text: // Copyright (c) 2016-2019 The Bitcoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #ifndef XCBC_VERSIONBITS_H
  #define XCBC_VERSIONBITS_H
  
  #include <chain.h>
  #include <sync.h>
  
  #include <map>
  
  /** What block version to use for new blocks (pre versionbits) */
  static const int32_t VERSIONBITS_LAST_OLD_BLOCK_VERSION = 4;
  /** What bits to set in version for versionbits blocks */
  static const int32_t VERSIONBITS_TOP_BITS = 0x20000000UL;
  /** What bitmask determines whether versionbits is in use */
  static const int32_t VERSIONBITS_TOP_MASK = 0xE0000000UL;
  /** Total bits available for versionbits */
  static const int32_t VERSIONBITS_NUM_BITS = 29;
  
  /** BIP 9 defines a finite-state-machine to deploy a softfork in multiple stages.
   *  State transitions happen during retarget period if conditions are met
   *  In case of reorg, transitions can go backward. Without transition, state is
   *  inherited between periods. All blocks of a period share the same state.
   */
  enum class ThresholdState {
      DEFINED,   // First state that each softfork starts out as. The genesis block is by definition in this state for each deployment.
      STARTED,   // For blocks past the starttime.
      LOCKED_IN, // For at least one retarget period after the first retarget period with STARTED blocks of which at least threshold have the associated bit set in nVersion, until min_activation_height is reached.
      ACTIVE,    // For all blocks after the LOCKED_IN retarget period (final state)
      FAILED,    // For all blocks once the first retarget period after the timeout time is hit, if LOCKED_IN wasn't already reached (final state)
  };
  
  // A map that gives the state for blocks whose height is a multiple of Period().
  // The map is indexed by the block's parent, however, so all keys in the map
  // will either be nullptr or a block with (height + 1) % Period() == 0.
  typedef std::map<const CBlockIndex*, ThresholdState> ThresholdConditionCache;
  
  /** Display status of an in-progress BIP9 softfork */
  struct BIP9Stats {
      /** Length of blocks of the BIP9 signalling period */
      int period;
      /** Number of blocks with the version bit set required to activate the softfork */
      int threshold;
      /** Number of blocks elapsed since the beginning of the current period */
      int elapsed;
      /** Number of blocks with the version bit set since the beginning of the current period */
      int count;
      /** False if there are not enough blocks left in this period to pass activation threshold */
      bool possible;
  };
  
  /**
   * Abstract class that implements BIP9-style threshold logic, and caches results.
   */
  class AbstractThresholdConditionChecker {
  protected:
      virtual bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const =0;
      virtual int64_t BeginTime(const Consensus::Params& params) const =0;
      virtual int64_t EndTime(const Consensus::Params& params) const =0;
      virtual int MinActivationHeight(const Consensus::Params& params) const { return 0; }
      virtual int Period(const Consensus::Params& params) const =0;
      virtual int Threshold(const Consensus::Params& params) const =0;
  
  public:
      /** Returns the numerical statistics of an in-progress BIP9 softfork in the current period */
      BIP9Stats GetStateStatisticsFor(const CBlockIndex* pindex, const Consensus::Params& params) const;
      /** Returns the state for pindex A based on parent pindexPrev B. Applies any state transition if conditions are present.
       *  Caches state from first block of period. */
      ThresholdState GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;
      /** Returns the height since when the ThresholdState has started for pindex A based on parent pindexPrev B, all blocks of a period share the same */
      int GetStateSinceHeightFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;
  };
  
  /** BIP 9 allows multiple softforks to be deployed in parallel. We cache
   *  per-period state for every one of them. */
  class VersionBitsCache
  {
  private:
      Mutex m_mutex;
      ThresholdConditionCache m_caches[Consensus::MAX_VERSION_BITS_DEPLOYMENTS] GUARDED_BY(m_mutex);
  
  public:
      /** Get the numerical statistics for a given deployment for the signalling period that includes the block after pindexPrev. */
      static BIP9Stats Statistics(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos);
  
      static uint32_t Mask(const Consensus::Params& params, Consensus::DeploymentPos pos);
  
      /** Get the BIP9 state for a given deployment for the block after pindexPrev. */
      ThresholdState State(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos);
  
      /** Get the block height at which the BIP9 deployment switched into the state for the block after pindexPrev. */
      int StateSinceHeight(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos);
  
      /** Determine what nVersion a new block should use
       */
      int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params);
  
      void Clear();
  };
  
  #endif // XCBC_VERSIONBITS_H
  