214 lines
8.6 KiB
C++
214 lines
8.6 KiB
C++
// Copyright (c) 2016-2018 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include <versionbits.h>
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#include <consensus/params.h>
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ThresholdState AbstractThresholdConditionChecker::GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const
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{
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int nPeriod = Period(params);
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int nThreshold = Threshold(params);
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int64_t nTimeStart = BeginTime(params);
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int64_t nTimeTimeout = EndTime(params);
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// Check if this deployment is always active.
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if (nTimeStart == Consensus::BIP9Deployment::ALWAYS_ACTIVE) {
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return ThresholdState::ACTIVE;
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}
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// 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.
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if (pindexPrev != nullptr) {
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pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - ((pindexPrev->nHeight + 1) % nPeriod));
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}
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// Walk backwards in steps of nPeriod to find a pindexPrev whose information is known
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std::vector<const CBlockIndex*> vToCompute;
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while (cache.count(pindexPrev) == 0) {
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if (pindexPrev == nullptr) {
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// The genesis block is by definition defined.
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cache[pindexPrev] = ThresholdState::DEFINED;
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break;
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}
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if (pindexPrev->GetMedianTimePast() < nTimeStart) {
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// Optimization: don't recompute down further, as we know every earlier block will be before the start time
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cache[pindexPrev] = ThresholdState::DEFINED;
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break;
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}
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vToCompute.push_back(pindexPrev);
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pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
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}
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// At this point, cache[pindexPrev] is known
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assert(cache.count(pindexPrev));
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ThresholdState state = cache[pindexPrev];
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// Now walk forward and compute the state of descendants of pindexPrev
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while (!vToCompute.empty()) {
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ThresholdState stateNext = state;
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pindexPrev = vToCompute.back();
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vToCompute.pop_back();
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switch (state) {
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case ThresholdState::DEFINED: {
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if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
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stateNext = ThresholdState::FAILED;
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} else if (pindexPrev->GetMedianTimePast() >= nTimeStart) {
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stateNext = ThresholdState::STARTED;
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}
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break;
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}
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case ThresholdState::STARTED: {
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if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
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stateNext = ThresholdState::FAILED;
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break;
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}
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// We need to count
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const CBlockIndex* pindexCount = pindexPrev;
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int count = 0;
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for (int i = 0; i < nPeriod; i++) {
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if (Condition(pindexCount, params)) {
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count++;
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}
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pindexCount = pindexCount->pprev;
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}
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if (count >= nThreshold) {
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stateNext = ThresholdState::LOCKED_IN;
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}
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break;
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}
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case ThresholdState::LOCKED_IN: {
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// Always progresses into ACTIVE.
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stateNext = ThresholdState::ACTIVE;
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break;
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}
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case ThresholdState::FAILED:
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case ThresholdState::ACTIVE: {
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// Nothing happens, these are terminal states.
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break;
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}
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}
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cache[pindexPrev] = state = stateNext;
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}
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return state;
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}
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// return the numerical statistics of blocks signalling the specified BIP9 condition in this current period
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BIP9Stats AbstractThresholdConditionChecker::GetStateStatisticsFor(const CBlockIndex* pindex, const Consensus::Params& params) const
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{
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BIP9Stats stats = {};
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stats.period = Period(params);
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stats.threshold = Threshold(params);
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if (pindex == nullptr)
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return stats;
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// Find beginning of period
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const CBlockIndex* pindexEndOfPrevPeriod = pindex->GetAncestor(pindex->nHeight - ((pindex->nHeight + 1) % stats.period));
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stats.elapsed = pindex->nHeight - pindexEndOfPrevPeriod->nHeight;
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// Count from current block to beginning of period
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int count = 0;
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const CBlockIndex* currentIndex = pindex;
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while (pindexEndOfPrevPeriod->nHeight != currentIndex->nHeight){
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if (Condition(currentIndex, params))
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count++;
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currentIndex = currentIndex->pprev;
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}
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stats.count = count;
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stats.possible = (stats.period - stats.threshold ) >= (stats.elapsed - count);
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return stats;
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}
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int AbstractThresholdConditionChecker::GetStateSinceHeightFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const
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{
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int64_t start_time = BeginTime(params);
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if (start_time == Consensus::BIP9Deployment::ALWAYS_ACTIVE) {
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return 0;
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}
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const ThresholdState initialState = GetStateFor(pindexPrev, params, cache);
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// BIP 9 about state DEFINED: "The genesis block is by definition in this state for each deployment."
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if (initialState == ThresholdState::DEFINED) {
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return 0;
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}
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const int nPeriod = Period(params);
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// 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.
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// To ease understanding of the following height calculation, it helps to remember that
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// right now pindexPrev points to the block prior to the block that we are computing for, thus:
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// if we are computing for the last block of a period, then pindexPrev points to the second to last block of the period, and
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// if we are computing for the first block of a period, then pindexPrev points to the last block of the previous period.
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// The parent of the genesis block is represented by nullptr.
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pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - ((pindexPrev->nHeight + 1) % nPeriod));
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const CBlockIndex* previousPeriodParent = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
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while (previousPeriodParent != nullptr && GetStateFor(previousPeriodParent, params, cache) == initialState) {
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pindexPrev = previousPeriodParent;
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previousPeriodParent = pindexPrev->GetAncestor(pindexPrev->nHeight - nPeriod);
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}
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// Adjust the result because right now we point to the parent block.
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return pindexPrev->nHeight + 1;
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}
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namespace
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{
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/**
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* Class to implement versionbits logic.
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*/
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class VersionBitsConditionChecker : public AbstractThresholdConditionChecker {
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private:
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const Consensus::DeploymentPos id;
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protected:
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int64_t BeginTime(const Consensus::Params& params) const override { return params.vDeployments[id].nStartTime; }
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int64_t EndTime(const Consensus::Params& params) const override { return params.vDeployments[id].nTimeout; }
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int Period(const Consensus::Params& params) const override { return params.nMinerConfirmationWindow; }
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int Threshold(const Consensus::Params& params) const override { return params.nRuleChangeActivationThreshold; }
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bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const override
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{
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return (((pindex->nVersion & VERSIONBITS_TOP_MASK) == VERSIONBITS_TOP_BITS) && (pindex->nVersion & Mask(params)) != 0);
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}
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public:
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explicit VersionBitsConditionChecker(Consensus::DeploymentPos id_) : id(id_) {}
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uint32_t Mask(const Consensus::Params& params) const { return ((uint32_t)1) << params.vDeployments[id].bit; }
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};
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} // namespace
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ThresholdState VersionBitsState(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos, VersionBitsCache& cache)
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{
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return VersionBitsConditionChecker(pos).GetStateFor(pindexPrev, params, cache.caches[pos]);
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}
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BIP9Stats VersionBitsStatistics(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos)
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{
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return VersionBitsConditionChecker(pos).GetStateStatisticsFor(pindexPrev, params);
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}
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int VersionBitsStateSinceHeight(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos, VersionBitsCache& cache)
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{
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return VersionBitsConditionChecker(pos).GetStateSinceHeightFor(pindexPrev, params, cache.caches[pos]);
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}
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uint32_t VersionBitsMask(const Consensus::Params& params, Consensus::DeploymentPos pos)
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{
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return VersionBitsConditionChecker(pos).Mask(params);
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}
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void VersionBitsCache::Clear()
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{
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for (unsigned int d = 0; d < Consensus::MAX_VERSION_BITS_DEPLOYMENTS; d++) {
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caches[d].clear();
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}
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}
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