mirror of https://github.com/bitcoin/bitcoin
Inspired by former implementations by Eric Lombrozo and Rusty Russell, and based on code by Jorge Timon.pull/7575/head
Pieter Wuille
9 years ago
parent
a6a860796a
commit
6851107b3a
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// Copyright (c) 2016 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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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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// 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 != NULL) {
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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 == NULL) {
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// The genesis block is by definition defined.
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cache[pindexPrev] = THRESHOLD_DEFINED;
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break;
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}
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if (pindexPrev->GetMedianTimePast() < nTimeStart) {
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// Optimizaton: don't recompute down further, as we know every earlier block will be before the start time
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cache[pindexPrev] = THRESHOLD_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 THRESHOLD_DEFINED: {
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if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
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stateNext = THRESHOLD_FAILED;
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} else if (pindexPrev->GetMedianTimePast() >= nTimeStart) {
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stateNext = THRESHOLD_STARTED;
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}
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break;
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}
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case THRESHOLD_STARTED: {
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if (pindexPrev->GetMedianTimePast() >= nTimeTimeout) {
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stateNext = THRESHOLD_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 = THRESHOLD_LOCKED_IN;
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}
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break;
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}
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case THRESHOLD_LOCKED_IN: {
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// Always progresses into ACTIVE.
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stateNext = THRESHOLD_ACTIVE;
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break;
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}
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case THRESHOLD_FAILED:
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case THRESHOLD_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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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 { return params.vDeployments[id].nStartTime; }
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int64_t EndTime(const Consensus::Params& params) const { return params.vDeployments[id].nTimeout; }
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int Period(const Consensus::Params& params) const { return params.nMinerConfirmationWindow; }
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int Threshold(const Consensus::Params& params) const { return params.nRuleChangeActivationThreshold; }
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bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const
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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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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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}
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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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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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@ -0,0 +1,59 @@
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// Copyright (c) 2016 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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#ifndef BITCOIN_CONSENSUS_VERSIONBITS
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#define BITCOIN_CONSENSUS_VERSIONBITS
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#include "chain.h"
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#include <map>
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/** What block version to use for new blocks (pre versionbits) */
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static const int32_t VERSIONBITS_LAST_OLD_BLOCK_VERSION = 4;
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/** What bits to set in version for versionbits blocks */
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static const int32_t VERSIONBITS_TOP_BITS = 0x20000000UL;
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/** What bitmask determines whether versionbits is in use */
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static const int32_t VERSIONBITS_TOP_MASK = 0xE0000000UL;
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/** Total bits available for versionbits */
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static const int32_t VERSIONBITS_NUM_BITS = 29;
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enum ThresholdState {
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THRESHOLD_DEFINED,
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THRESHOLD_STARTED,
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THRESHOLD_LOCKED_IN,
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THRESHOLD_ACTIVE,
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THRESHOLD_FAILED,
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};
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// A map that gives the state for blocks whose height is a multiple of Period().
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// The map is indexed by the block's parent, however, so all keys in the map
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// will either be NULL or a block with (height + 1) % Period() == 0.
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typedef std::map<const CBlockIndex*, ThresholdState> ThresholdConditionCache;
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/**
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* Abstract class that implements BIP9-style threshold logic, and caches results.
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*/
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class AbstractThresholdConditionChecker {
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protected:
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virtual bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const =0;
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virtual int64_t BeginTime(const Consensus::Params& params) const =0;
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virtual int64_t EndTime(const Consensus::Params& params) const =0;
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virtual int Period(const Consensus::Params& params) const =0;
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virtual int Threshold(const Consensus::Params& params) const =0;
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public:
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// Note that the function below takes a pindexPrev as input: they compute information for block B based on its parent.
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ThresholdState GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;
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};
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struct VersionBitsCache
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{
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ThresholdConditionCache caches[Consensus::MAX_VERSION_BITS_DEPLOYMENTS];
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void Clear();
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};
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ThresholdState VersionBitsState(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos, VersionBitsCache& cache);
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uint32_t VersionBitsMask(const Consensus::Params& params, Consensus::DeploymentPos pos);
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#endif
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