std::pair<int, int64_t> CalculateSequenceLocks(const CTransaction &tx, int flags, std::vector<int>* prevHeights, const CBlockIndex& block) { assert(prevHeights->size() == tx.vin.size()); // Will be set to the equivalent height- and time-based nLockTime // values that would be necessary to satisfy all relative lock- // time constraints given our view of block chain history. // The semantics of nLockTime are the last invalid height/time, so // use -1 to have the effect of any height or time being valid. int nMinHeight = -1; int64_t nMinTime = -1; // tx.nVersion is signed integer so requires cast to unsigned otherwise // we would be doing a signed comparison and half the range of nVersion // wouldn't support BIP 68. bool fEnforceBIP68 = static_cast<uint32_t>(tx.nVersion) >= 2 && flags & LOCKTIME_VERIFY_SEQUENCE; // Do not enforce sequence numbers as a relative lock time // unless we have been instructed to if (!fEnforceBIP68) { return std::make_pair(nMinHeight, nMinTime); } for (size_t txinIndex = 0; txinIndex < tx.vin.size(); txinIndex++) { const CTxIn& txin = tx.vin[txinIndex]; // Sequence numbers with the most significant bit set are not // treated as relative lock-times, nor are they given any // consensus-enforced meaning at this point. if (txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_DISABLE_FLAG) { // The height of this input is not relevant for sequence locks (*prevHeights)[txinIndex] = 0; continue; } int nCoinHeight = (*prevHeights)[txinIndex]; if (txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_TYPE_FLAG) { int64_t nCoinTime = block.GetAncestor(std::max(nCoinHeight-1, 0))->GetMedianTimePast(); // NOTE: Subtract 1 to maintain nLockTime semantics // BIP 68 relative lock times have the semantics of calculating // the first block or time at which the transaction would be // valid. When calculating the effective block time or height // for the entire transaction, we switch to using the // semantics of nLockTime which is the last invalid block // time or height. Thus we subtract 1 from the calculated // time or height. // Time-based relative lock-times are measured from the // smallest allowed timestamp of the block containing the // txout being spent, which is the median time past of the // block prior. nMinTime = std::max(nMinTime, nCoinTime + (int64_t)((txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_MASK) << CTxIn::SEQUENCE_LOCKTIME_GRANULARITY) - 1); } else { nMinHeight = std::max(nMinHeight, nCoinHeight + (int)(txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_MASK) - 1); } } return std::make_pair(nMinHeight, nMinTime); }