gitlab.com/yannislg/go-pulse@v0.0.0-20210722055913-a3e24e95638d/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/ethereum/go-ethereum/common"
    29  	"github.com/ethereum/go-ethereum/common/math"
    30  	"github.com/ethereum/go-ethereum/consensus"
    31  	"github.com/ethereum/go-ethereum/consensus/misc"
    32  	"github.com/ethereum/go-ethereum/core/state"
    33  	"github.com/ethereum/go-ethereum/core/types"
    34  	"github.com/ethereum/go-ethereum/params"
    35  	"github.com/ethereum/go-ethereum/rlp"
    36  	"golang.org/x/crypto/sha3"
    37  )
    38  
    39  // Ethash proof-of-work protocol constants.
    40  var (
    41  	FrontierBlockReward       = big.NewInt(5e+18) // Block reward in wei for successfully mining a block
    42  	ByzantiumBlockReward      = big.NewInt(3e+18) // Block reward in wei for successfully mining a block upward from Byzantium
    43  	ConstantinopleBlockReward = big.NewInt(2e+18) // Block reward in wei for successfully mining a block upward from Constantinople
    44  	maxUncles                 = 2                 // Maximum number of uncles allowed in a single block
    45  	allowedFutureBlockTime    = 15 * time.Second  // Max time from current time allowed for blocks, before they're considered future blocks
    46  
    47  	// calcDifficultyEip2384 is the difficulty adjustment algorithm as specified by EIP 2384.
    48  	// It offsets the bomb 4M blocks from Constantinople, so in total 9M blocks.
    49  	// Specification EIP-2384: https://eips.ethereum.org/EIPS/eip-2384
    50  	calcDifficultyEip2384 = makeDifficultyCalculator(big.NewInt(9000000))
    51  
    52  	// calcDifficultyConstantinople is the difficulty adjustment algorithm for Constantinople.
    53  	// It returns the difficulty that a new block should have when created at time given the
    54  	// parent block's time and difficulty. The calculation uses the Byzantium rules, but with
    55  	// bomb offset 5M.
    56  	// Specification EIP-1234: https://eips.ethereum.org/EIPS/eip-1234
    57  	calcDifficultyConstantinople = makeDifficultyCalculator(big.NewInt(5000000))
    58  
    59  	// calcDifficultyByzantium is the difficulty adjustment algorithm. It returns
    60  	// the difficulty that a new block should have when created at time given the
    61  	// parent block's time and difficulty. The calculation uses the Byzantium rules.
    62  	// Specification EIP-649: https://eips.ethereum.org/EIPS/eip-649
    63  	calcDifficultyByzantium = makeDifficultyCalculator(big.NewInt(3000000))
    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  	errOlderBlockTime    = errors.New("timestamp older than parent")
    72  	errTooManyUncles     = errors.New("too many uncles")
    73  	errDuplicateUncle    = errors.New("duplicate uncle")
    74  	errUncleIsAncestor   = errors.New("uncle is ancestor")
    75  	errDanglingUncle     = errors.New("uncle's parent is not ancestor")
    76  	errInvalidDifficulty = errors.New("non-positive difficulty")
    77  	errInvalidMixDigest  = errors.New("invalid mix digest")
    78  	errInvalidPoW        = errors.New("invalid proof-of-work")
    79  )
    80  
    81  // Author implements consensus.Engine, returning the header's coinbase as the
    82  // proof-of-work verified author of the block.
    83  func (ethash *Ethash) Author(header *types.Header) (common.Address, error) {
    84  	return header.Coinbase, nil
    85  }
    86  
    87  // VerifyHeader checks whether a header conforms to the consensus rules of the
    88  // stock Ethereum ethash engine.
