github.com/ebceco/ebc@v1.8.19-0.20190309150932-8cb0b9e06484/consensus/ethash/consensus.go (about)

     1  // Copyright 2017 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  package ethash
    18  
    19  import (
    20  	"bytes"
    21  	"errors"
    22  	"fmt"
    23  	"math/big"
    24  	"runtime"
    25  	"time"
    26  
    27  	mapset "github.com/deckarep/golang-set"
    28  	"github.com/ebceco/ebc/common"
    29  	"github.com/ebceco/ebc/common/math"
    30  	"github.com/ebceco/ebc/consensus"
    31  	"github.com/ebceco/ebc/consensus/misc"
    32  	"github.com/ebceco/ebc/core/state"
    33  	"github.com/ebceco/ebc/core/types"
    34  	"github.com/ebceco/ebc/params"
    35  	"github.com/ebceco/ebc/rlp"
    36  	"golang.org/x/crypto/sha3"
    37  )
    38  
    39  // Ethash proof-of-work protocol constants.
    40  var (
    41  	FrontierBlockReward       = big.NewInt(1e+14) // Block reward in wei for successfully mining a block
    42  	ByzantiumBlockReward      = big.NewInt(1e+14) // Block reward in wei for successfully mining a block upward from Byzantium
    43  	ConstantinopleBlockReward = big.NewInt(1e+14) // Block reward in wei for successfully mining a block upward from Constantinople
    44  	SappertonBlockReward      = big.NewInt(1e+14) // Block reward in wei for successfully mining a block upward from Sapperton
    45  	EIP998BlockReward         = big.NewInt(0)     // Block reward in wei for successfully mining a block upward from EIP998
    46  	maxUncles                 = 2                 // Maximum number of uncles allowed in a single block
    47  	allowedFutureBlockTime    = 15 * time.Second  // Max time from current time allowed for blocks, before they're considered future blocks
    48  
    49  	// calcDifficultyConstantinople is the difficulty adjustment algorithm for Constantinople.
    50  	// It returns the difficulty that a new block should have when created at time given the
    51  	// parent block's time and difficulty. The calculation uses the Byzantium rules, but with
    52  	// bomb offset 5M.
    53  	// Specification EIP-1234: https://eips.ethereum.org/EIPS/eip-1234
    54  	calcDifficultyConstantinople = makeDifficultyCalculator(big.NewInt(5000000))
    55  
    56  	// calcDifficultyByzantium is the difficulty adjustment algorithm. It returns
    57  	// the difficulty that a new block should have when created at time given the
    58  	// parent block's time and difficulty. The calculation uses the Byzantium rules.
    59  	// Specification EIP-649: https://eips.ethereum.org/EIPS/eip-649
    60  	calcDifficultyByzantium = makeDifficultyCalculator(big.NewInt(5000000))
    61  
    62  	calcDifficultyEIP998    = makeDifficultyCalculator(big.NewInt(5000000))
    63  	calcDifficultySapperton = makeDifficultyCalculator(big.NewInt(5000000))
    64  )
    65  
    66  // Various error messages to mark blocks invalid. These should be private to
    67  // prevent engine specific errors from being referenced in the remainder of the
    68  // codebase, inherently breaking if the engine is swapped out. Please put common
    69  // error types into the consensus package.
    70  var (
    71  	errLargeBlockTime    = errors.New("timestamp too big")
    72  	errZeroBlockTime     = errors.New("timestamp equals parent's")
    73  	errTooManyUncles     = errors.New("too many uncles")
    74  	errDuplicateUncle    = errors.New("duplicate uncle")
    75  	errUncleIsAncestor   = errors.New("uncle is ancestor")
    76  	errDanglingUncle     = errors.New("uncle's parent is not ancestor")
    77  	errInvalidDifficulty = errors.New("non-positive difficulty")
    78  	errInvalidMixDigest  = errors.New("invalid mix digest")
    79  	errInvalidPoW        = errors.New("invalid proof-of-work")
    80  )
    81  
    82  // Author implements consensus.Engine, returning the header's coinbase as the
    83  // proof-of-work verified author of the block.
    84  func (ethash *Ethash) Author(header *types.Header) (common.Address, error) {
    85  	return header.Coinbase, nil
    86  }
    87  
    88  // VerifyHeader checks whether a header conforms to the consensus rules of the
    89  // stock Ethereum ethash engine.
