Implement protocol entry changeable magnitude unit

The magnitude unit has been fixed at 1/4 since Fern. This commit
allows the magnitude unit to be changed via a protocol entry for block
V13+.

src/gridcoin/accrual/snapshot.h

@@ -13,7 +13,10 @@
 #include "gridcoin/accrual/computer.h"
 #include "gridcoin/beacon.h"
 #include "gridcoin/cpid.h"
+#include "gridcoin/protocol.h"
+#include "gridcoin/sidestake.h"
 #include "gridcoin/superblock.h"
+#include "gridcoin/support/block_finder.h"
 #include "gridcoin/support/filehash.h"
 #include "node/blockstorage.h"
 #include "serialize.h"
@@ -29,6 +32,7 @@ namespace {
 using namespace GRC;
 using LogFlags = BCLog::LogFlags;
 
+/*
 //!
 //! \brief Numerator of the static magnitude unit coefficient for snapshot
 //! accrual (block version 11 and greater).
@@ -40,6 +44,7 @@ constexpr int64_t MAG_UNIT_NUMERATOR = 1;
 //! accrual (block version 11 and greater).
 //!
 constexpr int64_t MAG_UNIT_DENOMINATOR = 4;
+*/
 
 //!
 //! \brief Calculates the current accrual for a CPID by adding the snapshot of
@@ -61,6 +66,66 @@ class SnapshotCalculator
     {
     }
 
+    //!
+    //! \brief Returns the current magnitude unit allocation fraction as of the provided superblock. Prior to block v13 this is
+    //! fixed at 1/4.
+    //!
+    //! The magnitude unit here will only change along superblock boundaries. Whatever the active value of the magnitude unit is
+    //! at the superblock provided will be used for accruals.
+    //!
+    //! \return Allocation Fraction representing Magnitude Unit.
+    //!
+    Allocation GetMagnitudeUnit() const
+    {
+        Allocation magnitude_unit = Params().GetConsensus().DefaultMagnitudeUnit;
+
+        // Before V13 magnitude unit is 1/4.
+        if (!IsV13Enabled(m_superblock.m_height)) {
+            return Allocation(1, 4);
+        }
+
+        // Find the current protocol entry value for Magnitude Weight Factor, if it exists.
+        ProtocolEntryOption protocol_entry = GetProtocolRegistry().TryLastBeforeTimestamp("magnitudeunit", m_superblock.m_timestamp);
+
+        // If their is an entry prior or equal in timestamp to the superblock and it is active then set the magnitude unit
+        // to that value. If the last entry is not active (i.e. deleted), then leave at the default.
+        if (protocol_entry != nullptr && protocol_entry->m_status == ProtocolEntryStatus::ACTIVE) {
+            magnitude_unit = Fraction().FromString(protocol_entry->m_value);
+        }
+
+        return magnitude_unit;
+    }
+
+    //!
+    //! \brief Static version of GetMagnitudeUnit used in Tally class.
+    //!
+    //! \param index for which to return the current magnitude unit.
+    //!
+    //! \return Allocation fraction representing magnitude unit.
+    //!
+    static Allocation GetMagnitudeUnit(CBlockIndex* index)
+    {
+        CBlockIndex* sb_index = BlockFinder::FindLatestSuperblock(index);
+
+        Allocation magnitude_unit = Params().GetConsensus().DefaultMagnitudeUnit;
+
+               // Before V13 magnitude unit is 1/4.
+        if (!IsV13Enabled(sb_index->nHeight)) {
+            return Allocation(1, 4);
+        }
+
+               // Find the current protocol entry value for Magnitude Weight Factor, if it exists.
+        ProtocolEntryOption protocol_entry = GetProtocolRegistry().TryLastBeforeTimestamp("magnitudeunit", sb_index->GetBlockTime());
+
+               // If their is an entry prior or equal in timestamp to the superblock and it is active then set the magnitude unit
+               // to that value. If the last entry is not active (i.e. deleted), then leave at the default.
+        if (protocol_entry != nullptr && protocol_entry->m_status == ProtocolEntryStatus::ACTIVE) {
+            magnitude_unit = Fraction().FromString(protocol_entry->m_value);
+        }
+
+        return magnitude_unit;
+    }
+
     //!
     //! \brief Get the magnitude unit factored into the reward calculation.
     //!
@@ -72,15 +137,15 @@ class SnapshotCalculator
     //!
     //! \return Amount paid per unit of magnitude per day in units of GRC.
     //!
-    static double MagnitudeUnit()
+    double MagnitudeUnit() const
     {
         // Superblock-based accrual calculations do not rely on the rolling
         // two-week network payment average. Instead, we calculate research
         // rewards using the magnitude unit that represents the equilibrium
         // quantity of the formula used to determine the magnitude unit for
         // the legacy research age accrual calculations.
         //
-        // Where...
+        // Where (prior to block v13) ...
         //
         //   blocks_per_day = 960
         //   grc_per_block = 50
@@ -95,7 +160,8 @@ class SnapshotCalculator
         //
         // ...rounded-up to 0.25:
         //
-        return static_cast<double>(MAG_UNIT_NUMERATOR) / MAG_UNIT_DENOMINATOR;
+        // V13+, the magnitude unit can be set by protocol entry.
+        return GetMagnitudeUnit().ToDouble();
     }
 
