src/pow.cpp

   1 // Copyright (c) 2009-2010 Satoshi Nakamoto
   2 // Copyright (c) 2009-2015 The Bitcoin Core developers
   3 // Distributed under the MIT software license, see the accompanying
   4 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   5
   6 #include "pow.h"
   7
   8 #include "arith_uint256.h"
   9 #include "chain.h"
  10 #include "primitives/block.h"
  11 #include "uint256.h"
  12
  13 unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock, const Consensus::Params& params)
  14 {
  15     unsigned int nProofOfWorkLimit = UintToArith256(params.powLimit).GetCompact();
  16
  17     // Genesis block
  18     if (pindexLast == NULL)
  19         return nProofOfWorkLimit;
  20
  21     // Only change once per difficulty adjustment interval
  22     if ((pindexLast->nHeight+1) % params.DifficultyAdjustmentInterval() != 0)
  23     {
  24         if (params.fPowAllowMinDifficultyBlocks)
  25         {
  26             // Special difficulty rule for testnet:
  27             // If the new block's timestamp is more than 2* 10 minutes
  28             // then allow mining of a min-difficulty block.
  29             if (pblock->GetBlockTime() > pindexLast->GetBlockTime() + params.nPowTargetSpacing*2)
  30                 return nProofOfWorkLimit;
  31             else
  32             {
  33                 // Return the last non-special-min-difficulty-rules-block
  34                 const CBlockIndex* pindex = pindexLast;
  35                 while (pindex->pprev && pindex->nHeight % params.DifficultyAdjustmentInterval() != 0 && pindex->nBits == nProofOfWorkLimit)
  36                     pindex = pindex->pprev;
  37                 return pindex->nBits;
  38             }
  39         }
  40         return pindexLast->nBits;
  41     }
  42
  43     // Go back by what we want to be 14 days worth of blocks
  44     int nHeightFirst = pindexLast->nHeight - (params.DifficultyAdjustmentInterval()-1);
  45     assert(nHeightFirst >= 0);
  46     const CBlockIndex* pindexFirst = pindexLast->GetAncestor(nHeightFirst);
  47     assert(pindexFirst);
  48
  49     return CalculateNextWorkRequired(pindexLast, pindexFirst->GetBlockTime(), params);
  50 }
  51
  52 unsigned int CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime, const Consensus::Params& params)
  53 {
  54     if (params.fPowNoRetargeting)
  55         return pindexLast->nBits;
  56
  57     // Limit adjustment step
  58     int64_t nActualTimespan = pindexLast->GetBlockTime() - nFirstBlockTime;
  59     if (nActualTimespan < params.nPowTargetTimespan/4)
  60         nActualTimespan = params.nPowTargetTimespan/4;
  61     if (nActualTimespan > params.nPowTargetTimespan*4)
  62         nActualTimespan = params.nPowTargetTimespan*4;
  63
  64     // Retarget
  65     const arith_uint256 bnPowLimit = UintToArith256(params.powLimit);
  66     arith_uint256 bnNew;
  67     bnNew.SetCompact(pindexLast->nBits);
  68     bnNew *= nActualTimespan;
  69     bnNew /= params.nPowTargetTimespan;
  70
  71     if (bnNew > bnPowLimit)
  72         bnNew = bnPowLimit;
  73
  74     return bnNew.GetCompact();
  75 }
  76
  77 bool CheckProofOfWork(uint256 hash, unsigned int nBits, const Consensus::Params& params)
  78 {
  79     bool fNegative;
  80     bool fOverflow;
  81     arith_uint256 bnTarget;
  82
  83     bnTarget.SetCompact(nBits, &fNegative, &fOverflow);
  84
  85     // Check range
  86     if (fNegative || bnTarget == 0 || fOverflow || bnTarget > UintToArith256(params.powLimit))
  87         return false;
  88
  89     // Check proof of work matches claimed amount
  90     if (UintToArith256(hash) > bnTarget)
  91         return false;
  92
  93     return true;
  94 }