    90  func (ethash *Ethash) VerifyHeader(chain consensus.ChainReader, header *types.Header, seal bool) error {
    91  	// If we're running a full engine faking, accept any input as valid
    92  	if ethash.config.PowMode == ModeFullFake {
    93  		return nil
    94  	}
    95  	// Short circuit if the header is known, or it's parent not
    96  	number := header.Number.Uint64()
    97  	if chain.GetHeader(header.Hash(), number) != nil {
    98  		return nil
    99  	}
   100  	parent := chain.GetHeader(header.ParentHash, number-1)
   101  	if parent == nil {
   102  		return consensus.ErrUnknownAncestor
   103  	}
   104  	// Sanity checks passed, do a proper verification
   105  	return ethash.verifyHeader(chain, header, parent, false, seal)
   106  }
   107  
   108  // VerifyHeaders is similar to VerifyHeader, but verifies a batch of headers
   109  // concurrently. The method returns a quit channel to abort the operations and
   110  // a results channel to retrieve the async verifications.
   111  func (ethash *Ethash) VerifyHeaders(chain consensus.ChainReader, headers []*types.Header, seals []bool) (chan<- struct{}, <-chan error) {
   112  	// If we're running a full engine faking, accept any input as valid
   113  	if ethash.config.PowMode == ModeFullFake || len(headers) == 0 {
   114  		abort, results := make(chan struct{}), make(chan error, len(headers))
   115  		for i := 0; i < len(headers); i++ {
   116  			results <- nil
   117  		}
   118  		return abort, results
   119  	}
   120  
   121  	// Spawn as many workers as allowed threads
   122  	workers := runtime.GOMAXPROCS(0)
   123  	if len(headers) < workers {
   124  		workers = len(headers)
   125  	}
   126  
   127  	// Create a task channel and spawn the verifiers
   128  	var (
   129  		inputs = make(chan int)
   130  		done   = make(chan int, workers)
   131  		errors = make([]error, len(headers))
   132  		abort  = make(chan struct{})
   133  	)
   134  	for i := 0; i < workers; i++ {
   135  		go func() {
   136  			for index := range inputs {
   137  				errors[index] = ethash.verifyHeaderWorker(chain, headers, seals, index)
   138  				done <- index
   139  			}
   140  		}()
   141  	}
   142  
   143  	errorsOut := make(chan error, len(headers))
   144  	go func() {
   145  		defer close(inputs)
   146  		var (
   147  			in, out = 0, 0
   148  			checked = make([]bool, len(headers))
   149  			inputs  = inputs
   150  		)
   151  		for {
   152  			select {
   153  			case inputs <- in:
   154  				if in++; in == len(headers) {
   155  					// Reached end of headers. Stop sending to workers.
   156  					inputs = nil
   157  				}
   158  			case index := <-done:
   159  				for checked[index] = true; checked[out]; out++ {
   160  					errorsOut <- errors[out]
   161  					if out == len(headers)-1 {
   162  						return
   163  					}
   164  				}
   165  			case <-abort:
   166  				return
   167  			}
   168  		}
   169  	}()
   170  	return abort, errorsOut
   171  }
   172  
   173  func (ethash *Ethash) verifyHeaderWorker(chain consensus.ChainReader, headers []*types.Header, seals []bool, index int) error {
   174  	var parent *types.Header
   175  	if index == 0 {
   176  		parent = chain.GetHeader(headers[0].ParentHash, headers[0].Number.Uint64()-1)
   177  	} else if headers[index-1].Hash() == headers[index].ParentHash {
   178  		parent = headers[index-1]
   179  	}
   180  	if parent == nil {
   181  		return consensus.ErrUnknownAncestor
   182  	}
   183  	if chain.GetHeader(headers[index].Hash(), headers[index].Number.Uint64()) != nil {
   184  		return nil // known block
   185  	}
   186  	return ethash.verifyHeader(chain, headers[index], parent, false, seals[index])
   187  }
   188  
   189  // VerifyUncles verifies that the given block's uncles conform to the consensus
   190  // rules of the stock Ethereum ethash engine.
