConditionChecker(pos).GetStateStatisticsFor(pindex, params, signalling_blocks);
  }
  
  int VersionBitsCache::StateSinceHeight(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos)
  {
      LOCK(m_mutex);
      return VersionBitsConditionChecker(pos).GetStateSinceHeightFor(pindexPrev, params, m_caches[pos]);
  }
  
  uint32_t VersionBitsCache::Mask(const Consensus::Params& params, Consensus::DeploymentPos pos)
  {
      return VersionBitsConditionChecker(pos).Mask(params);
  }
  
  int32_t VersionBitsCache::ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params)
  {
      LOCK(m_mutex);
      int32_t nVersion = VERSIONBITS_TOP_BITS;
  
      for (int i = 0; i < (int)Consensus::MAX_VERSION_BITS_DEPLOYMENTS; i++) {
          Consensus::DeploymentPos pos = static_cast<Consensus::DeploymentPos>(i);
          ThresholdState state = VersionBitsConditionChecker(pos).GetStateFor(pindexPrev, params, m_caches[pos]);
          if (state == ThresholdState::LOCKED_IN || state == ThresholdState::STARTED) {
              nVersion |= Mask(params, pos);
          }
      }
  
      return nVersion;
  }
  
  void VersionBitsCache::Clear()
  {
      LOCK(m_mutex);
      for (unsigned int d = 0; d < Consensus::MAX_VERSION_BITS_DEPLOYMENTS; d++) {
          m_caches[d].clear();
      }
  }
  