consensus, core/*, params: metropolis preparation refactor

This commit is a preparation for the upcoming metropolis hardfork. It
prepares the state, core and vm packages such that integration with
metropolis becomes less of a hassle.

* Difficulty calculation requires header instead of individual
  parameters
* statedb.StartRecord renamed to statedb.Prepare and added Finalise
  method required by metropolis, which removes unwanted accounts from
  the state (i.e. selfdestruct)
* State keeps record of destructed objects (in addition to dirty
  objects)
* core/vm pre-compiles may now return errors
* core/vm pre-compiles gas check now take the full byte slice as argument
  instead of just the size
* core/vm now keeps several hard-fork instruction tables instead of a
  single instruction table and removes the need for hard-fork checks in
  the instructions
* core/vm contains a empty restruction function which is added in
  preparation of metropolis write-only mode operations
* Adds the bn256 curve
* Adds and sets the metropolis chain config block parameters (2^64-1)

2 files changed, 30 insertions, 23 deletions

diff --git a/consensus/ethash/consensus.go b/consensus/ethash/consensus.go
index 2930032e5..d02542224 100644
--- a/consensus/ethash/consensus.go
+++ b/consensus/ethash/consensus.go
@@ -239,7 +239,7 @@ func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *
 		return errZeroBlockTime
 	}
 	// Verify the block's difficulty based in it's timestamp and parent's difficulty
-	expected := CalcDifficulty(chain.Config(), header.Time.Uint64(), parent.Time.Uint64(), parent.Number, parent.Difficulty)
+	expected := CalcDifficulty(chain.Config(), header.Time.Uint64(), parent)
 	if expected.Cmp(header.Difficulty) != 0 {
 		return fmt.Errorf("invalid difficulty: have %v, want %v", header.Difficulty, expected)
 	}
@@ -283,16 +283,19 @@ func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *
 	return nil
 }
 
-// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
-// that a new block should have when created at time given the parent block's time
-// and difficulty.
+// CalcDifficulty is the difficulty adjustment algorithm. It returns
+// the difficulty that a new block should have when created at time
+// given the parent block's time and difficulty.
 //
 // TODO (karalabe): Move the chain maker into this package and make this private!
-func CalcDifficulty(config *params.ChainConfig, time, parentTime uint64, parentNumber, parentDiff *big.Int) *big.Int {
-	if config.IsHomestead(new(big.Int).Add(parentNumber, common.Big1)) {
-		return calcDifficultyHomestead(time, parentTime, parentNumber, parentDiff)
+func CalcDifficulty(config *params.ChainConfig, time uint64, parent *types.Header) *big.Int {
+	next := new(big.Int).Add(parent.Number, common.Big1)
+	switch {
+	case config.IsHomestead(next):
+		return calcDifficultyHomestead(time, parent)
+	default:
+		return calcDifficultyFrontier(time, parent)
 	}
-	return calcDifficultyFrontier(time, parentTime, parentNumber, parentDiff)
 }
 
 // Some weird constants to avoid constant memory allocs for them.
@@ -305,15 +308,15 @@ var (
 // calcDifficultyHomestead is the difficulty adjustment algorithm. It returns
 // the difficulty that a new block should have when created at time given the
 // parent block's time and difficulty. The calculation uses the Homestead rules.
-func calcDifficultyHomestead(time, parentTime uint64, parentNumber, parentDiff *big.Int) *big.Int {
+func calcDifficultyHomestead(time uint64, parent *types.Header) *big.Int {
 	// https://github.com/ethereum/EIPs/blob/master/EIPS/eip-2.mediawiki
 	// algorithm:
 	// diff = (parent_diff +
 	//         (parent_diff / 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99))
 	//        ) + 2^(periodCount - 2)
 
-	bigTime := new(big.Int).SetUint64(time)
-	bigParentTime := new(big.Int).SetUint64(parentTime)
+	bigTime := new(big.Int).Set(parent.Time)
+	bigParentTime := new(big.Int).Set(parent.Time)
 
 	// holds intermediate values to make the algo easier to read & audit
 	x := new(big.Int)
@@ -329,16 +332,16 @@ func calcDifficultyHomestead(time, parentTime uint64, parentNumber, parentDiff *
 		x.Set(bigMinus99)
 	}
 	// (parent_diff + parent_diff // 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99))
-	y.Div(parentDiff, params.DifficultyBoundDivisor)
+	y.Div(parent.Difficulty, params.DifficultyBoundDivisor)
 	x.Mul(y, x)
-	x.Add(parentDiff, x)
+	x.Add(parent.Difficulty, x)
 