   191  func (ethash *Ethash) VerifyUncles(chain consensus.ChainReader, block *types.Block) error {
   192  	// If we're running a full engine faking, accept any input as valid
   193  	if ethash.config.PowMode == ModeFullFake {
   194  		return nil
   195  	}
   196  	// Verify that there are at most 2 uncles included in this block
   197  	if len(block.Uncles()) > maxUncles {
   198  		return errTooManyUncles
   199  	}
   200  	// Gather the set of past uncles and ancestors
   201  	uncles, ancestors := mapset.NewSet(), make(map[common.Hash]*types.Header)
   202  
   203  	number, parent := block.NumberU64()-1, block.ParentHash()
   204  	for i := 0; i < 7; i++ {
   205  		ancestor := chain.GetBlock(parent, number)
   206  		if ancestor == nil {
   207  			break
   208  		}
   209  		ancestors[ancestor.Hash()] = ancestor.Header()
   210  		for _, uncle := range ancestor.Uncles() {
   211  			uncles.Add(uncle.Hash())
   212  		}
   213  		parent, number = ancestor.ParentHash(), number-1
   214  	}
   215  	ancestors[block.Hash()] = block.Header()
   216  	uncles.Add(block.Hash())
   217  
   218  	// Verify each of the uncles that it's recent, but not an ancestor
   219  	for _, uncle := range block.Uncles() {
   220  		// Make sure every uncle is rewarded only once
   221  		hash := uncle.Hash()
   222  		if uncles.Contains(hash) {
   223  			return errDuplicateUncle
   224  		}
   225  		uncles.Add(hash)
   226  
   227  		// Make sure the uncle has a valid ancestry
   228  		if ancestors[hash] != nil {
   229  			return errUncleIsAncestor
   230  		}
   231  		if ancestors[uncle.ParentHash] == nil || uncle.ParentHash == block.ParentHash() {
   232  			return errDanglingUncle
   233  		}
   234  		if err := ethash.verifyHeader(chain, uncle, ancestors[uncle.ParentHash], true, true); err != nil {
   235  			return err
   236  		}
   237  	}
   238  	return nil
   239  }
   240  
   241  // verifyHeader checks whether a header conforms to the consensus rules of the
   242  // stock Ethereum ethash engine.
   243  // See YP section 4.3.4. "Block Header Validity"
   244  func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *types.Header, uncle bool, seal bool) error {
   245  	// Ensure that the header's extra-data section is of a reasonable size
   246  	if uint64(len(header.Extra)) > params.MaximumExtraDataSize {
   247  		return fmt.Errorf("extra-data too long: %d > %d", len(header.Extra), params.MaximumExtraDataSize)
   248  	}
   249  	// Verify the header's timestamp
   250  	if uncle {
   251  		if header.Time.Cmp(math.MaxBig256) > 0 {
   252  			return errLargeBlockTime
   253  		}
   254  	} else {
   255  		if header.Time.Cmp(big.NewInt(time.Now().Add(allowedFutureBlockTime).Unix())) > 0 {
   256  			return consensus.ErrFutureBlock
   257  		}
   258  	}
   259  	if header.Time.Cmp(parent.Time) <= 0 {
   260  		return errZeroBlockTime
   261  	}
   262  	// Verify the block's difficulty based in it's timestamp and parent's difficulty
   263  	expected := ethash.CalcDifficulty(chain, header.Time.Uint64(), parent)
   264  
   265  	if expected.Cmp(header.Difficulty) != 0 {
   266  		return fmt.Errorf("invalid difficulty: have %v, want %v", header.Difficulty, expected)
   267  	}
   268  	// Verify that the gas limit is <= 2^63-1
   269  	cap := uint64(0x7fffffffffffffff)
   270  	if header.GasLimit > cap {
   271  		return fmt.Errorf("invalid gasLimit: have %v, max %v", header.GasLimit, cap)
   272  	}
   273  	// Verify that the gasUsed is <= gasLimit
   274  	if header.GasUsed > header.GasLimit {
   275  		return fmt.Errorf("invalid gasUsed: have %d, gasLimit %d", header.GasUsed, header.GasLimit)
   276  	}
   277  
   278  	// Verify that the gas limit remains within allowed bounds
   279  	diff := int64(parent.GasLimit) - int64(header.GasLimit)
   280  	if diff < 0 {
   281  		diff *= -1
   282  	}
   283  	limit := parent.GasLimit / params.GasLimitBoundDivisor
   284  
   285  	if uint64(diff) >= limit || header.GasLimit < params.MinGasLimit {
   286  		return fmt.Errorf("invalid gas limit: have %d, want %d += %d", header.GasLimit, parent.GasLimit, limit)
   287  	}
   288  	// Verify that the block number is parent's +1
   289  	if diff := new(big.Int).Sub(header.Number, parent.Number); diff.Cmp(big.NewInt(1)) != 0 {
   290  		return consensus.ErrInvalidNumber
   291  	}
   292  	// Verify the engine specific seal securing the block
   293  	if seal {
   294  		if err := ethash.VerifySeal(chain, header); err != nil {
   295  			return err
   296  		}
   297  	}
   298  	// If all checks passed, validate any special fields for hard forks
   299  	if err := misc.VerifyDAOHeaderExtraData(chain.Config(), header); err != nil {
   300  		return err
   301  	}
   302  	if err := misc.VerifyForkHashes(chain.Config(), header, uncle); err != nil {
   303  		return err
   304  	}
   305  	return nil
   306  }
   307  
   308  // CalcDifficulty is the difficulty adjustment algorithm. It returns
   309  // the difficulty that a new block should have when created at time
   310  // given the parent block's time and difficulty.
