Bitcoin Core  0.20.99
P2P Digital Currency
pow.cpp
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1 // Copyright (c) 2009-2010 Satoshi Nakamoto
2 // Copyright (c) 2009-2018 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  assert(pindexLast != nullptr);
16  unsigned int nProofOfWorkLimit = UintToArith256(params.powLimit).GetCompact();
17 
18  // Only change once per difficulty adjustment interval
19  if ((pindexLast->nHeight+1) % params.DifficultyAdjustmentInterval() != 0)
20  {
22  {
23  // Special difficulty rule for testnet:
24  // If the new block's timestamp is more than 2* 10 minutes
25  // then allow mining of a min-difficulty block.
26  if (pblock->GetBlockTime() > pindexLast->GetBlockTime() + params.nPowTargetSpacing*2)
27  return nProofOfWorkLimit;
28  else
29  {
30  // Return the last non-special-min-difficulty-rules-block
31  const CBlockIndex* pindex = pindexLast;
32  while (pindex->pprev && pindex->nHeight % params.DifficultyAdjustmentInterval() != 0 && pindex->nBits == nProofOfWorkLimit)
33  pindex = pindex->pprev;
34  return pindex->nBits;
35  }
36  }
37  return pindexLast->nBits;
38  }
39 
40  // Go back by what we want to be 14 days worth of blocks
41  int nHeightFirst = pindexLast->nHeight - (params.DifficultyAdjustmentInterval()-1);
42  assert(nHeightFirst >= 0);
43  const CBlockIndex* pindexFirst = pindexLast->GetAncestor(nHeightFirst);
44  assert(pindexFirst);
45 
46  return CalculateNextWorkRequired(pindexLast, pindexFirst->GetBlockTime(), params);
47 }
48 
49 unsigned int CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime, const Consensus::Params& params)
50 {
51  if (params.fPowNoRetargeting)
52  return pindexLast->nBits;
53 
54  // Limit adjustment step
55  int64_t nActualTimespan = pindexLast->GetBlockTime() - nFirstBlockTime;
56  if (nActualTimespan < params.nPowTargetTimespan/4)
57  nActualTimespan = params.nPowTargetTimespan/4;
58  if (nActualTimespan > params.nPowTargetTimespan*4)
59  nActualTimespan = params.nPowTargetTimespan*4;
60 
61  // Retarget
62  const arith_uint256 bnPowLimit = UintToArith256(params.powLimit);
63  arith_uint256 bnNew;
64  bnNew.SetCompact(pindexLast->nBits);
65  bnNew *= nActualTimespan;
66  bnNew /= params.nPowTargetTimespan;
67 
68  if (bnNew > bnPowLimit)
69  bnNew = bnPowLimit;
70 
71  return bnNew.GetCompact();
72 }
73 
74 bool CheckProofOfWork(uint256 hash, unsigned int nBits, const Consensus::Params& params)
75 {
76  bool fNegative;
77  bool fOverflow;
78  arith_uint256 bnTarget;
79 
80  bnTarget.SetCompact(nBits, &fNegative, &fOverflow);
81 
82  // Check range
83  if (fNegative || bnTarget == 0 || fOverflow || bnTarget > UintToArith256(params.powLimit))
84  return false;
85 
86  // Check proof of work matches claimed amount
87  if (UintToArith256(hash) > bnTarget)
88  return false;
89 
90  return true;
91 }
int64_t GetBlockTime() const
Definition: chain.h:247
int64_t nPowTargetTimespan
Definition: params.h:79
CBlockIndex * pprev
pointer to the index of the predecessor of this block
Definition: chain.h:144
bool fPowNoRetargeting
Definition: params.h:77
bool fPowAllowMinDifficultyBlocks
Definition: params.h:76
unsigned int CalculateNextWorkRequired(const CBlockIndex *pindexLast, int64_t nFirstBlockTime, const Consensus::Params &params)
Definition: pow.cpp:49
uint32_t GetCompact(bool fNegative=false) const
arith_uint256 UintToArith256(const uint256 &a)
uint256 powLimit
Proof of work parameters.
Definition: params.h:75
unsigned int GetNextWorkRequired(const CBlockIndex *pindexLast, const CBlockHeader *pblock, const Consensus::Params &params)
Definition: pow.cpp:13
int64_t nPowTargetSpacing
Definition: params.h:78
Parameters that influence chain consensus.
Definition: params.h:45
bool CheckProofOfWork(uint256 hash, unsigned int nBits, const Consensus::Params &params)
Check whether a block hash satisfies the proof-of-work requirement specified by nBits.
Definition: pow.cpp:74
int64_t GetBlockTime() const
Definition: block.h:55
256-bit unsigned big integer.
int64_t DifficultyAdjustmentInterval() const
Definition: params.h:80
256-bit opaque blob.
Definition: uint256.h:120
The block chain is a tree shaped structure starting with the genesis block at the root...
Definition: chain.h:137
arith_uint256 & SetCompact(uint32_t nCompact, bool *pfNegative=nullptr, bool *pfOverflow=nullptr)
The "compact" format is a representation of a whole number N using an unsigned 32bit number similar t...
int nHeight
height of the entry in the chain. The genesis block has height 0
Definition: chain.h:150
CBlockIndex * GetAncestor(int height)
Efficiently find an ancestor of this block.
Definition: chain.cpp:111
uint32_t nBits
Definition: chain.h:180
Nodes collect new transactions into a block, hash them into a hash tree, and scan through nonce value...
Definition: block.h:20