Use math.bits in common math Safe* for performance (#556)

* Use math.bits in comoon math Safe* for performance (the compiler optimizes away  math.bits)

* Prettier code in opExp

common/math/integer.go

@@ -18,6 +18,7 @@ package math
 
 import (
 	"fmt"
+	"math/bits"
 	"strconv"
 )
 
@@ -78,22 +79,20 @@ func MustParseUint64(s string) uint64 {
 	return v
 }
 
-// NOTE: The following methods need to be optimised using either bit checking or asm
-
 // SafeSub returns subtraction result and whether overflow occurred.
 func SafeSub(x, y uint64) (uint64, bool) {
-	return x - y, x < y
+	diff, borrowOut := bits.Sub64(x, y, 0)
+	return diff, borrowOut != 0
 }
 
 // SafeAdd returns the result and whether overflow occurred.
 func SafeAdd(x, y uint64) (uint64, bool) {
-	return x + y, y > MaxUint64-x
+	sum, carryOut := bits.Add64(x, y, 0)
+	return sum, carryOut != 0
 }
 
 // SafeMul returns multiplication result and whether overflow occurred.
 func SafeMul(x, y uint64) (uint64, bool) {
-	if x == 0 || y == 0 {
+	hi, lo := bits.Mul64(x, y)
-		return 0, false
+	return lo, hi != 0
-	}
-	return x * y, y > MaxUint64/x
 }

core/vm/instructions.go

@@ -69,20 +69,20 @@ func opSmod(pc *uint64, interpreter *EVMInterpreter, callContext *callCtx) ([]by
 
 func opExp(pc *uint64, interpreter *EVMInterpreter, callContext *callCtx) ([]byte, error) {
 	base, exponent := callContext.stack.pop(), callContext.stack.peek()
-	// some shortcuts
+	switch {
-	if exponent.IsZero() {
+	case exponent.IsZero():
 		// x ^ 0 == 1
 		exponent.SetOne()
-	} else if base.IsZero() {
+	case base.IsZero():
 		// 0 ^ y, if y != 0, == 0
 		exponent.Clear()
-	} else if exponent.LtUint64(2) { // exponent == 1
+	case exponent.LtUint64(2): // exponent == 1
 		// x ^ 1 == x
 		exponent.Set(&base)
-	} else if base.LtUint64(2) { // base == 1
+	case base.LtUint64(2): // base == 1
 		// 1 ^ y == 1
 		exponent.SetOne()
-	} else if base.LtUint64(3) { // base == 2
+	case base.LtUint64(3): // base == 2
 		if exponent.LtUint64(256) {
 			n := uint(exponent.Uint64())
 			exponent.SetOne()
@@ -90,7 +90,7 @@ func opExp(pc *uint64, interpreter *EVMInterpreter, callContext *callCtx) ([]byt
 		} else {
 			exponent.Clear()
 		}
-	} else {
+	default:
 		exponent.Exp(&base, exponent)
 	}
 	return nil, nil