   311  func (ethash *Ethash) CalcDifficulty(chain consensus.ChainReader, time uint64, parent *types.Header) *big.Int {
   312  	return CalcDifficulty(chain.Config(), time, parent)
   313  }
   314  
   315  // CalcDifficulty is the difficulty adjustment algorithm. It returns
   316  // the difficulty that a new block should have when created at time
   317  // given the parent block's time and difficulty.
   318  func CalcDifficulty(config *params.ChainConfig, time uint64, parent *types.Header) *big.Int {
   319  	next := new(big.Int).Add(parent.Number, big1)
   320  	switch {
   321  	case config.IsEIP998(next):
   322  		return calcDifficultyEIP998(time, parent)
   323  	case config.IsSapperton(next):
   324  		return calcDifficultySapperton(time, parent)
   325  	case config.IsConstantinople(next):
   326  		return calcDifficultyConstantinople(time, parent)
   327  	case config.IsByzantium(next):
   328  		return calcDifficultyByzantium(time, parent)
   329  	case config.IsHomestead(next):
   330  		return calcDifficultyHomestead(time, parent)
   331  	default:
   332  		return calcDifficultyFrontier(time, parent)
   333  	}
   334  }
   335  
   336  // Some weird constants to avoid constant memory allocs for them.
   337  var (
   338  	expDiffPeriod = big.NewInt(100000)
   339  	big1          = big.NewInt(1)
   340  	big2          = big.NewInt(2)
   341  	big9          = big.NewInt(9)
   342  	big10         = big.NewInt(10)
   343  	bigMinus99    = big.NewInt(-99)
   344  )
   345  
   346  // makeDifficultyCalculator creates a difficultyCalculator with the given bomb-delay.
   347  // the difficulty is calculated with Byzantium rules, which differs from Homestead in
   348  // how uncles affect the calculation
   349  func makeDifficultyCalculator(bombDelay *big.Int) func(time uint64, parent *types.Header) *big.Int {
   350  	// Note, the calculations below looks at the parent number, which is 1 below
   351  	// the block number. Thus we remove one from the delay given
   352  	bombDelayFromParent := new(big.Int).Sub(bombDelay, big1)
   353  	return func(time uint64, parent *types.Header) *big.Int {
   354  		// https://github.com/ethereum/EIPs/issues/100.