    89  func (ethash *Ethash) VerifyHeader(chain consensus.ChainReader, header *types.Header, seal bool) error {
    90  	// If we're running a full engine faking, accept any input as valid
    91  	if ethash.config.PowMode == ModeFullFake {
    92  		return nil
    93  	}
    94  	// Short circuit if the header is known, or its parent not
    95  	number := header.Number.Uint64()
    96  	if chain.GetHeader(header.Hash(), number) != nil {
    97  		return nil
    98  	}
    99  	parent := chain.GetHeader(header.ParentHash, number-1)
   100  	if parent == nil {
   101  		return consensus.ErrUnknownAncestor
   102  	}
   103  	// Sanity checks passed, do a proper verification
   104  	return ethash.verifyHeader(chain, header, parent, false, seal)
   105  }
   106  
   107  // VerifyHeaders is similar to VerifyHeader, but verifies a batch of headers
   108  // concurrently. The method returns a quit channel to abort the operations and
   109  // a results channel to retrieve the async verifications.
   110  func (ethash *Ethash) VerifyHeaders(chain consensus.ChainReader, headers []*types.Header, seals []bool) (chan<- struct{}, <-chan error) {
   111  	// If we're running a full engine faking, accept any input as valid
   112  	if ethash.config.PowMode == ModeFullFake || len(headers) == 0 {
   113  		abort, results := make(chan struct{}), make(chan error, len(headers))
   114  		for i := 0; i < len(headers); i++ {
   115  			results <- nil
   116  		}
   117  		return abort, results
   118  	}
   119  
   120  	// Spawn as many workers as allowed threads
   121  	workers := runtime.GOMAXPROCS(0)
   122  	if len(headers) < workers {
   123  		workers = len(headers)
   124  	}
   125  
   126  	// Create a task channel and spawn the verifiers
   127  	var (
   128  		inputs = make(chan int)
   129  		done   = make(chan int, workers)
   130  		errors = make([]error, len(headers))
   131  		abort  = make(chan struct{})
   132  	)
   133  	for i := 0; i < workers; i++ {
   134  		go func() {
   135  			for index := range inputs {
   136  				errors[index] = ethash.verifyHeaderWorker(chain, headers, seals, index)
   137  				done <- index
   138  			}
   139  		}()
   140  	}
   141  
   142  	errorsOut := make(chan error, len(headers))
   143  	go func() {
   144  		defer close(inputs)
   145  		var (
   146  			in, out = 0, 0
   147  			checked = make([]bool, len(headers))
   148  			inputs  = inputs
   149  		)
   150  		for {
   151  			select {
   152  			case inputs <- in:
   153  				if in++; in == len(headers) {
   154  					// Reached end of headers. Stop sending to workers.
   155  					inputs = nil
   156  				}
   157  			case index := <-done:
   158  				for checked[index] = true; checked[out]; out++ {
   159  					errorsOut <- errors[out]
   160  					if out == len(headers)-1 {
   161  						return
   162  					}
   163  				}
   164  			case <-abort:
   165  				return
   166  			}
   167  		}
   168  	}()
   169  	return abort, errorsOut
   170  }
   171  
   172  func (ethash *Ethash) verifyHeaderWorker(chain consensus.ChainReader, headers []*types.Header, seals []bool, index int) error {
   173  	var parent *types.Header
   174  	if index == 0 {
   175  		parent = chain.GetHeader(headers[0].ParentHash, headers[0].Number.Uint64()-1)
   176  	} else if headers[index-1].Hash() == headers[index].ParentHash {
   177  		parent = headers[index-1]
   178  	}
   179  	if parent == nil {
   180  		return consensus.ErrUnknownAncestor
   181  	}
   182  	if chain.GetHeader(headers[index].Hash(), headers[index].Number.Uint64()) != nil {
   183  		return nil // known block
   184  	}
   185  	return ethash.verifyHeader(chain, headers[index], parent, false, seals[index])
   186  }
   187  
   188  // VerifyUncles verifies that the given block's uncles conform to the consensus
   189  // rules of the stock Ethereum ethash engine.
