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doc: Improve versionbits.h documentation

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This commit is contained in:
Antoine Riard 2019-08-06 22:18:36 -04:00
parent 00dad5e0e1
commit 6576a8765f
2 changed files with 22 additions and 7 deletions
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1
src/versionbits.cpp
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@ -94,7 +94,6 @@ ThresholdState AbstractThresholdConditionChecker::GetStateFor(const CBlockIndex*
return state;
}
// return the numerical statistics of blocks signalling the specified BIP9 condition in this current period
BIP9Stats AbstractThresholdConditionChecker::GetStateStatisticsFor(const CBlockIndex* pindex, const Consensus::Params& params) const
{
BIP9Stats stats = {};

28
src/versionbits.h
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@ -17,12 +17,17 @@ 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,
STARTED,
LOCKED_IN,
ACTIVE,
FAILED,
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 one retarget period after the first retarget period with STARTED blocks of which at least threshold have the associated bit set in nVersion.
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().
@ -30,11 +35,17 @@ enum class ThresholdState {
// 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;
};
@ -50,12 +61,17 @@ protected:
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;
// Note that the functions below take a pindexPrev as input: they compute information for block B based on its parent.
/** 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
* keyed by the bit position used to signal support. */
struct VersionBitsCache
{
ThresholdConditionCache caches[Consensus::MAX_VERSION_BITS_DEPLOYMENTS];