     //!
@@ -142,7 +208,7 @@ class SnapshotCalculator
         //
         const uint64_t base_accrual = accrual_timespan
             * CurrentMagnitude(cpid).Scaled()
-            * MAG_UNIT_NUMERATOR;
+            * GetMagnitudeUnit().GetNumerator();
 
         // If the accrual calculation will overflow a 64-bit integer, we need
         // more bits. Arithmetic with the big integer type is much slower and
@@ -155,15 +221,15 @@ class SnapshotCalculator
             accrual_bn *= COIN;
             accrual_bn /= 86400;
             accrual_bn /= Magnitude::SCALE_FACTOR;
-            accrual_bn /= MAG_UNIT_DENOMINATOR;
+            accrual_bn /= GetMagnitudeUnit().GetDenominator();
 
             accrual = accrual_bn.GetLow64();
         } else {
             accrual = base_accrual
                     * COIN
                     / 86400
                     / Magnitude::SCALE_FACTOR
-                    / MAG_UNIT_DENOMINATOR;
+                    / GetMagnitudeUnit().GetDenominator();
         }
 
         LogPrint(BCLog::LogFlags::ACCRUAL, "INFO %s: CPID = %s, LastRewardHeight() = %u, accrual_timespan = %" PRId64 ", "
@@ -263,7 +329,7 @@ class SnapshotAccrualComputer : public IAccrualComputer, SnapshotCalculator
         // the amount of accrual that a CPID can collect over two days when the
         // CPID achieves the maximum magnitude value supported in a superblock.
         //
-        // Where...
+        // Where... (for block versions below V13)
         //
         //   max_magnitude = 32767
         //   magnitude_unit = 0.25
@@ -272,9 +338,10 @@ class SnapshotAccrualComputer : public IAccrualComputer, SnapshotCalculator
         //
         //   max_magnitude * magnitude_unit * 2 = max_accrual = 16383.5
         //
-        // ...rounded-up to:
+        // ...rounded-up to 16384.
         //
-        return 16384 * COIN;
+        // For V13+, the magnitude unit can be set by protocol entry.
+        return (GetMagnitudeUnit() * 32768 * 2 * COIN).ToCAmount();
     }
 
     //!
@@ -290,7 +357,7 @@ class SnapshotAccrualComputer : public IAccrualComputer, SnapshotCalculator
     //!
     double MagnitudeUnit() const override
     {
-        return SnapshotCalculator::MagnitudeUnit();
+        return GetMagnitudeUnit().ToDouble();
     }
 
     int64_t AccrualAge() const override

src/gridcoin/support/block_finder.cpp

@@ -57,11 +57,13 @@ CBlockIndex* BlockFinder::FindByMinTime(int64_t time)
 }
 
 // The arguments are passed by value on purpose.
-CBlockIndex* BlockFinder::FindByMinTimeFromGivenIndex(int64_t time, CBlockIndex* index)
+CBlockIndex* BlockFinder::FindByMinTimeFromGivenIndex(int64_t time, CBlockIndex* const index_in)
 {
+    CBlockIndex* index = index_in;
+
     // If no starting index is provided (i.e. second parameter is omitted or nullptr is passed in,
     // then start at the Genesis Block. This is in general expensive and should be avoided.
-    if (!index) {
+    if (index == nullptr) {
         index = pindexGenesisBlock;
     }
 
@@ -71,3 +73,23 @@ CBlockIndex* BlockFinder::FindByMinTimeFromGivenIndex(int64_t time, CBlockIndex*
 
     return index;
 }
+
+CBlockIndex* BlockFinder::FindLatestSuperblock(CBlockIndex* const index_in)
+{
+    CBlockIndex* index = index_in;
+
+    // If no input index is provided, start at the head of the chain.
+    if (index == nullptr) {
+        index = pindexBest;
+    }
+
+    while (index && index->pprev) {
+        if (index->IsSuperblock()) {
+            break;
+        }
+
+        index = index->pprev;
+    }
+
+    return index;
+}

src/gridcoin/support/block_finder.h

@@ -48,7 +48,14 @@ class BlockFinder
     //! \return CBlockIndex pointing to the youngest block which is not older than \p time, or
     //! the head of the chain if it is older than \p time.
     //!
-    static CBlockIndex* FindByMinTimeFromGivenIndex(int64_t time, CBlockIndex* index = nullptr);
+    static CBlockIndex* FindByMinTimeFromGivenIndex(int64_t time, CBlockIndex* const index_in = nullptr);
+
+    //!
+    //! \brief Find the last superblock at or before the provided index.
+    //! \param CBlockIndex from where to start.
+    //! \return CBlockIndex pointing to the block containing the last superblock contract.
+    //!
+    static CBlockIndex* FindLatestSuperblock(CBlockIndex * const index_in = nullptr);
 };
 } // namespace GRC
 

src/gridcoin/tally.cpp

@@ -1063,10 +1063,10 @@ CAmount Tally::MaxEmission(const int64_t payment_time)
     return NetworkTally::MaxEmission(payment_time) * COIN;
 }
 