   190  func (ethash *Ethash) VerifyUncles(chain consensus.ChainReader, block *types.Block) error {
   191  	// If we're running a full engine faking, accept any input as valid
   192  	if ethash.config.PowMode == ModeFullFake {
   193  		return nil
   194  	}
   195  	// Verify that there are at most 2 uncles included in this block
   196  	if len(block.Uncles()) > maxUncles {
   197  		return errTooManyUncles
   198  	}
   199  	if len(block.Uncles()) == 0 {
   200  		return nil
   201  	}
   202  	// Gather the set of past uncles and ancestors
   203  	uncles, ancestors := mapset.NewSet(), make(map[common.Hash]*types.Header)
   204  
   205  	number, parent := block.NumberU64()-1, block.ParentHash()
   206  	for i := 0; i < 7; i++ {
   207  		ancestor := chain.GetBlock(parent, number)
   208  		if ancestor == nil {
   209  			break
   210  		}
   211  		ancestors[ancestor.Hash()] = ancestor.Header()
   212  		for _, uncle := range ancestor.Uncles() {
   213  			uncles.Add(uncle.Hash())
   214  		}
   215  		parent, number = ancestor.ParentHash(), number-1
   216  	}
   217  	ancestors[block.Hash()] = block.Header()
   218  	uncles.Add(block.Hash())
   219  
   220  	// Verify each of the uncles that it's recent, but not an ancestor
   221  	for _, uncle := range block.Uncles() {
   222  		// Make sure every uncle is rewarded only once
   223  		hash := uncle.Hash()
   224  		if uncles.Contains(hash) {
   225  			return errDuplicateUncle
   226  		}
   227  		uncles.Add(hash)
   228  
   229  		// Make sure the uncle has a valid ancestry
   230  		if ancestors[hash] != nil {
   231  			return errUncleIsAncestor
   232  		}
   233  		if ancestors[uncle.ParentHash] == nil || uncle.ParentHash == block.ParentHash() {
   234  			return errDanglingUncle
   235  		}
   236  		if err := ethash.verifyHeader(chain, uncle, ancestors[uncle.ParentHash], true, true); err != nil {
   237  			return err
   238  		}
   239  	}
   240  	return nil
   241  }
   242  
   243  // verifyHeader checks whether a header conforms to the consensus rules of the
   244  // stock Ethereum ethash engine.
   245  // See YP section 4.3.4. "Block Header Validity"
   246  func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *types.Header, uncle bool, seal bool) error {
   247  	// Ensure that the header's extra-data section is of a reasonable size
   248  	if uint64(len(header.Extra)) > params.MaximumExtraDataSize {
   249  		return fmt.Errorf("extra-data too long: %d > %d", len(header.Extra), params.MaximumExtraDataSize)
   250  	}
   251  	// Verify the header's timestamp
   252  	if !uncle {
   253  		if header.Time > uint64(time.Now().Add(allowedFutureBlockTime).Unix()) {
   254  			return consensus.ErrFutureBlock
   255  		}
   256  	}
   257  	if header.Time <= parent.Time {
   258  		return errOlderBlockTime
   259  	}
   260  	// Verify the block's difficulty based on its timestamp and parent's difficulty
   261  	expected := ethash.CalcDifficulty(chain, header.Time, parent)
   262  
   263  	if expected.Cmp(header.Difficulty) != 0 {
   264  		return fmt.Errorf("invalid difficulty: have %v, want %v", header.Difficulty, expected)
   265  	}
   266  	// Verify that the gas limit is <= 2^63-1
   267  	cap := uint64(0x7fffffffffffffff)
   268  	if header.GasLimit > cap {
   269  		return fmt.Errorf("invalid gasLimit: have %v, max %v", header.GasLimit, cap)
   270  	}
   271  	// Verify that the gasUsed is <= gasLimit
   272  	if header.GasUsed > header.GasLimit {
   273  		return fmt.Errorf("invalid gasUsed: have %d, gasLimit %d", header.GasUsed, header.GasLimit)
   274  	}
   275  
   276  	// Verify that the gas limit remains within allowed bounds
   277  	diff := int64(parent.GasLimit) - int64(header.GasLimit)
   278  	if diff < 0 {
   279  		diff *= -1
   280  	}
   281  	limit := parent.GasLimit / params.GasLimitBoundDivisor
   282  
   283  	if uint64(diff) >= limit || header.GasLimit < params.MinGasLimit {
   284  		return fmt.Errorf("invalid gas limit: have %d, want %d += %d", header.GasLimit, parent.GasLimit, limit)
   285  	}
   286  	// Verify that the block number is parent's +1
   287  	if diff := new(big.Int).Sub(header.Number, parent.Number); diff.Cmp(big.NewInt(1)) != 0 {
   288  		return consensus.ErrInvalidNumber
   289  	}
   290  	// Verify the engine specific seal securing the block
   291  	if seal {
   292  		if err := ethash.VerifySeal(chain, header); err != nil {
   293  			return err
   294  		}
   295  	}
   296  	// If all checks passed, validate any special fields for hard forks
   297  	if err := misc.VerifyDAOHeaderExtraData(chain.Config(), header); err != nil {
   298  		return err
   299  	}
   300  	if err := misc.VerifyForkHashes(chain.Config(), header, uncle); err != nil {
   301  		return err
   302  	}
   303  	return nil
   304  }
   305  
   306  // CalcDifficulty is the difficulty adjustment algorithm. It returns
   307  // the difficulty that a new block should have when created at time
   308  // given the parent block's time and difficulty.
