diff options
| -rw-r--r-- | common/math/exp.go | 28 | ||||
| -rw-r--r-- | core/vm/instructions.go | 5 |
2 files changed, 31 insertions, 2 deletions
diff --git a/common/math/exp.go b/common/math/exp.go new file mode 100644 index 000000000..bd6eeb031 --- /dev/null +++ b/common/math/exp.go @@ -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 +} diff --git a/core/vm/instructions.go b/core/vm/instructions.go index 3352877c1..94a8c6348 100644 --- a/core/vm/instructions.go +++ b/core/vm/instructions.go @@ -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) { |