ethash: less copy-paste for EIP 1234

consensus/ethash/consensus.go

@@ -43,6 +43,16 @@ var (
 	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
+
+	// calcDifficultyConstantinople is the difficulty adjustment algorithm for Constantinople.
+	// 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, but with bomb offset 5M.
+	calcDifficultyConstantinople = makeDifficultyCalculator(big.NewInt(4999999))
+
+	// 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.
+	calcDifficultyByzantium = makeDifficultyCalculator(big.NewInt(2999999))
 )
 
 // Various error messages to mark blocks invalid. These should be private to
@@ -319,73 +329,13 @@ var (
 	big9          = big.NewInt(9)
 	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.
-func calcDifficultyByzantium(time uint64, parent *types.Header) *big.Int {
+// makeDifficultyCalculator creates a difficultyCalculator with the given bomb-delay.
+// the difficulty is calculated with Byzantium rules, which differs from Homestead in
+// how uncles affect the calculation
+func makeDifficultyCalculator(bombDelay *big.Int) func(time uint64, parent *types.Header) *big.Int {
+	return func(time uint64, parent *types.Header) *big.Int {
 		// https://github.com/ethereum/EIPs/issues/100.
 		// algorithm:
 		// diff = (parent_diff +
@@ -424,8 +374,8 @@ func calcDifficultyByzantium(time uint64, parent *types.Header) *big.Int {
 		// https://github.com/ethereum/EIPs/pull/669
 		// fake_block_number = max(0, block.number - 3_000_000)
 		fakeBlockNumber := new(big.Int)
-	if parent.Number.Cmp(big2999999) >= 0 {
-		fakeBlockNumber = fakeBlockNumber.Sub(parent.Number, big2999999) // Note, parent is 1 less than the actual block number
+		if parent.Number.Cmp(bombDelay) >= 0 {
+			fakeBlockNumber = fakeBlockNumber.Sub(parent.Number, bombDelay) // Note, parent is 1 less than the actual block number
 		}
 		// for the exponential factor
 		periodCount := fakeBlockNumber
@@ -439,6 +389,7 @@ func calcDifficultyByzantium(time uint64, parent *types.Header) *big.Int {
 			x.Add(x, y)
 		}
 		return x
+	}
 }
 
 // calcDifficultyHomestead is the difficulty adjustment algorithm. It returns