mirror of https://github.com/ethereum/go-ethereum
consensus/ethash: implement faster difficulty calculators (#21976)
This PR adds re-written difficulty calculators, which are based on uint256. It also adds a fuzzer + oss-fuzz integration for the new fuzzer. It does differential fuzzing between the new and old calculators. Note: this PR does not actually enable the new calculators.pull/21971/head
Martin Holst Swende
4 years ago
committed by
GitHub
parent
88c696240d
commit
efe6dd2904
@ -0,0 +1,193 @@ |
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// Copyright 2020 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package ethash |
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import ( |
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"math/big" |
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"github.com/ethereum/go-ethereum/core/types" |
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"github.com/holiman/uint256" |
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) |
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const ( |
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// frontierDurationLimit is for Frontier:
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// The decision boundary on the blocktime duration used to determine
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// whether difficulty should go up or down.
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frontierDurationLimit = 13 |
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// minimumDifficulty The minimum that the difficulty may ever be.
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minimumDifficulty = 131072 |
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// expDiffPeriod is the exponential difficulty period
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expDiffPeriodUint = 100000 |
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// difficultyBoundDivisorBitShift is the bound divisor of the difficulty (2048),
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// This constant is the right-shifts to use for the division.
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difficultyBoundDivisor = 11 |
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) |
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// CalcDifficultyFrontierU256 is the difficulty adjustment algorithm. It returns the
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// difficulty that a new block should have when created at time given the parent
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// block's time and difficulty. The calculation uses the Frontier rules.
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func CalcDifficultyFrontierU256(time uint64, parent *types.Header) *big.Int { |
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/* |
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Algorithm |
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block_diff = pdiff + pdiff / 2048 * (1 if time - ptime < 13 else -1) + int(2^((num // 100000) - 2))
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Where: |
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- pdiff = parent.difficulty |
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- ptime = parent.time |
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- time = block.timestamp |
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- num = block.number |
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*/ |
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pDiff := uint256.NewInt() |
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pDiff.SetFromBig(parent.Difficulty) // pDiff: pdiff
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adjust := pDiff.Clone() |
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adjust.Rsh(adjust, difficultyBoundDivisor) // adjust: pDiff / 2048
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if time-parent.Time < frontierDurationLimit { |
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pDiff.Add(pDiff, adjust) |
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} else { |
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pDiff.Sub(pDiff, adjust) |
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} |
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if pDiff.LtUint64(minimumDifficulty) { |
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pDiff.SetUint64(minimumDifficulty) |
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} |
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// 'pdiff' now contains:
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// pdiff + pdiff / 2048 * (1 if time - ptime < 13 else -1)
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if periodCount := (parent.Number.Uint64() + 1) / expDiffPeriodUint; periodCount > 1 { |
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// diff = diff + 2^(periodCount - 2)
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expDiff := adjust.SetOne() |
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expDiff.Lsh(expDiff, uint(periodCount-2)) // expdiff: 2 ^ (periodCount -2)
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pDiff.Add(pDiff, expDiff) |
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} |
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return pDiff.ToBig() |
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} |
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// CalcDifficultyHomesteadU256 is the difficulty adjustment algorithm. It returns
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// the difficulty that a new block should have when created at time given the
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// parent block's time and difficulty. The calculation uses the Homestead rules.
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func CalcDifficultyHomesteadU256(time uint64, parent *types.Header) *big.Int { |
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/* |
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https://github.com/ethereum/EIPs/blob/master/EIPS/eip-2.md
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Algorithm: |
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block_diff = pdiff + pdiff / 2048 * max(1 - (time - ptime) / 10, -99) + 2 ^ int((num / 100000) - 2)) |
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Our modification, to use unsigned ints: |
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block_diff = pdiff - pdiff / 2048 * max((time - ptime) / 10 - 1, 99) + 2 ^ int((num / 100000) - 2)) |
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Where: |
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- pdiff = parent.difficulty |
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- ptime = parent.time |
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- time = block.timestamp |
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- num = block.number |
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*/ |
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pDiff := uint256.NewInt() |
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pDiff.SetFromBig(parent.Difficulty) // pDiff: pdiff
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adjust := pDiff.Clone() |
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adjust.Rsh(adjust, difficultyBoundDivisor) // adjust: pDiff / 2048
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x := (time - parent.Time) / 10 // (time - ptime) / 10)
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var neg = true |
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if x == 0 { |
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x = 1 |
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neg = false |
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} else if x >= 100 { |
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x = 99 |
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} else { |
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x = x - 1 |
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} |
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z := new(uint256.Int).SetUint64(x) |
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adjust.Mul(adjust, z) // adjust: (pdiff / 2048) * max((time - ptime) / 10 - 1, 99)
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if neg { |
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pDiff.Sub(pDiff, adjust) // pdiff - pdiff / 2048 * max((time - ptime) / 10 - 1, 99)
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} else { |
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pDiff.Add(pDiff, adjust) // pdiff + pdiff / 2048 * max((time - ptime) / 10 - 1, 99)
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} |
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if pDiff.LtUint64(minimumDifficulty) { |
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pDiff.SetUint64(minimumDifficulty) |
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} |
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// for the exponential factor, a.k.a "the bomb"
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// diff = diff + 2^(periodCount - 2)
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if periodCount := (1 + parent.Number.Uint64()) / expDiffPeriodUint; periodCount > 1 { |
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expFactor := adjust.Lsh(adjust.SetOne(), uint(periodCount-2)) |
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pDiff.Add(pDiff, expFactor) |
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} |
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return pDiff.ToBig() |
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} |
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// MakeDifficultyCalculatorU256 creates a difficultyCalculator with the given bomb-delay.
