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// 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 "timedata.h"
#include "uint256.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 interval
if ((pindexLast->nHeight+1) % Params().Interval() != 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().Interval() != 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().Interval()-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
uint256 bnNew;
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;
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;
}
//
// true if nBits is greater than the minimum amount of work that could
// possibly be required deltaTime after minimum work required was nBase
//
bool CheckMinWork(unsigned int nBits, unsigned int nBase, int64_t deltaTime)
{
bool fOverflow = false;
uint256 bnNewBlock;
bnNewBlock.SetCompact(nBits, NULL, &fOverflow);
if (fOverflow)
return false;
const uint256 &bnLimit = Params().ProofOfWorkLimit();
// Testnet has min-difficulty blocks
// after Params().TargetSpacing()*2 time between blocks:
if (Params().AllowMinDifficultyBlocks() && deltaTime > Params().TargetSpacing()*2)
return bnNewBlock <= bnLimit;
uint256 bnResult;
bnResult.SetCompact(nBase);
while (deltaTime > 0 && bnResult < bnLimit)
{
// Maximum 400% adjustment...
bnResult *= 4;
// ... in best-case exactly 4-times-normal target time
deltaTime -= Params().TargetTimespan()*4;
}
if (bnResult > bnLimit)
bnResult = bnLimit;
return bnNewBlock <= bnResult;
}
void UpdateTime(CBlockHeader* pblock, const CBlockIndex* pindexPrev)
{
pblock->nTime = std::max(pindexPrev->GetMedianTimePast()+1, GetAdjustedTime());
// Updating time can change work required on testnet:
if (Params().AllowMinDifficultyBlocks())
pblock->nBits = GetNextWorkRequired(pindexPrev, pblock);
}
uint256 GetProofIncrement(unsigned int nBits)
{
uint256 bnTarget;
bool fNegative;
bool fOverflow;
bnTarget.SetCompact(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 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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