src/versionbits.cpp

   1 // Copyright (c) 2016-2017 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 #include <versionbits.h>
   6 #include <consensus/params.h>
   7
   8 const struct VBDeploymentInfo VersionBitsDeploymentInfo[Consensus::MAX_VERSION_BITS_DEPLOYMENTS] = {
   9     {
  10         /*.name =*/ "testdummy",
  11         /*.gbt_force =*/ true,
  12     },
  13     {
  14         /*.name =*/ "csv",
  15         /*.gbt_force =*/ true,
  16     },
  17     {
  18         /*.name =*/ "segwit",
  19         /*.gbt_force =*/ true,
  20     }
  21 };
  22
  23 ThresholdState AbstractThresholdConditionChecker::GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const
  24 {
  25     int nPeriod = Period(params);
  26     int nThreshold = Threshold(params);
  27     int64_t nTimeStart = BeginTime(params);
  28     int64_t nTimeTimeout = EndTime(params);
  29
  30     // Check if this deployment is always active.
  31     if (nTimeStart == Consensus::BIP9Deployment::ALWAYS_ACTIVE) {
  32         return THRESHOLD_ACTIVE;
  33     }
  34
  35     // 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.
  36     if (pindexPrev != nullptr) {
  37         pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - ((pindexPrev->nHeight + 1) % nPeriod));
  38     }
  39
  40     // Walk backwards in steps of nPeriod to find a pindexPrev whose information is known
  41     std::vector<const CBlockIndex*> vToCompute;
  42     while (cache.count(pindexPrev) == 0) {
  43         if (pindexPrev == nullptr) {
  44             // The genesis block is by definition defined.
  45             cache[pindexPrev] = THRESHOLD_DEFINED;
  46             break;
  47         }
  48         if (pindexPrev->GetMedianTimePast() < nTimeStart) {
  49             // Optimization: don't recompute down further, as we know every earlier block will be before the start time
  50             cache[pindexPrev] = THRESHOLD_DEFINED;
  51             break;
  52         }
  53         vToCompute.push_back(pindexPrev);
  54         pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
  55     }
  56
  57     // At this point, cache[pindexPrev] is known
  58     assert(cache.count(pindexPrev));
  59     ThresholdState state = cache[pindexPrev];
  60
  61     // Now walk forward and compute the state of descendants of pindexPrev
  62     while (!vToCompute.empty()) {
  63         ThresholdState stateNext = state;
  64         pindexPrev = vToCompute.back();
  65         vToCompute.pop_back();
  66
  67         switch (state) {
  68             case THRESHOLD_DEFINED: {
  69                 if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
  70                     stateNext = THRESHOLD_FAILED;
  71                 } else if (pindexPrev->GetMedianTimePast() >= nTimeStart) {
  72                     stateNext = THRESHOLD_STARTED;
  73                 }
  74                 break;
  75             }
  76             case THRESHOLD_STARTED: {
  77                 if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
  78                     stateNext = THRESHOLD_FAILED;
  79                     break;
  80                 }
  81                 // We need to count
  82                 const CBlockIndex* pindexCount = pindexPrev;
  83                 int count = 0;
  84                 for (int i = 0; i < nPeriod; i++) {
  85                     if (Condition(pindexCount, params)) {
  86                         count++;
  87                     }
  88                     pindexCount = pindexCount->pprev;
  89                 }
  90                 if (count >= nThreshold) {
  91                     stateNext = THRESHOLD_LOCKED_IN;
  92                 }
  93                 break;
  94             }
  95             case THRESHOLD_LOCKED_IN: {
  96                 // Always progresses into ACTIVE.
  97                 stateNext = THRESHOLD_ACTIVE;
  98                 break;
  99             }
 100             case THRESHOLD_FAILED:
 101             case THRESHOLD_ACTIVE: {
 102                 // Nothing happens, these are terminal states.
