consensus: implement Constantinople EIP 1234

consensus/ethash/consensus.go

@@ -40,6 +40,7 @@ import (
 var (
 	FrontierBlockReward       = big.NewInt(5e+18) // Block reward in wei for successfully mining a block
 	ByzantiumBlockReward      = big.NewInt(3e+18) // Block reward in wei for successfully mining a block upward from Byzantium
+	ConstantinopleBlockReward = big.NewInt(2e+18) // Block reward in wei for successfully mining a block upward from Constantinople
 	maxUncles                 = 2                 // Maximum number of uncles allowed in a single block
 	allowedFutureBlockTime    = 15 * time.Second  // Max time from current time allowed for blocks, before they're considered future blocks
 )
@@ -299,6 +300,8 @@ func (ethash *Ethash) CalcDifficulty(chain consensus.ChainReader, time uint64, p
 func CalcDifficulty(config *params.ChainConfig, time uint64, parent *types.Header) *big.Int {
 	next := new(big.Int).Add(parent.Number, big1)
 	switch {
+	case config.IsConstantinople(next):
+		return calcDifficultyConstantinople(time, parent)
 	case config.IsByzantium(next):
 		return calcDifficultyByzantium(time, parent)
 	case config.IsHomestead(next):
@@ -317,8 +320,68 @@ var (
 	big10         = big.NewInt(10)
 	bigMinus99    = big.NewInt(-99)
 	big2999999    = big.NewInt(2999999)
+	big4999999    = big.NewInt(4999999)
 )
 
+// calcDifficultyConstantinople 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 Constantinople rules.
+func calcDifficultyConstantinople(time uint64, parent *types.Header) *big.Int {
+	// https://github.com/ethereum/EIPs/issues/100.
+	// algorithm:
+	// diff = (parent_diff +
+	//         (parent_diff / 2048 * max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99))
+	//        ) + 2^(periodCount - 2)
+
+	bigTime := new(big.Int).SetUint64(time)
+	bigParentTime := new(big.Int).Set(parent.Time)
+
+	// holds intermediate values to make the algo easier to read & audit
+	x := new(big.Int)
+	y := new(big.Int)
+
+	// (2 if len(parent_uncles) else 1) - (block_timestamp - parent_timestamp) // 9
+	x.Sub(bigTime, bigParentTime)
+	x.Div(x, big9)
+	if parent.UncleHash == types.EmptyUncleHash {
+		x.Sub(big1, x)
+	} else {
+		x.Sub(big2, x)
+	}
+	// max((2 if len(parent_uncles) else 1) - (block_timestamp - parent_timestamp) // 9, -99)
+	if x.Cmp(bigMinus99) < 0 {
+		x.Set(bigMinus99)
+	}
+	// parent_diff + (parent_diff / 2048 * max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99))
+	y.Div(parent.Difficulty, params.DifficultyBoundDivisor)
+	x.Mul(y, x)
+	x.Add(parent.Difficulty, x)
+
+	// minimum difficulty can ever be (before exponential factor)
+	if x.Cmp(params.MinimumDifficulty) < 0 {
+		x.Set(params.MinimumDifficulty)
+	}
+	// calculate a fake block number for the ice-age delay:
+	// https://github.com/ethereum/EIPs/pull/1234
+	// fake_block_number = max(0, block.number - 5_000_000)
+	fakeBlockNumber := new(big.Int)
+	if parent.Number.Cmp(big4999999) >= 0 {
+		fakeBlockNumber = fakeBlockNumber.Sub(parent.Number, big4999999) // Note, parent is 1 less than the actual block number
+	}
+	// for the exponential factor
+	periodCount := fakeBlockNumber
+	periodCount.Div(periodCount, expDiffPeriod)
+
+	// the exponential factor, commonly referred to as "the bomb"
+	// diff = diff + 2^(periodCount - 2)
+	if periodCount.Cmp(big1) > 0 {
+		y.Sub(periodCount, big2)
+		y.Exp(big2, y, nil)
+		x.Add(x, y)
+	}
+	return x
+}
+
 // calcDifficultyByzantium 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 Byzantium rules.
@@ -592,6 +655,9 @@ func accumulateRewards(config *params.ChainConfig, state *state.StateDB, header
 	if config.IsByzantium(header.Number) {
 		blockReward = ByzantiumBlockReward
 	}
+	if config.IsConstantinople(header.Number) {
+		blockReward = ConstantinopleBlockReward
+	}
 	// Accumulate the rewards for the miner and any included uncles
 	reward := new(big.Int).Set(blockReward)
 	r := new(big.Int)