   309  func (ethash *Ethash) CalcDifficulty(chain consensus.ChainReader, time uint64, parent *types.Header) *big.Int {
   310  	return CalcDifficulty(chain.Config(), time, parent)
   311  }
   312  
   313  // CalcDifficulty is the difficulty adjustment algorithm. It returns
   314  // the difficulty that a new block should have when created at time
   315  // given the parent block's time and difficulty.
   316  func CalcDifficulty(config *params.ChainConfig, time uint64, parent *types.Header) *big.Int {
   317  	next := new(big.Int).Add(parent.Number, big1)
   318  	switch {
   319  	case config.IsMuirGlacier(next):
   320  		return calcDifficultyEip2384(time, parent)
   321  	case config.IsConstantinople(next):
   322  		return calcDifficultyConstantinople(time, parent)
   323  	case config.IsByzantium(next):
   324  		return calcDifficultyByzantium(time, parent)
   325  	case config.IsHomestead(next):
   326  		return calcDifficultyHomestead(time, parent)
   327  	default:
   328  		return calcDifficultyFrontier(time, parent)
   329  	}
   330  }
   331  
   332  // Some weird constants to avoid constant memory allocs for them.
   333  var (
   334  	expDiffPeriod = big.NewInt(100000)
   335  	big1          = big.NewInt(1)
   336  	big2          = big.NewInt(2)
   337  	big9          = big.NewInt(9)
   338  	big10         = big.NewInt(10)
   339  	bigMinus99    = big.NewInt(-99)
   340  )
   341  
   342  // makeDifficultyCalculator creates a difficultyCalculator with the given bomb-delay.
   343  // the difficulty is calculated with Byzantium rules, which differs from Homestead in
   344  // how uncles affect the calculation
   345  func makeDifficultyCalculator(bombDelay *big.Int) func(time uint64, parent *types.Header) *big.Int {
   346  	// Note, the calculations below looks at the parent number, which is 1 below
   347  	// the block number. Thus we remove one from the delay given
   348  	bombDelayFromParent := new(big.Int).Sub(bombDelay, big1)
   349  	return func(time uint64, parent *types.Header) *big.Int {
   350  		// https://github.com/ethereum/EIPs/issues/100.