   355  		// algorithm:
   356  		// diff = (parent_diff +
   357  		//         (parent_diff / 2048 * max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99))
   358  		//        ) + 2^(periodCount - 2)
   359  
   360  		bigTime := new(big.Int).SetUint64(time)
   361  		bigParentTime := new(big.Int).Set(parent.Time)
   362  
   363  		// holds intermediate values to make the algo easier to read & audit
   364  		x := new(big.Int)
   365  		y := new(big.Int)
   366  
   367  		// (2 if len(parent_uncles) else 1) - (block_timestamp - parent_timestamp) // 9
   368  		x.Sub(bigTime, bigParentTime)
   369  		x.Div(x, big9)
   370  		if parent.UncleHash == types.EmptyUncleHash {
   371  			x.Sub(big1, x)
   372  		} else {
   373  			x.Sub(big2, x)
   374  		}
   375  		// max((2 if len(parent_uncles) else 1) - (block_timestamp - parent_timestamp) // 9, -99)
   376  		if x.Cmp(bigMinus99) < 0 {
   377  			x.Set(bigMinus99)
   378  		}
   379  		// parent_diff + (parent_diff / 2048 * max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99))
   380  		y.Div(parent.Difficulty, params.DifficultyBoundDivisor)
   381  		x.Mul(y, x)
   382  		x.Add(parent.Difficulty, x)
   383  
   384  		// minimum difficulty can ever be (before exponential factor)
   385  		if x.Cmp(params.MinimumDifficulty) < 0 {
   386  			x.Set(params.MinimumDifficulty)
   387  		}
   388  		// calculate a fake block number for the ice-age delay
   389  		// Specification: https://eips.ethereum.org/EIPS/eip-1234
   390  		fakeBlockNumber := new(big.Int)
   391  		if parent.Number.Cmp(bombDelayFromParent) >= 0 {
   392  			fakeBlockNumber = fakeBlockNumber.Sub(parent.Number, bombDelayFromParent)
   393  		}
   394  		// for the exponential factor
   395  		periodCount := fakeBlockNumber
   396  		periodCount.Div(periodCount, expDiffPeriod)
   397  
   398  		// the exponential factor, commonly referred to as "the bomb"
   399  		// diff = diff + 2^(periodCount - 2)
   400  		if periodCount.Cmp(big1) > 0 {
   401  			y.Sub(periodCount, big2)
   402  			y.Exp(big2, y, nil)
   403  			x.Add(x, y)
   404  		}
   405  		return x
   406  	}
   407  }
   408  
   409  // calcDifficultyHomestead is the difficulty adjustment algorithm. It returns
   410  // the difficulty that a new block should have when created at time given the
   411  // parent block's time and difficulty. The calculation uses the Homestead rules.
   412  func calcDifficultyHomestead(time uint64, parent *types.Header) *big.Int {
   413  	// https://github.com/ethereum/EIPs/blob/master/EIPS/eip-2.md
   414  	// algorithm:
   415  	// diff = (parent_diff +
   416  	//         (parent_diff / 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99))
   417  	//        ) + 2^(periodCount - 2)
   418  
   419  	bigTime := new(big.Int).SetUint64(time)
   420  	bigParentTime := new(big.Int).Set(parent.Time)
   421  
   422  	// holds intermediate values to make the algo easier to read & audit
   423  	x := new(big.Int)
   424  	y := new(big.Int)
   425  
   426  	// 1 - (block_timestamp - parent_timestamp) // 10
   427  	x.Sub(bigTime, bigParentTime)
   428  	x.Div(x, big10)
   429  	x.Sub(big1, x)
   430  
   431  	// max(1 - (block_timestamp - parent_timestamp) // 10, -99)
   432  	if x.Cmp(bigMinus99) < 0 {
   433  		x.Set(bigMinus99)
   434  	}
   435  	// (parent_diff + parent_diff // 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99))
   436  	y.Div(parent.Difficulty, params.DifficultyBoundDivisor)
   437  	x.Mul(y, x)
   438  	x.Add(parent.Difficulty, x)
   439  
   440  	// minimum difficulty can ever be (before exponential factor)
   441  	if x.Cmp(params.MinimumDifficulty) < 0 {
   442  		x.Set(params.MinimumDifficulty)
   443  	}
   444  	// for the exponential factor
   445  	periodCount := new(big.Int).Add(parent.Number, big1)
   446  	periodCount.Div(periodCount, expDiffPeriod)
   447  
   448  	// the exponential factor, commonly referred to as "the bomb"
   449  	// diff = diff + 2^(periodCount - 2)
   450  	if periodCount.Cmp(big1) > 0 {
   451  		y.Sub(periodCount, big2)
   452  		y.Exp(big2, y, nil)
   453  		x.Add(x, y)
   454  	}
   455  	return x
   456  }
   457  
   458  // calcDifficultyFrontier is the difficulty adjustment algorithm. It returns the
   459  // difficulty that a new block should have when created at time given the parent
   460  // block's time and difficulty. The calculation uses the Frontier rules.