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// the difficulty is calculated with Byzantium rules, which differs from Homestead in
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// how uncles affect the calculation
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func MakeDifficultyCalculatorU256(bombDelay *big.Int) func(time uint64, parent *types.Header) *big.Int { |
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// Note, the calculations below looks at the parent number, which is 1 below
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// the block number. Thus we remove one from the delay given
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bombDelayFromParent := bombDelay.Uint64() - 1 |
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return func(time uint64, parent *types.Header) *big.Int { |
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/* |
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https://github.com/ethereum/EIPs/issues/100
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pDiff = parent.difficulty |
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BLOCK_DIFF_FACTOR = 9 |
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a = pDiff + (pDiff // BLOCK_DIFF_FACTOR) * adj_factor
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b = min(parent.difficulty, MIN_DIFF) |
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child_diff = max(a,b ) |
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*/ |
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x := (time - parent.Time) / 9 // (block_timestamp - parent_timestamp) // 9
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c := uint64(1) // if parent.unclehash == emptyUncleHashHash
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if parent.UncleHash != types.EmptyUncleHash { |
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c = 2 |
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} |
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xNeg := x >= c |
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if xNeg { |
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// x is now _negative_ adjustment factor
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x = x - c // - ( (t-p)/p -( 2 or 1) )
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} else { |
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x = c - x // (2 or 1) - (t-p)/9
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} |
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if x > 99 { |
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x = 99 // max(x, 99)
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} |
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// parent_diff + (parent_diff / 2048 * max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99))
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y := new(uint256.Int) |
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y.SetFromBig(parent.Difficulty) // y: p_diff
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pDiff := y.Clone() // pdiff: p_diff
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z := new(uint256.Int).SetUint64(x) //z : +-adj_factor (either pos or negative)
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y.Rsh(y, difficultyBoundDivisor) // y: p__diff / 2048
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z.Mul(y, z) // z: (p_diff / 2048 ) * (+- adj_factor)
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if xNeg { |
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y.Sub(pDiff, z) // y: parent_diff + parent_diff/2048 * adjustment_factor
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} else { |
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y.Add(pDiff, z) // y: parent_diff + parent_diff/2048 * adjustment_factor
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} |
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// minimum difficulty can ever be (before exponential factor)
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if y.LtUint64(minimumDifficulty) { |
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y.SetUint64(minimumDifficulty) |
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} |
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// calculate a fake block number for the ice-age delay
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// Specification: https://eips.ethereum.org/EIPS/eip-1234
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var pNum = parent.Number.Uint64() |
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if pNum >= bombDelayFromParent { |
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if fakeBlockNumber := pNum - bombDelayFromParent; fakeBlockNumber >= 2*expDiffPeriodUint { |
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z.SetOne() |
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z.Lsh(z, uint(fakeBlockNumber/expDiffPeriodUint-2)) |
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y.Add(z, y) |
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} |
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} |
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return y.ToBig() |
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} |
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} |
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@ -0,0 +1,23 @@ |
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package main |
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import ( |
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"fmt" |
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"io/ioutil" |
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"os" |
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"github.com/ethereum/go-ethereum/tests/fuzzers/difficulty" |
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) |
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func main() { |
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if len(os.Args) != 2 { |
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fmt.Fprintf(os.Stderr, "Usage: debug <file>") |
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os.Exit(1) |
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} |
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crasher := os.Args[1] |
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data, err := ioutil.ReadFile(crasher) |
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if err != nil { |
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fmt.Fprintf(os.Stderr, "error loading crasher %v: %v", crasher, err) |
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os.Exit(1) |
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} |
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difficulty.Fuzz(data) |
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} |
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@ -0,0 +1,145 @@ |
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// Copyright 2020 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package difficulty |
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import ( |
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"bytes" |
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"encoding/binary" |
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"fmt" |
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"io" |
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"math/big" |
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"github.com/ethereum/go-ethereum/consensus/ethash" |
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"github.com/ethereum/go-ethereum/core/types" |
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) |
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type fuzzer struct { |
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input io.Reader |
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exhausted bool |
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debugging bool |
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} |
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func (f *fuzzer) read(size int) []byte { |
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out := make([]byte, size) |
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if _, err := f.input.Read(out); err != nil { |
