Always-active versionbits support

Author: sipa

src/consensus/params.h

@@ -35,6 +35,12 @@ struct BIP9Deployment {
 
     /** Constant for nTimeout very far in the future. */
     static constexpr int64_t NO_TIMEOUT = std::numeric_limits<int64_t>::max();
+
+    /** Special value for nStartTime indicating that the deployment is always active.
+     *  This is useful for testing, as it means tests don't need to deal with the activation
+     *  process (which takes at least 3 BIP9 intervals). Only tests that specifically test the
+     *  behaviour during activation cannot use this. */
+    static constexpr int64_t ALWAYS_ACTIVE = -1;
 };
 
 /**

src/versionbits.cpp

@@ -27,6 +27,11 @@ ThresholdState AbstractThresholdConditionChecker::GetStateFor(const CBlockIndex*
     int64_t nTimeStart = BeginTime(params);
     int64_t nTimeTimeout = EndTime(params);
 
+    // Check if this deployment is always active.
+    if (nTimeStart == Consensus::BIP9Deployment::ALWAYS_ACTIVE) {
+        return THRESHOLD_ACTIVE;
+    }
+
     // 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.
     if (pindexPrev != nullptr) {
         pindexPrev = pindexPrev->GetAncestor(pindexPrev->nHeight - ((pindexPrev->nHeight + 1) % nPeriod));
@@ -136,6 +141,11 @@ BIP9Stats AbstractThresholdConditionChecker::GetStateStatisticsFor(const CBlockI
 
 int AbstractThresholdConditionChecker::GetStateSinceHeightFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const
 {
+    int64_t start_time = BeginTime(params);
+    if (start_time == Consensus::BIP9Deployment::ALWAYS_ACTIVE) {
+        return 0;
+    }
+
     const ThresholdState initialState = GetStateFor(pindexPrev, params, cache);
 
     // BIP 9 about state DEFINED: "The genesis block is by definition in this state for each deployment."