mirror of https://github.com/ethereum/go-ethereum
common/math, tests/fuzzers: use big.Int clone (#26006)
* common/math, tests/fuzzers: use big.Int clone * common/math: licensepull/24766/head
Martin Holst Swende
2 years ago
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GitHub
parent
fb75f11e87
commit
15b7e0b254
@ -1,82 +0,0 @@ |
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// Copyright 2020 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package math |
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import ( |
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"math/big" |
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"math/bits" |
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"github.com/ethereum/go-ethereum/common" |
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) |
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// FastExp is semantically equivalent to x.Exp(x,y, m), but is faster for even
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// modulus.
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func FastExp(x, y, m *big.Int) *big.Int { |
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// Split m = m1 × m2 where m1 = 2ⁿ
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n := m.TrailingZeroBits() |
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m1 := new(big.Int).Lsh(common.Big1, n) |
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mask := new(big.Int).Sub(m1, common.Big1) |
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m2 := new(big.Int).Rsh(m, n) |
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// We want z = x**y mod m.
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// z1 = x**y mod m1 = (x**y mod m) mod m1 = z mod m1
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// z2 = x**y mod m2 = (x**y mod m) mod m2 = z mod m2
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z1 := fastExpPow2(x, y, mask) |
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z2 := new(big.Int).Exp(x, y, m2) |
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// Reconstruct z from z1, z2 using CRT, using algorithm from paper,
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// which uses only a single modInverse.
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// p = (z1 - z2) * m2⁻¹ (mod m1)
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// z = z2 + p * m2
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z := new(big.Int).Set(z2) |
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// Compute (z1 - z2) mod m1 [m1 == 2**n] into z1.
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z1 = z1.And(z1, mask) |
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z2 = z2.And(z2, mask) |
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z1 = z1.Sub(z1, z2) |
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if z1.Sign() < 0 { |
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z1 = z1.Add(z1, m1) |
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} |
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// Reuse z2 for p = z1 * m2inv.
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m2inv := new(big.Int).ModInverse(m2, m1) |
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z2 = z2.Mul(z1, m2inv) |
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z2 = z2.And(z2, mask) |
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// Reuse z1 for m2 * p.
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z = z.Add(z, z1.Mul(z2, m2)) |
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z = z.Rem(z, m) |
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return z |
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} |
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func fastExpPow2(x, y *big.Int, mask *big.Int) *big.Int { |
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z := big.NewInt(1) |
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if y.Sign() == 0 { |
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return z |
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} |
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p := new(big.Int).Set(x) |
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p = p.And(p, mask) |
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if p.Cmp(z) <= 0 { // p <= 1
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return p |
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} |
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if y.Cmp(mask) > 0 { |
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y = new(big.Int).And(y, mask) |
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} |
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t := new(big.Int) |
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for _, b := range y.Bits() { |
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for i := 0; i < bits.UintSize; i++ { |
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if b&1 != 0 { |
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z, t = t.Mul(z, p), z |
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z = z.And(z, mask) |
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} |
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p, t = t.Mul(p, p), p |
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p = p.And(p, mask) |
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b >>= 1 |
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} |
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} |
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return z |
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} |
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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 main |
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import ( |
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"fmt" |
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"os" |
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"github.com/ethereum/go-ethereum/tests/fuzzers/modexp" |
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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>\n") |
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fmt.Fprintf(os.Stderr, "Example\n") |
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fmt.Fprintf(os.Stderr, " $ debug ../crashers/4bbef6857c733a87ecf6fd8b9e7238f65eb9862a\n") |
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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 := os.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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modexp.Fuzz(data) |
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} |
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