github.com/aquanetwork/aquachain@v1.7.8/consensus/aquahash/difficulty.go

package aquahash

import (
	"math/big"

	"gitlab.com/aquachain/aquachain/common/math"
	"gitlab.com/aquachain/aquachain/core/types"
	"gitlab.com/aquachain/aquachain/params"
)

// Some weird constants to avoid constant memory allocs for them.
var (
	expDiffPeriod = big.NewInt(100000)
	big1          = big.NewInt(1)
	big2          = big.NewInt(2)
	big10         = big.NewInt(10)
	big240        = big.NewInt(240)
	bigMinus99    = big.NewInt(-99)
	big10000      = big.NewInt(10000)
)

// 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 uint64, parent *types.Header, chainID uint64) *big.Int {
	// https://github.com/aquanetwork/EIPs/blob/master/EIPS/eip-2.md
	// 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).Set(parent.Time)

	// holds intermediate values to make the algo easier to read & audit
	x := new(big.Int)
	y := new(big.Int)

	// 1 - (block_timestamp - parent_timestamp) // 10
	x.Sub(bigTime, bigParentTime)
	x.Div(x, big10)
	x.Sub(big1, x)

	// max(1 - (block_timestamp - parent_timestamp) // 10, -99)
	if x.Cmp(bigMinus99) < 0 {
		x.Set(bigMinus99)
	}
	// (parent_diff + parent_diff // 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99))
	y.Div(parent.Difficulty, params.DifficultyBoundDivisor)
	x.Mul(y, x)
	x.Add(parent.Difficulty, x)

	// testnet no minimum
	if chainID == params.MainnetChainConfig.ChainId.Uint64() {
		x = math.BigMax(x, params.MinimumDifficultyGenesis)
	}
	return x
}

// calcDifficultyHF1 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 modified Homestead rules.
// It is flawed, target 10 seconds
func calcDifficultyHF1(time uint64, parent *types.Header, chainID uint64) *big.Int {
	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)

	// 1 - (block_timestamp - parent_timestamp) // 10
	x.Sub(bigTime, bigParentTime)
	x.Div(x, big10)
	x.Sub(big1, x)

	// max(1 - (block_timestamp - parent_timestamp) // 10, -99)
	if x.Cmp(bigMinus99) < 0 {
		x.Set(bigMinus99)
	}
	// (parent_diff + parent_diff // 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -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 chainID == params.MainnetChainConfig.ChainId.Uint64() {
		x = math.BigMax(x, params.MinimumDifficultyHF1)
	}
	return x
}

// calcDifficultyHFX combines all difficulty algorithms
func calcDifficultyHFX(config *params.ChainConfig, time uint64, parent, grandparent *types.Header) *big.Int {
	var (
		diff          = new(big.Int)
		next          = new(big.Int).Add(parent.Number, big1)
		chainID       = config.ChainId.Uint64()
		hf            = config.UseHF(next)
		adjust        *big.Int
		bigTime       = new(big.Int)
		bigParentTime = new(big.Int)
		limit         = params.DurationLimitHF6 // target 240 seconds
		min           = params.MinimumDifficultyHF5
		mainnet       = params.MainnetChainConfig.ChainId.Uint64() == chainID // bool
	)
	if !mainnet {
		min = params.MinimumDifficultyHF5Testnet
	}

	if hf > params.KnownHF {
		panic("unknown HF not implemented")
	}

	switch hf {
	case 9:
		return calcDifficultyGrandparent(time, parent, grandparent, hf, chainID)
	case 8:
		if next.Cmp(config.GetHF(8)) == 0 && mainnet {
			return params.MinimumDifficultyHF5
		}
		if next.Cmp(config.GetHF(8)) == 0 && !mainnet {
			return params.MinimumDifficultyHF8Testnet
		}
		adjust = new(big.Int).Div(parent.Difficulty, params.DifficultyBoundDivisorHF8)
		if !mainnet {
			adjust = new(big.Int).Div(parent.Difficulty, params.DifficultyBoundDivisorHF8Testnet)
			min = params.MinimumDifficultyHF8Testnet
		}
	case 6, 7:
		adjust = new(big.Int).Div(parent.Difficulty, params.DifficultyBoundDivisorHF6)
	case 5:
		if next.Cmp(config.GetHF(5)) == 0 && mainnet {
			return params.MinimumDifficultyHF5
		}
		if next.Cmp(config.GetHF(5)) == 0 && !mainnet {
			return params.MinimumDifficultyHF5Testnet
		}
		limit = params.DurationLimit // not accurate, fixed in hf6
		adjust = new(big.Int).Div(parent.Difficulty, params.DifficultyBoundDivisorHF5)
		if mainnet {
			min = params.MinimumDifficultyHF5
		}
	case 3, 4:
		limit = params.DurationLimit // not accurate, fixed in hf6
		adjust = new(big.Int).Div(parent.Difficulty, params.DifficultyBoundDivisor)
		if mainnet {
			min = params.MinimumDifficultyHF3
		}
	case 2:
		limit = params.DurationLimit // not accurate, fixed in hf6
		adjust = new(big.Int).Div(parent.Difficulty, params.DifficultyBoundDivisor)
		if mainnet {
			min = params.MinimumDifficultyHF1
		}
	case 1:
		return calcDifficultyHF1(time, parent, chainID)
	case 0:
		return calcDifficultyHomestead(time, parent, chainID)
	default:
		panic("calcDifficulty: invalid hf")
	}

	bigTime.SetUint64(time)
	bigParentTime.Set(parent.Time)

	// calculate difficulty
	if bigTime.Sub(bigTime, bigParentTime).Cmp(limit) < 0 {
		diff.Add(parent.Difficulty, adjust)
	} else {
		diff.Sub(parent.Difficulty, adjust)
	}

	if diff.Cmp(min) < 0 {
		diff.Set(min)
	}

	return diff
}

// calcDifficultyGrandparent experimental
func calcDifficultyGrandparent(time uint64, parent, grandparent *types.Header, hf int, chainID uint64) *big.Int {
	bigGrandparentTime := new(big.Int).Set(grandparent.Time)
	bigParentTime := new(big.Int).Set(parent.Time)
	if bigParentTime.Cmp(bigGrandparentTime) <= 0 {
		panic("invalid code")
	}
	// holds intermediate values to make the algo easier to read & audit
	x := new(big.Int)
	y := new(big.Int)

	divisor := params.DifficultyBoundDivisorHF5

	// 1 - (block_timestamp - parent_timestamp) // 240
	x.Sub(bigParentTime, bigGrandparentTime)
	x.Div(x, big240)
	x.Sub(big1, x)

	// max(1 - (block_timestamp - parent_timestamp) // 240, -99)
	if x.Cmp(bigMinus99) < 0 {
		x.Set(bigMinus99)
	}

	if grandparent.Difficulty.Cmp(big10000) < 0 {
		divisor = params.DifficultyBoundDivisorHF5
	} else {
		divisor = params.DifficultyBoundDivisorHF8
	}
	// (parent_diff + parent_diff // 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99))
	y.Div(grandparent.Difficulty, divisor)
	x.Mul(y, x)
	x.Add(grandparent.Difficulty, x)

	// minimum difficulty can ever be (before exponential factor)
	if chainID == params.MainnetChainConfig.ChainId.Uint64() {
		x = math.BigMax(x, params.MinimumDifficultyHF5)
	} else {
		x = math.BigMax(x, params.MinimumDifficultyHF5Testnet)
	}
	return x
}