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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 "arith_uint256.h"
#include "chain.h"
#include "chainparams.h"
#include "primitives/block.h"
#include "uint256.h"
#include "util.h"
#include <math.h>
unsigned int static KimotoGravityWell(const CBlockIndex* pindexLast) {
const CBlockIndex *BlockLastSolved = pindexLast;
const CBlockIndex *BlockReading = pindexLast;
uint64_t PastBlocksMass = 0;
int64_t PastRateActualSeconds = 0;
int64_t PastRateTargetSeconds = 0;
double PastRateAdjustmentRatio = double(1);
arith_uint256 PastDifficultyAverage;
arith_uint256 PastDifficultyAveragePrev;
double EventHorizonDeviation;
double EventHorizonDeviationFast;
double EventHorizonDeviationSlow;
uint64_t pastSecondsMin = Params().TargetTimespan() * 0.025;
uint64_t pastSecondsMax = Params().TargetTimespan() * 7;
uint64_t PastBlocksMin = pastSecondsMin / Params().TargetSpacing();
uint64_t PastBlocksMax = pastSecondsMax / Params().TargetSpacing();
if (BlockLastSolved == NULL || BlockLastSolved->nHeight == 0 || (uint64_t)BlockLastSolved->nHeight < PastBlocksMin) { return Params().ProofOfWorkLimit().GetCompact(); }
for (unsigned int i = 1; BlockReading && BlockReading->nHeight > 0; i++) {
if (PastBlocksMax > 0 && i > PastBlocksMax) { break; }
PastBlocksMass++;
PastDifficultyAverage.SetCompact(BlockReading->nBits);
if (i > 1) {
// handle negative uint256
if(PastDifficultyAverage >= PastDifficultyAveragePrev)
PastDifficultyAverage = ((PastDifficultyAverage - PastDifficultyAveragePrev) / i) + PastDifficultyAveragePrev;
else
PastDifficultyAverage = PastDifficultyAveragePrev - ((PastDifficultyAveragePrev - PastDifficultyAverage) / i);
}
PastDifficultyAveragePrev = PastDifficultyAverage;
PastRateActualSeconds = BlockLastSolved->GetBlockTime() - BlockReading->GetBlockTime();
PastRateTargetSeconds = Params().TargetSpacing() * PastBlocksMass;
PastRateAdjustmentRatio = double(1);
if (PastRateActualSeconds < 0) { PastRateActualSeconds = 0; }
if (PastRateActualSeconds != 0 && PastRateTargetSeconds != 0) {
PastRateAdjustmentRatio = double(PastRateTargetSeconds) / double(PastRateActualSeconds);
}
EventHorizonDeviation = 1 + (0.7084 * pow((double(PastBlocksMass)/double(28.2)), -1.228));
EventHorizonDeviationFast = EventHorizonDeviation;
EventHorizonDeviationSlow = 1 / EventHorizonDeviation;
if (PastBlocksMass >= PastBlocksMin) {
if ((PastRateAdjustmentRatio <= EventHorizonDeviationSlow) || (PastRateAdjustmentRatio >= EventHorizonDeviationFast))
{ assert(BlockReading); break; }
}
if (BlockReading->pprev == NULL) { assert(BlockReading); break; }
BlockReading = BlockReading->pprev;
}
arith_uint256 bnNew(PastDifficultyAverage);
if (PastRateActualSeconds != 0 && PastRateTargetSeconds != 0) {
bnNew *= PastRateActualSeconds;
bnNew /= PastRateTargetSeconds;
}
if (bnNew > Params().ProofOfWorkLimit()) {
bnNew = Params().ProofOfWorkLimit();
}
return bnNew.GetCompact();
}
unsigned int static DarkGravityWave(const CBlockIndex* pindexLast) {
/* current difficulty formula, crown - DarkGravity v3, written by Evan Duffield - evan@crown.tech */
const CBlockIndex *BlockLastSolved = pindexLast;
const CBlockIndex *BlockReading = pindexLast;
int64_t nActualTimespan = 0;
int64_t LastBlockTime = 0;
int64_t PastBlocksMin = 24;
int64_t PastBlocksMax = 24;
int64_t CountBlocks = 0;
arith_uint256 PastDifficultyAverage;
arith_uint256 PastDifficultyAveragePrev;
if (BlockLastSolved == NULL || BlockLastSolved->nHeight == 0 || BlockLastSolved->nHeight < PastBlocksMin) {
return Params().ProofOfWorkLimit().GetCompact();
}
for (unsigned int i = 1; BlockReading && BlockReading->nHeight > 0; i++) {
if (PastBlocksMax > 0 && i > PastBlocksMax) { break; }
CountBlocks++;
if(CountBlocks <= PastBlocksMin) {
if (CountBlocks == 1) { PastDifficultyAverage.SetCompact(BlockReading->nBits); }
else { PastDifficultyAverage = ((PastDifficultyAveragePrev * CountBlocks) + (arith_uint256().SetCompact(BlockReading->nBits))) / (CountBlocks + 1); }
PastDifficultyAveragePrev = PastDifficultyAverage;
}
if(LastBlockTime > 0){
int64_t Diff = (LastBlockTime - BlockReading->GetBlockTime());
nActualTimespan += Diff;
}
LastBlockTime = BlockReading->GetBlockTime();
if (BlockReading->pprev == NULL) { assert(BlockReading); break; }
BlockReading = BlockReading->pprev;
}
arith_uint256 bnNew(PastDifficultyAverage);
int64_t _nTargetTimespan = CountBlocks * Params().TargetSpacing();
if (nActualTimespan < _nTargetTimespan/3)
nActualTimespan = _nTargetTimespan/3;
if (nActualTimespan > _nTargetTimespan*3)
nActualTimespan = _nTargetTimespan*3;
// Retarget
bnNew *= nActualTimespan;
bnNew /= _nTargetTimespan;
if (bnNew > Params().ProofOfWorkLimit()){
bnNew = Params().ProofOfWorkLimit();
}
return bnNew.GetCompact();
}
unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock)
{
unsigned int retarget = DIFF_DGW;
if (pindexLast->nHeight + 1 >= 1059780) retarget = DIFF_DGW;
else retarget = DIFF_BTC;
if (Params().NetworkID() == CBaseChainParams::TESTNET && pindexLast->nHeight >= 10000)
retarget = DIFF_DGW;
// Default Bitcoin style retargeting
if (retarget == DIFF_BTC)
{
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* 2.5 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 1 day 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
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 at %d\n", pindexLast->nHeight + 1);
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();
}
// Retarget using Kimoto Gravity Wave
else if (retarget == DIFF_KGW)
{
return KimotoGravityWell(pindexLast);
}
// Retarget using Dark Gravity Wave 3
else if (retarget == DIFF_DGW)
{
return DarkGravityWave(pindexLast);
}
return DarkGravityWave(pindexLast);
}
bool CheckProofOfWork(uint256 hash, unsigned int nBits)
{
bool fNegative;
bool fOverflow;
arith_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 (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;
}