// Get the last stake modifier and its generation time from a given block
private bool GetLastStakeModifier(ChainedBlock pindex, StakeValidator.StakeModifierContext stakeModifier)
{
stakeModifier.StakeModifier = 0;
stakeModifier.ModifierTime = 0;
if (pindex == null)
{
return(false);
}
var blockStake = this.stakeChain.Get(pindex.HashBlock);
while (pindex != null && pindex.Previous != null && !blockStake.GeneratedStakeModifier())
{
pindex = pindex.Previous;
blockStake = this.stakeChain.Get(pindex.HashBlock);
}
if (!blockStake.GeneratedStakeModifier())
{
return(false); // error("GetLastStakeModifier: no generation at genesis block");
}
stakeModifier.StakeModifier = blockStake.StakeModifier;
stakeModifier.ModifierTime = pindex.Header.Time;
return(true);
}
// Stake Modifier (hash modifier of proof-of-stake):
// The purpose of stake modifier is to prevent a txout (coin) owner from
// computing future proof-of-stake generated by this txout at the time
// of transaction confirmation. To meet kernel protocol, the txout
// must hash with a future stake modifier to generate the proof.
// Stake modifier consists of bits each of which is contributed from a
// selected block of a given block group in the past.
// The selection of a block is based on a hash of the block's proof-hash and
// the previous stake modifier.
// Stake modifier is recomputed at a fixed time interval instead of every
// block. This is to make it difficult for an attacker to gain control of
// additional bits in the stake modifier, even after generating a chain of
// blocks.
public void ComputeNextStakeModifier(ChainBase chainIndex, ChainedBlock pindexPrev, StakeValidator.StakeModifierContext stakeModifier)
{
stakeModifier.StakeModifier = 0;
stakeModifier.GeneratedStakeModifier = false;
if (pindexPrev == null)
{
stakeModifier.GeneratedStakeModifier = true;
return; // genesis block's modifier is 0
}
// First find current stake modifier and its generation block time
// if it's not old enough, return the same stake modifier
long nModifierTime = 0;
if (!this.GetLastStakeModifier(pindexPrev, stakeModifier))
{
ConsensusErrors.ModifierNotFound.Throw();
}
if (nModifierTime / this.consensusOptions.StakeModifierInterval >= pindexPrev.Header.Time / this.consensusOptions.StakeModifierInterval)
{
return;
}
// Sort candidate blocks by timestamp
var sortedByTimestamp = new SortedDictionary <uint, ChainedBlock>();
long nSelectionInterval = GetStakeModifierSelectionInterval();
long nSelectionIntervalStart = (pindexPrev.Header.Time / this.consensusOptions.StakeModifierInterval) * this.consensusOptions.StakeModifierInterval - nSelectionInterval;
var pindex = pindexPrev;
while (pindex != null && pindex.Header.Time >= nSelectionIntervalStart)
{
sortedByTimestamp.Add(pindex.Header.Time, pindex);
pindex = pindex.Previous;
}
//int nHeightFirstCandidate = pindex?.Height + 1 ?? 0;
// Select 64 blocks from candidate blocks to generate stake modifier
ulong nStakeModifierNew = 0;
long nSelectionIntervalStop = nSelectionIntervalStart;
var mapSelectedBlocks = new Dictionary <uint256, ChainedBlock>();
var counter = sortedByTimestamp.Count;
var sorted = sortedByTimestamp.Values.ToArray();
for (int nRound = 0; nRound < Math.Min(64, counter); nRound++)
{
// add an interval section to the current selection round
nSelectionIntervalStop += GetStakeModifierSelectionIntervalSection(nRound);
// select a block from the candidates of current round
BlockStake blockStake;
if (!this.SelectBlockFromCandidates(sorted, mapSelectedBlocks, nSelectionIntervalStop, stakeModifier.StakeModifier, out pindex, out blockStake))
{
ConsensusErrors.FailedSelectBlock.Throw();
}
// write the entropy bit of the selected block
nStakeModifierNew |= ((ulong)blockStake.GetStakeEntropyBit() << nRound);
// add the selected block from candidates to selected list
mapSelectedBlocks.Add(pindex.HashBlock, pindex);
//LogPrint("stakemodifier", "ComputeNextStakeModifier: selected round %d stop=%s height=%d bit=%d\n", nRound, DateTimeStrFormat(nSelectionIntervalStop), pindex->nHeight, pindex->GetStakeEntropyBit());
}
// // Print selection map for visualization of the selected blocks
// if (LogAcceptCategory("stakemodifier"))
// {
// string strSelectionMap = "";
// '-' indicates proof-of-work blocks not selected
// strSelectionMap.insert(0, pindexPrev->nHeight - nHeightFirstCandidate + 1, '-');
// pindex = pindexPrev;
// while (pindex && pindex->nHeight >= nHeightFirstCandidate)
// {
// // '=' indicates proof-of-stake blocks not selected
// if (pindex->IsProofOfStake())
// strSelectionMap.replace(pindex->nHeight - nHeightFirstCandidate, 1, "=");
// pindex = pindex->pprev;
// }
// BOOST_FOREACH(const PAIRTYPE(uint256, const CBlockIndex*)& item, mapSelectedBlocks)
// {
// // 'S' indicates selected proof-of-stake blocks
// // 'W' indicates selected proof-of-work blocks
// strSelectionMap.replace(item.second->nHeight - nHeightFirstCandidate, 1, item.second->IsProofOfStake()? "S" : "W");
// }
// LogPrintf("ComputeNextStakeModifier: selection height [%d, %d] map %s\n", nHeightFirstCandidate, pindexPrev->nHeight, strSelectionMap);
// }
//LogPrint("stakemodifier", "ComputeNextStakeModifier: new modifier=0x%016x time=%s\n", nStakeModifierNew, DateTimeStrFormat(pindexPrev->GetBlockTime()));
stakeModifier.StakeModifier = nStakeModifierNew;
stakeModifier.GeneratedStakeModifier = true;
}