   351  		// algorithm:
   352  		// diff = (parent_diff +
   353  		//         (parent_diff / 2048 * max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99))
   354  		//        ) + 2^(periodCount - 2)
   355  
   356  		bigTime := new(big.Int).SetUint64(time)
   357  		bigParentTime := new(big.Int).SetUint64(parent.Time)
   358  
   359  		// holds intermediate values to make the algo easier to read & audit
   360  		x := new(big.Int)
   361  		y := new(big.Int)
   362  
   363  		// (2 if len(parent_uncles) else 1) - (block_timestamp - parent_timestamp) // 9
   364  		x.Sub(bigTime, bigParentTime)
   365  		x.Div(x, big9)
   366  		if parent.UncleHash == types.EmptyUncleHash {
   367  			x.Sub(big1, x)
   368  		} else {
   369  			x.Sub(big2, x)
   370  		}
   371  		// max((2 if len(parent_uncles) else 1) - (block_timestamp - parent_timestamp) // 9, -99)
   372  		if x.Cmp(bigMinus99) < 0 {
   373  			x.Set(bigMinus99)
   374  		}
   375  		// parent_diff + (parent_diff / 2048 * max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99))
   376  		y.Div(parent.Difficulty, params.DifficultyBoundDivisor)
   377  		x.Mul(y, x)
   378  		x.Add(parent.Difficulty, x)
   379  
   380  		// minimum difficulty can ever be (before exponential factor)
   381  		if x.Cmp(params.MinimumDifficulty) < 0 {
   382  			x.Set(params.MinimumDifficulty)
   383  		}
   384  		// calculate a fake block number for the ice-age delay
   385  		// Specification: https://eips.ethereum.org/EIPS/eip-1234
   386  		fakeBlockNumber := new(big.Int)
   387  		if parent.Number.Cmp(bombDelayFromParent) >= 0 {
   388  			fakeBlockNumber = fakeBlockNumber.Sub(parent.Number, bombDelayFromParent)
   389  		}
   390  		// for the exponential factor
   391  		periodCount := fakeBlockNumber
   392  		periodCount.Div(periodCount, expDiffPeriod)
   393  
   394  		// the exponential factor, commonly referred to as "the bomb"
   395  		// diff = diff + 2^(periodCount - 2)
   396  		if periodCount.Cmp(big1) > 0 {
   397  			y.Sub(periodCount, big2)
   398  			y.Exp(big2, y, nil)
   399  			x.Add(x, y)
   400  		}
   401  		return x
   402  	}
   403  }
   404  
   405  // calcDifficultyHomestead is the difficulty adjustment algorithm. It returns
   406  // the difficulty that a new block should have when created at time given the
   407  // parent block's time and difficulty. The calculation uses the Homestead rules.
   408  func calcDifficultyHomestead(time uint64, parent *types.Header) *big.Int {
   409  	// https://github.com/ethereum/EIPs/blob/master/EIPS/eip-2.md
   410  	// algorithm:
   411  	// diff = (parent_diff +
   412  	//         (parent_diff / 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99))
   413  	//        ) + 2^(periodCount - 2)
   414  
   415  	bigTime := new(big.Int).SetUint64(time)
   416  	bigParentTime := new(big.Int).SetUint64(parent.Time)
   417  
   418  	// holds intermediate values to make the algo easier to read & audit
   419  	x := new(big.Int)
   420  	y := new(big.Int)
   421  
   422  	// 1 - (block_timestamp - parent_timestamp) // 10
   423  	x.Sub(bigTime, bigParentTime)
   424  	x.Div(x, big10)
   425  	x.Sub(big1, x)
   426  
   427  	// max(1 - (block_timestamp - parent_timestamp) // 10, -99)
   428  	if x.Cmp(bigMinus99) < 0 {
   429  		x.Set(bigMinus99)
   430  	}
   431  	// (parent_diff + parent_diff // 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99))
   432  	y.Div(parent.Difficulty, params.DifficultyBoundDivisor)
   433  	x.Mul(y, x)
   434  	x.Add(parent.Difficulty, x)
   435  
   436  	// minimum difficulty can ever be (before exponential factor)
   437  	if x.Cmp(params.MinimumDifficulty) < 0 {
   438  		x.Set(params.MinimumDifficulty)
   439  	}
   440  	// for the exponential factor
   441  	periodCount := new(big.Int).Add(parent.Number, big1)
   442  	periodCount.Div(periodCount, expDiffPeriod)
   443  
   444  	// the exponential factor, commonly referred to as "the bomb"
   445  	// diff = diff + 2^(periodCount - 2)
   446  	if periodCount.Cmp(big1) > 0 {
   447  		y.Sub(periodCount, big2)
   448  		y.Exp(big2, y, nil)
   449  		x.Add(x, y)
   450  	}
   451  	return x
   452  }
   453  
   454  // calcDifficultyFrontier is the difficulty adjustment algorithm. It returns the
   455  // difficulty that a new block should have when created at time given the parent
   456  // block's time and difficulty. The calculation uses the Frontier rules.