 	// minimum difficulty can ever be (before exponential factor)
 	if x.Cmp(params.MinimumDifficulty) < 0 {
 		x.Set(params.MinimumDifficulty)
 	}
 	// for the exponential factor
-	periodCount := new(big.Int).Add(parentNumber, common.Big1)
+	periodCount := new(big.Int).Add(parent.Number, common.Big1)
 	periodCount.Div(periodCount, expDiffPeriod)
 
 	// the exponential factor, commonly referred to as "the bomb"
@@ -354,25 +357,25 @@ func calcDifficultyHomestead(time, parentTime uint64, parentNumber, parentDiff *
 // calcDifficultyFrontier is the difficulty adjustment algorithm. It returns the
 // difficulty that a new block should have when created at time given the parent
 // block's time and difficulty. The calculation uses the Frontier rules.
-func calcDifficultyFrontier(time, parentTime uint64, parentNumber, parentDiff *big.Int) *big.Int {
+func calcDifficultyFrontier(time uint64, parent *types.Header) *big.Int {
 	diff := new(big.Int)
-	adjust := new(big.Int).Div(parentDiff, params.DifficultyBoundDivisor)
+	adjust := new(big.Int).Div(parent.Difficulty, params.DifficultyBoundDivisor)
 	bigTime := new(big.Int)
 	bigParentTime := new(big.Int)
 
 	bigTime.SetUint64(time)
-	bigParentTime.SetUint64(parentTime)
+	bigParentTime.Set(parent.Time)
 
 	if bigTime.Sub(bigTime, bigParentTime).Cmp(params.DurationLimit) < 0 {
-		diff.Add(parentDiff, adjust)
+		diff.Add(parent.Difficulty, adjust)
 	} else {
-		diff.Sub(parentDiff, adjust)
+		diff.Sub(parent.Difficulty, adjust)
 	}
 	if diff.Cmp(params.MinimumDifficulty) < 0 {
 		diff.Set(params.MinimumDifficulty)
 	}
 
-	periodCount := new(big.Int).Add(parentNumber, common.Big1)
+	periodCount := new(big.Int).Add(parent.Number, common.Big1)
 	periodCount.Div(periodCount, expDiffPeriod)
 	if periodCount.Cmp(common.Big1) > 0 {
 		// diff = diff + 2^(periodCount - 2)
@@ -434,8 +437,7 @@ func (ethash *Ethash) Prepare(chain consensus.ChainReader, header *types.Header)
 	if parent == nil {
 		return consensus.ErrUnknownAncestor
 	}
-	header.Difficulty = CalcDifficulty(chain.Config(), header.Time.Uint64(),
-		parent.Time.Uint64(), parent.Number, parent.Difficulty)
+	header.Difficulty = CalcDifficulty(chain.Config(), header.Time.Uint64(), parent)
 
 	return nil
 }
diff --git a/consensus/ethash/consensus_test.go b/consensus/ethash/consensus_test.go
index 683c10be4..78464bd22 100644
--- a/consensus/ethash/consensus_test.go
+++ b/consensus/ethash/consensus_test.go
@@ -23,6 +23,7 @@ import (
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common/math"
+	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/params"
 )
 
@@ -71,7 +72,11 @@ func TestCalcDifficulty(t *testing.T) {
 	config := &params.ChainConfig{HomesteadBlock: big.NewInt(1150000)}
 	for name, test := range tests {
 		number := new(big.Int).Sub(test.CurrentBlocknumber, big.NewInt(1))
-		diff := CalcDifficulty(config, test.CurrentTimestamp, test.ParentTimestamp, number, test.ParentDifficulty)
+		diff := CalcDifficulty(config, test.CurrentTimestamp, &types.Header{
+			Number:     number,
+			Time:       test.ParentTimestamp,
+			Difficulty: test.ParentDifficulty,
+		})
 		if diff.Cmp(test.CurrentDifficulty) != 0 {
 			t.Error(name, "failed. Expected", test.CurrentDifficulty, "and calculated", diff)
 		}