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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2014 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 "arith_uint256.h"
#include "chain.h"
#include "chainparams.h"
#include "primitives/block.h"
#include "uint256.h"
#include "util.h"
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 difficulty adjustment interval
if ((pindexLast->nHeight+1) % Params().DifficultyAdjustmentInterval() != 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->GetBlockTime() > pindexLast->GetBlockTime() + Params().TargetSpacing()*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;
}
// Go back by what we want to be 14 days worth of blocks
const CBlockIndex* pindexFirst = pindexLast;
for (int i = 0; pindexFirst && i < Params().DifficultyAdjustmentInterval()-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 < Params().TargetTimespan()/4)
nActualTimespan = Params().TargetTimespan()/4;
if (nActualTimespan > Params().TargetTimespan()*4)
nActualTimespan = Params().TargetTimespan()*4;
// Retarget
arith_uint256 bnNew;
arith_uint256 bnOld;
bnNew.SetCompact(pindexLast->nBits);
bnOld = bnNew;
bnNew *= nActualTimespan;
bnNew /= Params().TargetTimespan();
if (bnNew > Params().ProofOfWorkLimit())
bnNew = Params().ProofOfWorkLimit();
/// debug print
LogPrintf("GetNextWorkRequired RETARGET\n");
LogPrintf("Params().TargetTimespan() = %d nActualTimespan = %d\n", Params().TargetTimespan(), 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;
arith_uint256 bnTarget;
if (Params().SkipProofOfWorkCheck())
return true;
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 (UintToArith256(hash) > bnTarget)
return error("CheckProofOfWork(): hash doesn't match nBits");
return true;
}
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;
}
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