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108 lines
3.8 KiB
108 lines
3.8 KiB
// Copyright (c) 2009-2010 Satoshi Nakamoto |
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// Copyright (c) 2009-2017 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 <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, const Consensus::Params& params) |
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{ |
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assert(pindexLast != nullptr); |
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unsigned int nProofOfWorkLimit = UintToArith256(params.powLimit).GetCompact(); |
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// Only change once per difficulty adjustment interval |
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if ((pindexLast->nHeight+1) % params.DifficultyAdjustmentInterval() != 0) |
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{ |
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if (params.fPowAllowMinDifficultyBlocks) |
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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.nPowTargetSpacing*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.DifficultyAdjustmentInterval() != 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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// Litecoin: This fixes an issue where a 51% attack can change difficulty at will. |
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// Go back the full period unless it's the first retarget after genesis. Code courtesy of Art Forz |
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int blockstogoback = params.DifficultyAdjustmentInterval()-1; |
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if ((pindexLast->nHeight+1) != params.DifficultyAdjustmentInterval()) |
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blockstogoback = params.DifficultyAdjustmentInterval(); |
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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 < blockstogoback; i++) |
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pindexFirst = pindexFirst->pprev; |
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assert(pindexFirst); |
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return CalculateNextWorkRequired(pindexLast, pindexFirst->GetBlockTime(), params); |
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} |
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unsigned int CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime, const Consensus::Params& params) |
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{ |
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if (params.fPowNoRetargeting) |
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return pindexLast->nBits; |
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// Limit adjustment step |
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int64_t nActualTimespan = pindexLast->GetBlockTime() - nFirstBlockTime; |
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if (nActualTimespan < params.nPowTargetTimespan/4) |
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nActualTimespan = params.nPowTargetTimespan/4; |
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if (nActualTimespan > params.nPowTargetTimespan*4) |
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nActualTimespan = params.nPowTargetTimespan*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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// Litecoin: intermediate uint256 can overflow by 1 bit |
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const arith_uint256 bnPowLimit = UintToArith256(params.powLimit); |
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bool fShift = bnNew.bits() > bnPowLimit.bits() - 1; |
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if (fShift) |
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bnNew >>= 1; |
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bnNew *= nActualTimespan; |
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bnNew /= params.nPowTargetTimespan; |
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if (fShift) |
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bnNew <<= 1; |
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if (bnNew > bnPowLimit) |
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bnNew = bnPowLimit; |
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return bnNew.GetCompact(); |
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} |
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bool CheckProofOfWork(uint256 hash, unsigned int nBits, const Consensus::Params& params) |
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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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bnTarget.SetCompact(nBits, &fNegative, &fOverflow); |
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// Check range |
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if (fNegative || bnTarget == 0 || fOverflow || bnTarget > UintToArith256(params.powLimit)) |
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return false; |
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// Check proof of work matches claimed amount |
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if (UintToArith256(hash) > bnTarget) |
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return false; |
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return true; |
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}
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