   461  func calcDifficultyFrontier(time uint64, parent *types.Header) *big.Int {
   462  	diff := new(big.Int)
   463  	adjust := new(big.Int).Div(parent.Difficulty, params.DifficultyBoundDivisor)
   464  	bigTime := new(big.Int)
   465  	bigParentTime := new(big.Int)
   466  
   467  	bigTime.SetUint64(time)
   468  	bigParentTime.Set(parent.Time)
   469  
   470  	if bigTime.Sub(bigTime, bigParentTime).Cmp(params.DurationLimit) < 0 {
   471  		diff.Add(parent.Difficulty, adjust)
   472  	} else {
   473  		diff.Sub(parent.Difficulty, adjust)
   474  	}
   475  	if diff.Cmp(params.MinimumDifficulty) < 0 {
   476  		diff.Set(params.MinimumDifficulty)
   477  	}
   478  
   479  	periodCount := new(big.Int).Add(parent.Number, big1)
   480  	periodCount.Div(periodCount, expDiffPeriod)
   481  	if periodCount.Cmp(big1) > 0 {
   482  		// diff = diff + 2^(periodCount - 2)
   483  		expDiff := periodCount.Sub(periodCount, big2)
   484  		expDiff.Exp(big2, expDiff, nil)
   485  		diff.Add(diff, expDiff)
   486  		diff = math.BigMax(diff, params.MinimumDifficulty)
   487  	}
   488  	return diff
   489  }
   490  
   491  // VerifySeal implements consensus.Engine, checking whether the given block satisfies
   492  // the PoW difficulty requirements.
   493  func (ethash *Ethash) VerifySeal(chain consensus.ChainReader, header *types.Header) error {
   494  	return ethash.verifySeal(chain, header, false)
   495  }
   496  
   497  // verifySeal checks whether a block satisfies the PoW difficulty requirements,
   498  // either using the usual ethash cache for it, or alternatively using a full DAG
   499  // to make remote mining fast.
   500  func (ethash *Ethash) verifySeal(chain consensus.ChainReader, header *types.Header, fulldag bool) error {
   501  	// If we're running a fake PoW, accept any seal as valid
   502  	if ethash.config.PowMode == ModeFake || ethash.config.PowMode == ModeFullFake {
   503  		time.Sleep(ethash.fakeDelay)
   504  		if ethash.fakeFail == header.Number.Uint64() {
   505  			return errInvalidPoW
   506  		}
   507  		return nil
   508  	}
   509  	// If we're running a shared PoW, delegate verification to it
   510  	if ethash.shared != nil {
   511  		return ethash.shared.verifySeal(chain, header, fulldag)
   512  	}
   513  	// Ensure that we have a valid difficulty for the block
   514  	if header.Difficulty.Sign() <= 0 {
   515  		return errInvalidDifficulty
   516  	}
   517  	// Recompute the digest and PoW values
   518  	number := header.Number.Uint64()
   519  
   520  	var (
   521  		digest []byte
   522  		result []byte
   523  	)
   524  	// If fast-but-heavy PoW verification was requested, use an ethash dataset
   525  	if fulldag {
   526  		dataset := ethash.dataset(number, true)
   527  		if dataset.generated() {
   528  			digest, result = hashimotoFull(dataset.dataset, ethash.SealHash(header).Bytes(), header.Nonce.Uint64())
   529  
   530  			// Datasets are unmapped in a finalizer. Ensure that the dataset stays alive
   531  			// until after the call to hashimotoFull so it's not unmapped while being used.
   532  			runtime.KeepAlive(dataset)
   533  		} else {
   534  			// Dataset not yet generated, don't hang, use a cache instead
   535  			fulldag = false
   536  		}
   537  	}
   538  	// If slow-but-light PoW verification was requested (or DAG not yet ready), use an ethash cache
   539  	if !fulldag {
   540  		cache := ethash.cache(number)
   541  
   542  		size := datasetSize(number)
   543  		if ethash.config.PowMode == ModeTest {
   544  			size = 32 * 1024
   545  		}
   546  		digest, result = hashimotoLight(size, cache.cache, ethash.SealHash(header).Bytes(), header.Nonce.Uint64())
   547  
   548  		// Caches are unmapped in a finalizer. Ensure that the cache stays alive
   549  		// until after the call to hashimotoLight so it's not unmapped while being used.
