common/math, core/vm: Move optimizations to math

Move exponentiation optimizations in opExp to math.Exp

common/math/big.go

@@ -198,6 +198,18 @@ func S256(x *big.Int) *big.Int {
 // Courtesy @karalabe and @chfast
 func Exp(base, exponent *big.Int) *big.Int {
 	result := big.NewInt(1)
+	// some shortcuts
+	cmpToOne := exponent.Cmp(result)
+	if cmpToOne < 0 { // Exponent is zero
+		// x ^ 0 == 1
+		return result
+	} else if base.Sign() == 0 {
+		// 0 ^ y, if y != 0, == 0
+		return result.SetUint64(0)
+	} else if cmpToOne == 0 { // Exponent is one
+		// x ^ 1 == x
+		return result.Set(base)
+	}
 
 	for _, word := range exponent.Bits() {
 		for i := 0; i < wordBits; i++ {

core/vm/instructions.go

@@ -124,21 +124,8 @@ func opSmod(pc *uint64, interpreter *EVMInterpreter, contract *Contract, memory
 
 func opExp(pc *uint64, interpreter *EVMInterpreter, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	base, exponent := stack.pop(), stack.pop()
-	// some shortcuts
+	stack.push(math.Exp(base, exponent))
-	cmpToOne := exponent.Cmp(big1)
+	interpreter.intPool.put(base)
-	if cmpToOne < 0 { // Exponent is zero
-		// x ^ 0 == 1
-		stack.push(base.SetUint64(1))
-	} else if base.Sign() == 0 {
-		// 0 ^ y, if y != 0, == 0
-		stack.push(base.SetUint64(0))
-	} else if cmpToOne == 0 { // Exponent is one
-		// x ^ 1 == x
-		stack.push(base)
-	} else {
-		stack.push(math.Exp(base, exponent))
-		interpreter.intPool.put(base)
-	}
 	interpreter.intPool.put(exponent)
 	return nil, nil
 }