 103                 break;
 104             }
 105         }
 106         cache[pindexPrev] = state = stateNext;
 107     }
 108
 109     return state;
 110 }
 111
 112 // return the numerical statistics of blocks signalling the specified BIP9 condition in this current period
 113 BIP9Stats AbstractThresholdConditionChecker::GetStateStatisticsFor(const CBlockIndex* pindex, const Consensus::Params& params) const
 114 {
 115     BIP9Stats stats = {};
 116
 117     stats.period = Period(params);
 118     stats.threshold = Threshold(params);
 119
 120     if (pindex == nullptr)
 121         return stats;
 122
 123     // Find beginning of period
 124     const CBlockIndex* pindexEndOfPrevPeriod = pindex->GetAncestor(pindex->nHeight - ((pindex->nHeight + 1) % stats.period));
 125     stats.elapsed = pindex->nHeight - pindexEndOfPrevPeriod->nHeight;
 126
 127     // Count from current block to beginning of period
 128     int count = 0;
 129     const CBlockIndex* currentIndex = pindex;
 130     while (pindexEndOfPrevPeriod->nHeight != currentIndex->nHeight){
 131         if (Condition(currentIndex, params))
 132             count++;
 133         currentIndex = currentIndex->pprev;
 134     }
 135
 136     stats.count = count;
 137     stats.possible = (stats.period - stats.threshold ) >= (stats.elapsed - count);
 138
 139     return stats;
 140 }
 141
 142 int AbstractThresholdConditionChecker::GetStateSinceHeightFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const
 143 {
 144     int64_t start_time = BeginTime(params);
 145     if (start_time == Consensus::BIP9Deployment::ALWAYS_ACTIVE) {
 146         return 0;
 147     }
 148
 149     const ThresholdState initialState = GetStateFor(pindexPrev, params, cache);
 150
 151     // BIP 9 about state DEFINED: "The genesis block is by definition in this state for each deployment."
 152     if (initialState == THRESHOLD_DEFINED) {
 153         return 0;
 154     }
 155
 156     const int nPeriod = Period(params);
 157
 158     // 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.
 159     // To ease understanding of the following height calculation, it helps to remember that
 160     // right now pindexPrev points to the block prior to the block that we are computing for, thus:
 161     // if we are computing for the last block of a period, then pindexPrev points to the second to last block of the period, and
 162     // if we are computing for the first block of a period, then pindexPrev points to the last block of the previous period.
 163     // The parent of the genesis block is represented by nullptr.
 164     pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - ((pindexPrev->nHeight + 1) % nPeriod));
 165
 166     const CBlockIndex* previousPeriodParent = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
 167
 168     while (previousPeriodParent != nullptr && GetStateFor(previousPeriodParent, params, cache) == initialState) {
 169         pindexPrev = previousPeriodParent;
 170         previousPeriodParent = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
 171     }
 172
 173     // Adjust the result because right now we point to the parent block.
 174     return pindexPrev->nHeight + 1;
 175 }
 176
 177 namespace
 178 {
 179 /**
 180  * Class to implement versionbits logic.
 181  */
 182 class VersionBitsConditionChecker : public AbstractThresholdConditionChecker {
 183 private:
 184     const Consensus::DeploymentPos id;
 185
 186 protected:
 187     int64_t BeginTime(const Consensus::Params& params) const override { return params.vDeployments[id].nStartTime; }
 188     int64_t EndTime(const Consensus::Params& params) const override { return params.vDeployments[id].nTimeout; }
 189     int Period(const Consensus::Params& params) const override { return params.nMinerConfirmationWindow; }
 190     int Threshold(const Consensus::Params& params) const override { return params.nRuleChangeActivationThreshold; }
 191
 192     bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const override
 193     {
 194         return (((pindex->nVersion & VERSIONBITS_TOP_MASK) == VERSIONBITS_TOP_BITS) && (pindex->nVersion & Mask(params)) != 0);
 195     }
 196
 197 public:
 198     explicit VersionBitsConditionChecker(Consensus::DeploymentPos id_) : id(id_) {}
 199     uint32_t Mask(const Consensus::Params& params) const { return ((uint32_t)1) << params.vDeployments[id].bit; }
 200 };
 201
 202 } // namespace
 203
 204 ThresholdState VersionBitsState(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos, VersionBitsCache& cache)
 205 {
 206     return VersionBitsConditionChecker(pos).GetStateFor(pindexPrev, params, cache.caches[pos]);
 207 }
 208
 209 BIP9Stats VersionBitsStatistics(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos)
 210 {
 211     return VersionBitsConditionChecker(pos).GetStateStatisticsFor(pindexPrev, params);
 212 }
 213
 214 int VersionBitsStateSinceHeight(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos, VersionBitsCache& cache)
 215 {
 216     return VersionBitsConditionChecker(pos).GetStateSinceHeightFor(pindexPrev, params, cache.caches[pos]);
 217 }
 218
 219 uint32_t VersionBitsMask(const Consensus::Params& params, Consensus::DeploymentPos pos)
 220 {
 221     return VersionBitsConditionChecker(pos).Mask(params);
 222 }
 223
 224 void VersionBitsCache::Clear()
 225 {
 226     for (unsigned int d = 0; d < Consensus::MAX_VERSION_BITS_DEPLOYMENTS; d++) {
 227         caches[d].clear();
 228     }
 229 }