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blockindex.cpp
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// Copyright (c) 2009-2020 The Bitcoin developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <blockindex.h>
/**
* Turn the lowest '1' bit in the binary representation of a number into a '0'.
*/
static inline int InvertLowestOne(int n) {
return n & (n - 1);
}
/** Compute what height to jump back to with the CBlockIndex::pskip pointer. */
static inline int 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);
}
bool CBlockIndex::UpdateChainStats() {
if (pprev == nullptr) {
nChainTx = nTx;
nChainSize = nSize;
return true;
}
if (pprev->HaveTxsDownloaded()) {
nChainTx = pprev->nChainTx + nTx;
nChainSize = pprev->nChainSize + nSize;
return true;
}
nChainTx = 0;
nChainSize = 0;
return false;
}
const CBlockIndex *CBlockIndex::GetAncestor(int height) const {
if (height > nHeight || height < 0) {
return nullptr;
}
const CBlockIndex *pindexWalk = this;
int heightWalk = nHeight;
while (heightWalk > height) {
int heightSkip = GetSkipHeight(heightWalk);
int heightSkipPrev = GetSkipHeight(heightWalk - 1);
if (pindexWalk->pskip != nullptr &&
(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;
}
CBlockIndex *CBlockIndex::GetAncestor(int height) {
return const_cast<CBlockIndex *>(
const_cast<const CBlockIndex *>(this)->GetAncestor(height));
}
void CBlockIndex::BuildSkip() {
if (pprev) {
pskip = pprev->GetAncestor(GetSkipHeight(nHeight));
}
}

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