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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2016 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 "pow.h"
#include "auxpow.h"
#include "arith_uint256.h"
#include "chain.h"
#include "discoin.h"
#include "primitives/block.h"
#include "uint256.h"
#include "util.h"
// Determine if the for the given block, a min difficulty setting applies
bool AllowMinDifficultyForBlock(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params)
{
// check if the chain allows minimum difficulty blocks
if (!params.fPowAllowMinDifficultyBlocks)
return false;
// Discoin: Magic number at which reset protocol switches
// check if we allow minimum difficulty at this block-height
if (pindexLast->nHeight < 157500)
return false;
// Allow for a minimum block time if the elapsed time > 2*nTargetSpacing
return (pblock->GetBlockTime() > pindexLast->GetBlockTime() + params.nPowTargetSpacing*2);
}
unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params)
{
unsigned int nProofOfWorkLimit = UintToArith256(params.powLimit).GetCompact();
// Genesis block
if (pindexLast == NULL)
return nProofOfWorkLimit;
// Discoin: Special rules for minimum difficulty blocks with Digishield
if (AllowDigishieldMinDifficultyForBlock(pindexLast, pblock, params))
{
// Special difficulty rule for testnet:
// If the new block's timestamp is more than 2* nTargetSpacing minutes
// then allow mining of a min-difficulty block.
return nProofOfWorkLimit;
}
// Only change once per difficulty adjustment interval
bool fNewDifficultyProtocol = (pindexLast->nHeight >= 145000);
const int64_t difficultyAdjustmentInterval = fNewDifficultyProtocol
? 1
: params.DifficultyAdjustmentInterval();
if ((pindexLast->nHeight+1) % difficultyAdjustmentInterval != 0)
{
if (params.fPowAllowMinDifficultyBlocks)
{
// 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->GetBlockTime() > pindexLast->GetBlockTime() + params.nPowTargetSpacing*2)
return nProofOfWorkLimit;
else
{
// Return the last non-special-min-difficulty-rules-block
const CBlockIndex* pindex = pindexLast;
while (pindex->pprev && pindex->nHeight % params.DifficultyAdjustmentInterval() != 0 && pindex->nBits == nProofOfWorkLimit)
pindex = pindex->pprev;
return pindex->nBits;
}
}
return pindexLast->nBits;
}
// Litecoin: This fixes an issue where a 51% attack can change difficulty at will.
// Go back the full period unless it's the first retarget after genesis. Code courtesy of Art Forz
int blockstogoback = difficultyAdjustmentInterval-1;
if ((pindexLast->nHeight+1) != difficultyAdjustmentInterval)
blockstogoback = difficultyAdjustmentInterval;
// Go back by what we want to be 14 days worth of blocks
int nHeightFirst = pindexLast->nHeight - blockstogoback;
assert(nHeightFirst >= 0);
const CBlockIndex* pindexFirst = pindexLast->GetAncestor(nHeightFirst);
assert(pindexFirst);
return CalculateDiscoinNextWorkRequired(pindexLast, pindexFirst->GetBlockTime(), params);
}
unsigned int CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime, const Consensus::Params& params)
{
if (params.fPowNoRetargeting)
return pindexLast->nBits;
// Limit adjustment step
int64_t nActualTimespan = pindexLast->GetBlockTime() - nFirstBlockTime;
if (nActualTimespan < params.nPowTargetTimespan/4)
nActualTimespan = params.nPowTargetTimespan/4;
if (nActualTimespan > params.nPowTargetTimespan*4)
nActualTimespan = params.nPowTargetTimespan*4;
// Retarget
const arith_uint256 bnPowLimit = UintToArith256(params.powLimit);
arith_uint256 bnNew;
bnNew.SetCompact(pindexLast->nBits);
bnNew *= nActualTimespan;
bnNew /= params.nPowTargetTimespan;
if (bnNew > bnPowLimit)
bnNew = bnPowLimit;
return bnNew.GetCompact();
}
bool CheckProofOfWork(uint256 hash, unsigned int nBits, const Consensus::Params& params)
{
bool fNegative;
bool fOverflow;
arith_uint256 bnTarget;
bnTarget.SetCompact(nBits, &fNegative, &fOverflow);
// Check range
if (fNegative || bnTarget == 0 || fOverflow || bnTarget > UintToArith256(params.powLimit))
return false;
// Check proof of work matches claimed amount
if (UintToArith256(hash) > bnTarget)
return false;
return true;
}
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