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