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109 lines
3.3 KiB
109 lines
3.3 KiB
// 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 (pindexWalk->pskip != NULL && |
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(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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