   457  func calcDifficultyFrontier(time uint64, parent *types.Header) *big.Int {
   458  	diff := new(big.Int)
   459  	adjust := new(big.Int).Div(parent.Difficulty, params.DifficultyBoundDivisor)
   460  	bigTime := new(big.Int)
   461  	bigParentTime := new(big.Int)
   462  
   463  	bigTime.SetUint64(time)
   464  	bigParentTime.SetUint64(parent.Time)
   465  
   466  	if bigTime.Sub(bigTime, bigParentTime).Cmp(params.DurationLimit) < 0 {
   467  		diff.Add(parent.Difficulty, adjust)
   468  	} else {
   469  		diff.Sub(parent.Difficulty, adjust)
   470  	}
   471  	if diff.Cmp(params.MinimumDifficulty) < 0 {
   472  		diff.Set(params.MinimumDifficulty)
   473  	}
   474  
   475  	periodCount := new(big.Int).Add(parent.Number, big1)
   476  	periodCount.Div(periodCount, expDiffPeriod)
   477  	if periodCount.Cmp(big1) > 0 {
   478  		// diff = diff + 2^(periodCount - 2)
   479  		expDiff := periodCount.Sub(periodCount, big2)
   480  		expDiff.Exp(big2, expDiff, nil)
   481  		diff.Add(diff, expDiff)
   482  		diff = math.BigMax(diff, params.MinimumDifficulty)
   483  	}
   484  	return diff
   485  }
   486  
   487  // VerifySeal implements consensus.Engine, checking whether the given block satisfies
   488  // the PoW difficulty requirements.
   489  func (ethash *Ethash) VerifySeal(chain consensus.ChainReader, header *types.Header) error {
   490  	return ethash.verifySeal(chain, header, false)
   491  }
   492  
   493  // verifySeal checks whether a block satisfies the PoW difficulty requirements,
   494  // either using the usual ethash cache for it, or alternatively using a full DAG
   495  // to make remote mining fast.
   496  func (ethash *Ethash) verifySeal(chain consensus.ChainReader, header *types.Header, fulldag bool) error {
   497  	// If we're running a fake PoW, accept any seal as valid
   498  	if ethash.config.PowMode == ModeFake || ethash.config.PowMode == ModeFullFake {
   499  		time.Sleep(ethash.fakeDelay)
   500  		if ethash.fakeFail == header.Number.Uint64() {
   501  			return errInvalidPoW
   502  		}
   503  		return nil
   504  	}
   505  	// If we're running a shared PoW, delegate verification to it
   506  	if ethash.shared != nil {
   507  		return ethash.shared.verifySeal(chain, header, fulldag)
   508  	}
   509  	// Ensure that we have a valid difficulty for the block
   510  	if header.Difficulty.Sign() <= 0 {
   511  		return errInvalidDifficulty
   512  	}
   513  	// Recompute the digest and PoW values
   514  	number := header.Number.Uint64()
   515  
   516  	var (
   517  		digest []byte
   518  		result []byte
   519  	)
   520  	// If fast-but-heavy PoW verification was requested, use an ethash dataset
   521  	if fulldag {
   522  		dataset := ethash.dataset(number, true)
   523  		if dataset.generated() {
   524  			digest, result = hashimotoFull(dataset.dataset, ethash.SealHash(header).Bytes(), header.Nonce.Uint64())
   525  
   526  			// Datasets are unmapped in a finalizer. Ensure that the dataset stays alive
   527  			// until after the call to hashimotoFull so it's not unmapped while being used.
   528  			runtime.KeepAlive(dataset)
   529  		} else {
   530  			// Dataset not yet generated, don't hang, use a cache instead
   531  			fulldag = false
   532  		}
   533  	}
   534  	// If slow-but-light PoW verification was requested (or DAG not yet ready), use an ethash cache
   535  	if !fulldag {
   536  		cache := ethash.cache(number)
   537  
   538  		size := datasetSize(number)
   539  		if ethash.config.PowMode == ModeTest {
   540  			size = 32 * 1024
   541  		}
   542  		digest, result = hashimotoLight(size, cache.cache, ethash.SealHash(header).Bytes(), header.Nonce.Uint64())
   543  
   544  		// Caches are unmapped in a finalizer. Ensure that the cache stays alive
   545  		// until after the call to hashimotoLight so it's not unmapped while being used.
