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common/math: copy result in Exp (#29233)

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common/math: does not change base parameter
This commit is contained in:
Aaron Chen 2024-03-12 20:05:31 +08:00 committed by GitHub
parent 99bbbc0277
commit 4bd55a064c
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GPG Key ID: B5690EEEBB952194
1 changed files with 4 additions and 3 deletions
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7
common/math/big.go
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@ -224,7 +224,7 @@ func ReadBits(bigint *big.Int, buf []byte) {
}
}
// U256 encodes as a 256 bit two's complement number. This operation is destructive.
// U256 encodes x as a 256 bit two's complement number. This operation is destructive.
func U256(x *big.Int) *big.Int {
return x.And(x, tt256m1)
}
@ -255,14 +255,15 @@ func S256(x *big.Int) *big.Int {
//
// Courtesy @karalabe and @chfast
func Exp(base, exponent *big.Int) *big.Int {
copyBase := new(big.Int).Set(base)
result := big.NewInt(1)
for _, word := range exponent.Bits() {
for i := 0; i < wordBits; i++ {
if word&1 == 1 {
U256(result.Mul(result, base))
U256(result.Mul(result, copyBase))
}
U256(base.Mul(base, base))
U256(copyBase.Mul(copyBase, copyBase))
word >>= 1
}
}