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consensus/ethash: implement faster difficulty calculators (ethereum#2…
…1976) 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.
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,193 @@ | ||
| // 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" | ||
|
|
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| "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.NewInt() | ||
| pDiff.SetFromBig(parent.Difficulty) // pDiff: pdiff | ||
| adjust := pDiff.Clone() | ||
| adjust.Rsh(adjust, difficultyBoundDivisor) // adjust: pDiff / 2048 | ||
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|
||
| 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) | ||
|
|
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| 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 | ||
| */ | ||
|
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| pDiff := uint256.NewInt() | ||
| pDiff.SetFromBig(parent.Difficulty) // pDiff: pdiff | ||
| adjust := pDiff.Clone() | ||
| adjust.Rsh(adjust, difficultyBoundDivisor) // adjust: pDiff / 2048 | ||
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| 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() | ||
| } | ||
|
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||
| // 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() | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,23 @@ | ||
| package main | ||
|
|
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| import ( | ||
| "fmt" | ||
| "io/ioutil" | ||
| "os" | ||
|
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| "github.com/ethereum/go-ethereum/tests/fuzzers/difficulty" | ||
| ) | ||
|
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| func main() { | ||
| if len(os.Args) != 2 { | ||
| fmt.Fprintf(os.Stderr, "Usage: debug <file>") | ||
| os.Exit(1) | ||
| } | ||
| crasher := os.Args[1] | ||
| data, err := ioutil.ReadFile(crasher) | ||
| if err != nil { | ||
| fmt.Fprintf(os.Stderr, "error loading crasher %v: %v", crasher, err) | ||
| os.Exit(1) | ||
| } | ||
| difficulty.Fuzz(data) | ||
| } |
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