Function FindModifierBlockFromCandidates

src/stake.cpp:169–219

Finds a block from the candidate blocks in vSortedCandidates, excluding already selected blocks in vSelectedBlocks, and with timestamp up to nSelectionTime.

// already selected blocks in vSelectedBlocks, and with timestamp up to
// nSelectionTime.
static bool FindModifierBlockFromCandidates(vector <pair<int64_t, uint256>>& vSortedCandidates, map<uint256, const CBlockIndex*>& mSelectedBlocks, int64_t nSelectionTime, uint64_t nStakeModifierPrev, const CBlockIndex*& pindexSelected)
{
    uint256 hashBest = 0;

    pindexSelected = nullptr;

    for (auto& item : vSortedCandidates) {
        if (!mapBlockIndex.count(item.second))
            return error("%s: invalid candidate block %s", __func__, item.second.GetHex());

        const CBlockIndex* pindex = mapBlockIndex[item.second];
        if (pindex->IsProofOfStake() && pindex->hashProofOfStake == 0) {
            return error("%s: zero stake (block %s)", __func__, item.second.GetHex());
        }

        if (pindexSelected && pindex->GetBlockTime() > nSelectionTime) break;
        if (mSelectedBlocks.count(pindex->GetBlockHash()) > 0) continue;

        // compute the selection hash by hashing an input that is unique to that block
        CDataStream ss(SER_GETHASH, 0);
        ss << uint256(pindex->IsProofOfStake() ? pindex->hashProofOfStake : pindex->GetBlockHash())
           << nStakeModifierPrev;

        uint256 hashSelection(Hash(ss.begin(), ss.end()));

        // the selection hash is divided by 2**32 so that proof-of-stake block
        // is always favored over proof-of-work block. this is to preserve
        // the energy efficiency property
        if (pindex->IsProofOfStake())
            hashSelection >>= 32;

        if (pindexSelected == nullptr || hashSelection < hashBest) {
            pindexSelected = pindex;
            hashBest = hashSelection;
        }
    }

#   if defined(DEBUG_DUMP_STAKING_INFO) && false
    if (GetBoolArg("-printstakemodifier", false))
        LogPrintf("%s: selected block %d %s %s\n", __func__, 
                  pindexSelected->nHeight,
                  pindexSelected->GetBlockHash().GetHex(),
                  hashBest.ToString());
#   endif

    if (pindexSelected) {
        // add the selected block from candidates to selected list
        mSelectedBlocks.insert(make_pair(pindexSelected->GetBlockHash(), pindexSelected));
    }
    return pindexSelected != nullptr;
}

// Stake Modifier (hash modifier of proof-of-stake):
// The purpose of stake modifier is to prevent a txout (coin) owner from