Official Go implementation of the Ethereum protocol
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go-ethereum/consensus/ethash/difficulty.go

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6.8 KiB

// Copyright 2020 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package ethash
import (
"math/big"
"github.com/ethereum/go-ethereum/core/types"
"github.com/holiman/uint256"
)
const (
// frontierDurationLimit is for Frontier:
// The decision boundary on the blocktime duration used to determine
// whether difficulty should go up or down.
frontierDurationLimit = 13
// minimumDifficulty The minimum that the difficulty may ever be.
minimumDifficulty = 131072
// expDiffPeriod is the exponential difficulty period
expDiffPeriodUint = 100000
// difficultyBoundDivisorBitShift is the bound divisor of the difficulty (2048),
// This constant is the right-shifts to use for the division.
difficultyBoundDivisor = 11
)
// CalcDifficultyFrontierU256 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 CalcDifficultyFrontierU256(time uint64, parent *types.Header) *big.Int {
/*
Algorithm
block_diff = pdiff + pdiff / 2048 * (1 if time - ptime < 13 else -1) + int(2^((num // 100000) - 2))
Where:
- pdiff = parent.difficulty
- ptime = parent.time
- time = block.timestamp
- num = block.number
*/
pDiff, _ := uint256.FromBig(parent.Difficulty) // pDiff: pdiff
adjust := pDiff.Clone()
adjust.Rsh(adjust, difficultyBoundDivisor) // adjust: pDiff / 2048
if time-parent.Time < frontierDurationLimit {
pDiff.Add(pDiff, adjust)
} else {
pDiff.Sub(pDiff, adjust)
}
if pDiff.LtUint64(minimumDifficulty) {
pDiff.SetUint64(minimumDifficulty)
}
// 'pdiff' now contains:
// pdiff + pdiff / 2048 * (1 if time - ptime < 13 else -1)
if periodCount := (parent.Number.Uint64() + 1) / expDiffPeriodUint; periodCount > 1 {
// diff = diff + 2^(periodCount - 2)
expDiff := adjust.SetOne()
expDiff.Lsh(expDiff, uint(periodCount-2)) // expdiff: 2 ^ (periodCount -2)
pDiff.Add(pDiff, expDiff)
}
return pDiff.ToBig()
}
// CalcDifficultyHomesteadU256 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 CalcDifficultyHomesteadU256(time uint64, parent *types.Header) *big.Int {
/*
https://github.com/ethereum/EIPs/blob/master/EIPS/eip-2.md
Algorithm:
block_diff = pdiff + pdiff / 2048 * max(1 - (time - ptime) / 10, -99) + 2 ^ int((num / 100000) - 2))
Our modification, to use unsigned ints:
block_diff = pdiff - pdiff / 2048 * max((time - ptime) / 10 - 1, 99) + 2 ^ int((num / 100000) - 2))
Where:
- pdiff = parent.difficulty
- ptime = parent.time
- time = block.timestamp
- num = block.number
*/
pDiff, _ := uint256.FromBig(parent.Difficulty) // pDiff: pdiff
adjust := pDiff.Clone()
adjust.Rsh(adjust, difficultyBoundDivisor) // adjust: pDiff / 2048
x := (time - parent.Time) / 10 // (time - ptime) / 10)
var neg = true
if x == 0 {
x = 1
neg = false
} else if x >= 100 {
x = 99
} else {
x = x - 1
}
z := new(uint256.Int).SetUint64(x)
adjust.Mul(adjust, z) // adjust: (pdiff / 2048) * max((time - ptime) / 10 - 1, 99)
if neg {
pDiff.Sub(pDiff, adjust) // pdiff - pdiff / 2048 * max((time - ptime) / 10 - 1, 99)
} else {
pDiff.Add(pDiff, adjust) // pdiff + pdiff / 2048 * max((time - ptime) / 10 - 1, 99)
}
if pDiff.LtUint64(minimumDifficulty) {
pDiff.SetUint64(minimumDifficulty)
}
// for the exponential factor, a.k.a "the bomb"
// diff = diff + 2^(periodCount - 2)
if periodCount := (1 + parent.Number.Uint64()) / expDiffPeriodUint; periodCount > 1 {
expFactor := adjust.Lsh(adjust.SetOne(), uint(periodCount-2))
pDiff.Add(pDiff, expFactor)
}
return pDiff.ToBig()
}
// MakeDifficultyCalculatorU256 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 MakeDifficultyCalculatorU256(bombDelay *big.Int) func(time uint64, parent *types.Header) *big.Int {
// Note, the calculations below looks at the parent number, which is 1 below
// the block number. Thus we remove one from the delay given
bombDelayFromParent := bombDelay.Uint64() - 1
return func(time uint64, parent *types.Header) *big.Int {
/*
https://github.com/ethereum/EIPs/issues/100
pDiff = parent.difficulty
BLOCK_DIFF_FACTOR = 9
a = pDiff + (pDiff // BLOCK_DIFF_FACTOR) * adj_factor
b = min(parent.difficulty, MIN_DIFF)
child_diff = max(a,b )
*/
x := (time - parent.Time) / 9 // (block_timestamp - parent_timestamp) // 9
c := uint64(1) // if parent.unclehash == emptyUncleHashHash
if parent.UncleHash != types.EmptyUncleHash {
c = 2
}
xNeg := x >= c
if xNeg {
// x is now _negative_ adjustment factor
x = x - c // - ( (t-p)/p -( 2 or 1) )
} else {
x = c - x // (2 or 1) - (t-p)/9
}
if x > 99 {
x = 99 // max(x, 99)
}
// parent_diff + (parent_diff / 2048 * max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99))
y := new(uint256.Int)
y.SetFromBig(parent.Difficulty) // y: p_diff
pDiff := y.Clone() // pdiff: p_diff
z := new(uint256.Int).SetUint64(x) //z : +-adj_factor (either pos or negative)
y.Rsh(y, difficultyBoundDivisor) // y: p__diff / 2048
z.Mul(y, z) // z: (p_diff / 2048 ) * (+- adj_factor)
if xNeg {
y.Sub(pDiff, z) // y: parent_diff + parent_diff/2048 * adjustment_factor
} else {
y.Add(pDiff, z) // y: parent_diff + parent_diff/2048 * adjustment_factor
}
// minimum difficulty can ever be (before exponential factor)
if y.LtUint64(minimumDifficulty) {
y.SetUint64(minimumDifficulty)
}
// calculate a fake block number for the ice-age delay
// Specification: https://eips.ethereum.org/EIPS/eip-1234
var pNum = parent.Number.Uint64()
if pNum >= bombDelayFromParent {
if fakeBlockNumber := pNum - bombDelayFromParent; fakeBlockNumber >= 2*expDiffPeriodUint {
z.SetOne()
z.Lsh(z, uint(fakeBlockNumber/expDiffPeriodUint-2))
y.Add(z, y)
}
}
return y.ToBig()
}
}