-double Tally::GetMagnitudeUnit(const CBlockIndex* const pindex)
+double Tally::GetMagnitudeUnit(CBlockIndex* const pindex)
 {
     if (pindex->nVersion >= 11) {
-        return SnapshotCalculator::MagnitudeUnit();
+        return SnapshotCalculator::GetMagnitudeUnit(pindex).ToDouble();
     }
 
     return g_network_tally.GetMagnitudeUnit(pindex->nTime);
@@ -1158,7 +1158,9 @@ CAmount Tally::GetNewbieSuperblockAccrualCorrection(const Cpid& cpid, const Supe
     const auto tally_accrual_period = [&](
         const int64_t low_time,
         const int64_t high_time,
-        const GRC::Magnitude magnitude)
+        const GRC::Magnitude magnitude,
+        const Allocation magnitude_unit,
+        CAmount max_reward)
     {
         int64_t time_interval = high_time - low_time;
 
@@ -1175,7 +1177,7 @@ CAmount Tally::GetNewbieSuperblockAccrualCorrection(const Cpid& cpid, const Supe
         // correctly in the bignumber calculations.
         const uint64_t base_accrual = abs_time_interval
             * magnitude.Scaled()
-            * MAG_UNIT_NUMERATOR;
+            * magnitude_unit.GetNumerator();
 
         int64_t period = 0;
 
@@ -1184,7 +1186,7 @@ CAmount Tally::GetNewbieSuperblockAccrualCorrection(const Cpid& cpid, const Supe
             accrual_bn *= COIN;
             accrual_bn /= 86400;
             accrual_bn /= Magnitude::SCALE_FACTOR;
-            accrual_bn /= MAG_UNIT_DENOMINATOR;
+            accrual_bn /= magnitude_unit.GetDenominator();
 
             period = accrual_bn.GetLow64() * (int64_t) sign;
         }
@@ -1194,14 +1196,11 @@ CAmount Tally::GetNewbieSuperblockAccrualCorrection(const Cpid& cpid, const Supe
                     * COIN
                     / 86400
                     / Magnitude::SCALE_FACTOR
-                    / MAG_UNIT_DENOMINATOR;
+                    / magnitude_unit.GetDenominator();
         }
 
         accrual += period;
 
-        // TODO: Change this to refer to MaxReward() from the snapshot computer.
-        int64_t max_reward = 16384 * COIN;
-
         if (accrual > max_reward)
         {
             int64_t overage = accrual - max_reward;
@@ -1267,7 +1266,12 @@ CAmount Tally::GetNewbieSuperblockAccrualCorrection(const Cpid& cpid, const Supe
             // Stop the accrual when we get to a superblock that is before the beacon advertisement.
             if (pindex->nTime < beacon_ptr->m_timestamp) break;
 
-            CAmount period = tally_accrual_period(pindex->nTime, pindex_high->nTime, magnitude);
+            // We are only going to use the accrual computer here for the magnitude unit and max_reward.
+            AccrualComputer computer = GetSnapshotComputer(cpid, pindex->GetBlockTime(), pindex);
+
+            int64_t max_reward = computer->MaxReward();
+
+            CAmount period = tally_accrual_period(pindex->nTime, pindex_high->nTime, magnitude, computer->MagnitudeUnit(), max_reward);
 
             LogPrint(BCLog::LogFlags::ACCRUAL, "INFO %s: period_num = %u, "
                      "low height = %i, high height = %u, magnitude at low height SB = %f, "

src/gridcoin/tally.h

@@ -99,7 +99,7 @@ class Tally
     //!
     //! \return Current magnitude unit adjusted for the specified block.
     //!
-    static double GetMagnitudeUnit(const CBlockIndex* const pindex);
+    static double GetMagnitudeUnit(CBlockIndex * const pindex);
 
     //!
     //! \brief Get a traversable object for the research accounts stored in

src/rpc/blockchain.cpp

@@ -57,7 +57,7 @@ UniValue MRCToJson(const GRC::MRC& mrc) {
     return json;
 }
 
-UniValue ClaimToJson(const GRC::Claim& claim, const CBlockIndex* const pindex)
+UniValue ClaimToJson(const GRC::Claim& claim, CBlockIndex* pindex)
 {
     UniValue json(UniValue::VOBJ);
 
@@ -155,7 +155,7 @@ UniValue SuperblockToJson(const GRC::SuperblockPtr& superblock)
     return SuperblockToJson(*superblock);
 }
 
-UniValue blockToJSON(const CBlock& block, const CBlockIndex* blockindex, bool fPrintTransactionDetail)
+UniValue blockToJSON(const CBlock& block, CBlockIndex* blockindex, bool fPrintTransactionDetail)
 {
     UniValue result(UniValue::VOBJ);