mirror of https://github.com/ethereum/go-ethereum
common/math, core/vm: implement fast EXP (#3214)
* common/math, core/vm: implement fast EXP. Courtesy @chfast & @karalabe * common/math: fix go vet issues on exp calculationpull/3188/merge
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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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// 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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