aboutsummaryrefslogtreecommitdiff
path: root/src/pow.cpp
blob: 893f6c18be657a927d8993ae5bf7b075b5954a88 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
// 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 "chainparams.h"
#include "core.h"
#include "main.h"
#include "timedata.h"
#include "uint256.h"
#include "util.h"

unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHeader *pblock)
{
    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* 10 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 14 days 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
    uint256 bnNew;
    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\n");
    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();
}

bool CheckProofOfWork(uint256 hash, unsigned int nBits)
{
    bool fNegative;
    bool fOverflow;
    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 (hash > bnTarget)
        return error("CheckProofOfWork() : hash doesn't match nBits");

    return true;
}

//
// true if nBits is greater than the minimum amount of work that could
// possibly be required deltaTime after minimum work required was nBase
//
bool CheckMinWork(unsigned int nBits, unsigned int nBase, int64_t deltaTime)
{
    bool fOverflow = false;
    uint256 bnNewBlock;
    bnNewBlock.SetCompact(nBits, NULL, &fOverflow);
    if (fOverflow)
        return false;

    const uint256 &bnLimit = Params().ProofOfWorkLimit();
    // Testnet has min-difficulty blocks
    // after Params().TargetSpacing()*2 time between blocks:
    if (Params().AllowMinDifficultyBlocks() && deltaTime > Params().TargetSpacing()*2)
        return bnNewBlock <= bnLimit;

    uint256 bnResult;
    bnResult.SetCompact(nBase);
    while (deltaTime > 0 && bnResult < bnLimit)
    {
        // Maximum 400% adjustment...
        bnResult *= 4;
        // ... in best-case exactly 4-times-normal target time
        deltaTime -= Params().TargetTimespan()*4;
    }
    if (bnResult > bnLimit)
        bnResult = bnLimit;

    return bnNewBlock <= bnResult;
}

void UpdateTime(CBlockHeader* pblock, const CBlockIndex* pindexPrev)
{
    pblock->nTime = std::max(pindexPrev->GetMedianTimePast()+1, GetAdjustedTime());

    // Updating time can change work required on testnet:
    if (Params().AllowMinDifficultyBlocks())
        pblock->nBits = GetNextWorkRequired(pindexPrev, pblock);
}

uint256 GetProofIncrement(unsigned int nBits)
{
    uint256 bnTarget;
    bool fNegative;
    bool fOverflow;
    bnTarget.SetCompact(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 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;
}