   546  		runtime.KeepAlive(cache)
   547  	}
   548  	// Verify the calculated values against the ones provided in the header
   549  	if !bytes.Equal(header.MixDigest[:], digest) {
   550  		return errInvalidMixDigest
   551  	}
   552  	target := new(big.Int).Div(two256, header.Difficulty)
   553  	if new(big.Int).SetBytes(result).Cmp(target) > 0 {
   554  		return errInvalidPoW
   555  	}
   556  	return nil
   557  }
   558  
   559  // Prepare implements consensus.Engine, initializing the difficulty field of a
   560  // header to conform to the ethash protocol. The changes are done inline.
   561  func (ethash *Ethash) Prepare(chain consensus.ChainReader, header *types.Header) error {
   562  	parent := chain.GetHeader(header.ParentHash, header.Number.Uint64()-1)
   563  	if parent == nil {
   564  		return consensus.ErrUnknownAncestor
   565  	}
   566  	header.Difficulty = ethash.CalcDifficulty(chain, header.Time, parent)
   567  	return nil
   568  }
   569  
   570  // Finalize implements consensus.Engine, accumulating the block and uncle rewards,
   571  // setting the final state on the header
   572  func (ethash *Ethash) Finalize(chain consensus.ChainReader, header *types.Header, state *state.StateDB, txs *[]*types.Transaction, uncles []*types.Header,
   573  	receipts *[]*types.Receipt, _ *[]*types.Transaction, _ *uint64) (err error) {
   574  	// Accumulate any block and uncle rewards and commit the final state root
   575  	accumulateRewards(chain.Config(), state, header, uncles)
   576  	header.Root = state.IntermediateRoot(chain.Config().IsEIP158(header.Number))
   577  	return
   578  }
   579  
   580  // FinalizeAndAssemble implements consensus.Engine, accumulating the block and
   581  // uncle rewards, setting the final state and assembling the block.
   582  func (ethash *Ethash) FinalizeAndAssemble(chain consensus.ChainReader, header *types.Header, state *state.StateDB,
   583  	txs []*types.Transaction, uncles []*types.Header, receipts []*types.Receipt) (*types.Block, []*types.Receipt, error) {
   584  	// Accumulate any block and uncle rewards and commit the final state root
   585  	accumulateRewards(chain.Config(), state, header, uncles)
   586  	header.Root = state.IntermediateRoot(chain.Config().IsEIP158(header.Number))
   587  
   588  	// Header seems complete, assemble into a block and return
   589  	return types.NewBlock(header, txs, uncles, receipts), receipts, nil
   590  }
   591  
   592  // SealHash returns the hash of a block prior to it being sealed.
   593  func (ethash *Ethash) SealHash(header *types.Header) (hash common.Hash) {
   594  	hasher := sha3.NewLegacyKeccak256()
   595  
   596  	rlp.Encode(hasher, []interface{}{
   597  		header.ParentHash,
   598  		header.UncleHash,
   599  		header.Coinbase,
   600  		header.Root,
   601  		header.TxHash,
   602  		header.ReceiptHash,
   603  		header.Bloom,
   604  		header.Difficulty,
   605  		header.Number,
   606  		header.GasLimit,
   607  		header.GasUsed,
   608  		header.Time,
   609  		header.Extra,
   610  	})
   611  	hasher.Sum(hash[:0])
   612  	return hash
   613  }
   614  
   615  // Some weird constants to avoid constant memory allocs for them.
   616  var (
   617  	big8  = big.NewInt(8)
   618  	big32 = big.NewInt(32)
   619  )
   620  
   621  // AccumulateRewards credits the coinbase of the given block with the mining
   622  // reward. The total reward consists of the static block reward and rewards for
   623  // included uncles. The coinbase of each uncle block is also rewarded.
   624  func accumulateRewards(config *params.ChainConfig, state *state.StateDB, header *types.Header, uncles []*types.Header) {
   625  	// Select the correct block reward based on chain progression
   626  	blockReward := FrontierBlockReward
   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  }