1 files changed, 123 insertions, 0 deletions
diff --git a/src/pow.cpp b/src/pow.cpp
new file mode 100644
index 0000000000..274a5d6f98
--- /dev/null
+++ b/src/pow.cpp
@@ -0,0 +1,123 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2014 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "pow.h"
+
+#include "chainparams.h"
+#include "core.h"
+#include "main.h"
+#include "uint256.h"
+
+static const int64_t nTargetTimespan = 14 * 24 * 60 * 60; // two weeks
+static const int64_t nTargetSpacing = 10 * 60;
+static const int64_t nInterval = nTargetTimespan / nTargetSpacing;
+
+unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock)
+{
+    unsigned int nProofOfWorkLimit = Params().ProofOfWorkLimit().GetCompact();
+
+    // Genesis block
+    if (pindexLast == NULL)
+        return nProofOfWorkLimit;
+
+    // Only change once per interval
+    if ((pindexLast->nHeight+1) % nInterval != 0)
+    {
+        if (Params().AllowMinDifficultyBlocks())
+        {
+            // Special difficulty rule for testnet:
+            // If the new block's timestamp is more than 2* 10 minutes
+            // then allow mining of a min-difficulty block.
+            if (pblock->nTime > pindexLast->nTime + nTargetSpacing*2)
+                return nProofOfWorkLimit;
+            else
+            {
+                // Return the last non-special-min-difficulty-rules-block
+                const CBlockIndex* pindex = pindexLast;
+                while (pindex->pprev && pindex->nHeight % nInterval != 0 && pindex->nBits == nProofOfWorkLimit)
+                    pindex = pindex->pprev;
+                return pindex->nBits;
+            }
+        }
+        return pindexLast->nBits;
+    }
+
+    // Go back by what we want to be 14 days worth of blocks
+    const CBlockIndex* pindexFirst = pindexLast;
+    for (int i = 0; pindexFirst && i < nInterval-1; i++)
+        pindexFirst = pindexFirst->pprev;
+    assert(pindexFirst);
+
+    // Limit adjustment step
+    int64_t nActualTimespan = pindexLast->GetBlockTime() - pindexFirst->GetBlockTime();
+    LogPrintf("  nActualTimespan = %d  before bounds\n", nActualTimespan);
+    if (nActualTimespan < nTargetTimespan/4)
+        nActualTimespan = nTargetTimespan/4;
+    if (nActualTimespan > nTargetTimespan*4)
+        nActualTimespan = nTargetTimespan*4;
+
+    // Retarget
+    uint256 bnNew;
+    uint256 bnOld;
+    bnNew.SetCompact(pindexLast->nBits);
+    bnOld = bnNew;
+    bnNew *= nActualTimespan;
+    bnNew /= nTargetTimespan;
+
+    if (bnNew > Params().ProofOfWorkLimit())
+        bnNew = Params().ProofOfWorkLimit();
+
+    /// debug print
+    LogPrintf("GetNextWorkRequired RETARGET\n");
+    LogPrintf("nTargetTimespan = %d    nActualTimespan = %d\n", nTargetTimespan, nActualTimespan);
+    LogPrintf("Before: %08x  %s\n", pindexLast->nBits, bnOld.ToString());
+    LogPrintf("After:  %08x  %s\n", bnNew.GetCompact(), bnNew.ToString());
+
+    return bnNew.GetCompact();
+}
+
+bool CheckProofOfWork(uint256 hash, unsigned int nBits)
+{
+    bool fNegative;
+    bool fOverflow;
+    uint256 bnTarget;
+    bnTarget.SetCompact(nBits, &fNegative, &fOverflow);
+
+    // Check range
+    if (fNegative || bnTarget == 0 || fOverflow || bnTarget > Params().ProofOfWorkLimit())
+        return error("CheckProofOfWork() : nBits below minimum work");
+
+    // Check proof of work matches claimed amount
+    if (hash > bnTarget)
+        return error("CheckProofOfWork() : hash doesn't match nBits");
+
+    return true;
+}
+
+//
+// minimum amount of work that could possibly be required nTime after
+// minimum work required was nBase
+//
+unsigned int ComputeMinWork(unsigned int nBase, int64_t nTime)
+{
+    const uint256 &bnLimit = Params().ProofOfWorkLimit();
+    // Testnet has min-difficulty blocks
+    // after nTargetSpacing*2 time between blocks:
+    if (Params().AllowMinDifficultyBlocks() && nTime > nTargetSpacing*2)
+        return bnLimit.GetCompact();
+
+    uint256 bnResult;
+    bnResult.SetCompact(nBase);
+    while (nTime > 0 && bnResult < bnLimit)
+    {
+        // Maximum 400% adjustment...
+        bnResult *= 4;
+        // ... in best-case exactly 4-times-normal target time
+        nTime -= nTargetTimespan*4;
+    }
+    if (bnResult > bnLimit)
+        bnResult = bnLimit;
+    return bnResult.GetCompact();
+}