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common/math, core/vm: implement fast EXP (#3214)

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* common/math, core/vm: implement fast EXP.

Courtesy @chfast & @karalabe

* common/math: fix go vet issues on exp calculation
This commit is contained in:
Jeffrey Wilcke 2016-11-02 12:43:15 +01:00 committed by Péter Szilágyi
parent 36956da4d2
commit 1b73c79234
2 changed files with 31 additions and 2 deletions
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28
common/math/exp.go Normal file
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@ -0,0 +1,28 @@
package math
import (
"math/big"
"github.com/ethereum/go-ethereum/common"
)
// wordSize is the size number of bits in a big.Int Word.
const wordSize = 32 << (uint64(^big.Word(0))>>63)
// Exp implement exponentiation by squaring algorithm.
//
// Courtesy @karalabe and @chfast
func Exp(base, exponent *big.Int) *big.Int {
result := big.NewInt(1)
for _, word := range exponent.Bits() {
for i := 0; i < wordSize; i++ {
if word&1 == 1 {
common.U256(result.Mul(result, base))
}
common.U256(base.Mul(base, base))
word >>= 1
}
}
return result
}

5
core/vm/instructions.go
View File

@ -21,6 +21,7 @@ import (
"math/big"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/common/math"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/params"
)
@ -192,8 +193,8 @@ func opSmod(instr instruction, pc *uint64, env Environment, contract *Contract,
}
func opExp(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
x, y := stack.pop(), stack.pop()
stack.push(U256(x.Exp(x, y, Pow256)))
base, exponent := stack.pop(), stack.pop()
stack.push(math.Exp(base, exponent))
}
func opSignExtend(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {