1 files changed, 145 insertions, 0 deletions
diff --git a/src/chain.cpp b/src/chain.cpp
new file mode 100644
index 000000000..77e924e70
--- /dev/null
+++ b/src/chain.cpp
@@ -0,0 +1,145 @@
+// 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));
+}
+
+arith_uint256 GetBlockProof(const CBlockIndex& block)
+{
+    arith_uint256 bnTarget;
+    bool fNegative;
+    bool fOverflow;
+    bnTarget.SetCompact(block.nBits, &fNegative, &fOverflow);
+    if (fNegative || fOverflow || bnTarget == 0)
+        return 0;
+    // We need to compute 2**256 / (bnTarget+1), but we can't represent 2**256
+    // as it's too large for a arith_uint256. However, as 2**256 is at least as large
+    // as bnTarget+1, it is equal to ((2**256 - bnTarget - 1) / (bnTarget+1)) + 1,
+    // or ~bnTarget / (nTarget+1) + 1.
+    return (~bnTarget / (bnTarget + 1)) + 1;
+}
+
+int64_t GetBlockProofEquivalentTime(const CBlockIndex& to, const CBlockIndex& from, const CBlockIndex& tip, const Consensus::Params& params)
+{
+    arith_uint256 r;
+    int sign = 1;
+    if (to.nChainWork > from.nChainWork) {
+        r = to.nChainWork - from.nChainWork;
+    } else {
+        r = from.nChainWork - to.nChainWork;
+        sign = -1;
+    }
+    r = r * arith_uint256(params.nPowTargetSpacing) / GetBlockProof(tip);
+    if (r.bits() > 63) {
+        return sign * std::numeric_limits<int64_t>::max();
+    }
+    return sign * r.GetLow64();
+}