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f.exhausted = true |
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} |
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return out |
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} |
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func (f *fuzzer) readSlice(min, max int) []byte { |
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var a uint16 |
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binary.Read(f.input, binary.LittleEndian, &a) |
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size := min + int(a)%(max-min) |
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out := make([]byte, size) |
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if _, err := f.input.Read(out); err != nil { |
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f.exhausted = true |
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} |
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return out |
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} |
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func (f *fuzzer) readUint64(min, max uint64) uint64 { |
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if min == max { |
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return min |
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} |
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var a uint64 |
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if err := binary.Read(f.input, binary.LittleEndian, &a); err != nil { |
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f.exhausted = true |
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} |
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a = min + a%(max-min) |
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return a |
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} |
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func (f *fuzzer) readBool() bool { |
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return f.read(1)[0]&0x1 == 0 |
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} |
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// The function must return
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// 1 if the fuzzer should increase priority of the
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// given input during subsequent fuzzing (for example, the input is lexically
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// correct and was parsed successfully);
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// -1 if the input must not be added to corpus even if gives new coverage; and
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// 0 otherwise
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// other values are reserved for future use.
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func Fuzz(data []byte) int { |
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f := fuzzer{ |
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input: bytes.NewReader(data), |
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exhausted: false, |
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} |
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return f.fuzz() |
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} |
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var minDifficulty = big.NewInt(0x2000) |
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type calculator func(time uint64, parent *types.Header) *big.Int |
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func (f *fuzzer) fuzz() int { |
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// A parent header
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header := &types.Header{} |
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if f.readBool() { |
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header.UncleHash = types.EmptyUncleHash |
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} |
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// Difficulty can range between 0x2000 (2 bytes) and up to 32 bytes
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{ |
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diff := new(big.Int).SetBytes(f.readSlice(2, 32)) |
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if diff.Cmp(minDifficulty) < 0 { |
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diff.Set(minDifficulty) |
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} |
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header.Difficulty = diff |
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} |
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// Number can range between 0 and up to 32 bytes (but not so that the child exceeds it)
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{ |
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// However, if we use astronomic numbers, then the bomb exp karatsuba calculation
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// in the legacy methods)
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// times out, so we limit it to fit within reasonable bounds
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number := new(big.Int).SetBytes(f.readSlice(0, 4)) // 4 bytes: 32 bits: block num max 4 billion
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header.Number = number |
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} |
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// Both parent and child time must fit within uint64
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var time uint64 |
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{ |
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childTime := f.readUint64(1, 0xFFFFFFFFFFFFFFFF) |
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//fmt.Printf("childTime: %x\n",childTime)
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delta := f.readUint64(1, childTime) |
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//fmt.Printf("delta: %v\n", delta)
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pTime := childTime - delta |
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header.Time = pTime |
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time = childTime |
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} |
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// Bomb delay will never exceed uint64
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bombDelay := new(big.Int).SetUint64(f.readUint64(1, 0xFFFFFFFFFFFFFFFe)) |
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if f.exhausted { |
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return 0 |
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} |
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for i, pair := range []struct { |
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bigFn calculator |
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u256Fn calculator |
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}{ |
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{ethash.FrontierDifficultyCalulator, ethash.CalcDifficultyFrontierU256}, |
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{ethash.HomesteadDifficultyCalulator, ethash.CalcDifficultyHomesteadU256}, |
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{ethash.DynamicDifficultyCalculator(bombDelay), ethash.MakeDifficultyCalculatorU256(bombDelay)}, |
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} { |
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want := pair.bigFn(time, header) |
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have := pair.u256Fn(time, header) |
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if want.Cmp(have) != 0 { |
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panic(fmt.Sprintf("pair %d: want %x have %x\nparent.Number: %x\np.Time: %x\nc.Time: %x\nBombdelay: %v\n", i, want, have, |
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header.Number, header.Time, time, bombDelay)) |
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} |
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} |
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return 1 |
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} |
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