DeltaGravityWave.cpp

unsigned int static DeltaGravityWave(const CBlockIndex* pindexLast, const uint32_t nTime, const Consensus::Params& params) 
{
  /* DeltaGravityWave Difficulty Re-Adjustment Algorithm 
   *
   * Based on a combination of: 
   * -- DarkGravity v3, written by Evan Duffield 
   * -- Delta algorithm, written by Frank ([email protected]) with adjustments by Malcolm MacLeod ([email protected])
   * */
  const CBlockIndex *BlockLastSolved = pindexLast;
  const CBlockIndex *BlockReading = pindexLast;
  int64_t nActualTimespan = 0;
  int64_t LastBlockTime = 0;
  int64_t PastBlocksMin = 20; 
  int64_t PastBlocksMax = 4; 
  int64_t CountBlocks = 0;
  arith_uint256 PastDifficultyAverage;
  arith_uint256 PastDifficultyAveragePrev;

  if (BlockLastSolved == NULL || BlockLastSolved->nHeight == 0 || BlockLastSolved->nHeight < PastBlocksMin) 
  {
    return UintToArith256(params.powLimit).GetCompact();
  }

  for (unsigned int i = 1; BlockReading && BlockReading->nHeight > 0; i++) 
  {
    //LogPrintf("pblock hash = %s, i: %d, BlockReading && BlockReading->nHeight == %d\n", 
    //        pblock->GetHash().ToString().c_str(), i, (BlockReading && BlockReading->nHeight));

    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.nPowTargetSpacing; 

  if (nActualTimespan < _nTargetTimespan/2)
  {
    nActualTimespan = _nTargetTimespan/2;
  }

  if (nActualTimespan > _nTargetTimespan*2) 
  {
    nActualTimespan = _nTargetTimespan*2;
  }

  arith_uint256 bnOld = bnNew;

  // Retarget
  bnNew *= nActualTimespan;
  bnNew /= _nTargetTimespan;

  // DELTA retarget if block time is greater than nLongTimeLimit
  const int64_t nLongTimeLimit = 2 * 16 * 60;
  const int64_t nLongTimeStep = 15 * 60;

  if ((nTime - pindexLast->GetBlockTime()) > nLongTimeLimit)
  {
    // Reduce in a linear fashion at first, and then start to ramp up with a gradual exponential curve (to catch massive hash extinction events)
    int64_t nNumMissedSteps = ((nTime - pindexLast->GetBlockTime()) / nLongTimeStep);
    //LogPrintf("nLongTimeLimit check passed, retargeting %u steps due to %f-minute block\n", nNumMissedSteps, (nTime - pindexLast->GetBlockTime())/60);
    if (nNumMissedSteps <= 5)
      bnNew *= nNumMissedSteps;
    else
      bnNew *= 5 + (int64_t)std::floor(std::pow((float)1.14, (float)nNumMissedSteps - 5) + 0.5);
  }

  //LogPrintf("DGW: Height %f, NewDiff %08x     nActualTimespan %f    nTargetTimespan %f   Before %s, After %s \r\n",		
  //	(double)pindexLast->nHeight, bnNew.GetCompact(),	(double)nActualTimespan,(double)_nTargetTimespan, bnOld.ToString(), bnNew.ToString());

  if (bnNew > UintToArith256(params.powLimit))
  {
    bnNew = UintToArith256(params.powLimit);
  }

  return bnNew.GetCompact();
}