109 lines
3.3 KiB
C++
109 lines
3.3 KiB
C++
// Copyright (c) 2009-2010 Satoshi Nakamoto
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// Copyright (c) 2009-2014 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include "chain.h"
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using namespace std;
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/**
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* CChain implementation
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*/
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void CChain::SetTip(CBlockIndex *pindex) {
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if (pindex == NULL) {
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vChain.clear();
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return;
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}
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vChain.resize(pindex->nHeight + 1);
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while (pindex && vChain[pindex->nHeight] != pindex) {
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vChain[pindex->nHeight] = pindex;
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pindex = pindex->pprev;
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}
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}
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CBlockLocator CChain::GetLocator(const CBlockIndex *pindex) const {
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int nStep = 1;
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std::vector<uint256> vHave;
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vHave.reserve(32);
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if (!pindex)
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pindex = Tip();
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while (pindex) {
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vHave.push_back(pindex->GetBlockHash());
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// Stop when we have added the genesis block.
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if (pindex->nHeight == 0)
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break;
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// Exponentially larger steps back, plus the genesis block.
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int nHeight = std::max(pindex->nHeight - nStep, 0);
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if (Contains(pindex)) {
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// Use O(1) CChain index if possible.
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pindex = (*this)[nHeight];
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} else {
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// Otherwise, use O(log n) skiplist.
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pindex = pindex->GetAncestor(nHeight);
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}
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if (vHave.size() > 10)
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nStep *= 2;
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}
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return CBlockLocator(vHave);
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}
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const CBlockIndex *CChain::FindFork(const CBlockIndex *pindex) const {
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if (pindex->nHeight > Height())
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pindex = pindex->GetAncestor(Height());
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while (pindex && !Contains(pindex))
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pindex = pindex->pprev;
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return pindex;
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}
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/** Turn the lowest '1' bit in the binary representation of a number into a '0'. */
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int static inline InvertLowestOne(int n) { return n & (n - 1); }
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/** Compute what height to jump back to with the CBlockIndex::pskip pointer. */
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int static inline GetSkipHeight(int height) {
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if (height < 2)
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return 0;
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// Determine which height to jump back to. Any number strictly lower than height is acceptable,
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// but the following expression seems to perform well in simulations (max 110 steps to go back
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// up to 2**18 blocks).
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return (height & 1) ? InvertLowestOne(InvertLowestOne(height - 1)) + 1 : InvertLowestOne(height);
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}
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CBlockIndex* CBlockIndex::GetAncestor(int height)
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{
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if (height > nHeight || height < 0)
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return NULL;
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CBlockIndex* pindexWalk = this;
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int heightWalk = nHeight;
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while (heightWalk > height) {
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int heightSkip = GetSkipHeight(heightWalk);
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int heightSkipPrev = GetSkipHeight(heightWalk - 1);
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if (heightSkip == height ||
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(heightSkip > height && !(heightSkipPrev < heightSkip - 2 &&
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heightSkipPrev >= height))) {
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// Only follow pskip if pprev->pskip isn't better than pskip->pprev.
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pindexWalk = pindexWalk->pskip;
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heightWalk = heightSkip;
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} else {
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pindexWalk = pindexWalk->pprev;
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heightWalk--;
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}
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}
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return pindexWalk;
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}
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const CBlockIndex* CBlockIndex::GetAncestor(int height) const
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{
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return const_cast<CBlockIndex*>(this)->GetAncestor(height);
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}
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void CBlockIndex::BuildSkip()
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{
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if (pprev)
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pskip = pprev->GetAncestor(GetSkipHeight(nHeight));
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}
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