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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 "uint256.h"
static const int64_t nTargetTimespan = 14 * 24 * 60 * 60; // two weeks
static const int64_t nTargetSpacing = 10 * 60;
static const int64_t nInterval = nTargetTimespan / nTargetSpacing;
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) % nInterval != 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->nTime > pindexLast->nTime + nTargetSpacing*2)
return nProofOfWorkLimit;
else
{
// Return the last non-special-min-difficulty-rules-block
const CBlockIndex* pindex = pindexLast;
while (pindex->pprev && pindex->nHeight % nInterval != 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 < nInterval-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 < nTargetTimespan/4)
nActualTimespan = nTargetTimespan/4;
if (nActualTimespan > nTargetTimespan*4)
nActualTimespan = nTargetTimespan*4;
// Retarget
uint256 bnNew;
uint256 bnOld;
bnNew.SetCompact(pindexLast->nBits);
bnOld = bnNew;
bnNew *= nActualTimespan;
bnNew /= nTargetTimespan;
if (bnNew > Params().ProofOfWorkLimit())
bnNew = Params().ProofOfWorkLimit();
/// debug print
LogPrintf("GetNextWorkRequired RETARGET\n");
LogPrintf("nTargetTimespan = %d nActualTimespan = %d\n", nTargetTimespan, 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;
}
//
// minimum amount of work that could possibly be required nTime after
// minimum work required was nBase
//
unsigned int ComputeMinWork(unsigned int nBase, int64_t nTime)
{
const uint256 &bnLimit = Params().ProofOfWorkLimit();
// Testnet has min-difficulty blocks
// after nTargetSpacing*2 time between blocks:
if (Params().AllowMinDifficultyBlocks() && nTime > nTargetSpacing*2)
return bnLimit.GetCompact();
uint256 bnResult;
bnResult.SetCompact(nBase);
while (nTime > 0 && bnResult < bnLimit)
{
// Maximum 400% adjustment...
bnResult *= 4;
// ... in best-case exactly 4-times-normal target time
nTime -= nTargetTimespan*4;
}
if (bnResult > bnLimit)
bnResult = bnLimit;
return bnResult.GetCompact();
}