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48 lines
1.4 KiB
Go
48 lines
1.4 KiB
Go
// Copyright 2016 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 math
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import (
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"math/big"
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"github.com/ethereum/go-ethereum/common"
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)
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// wordSize is the size number of bits in a big.Int Word.
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const wordSize = 32 << (uint64(^big.Word(0)) >> 63)
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// Exp implement exponentiation by squaring algorithm.
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//
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// Exp return a new variable; base and exponent must
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// not be changed under any circumstance.
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//
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// Courtesy @karalabe and @chfast
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func Exp(base, exponent *big.Int) *big.Int {
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result := big.NewInt(1)
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for _, word := range exponent.Bits() {
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for i := 0; i < wordSize; i++ {
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if word&1 == 1 {
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common.U256(result.Mul(result, base))
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}
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common.U256(base.Mul(base, base))
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word >>= 1
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}
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}
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return result
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}
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