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       1                 :            : // Copyright (c) 2016-2022 The Bitcoin Core developers
       2                 :            : // Distributed under the MIT software license, see the accompanying
       3                 :            : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       4                 :            : 
       5                 :            : #ifndef BITCOIN_VERSIONBITS_H
       6                 :            : #define BITCOIN_VERSIONBITS_H
       7                 :            : 
       8                 :            : #include <chain.h>
       9                 :            : #include <sync.h>
      10                 :            : 
      11                 :            : #include <map>
      12                 :            : 
      13                 :            : /** What block version to use for new blocks (pre versionbits) */
      14                 :            : static const int32_t VERSIONBITS_LAST_OLD_BLOCK_VERSION = 4;
      15                 :            : /** What bits to set in version for versionbits blocks */
      16                 :            : static const int32_t VERSIONBITS_TOP_BITS = 0x20000000UL;
      17                 :            : /** What bitmask determines whether versionbits is in use */
      18                 :            : static const int32_t VERSIONBITS_TOP_MASK = 0xE0000000UL;
      19                 :            : /** Total bits available for versionbits */
      20                 :            : static const int32_t VERSIONBITS_NUM_BITS = 29;
      21                 :            : 
      22                 :            : /** BIP 9 defines a finite-state-machine to deploy a softfork in multiple stages.
      23                 :            :  *  State transitions happen during retarget period if conditions are met
      24                 :            :  *  In case of reorg, transitions can go backward. Without transition, state is
      25                 :            :  *  inherited between periods. All blocks of a period share the same state.
      26                 :            :  */
      27                 :            : enum class ThresholdState {
      28                 :            :     DEFINED,   // First state that each softfork starts out as. The genesis block is by definition in this state for each deployment.
      29                 :            :     STARTED,   // For blocks past the starttime.
      30                 :            :     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.
      31                 :            :     ACTIVE,    // For all blocks after the LOCKED_IN retarget period (final state)
      32                 :            :     FAILED,    // For all blocks once the first retarget period after the timeout time is hit, if LOCKED_IN wasn't already reached (final state)
      33                 :            : };
      34                 :            : 
      35                 :            : // A map that gives the state for blocks whose height is a multiple of Period().
      36                 :            : // The map is indexed by the block's parent, however, so all keys in the map
      37                 :            : // will either be nullptr or a block with (height + 1) % Period() == 0.
      38                 :            : typedef std::map<const CBlockIndex*, ThresholdState> ThresholdConditionCache;
      39                 :            : 
      40                 :            : /** Display status of an in-progress BIP9 softfork */
      41                 :            : struct BIP9Stats {
      42                 :            :     /** Length of blocks of the BIP9 signalling period */
      43                 :            :     int period;
      44                 :            :     /** Number of blocks with the version bit set required to activate the softfork */
      45                 :            :     int threshold;
      46                 :            :     /** Number of blocks elapsed since the beginning of the current period */
      47                 :            :     int elapsed;
      48                 :            :     /** Number of blocks with the version bit set since the beginning of the current period */
      49                 :            :     int count;
      50                 :            :     /** False if there are not enough blocks left in this period to pass activation threshold */
      51                 :            :     bool possible;
      52                 :            : };
      53                 :            : 
      54                 :            : /**
      55                 :            :  * Abstract class that implements BIP9-style threshold logic, and caches results.
      56                 :            :  */
      57                 :            : class AbstractThresholdConditionChecker {
      58                 :            : protected:
      59                 :            :     virtual bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const =0;
      60                 :            :     virtual int64_t BeginTime(const Consensus::Params& params) const =0;
      61                 :            :     virtual int64_t EndTime(const Consensus::Params& params) const =0;
      62                 :          0 :     virtual int MinActivationHeight(const Consensus::Params& params) const { return 0; }
      63                 :            :     virtual int Period(const Consensus::Params& params) const =0;
      64                 :            :     virtual int Threshold(const Consensus::Params& params) const =0;
      65                 :            : 
      66                 :            : public:
      67                 :            :     /** Returns the numerical statistics of an in-progress BIP9 softfork in the period including pindex
      68                 :            :      * If provided, signalling_blocks is set to true/false based on whether each block in the period signalled
      69                 :            :      */
      70                 :            :     BIP9Stats GetStateStatisticsFor(const CBlockIndex* pindex, const Consensus::Params& params, std::vector<bool>* signalling_blocks = nullptr) const;
      71                 :            :     /** Returns the state for pindex A based on parent pindexPrev B. Applies any state transition if conditions are present.
      72                 :            :      *  Caches state from first block of period. */
      73                 :            :     ThresholdState GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;
      74                 :            :     /** 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 */
      75                 :            :     int GetStateSinceHeightFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;
      76                 :            : };
      77                 :            : 
      78                 :            : /** BIP 9 allows multiple softforks to be deployed in parallel. We cache
      79                 :            :  *  per-period state for every one of them. */
      80                 :          2 : class VersionBitsCache
      81                 :            : {
      82                 :            : private:
      83                 :            :     Mutex m_mutex;
      84                 :            :     ThresholdConditionCache m_caches[Consensus::MAX_VERSION_BITS_DEPLOYMENTS] GUARDED_BY(m_mutex);
      85                 :            : 
      86                 :            : public:
      87                 :            :     /** Get the numerical statistics for a given deployment for the signalling period that includes pindex.
      88                 :            :      * If provided, signalling_blocks is set to true/false based on whether each block in the period signalled
      89                 :            :      */
      90                 :            :     static BIP9Stats Statistics(const CBlockIndex* pindex, const Consensus::Params& params, Consensus::DeploymentPos pos, std::vector<bool>* signalling_blocks = nullptr);
      91                 :            : 
      92                 :            :     static uint32_t Mask(const Consensus::Params& params, Consensus::DeploymentPos pos);
      93                 :            : 
      94                 :            :     /** Get the BIP9 state for a given deployment for the block after pindexPrev. */
      95                 :            :     ThresholdState State(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
      96                 :            : 
      97                 :            :     /** Get the block height at which the BIP9 deployment switched into the state for the block after pindexPrev. */
      98                 :            :     int StateSinceHeight(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
      99                 :            : 
     100                 :            :     /** Determine what nVersion a new block should use
     101                 :            :      */
     102                 :            :     int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
     103                 :            : 
     104                 :            :     void Clear() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
     105                 :            : };
     106                 :            : 
     107                 :            : #endif // BITCOIN_VERSIONBITS_H