   550  		runtime.KeepAlive(cache)
   551  	}
   552  	// Verify the calculated values against the ones provided in the header
   553  	if !bytes.Equal(header.MixDigest[:], digest) {
   554  		return errInvalidMixDigest
   555  	}
   556  	target := new(big.Int).Div(two256, header.Difficulty)
   557  	if new(big.Int).SetBytes(result).Cmp(target) > 0 {
   558  		return errInvalidPoW
   559  	}
   560  	return nil
   561  }
   562  
   563  // Prepare implements consensus.Engine, initializing the difficulty field of a
   564  // header to conform to the ethash protocol. The changes are done inline.
   565  func (ethash *Ethash) Prepare(chain consensus.ChainReader, header *types.Header) error {
   566  	parent := chain.GetHeader(header.ParentHash, header.Number.Uint64()-1)
   567  	if parent == nil {
   568  		return consensus.ErrUnknownAncestor
   569  	}
   570  	header.Difficulty = ethash.CalcDifficulty(chain, header.Time.Uint64(), parent)
   571  	return nil
   572  }
   573  
   574  // Finalize implements consensus.Engine, accumulating the block and uncle rewards,
   575  // setting the final state and assembling the block.
   576  func (ethash *Ethash) Finalize(chain consensus.ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction, uncles []*types.Header, receipts []*types.Receipt) (*types.Block, error) {
   577  	// Accumulate any block and uncle rewards and commit the final state root
   578  	accumulateRewards(chain.Config(), state, header, uncles)
   579  	header.Root = state.IntermediateRoot(chain.Config().IsEIP158(header.Number))
   580  
   581  	// Header seems complete, assemble into a block and return
   582  	return types.NewBlock(header, txs, uncles, receipts), nil
   583  }
   584  
   585  // SealHash returns the hash of a block prior to it being sealed.
   586  func (ethash *Ethash) SealHash(header *types.Header) (hash common.Hash) {
   587  	hasher := sha3.NewLegacyKeccak256()
   588  
   589  	rlp.Encode(hasher, []interface{}{
   590  		header.ParentHash,
   591  		header.UncleHash,
   592  		header.Coinbase,
   593  		header.Root,
   594  		header.TxHash,
   595  		header.ReceiptHash,
   596  		header.Bloom,
   597  		header.Difficulty,
   598  		header.Number,
   599  		header.GasLimit,
   600  		header.GasUsed,
   601  		header.Time,
   602  		header.Extra,
   603  	})
   604  	hasher.Sum(hash[:0])
   605  	return hash
   606  }
   607  
   608  // Some weird constants to avoid constant memory allocs for them.
   609  var (
   610  	big8  = big.NewInt(8)
   611  	big32 = big.NewInt(32)
   612  )
   613  
   614  // AccumulateRewards credits the coinbase of the given block with the mining
   615  // reward. The total reward consists of the static block reward and rewards for
   616  // included uncles. The coinbase of each uncle block is also rewarded.
   617  func accumulateRewards(config *params.ChainConfig, state *state.StateDB, header *types.Header, uncles []*types.Header) {
   618  	// Select the correct block reward based on chain progression
   619  	blockReward := FrontierBlockReward
   620  
   621  	if config.IsEIP998(header.Number) {
   622  		blockReward = EIP998BlockReward
   623  	}
   624  	if config.IsSapperton(header.Number) {
   625  		blockReward = SappertonBlockReward
   626  	}
   627  	if config.IsByzantium(header.Number) {
   628  		blockReward = ByzantiumBlockReward
   629  	}
   630  	if config.IsConstantinople(header.Number) {
   631  		blockReward = ConstantinopleBlockReward
   632  	}
   633  	// Accumulate the rewards for the miner and any included uncles
   634  	reward := new(big.Int).Set(blockReward)
   635  	r := new(big.Int)
   636  	for _, uncle := range uncles {
   637  		r.Add(uncle.Number, big8)
   638  		r.Sub(r, header.Number)
   639  		r.Mul(r, blockReward)
   640  		r.Div(r, big8)
   641  		state.AddBalance(uncle.Coinbase, r)
   642  
   643  		r.Div(blockReward, big32)
   644  		reward.Add(reward, r)
   645  	}
   646  	state.AddBalance(header.Coinbase, reward)
   647  }