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Implement new difficulty algorithm (#931)

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The algorithm is based on DigiShield v3/v4.
This commit is contained in:
Jack Grigg
2016-06-08 12:30:32 +12:00
parent 542da618df
commit f2c48e15e5
4 changed files with 45 additions and 36 deletions
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53
src/pow.cpp
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@@ -24,8 +24,6 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
if (pindexLast == NULL)
return nProofOfWorkLimit;
// Only change once per difficulty adjustment interval
if ((pindexLast->nHeight+1) % params.DifficultyAdjustmentInterval() != 0)
{
if (params.fPowAllowMinDifficultyBlocks)
{
@@ -34,36 +32,35 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
// 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;
}
// Go back by what we want to be 14 days worth of blocks
int nHeightFirst = pindexLast->nHeight - (params.DifficultyAdjustmentInterval()-1);
assert(nHeightFirst >= 0);
const CBlockIndex* pindexFirst = pindexLast->GetAncestor(nHeightFirst);
assert(pindexFirst);
// Find the first block in the averaging interval
const CBlockIndex* pindexFirst = pindexLast;
for (int i = 0; pindexFirst && i < params.nPowAveragingWindow; i++) {
pindexFirst = pindexFirst->pprev;
}
return CalculateNextWorkRequired(pindexLast, pindexFirst->GetBlockTime(), params);
// Check we have enough blocks
if (pindexFirst == NULL)
return nProofOfWorkLimit;
return CalculateNextWorkRequired(pindexLast, pindexFirst->GetMedianTimePast(), params);
}
unsigned int CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime, const Consensus::Params& params)
{
// Limit adjustment step
int64_t nActualTimespan = pindexLast->GetBlockTime() - nFirstBlockTime;
LogPrintf(" nActualTimespan = %d before bounds\n", nActualTimespan);
if (nActualTimespan < params.nPowTargetTimespan/4)
nActualTimespan = params.nPowTargetTimespan/4;
if (nActualTimespan > params.nPowTargetTimespan*4)
nActualTimespan = params.nPowTargetTimespan*4;
// Use medians to prevent time-warp attacks
int64_t nActualTimespan = pindexLast->GetMedianTimePast() - nFirstBlockTime;
LogPrint("pow", " nActualTimespan = %d before dampening\n", nActualTimespan);
nActualTimespan = params.AveragingWindowTimespan() + (nActualTimespan - params.AveragingWindowTimespan())/4;
LogPrint("pow", " nActualTimespan = %d before bounds\n", nActualTimespan);
if (nActualTimespan < params.MinActualTimespan())
nActualTimespan = params.MinActualTimespan();
if (nActualTimespan > params.MaxActualTimespan())
nActualTimespan = params.MaxActualTimespan();
// Retarget
const arith_uint256 bnPowLimit = UintToArith256(params.powLimit);
@@ -71,17 +68,17 @@ unsigned int CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nF
arith_uint256 bnOld;
bnNew.SetCompact(pindexLast->nBits);
bnOld = bnNew;
bnNew /= params.nPowTargetTimespan;
bnNew /= params.AveragingWindowTimespan();
bnNew *= nActualTimespan;
if (bnNew > bnPowLimit)
bnNew = bnPowLimit;
/// debug print
LogPrintf("GetNextWorkRequired RETARGET\n");
LogPrintf("params.nPowTargetTimespan = %d nActualTimespan = %d\n", params.nPowTargetTimespan, nActualTimespan);
LogPrintf("Before: %08x %s\n", pindexLast->nBits, bnOld.ToString());
LogPrintf("After: %08x %s\n", bnNew.GetCompact(), bnNew.ToString());
LogPrint("pow", "GetNextWorkRequired RETARGET\n");
LogPrint("pow", "params.AveragingWindowTimespan() = %d nActualTimespan = %d\n", params.AveragingWindowTimespan(), nActualTimespan);
LogPrint("pow", "Before: %08x %s\n", pindexLast->nBits, bnOld.ToString());
LogPrint("pow", "After: %08x %s\n", bnNew.GetCompact(), bnNew.ToString());
return bnNew.GetCompact();
}