114 lines
4 KiB
C++
114 lines
4 KiB
C++
// Copyright (c) 2009-2010 Satoshi Nakamoto
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// Copyright (c) 2009-2014 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include "pow.h"
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#include "arith_uint256.h"
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#include "chain.h"
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#include "chainparams.h"
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#include "primitives/block.h"
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#include "uint256.h"
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#include "util.h"
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unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock)
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{
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unsigned int nProofOfWorkLimit = Params().ProofOfWorkLimit().GetCompact();
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// Genesis block
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if (pindexLast == NULL)
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return nProofOfWorkLimit;
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// Only change once per interval
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if ((pindexLast->nHeight+1) % Params().Interval() != 0)
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{
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if (Params().AllowMinDifficultyBlocks())
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{
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// Special difficulty rule for testnet:
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// If the new block's timestamp is more than 2* 10 minutes
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// then allow mining of a min-difficulty block.
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if (pblock->GetBlockTime() > pindexLast->GetBlockTime() + Params().TargetSpacing()*2)
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return nProofOfWorkLimit;
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else
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{
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// Return the last non-special-min-difficulty-rules-block
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const CBlockIndex* pindex = pindexLast;
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while (pindex->pprev && pindex->nHeight % Params().Interval() != 0 && pindex->nBits == nProofOfWorkLimit)
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pindex = pindex->pprev;
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return pindex->nBits;
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}
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}
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return pindexLast->nBits;
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}
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// Go back by what we want to be 14 days worth of blocks
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const CBlockIndex* pindexFirst = pindexLast;
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for (int i = 0; pindexFirst && i < Params().Interval()-1; i++)
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pindexFirst = pindexFirst->pprev;
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assert(pindexFirst);
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// Limit adjustment step
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int64_t nActualTimespan = pindexLast->GetBlockTime() - pindexFirst->GetBlockTime();
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LogPrintf(" nActualTimespan = %d before bounds\n", nActualTimespan);
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if (nActualTimespan < Params().TargetTimespan()/4)
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nActualTimespan = Params().TargetTimespan()/4;
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if (nActualTimespan > Params().TargetTimespan()*4)
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nActualTimespan = Params().TargetTimespan()*4;
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// Retarget
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arith_uint256 bnNew;
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arith_uint256 bnOld;
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bnNew.SetCompact(pindexLast->nBits);
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bnOld = bnNew;
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bnNew *= nActualTimespan;
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bnNew /= Params().TargetTimespan();
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if (bnNew > Params().ProofOfWorkLimit())
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bnNew = Params().ProofOfWorkLimit();
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/// debug print
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LogPrintf("GetNextWorkRequired RETARGET\n");
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LogPrintf("Params().TargetTimespan() = %d nActualTimespan = %d\n", Params().TargetTimespan(), nActualTimespan);
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LogPrintf("Before: %08x %s\n", pindexLast->nBits, bnOld.ToString());
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LogPrintf("After: %08x %s\n", bnNew.GetCompact(), bnNew.ToString());
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return bnNew.GetCompact();
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}
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bool CheckProofOfWork(uint256 hash, unsigned int nBits)
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{
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bool fNegative;
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bool fOverflow;
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arith_uint256 bnTarget;
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if (Params().SkipProofOfWorkCheck())
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return true;
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bnTarget.SetCompact(nBits, &fNegative, &fOverflow);
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// Check range
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if (fNegative || bnTarget == 0 || fOverflow || bnTarget > Params().ProofOfWorkLimit())
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return error("CheckProofOfWork() : nBits below minimum work");
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// Check proof of work matches claimed amount
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if (UintToArith256(hash) > bnTarget)
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return error("CheckProofOfWork() : hash doesn't match nBits");
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return true;
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}
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arith_uint256 GetBlockProof(const CBlockIndex& block)
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{
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arith_uint256 bnTarget;
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bool fNegative;
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bool fOverflow;
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bnTarget.SetCompact(block.nBits, &fNegative, &fOverflow);
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if (fNegative || fOverflow || bnTarget == 0)
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return 0;
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// We need to compute 2**256 / (bnTarget+1), but we can't represent 2**256
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// as it's too large for a arith_uint256. However, as 2**256 is at least as large
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// as bnTarget+1, it is equal to ((2**256 - bnTarget - 1) / (bnTarget+1)) + 1,
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// or ~bnTarget / (nTarget+1) + 1.
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return (~bnTarget / (bnTarget + 1)) + 1;
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}
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