From e86756193ebdbf71504e2a1a8db43e38d57f9673 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jorge=20Tim=C3=B3n?= <jtimon@jtimon.cc>
Date: Mon, 30 Nov 2015 00:46:49 +0100
Subject: MOVEONLY: non-consensus: from pow to chain:

- GetBlockProof
- GetBlockProofEquivalentTime
---
 src/chain.cpp | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

(limited to 'src/chain.cpp')

diff --git a/src/chain.cpp b/src/chain.cpp
index 3450ed6c3..32f6480f8 100644
--- a/src/chain.cpp
+++ b/src/chain.cpp
@@ -110,3 +110,35 @@ 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();
+}
-- 
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