Fixed issue with overflowing 256 bit integers

ethvm/vm.go

@@ -245,6 +245,8 @@ func (self *Vm) RunClosure(closure *Closure) (ret []byte, err error) {
 
 			base.Add(y, x)
 
+			ensure256(base)
+
 			self.Printf(" = %v", base)
 			// Pop result back on the stack
 			stack.Push(base)
@@ -255,6 +257,8 @@ func (self *Vm) RunClosure(closure *Closure) (ret []byte, err error) {
 
 			base.Sub(y, x)
 
+			ensure256(base)
+
 			self.Printf(" = %v", base)
 			// Pop result back on the stack
 			stack.Push(base)
@@ -265,6 +269,8 @@ func (self *Vm) RunClosure(closure *Closure) (ret []byte, err error) {
 
 			base.Mul(y, x)
 
+			ensure256(base)
+
 			self.Printf(" = %v", base)
 			// Pop result back on the stack
 			stack.Push(base)
@@ -277,6 +283,8 @@ func (self *Vm) RunClosure(closure *Closure) (ret []byte, err error) {
 				base.Div(y, x)
 			}
 
+			ensure256(base)
+
 			self.Printf(" = %v", base)
 			// Pop result back on the stack
 			stack.Push(base)
@@ -289,6 +297,8 @@ func (self *Vm) RunClosure(closure *Closure) (ret []byte, err error) {
 				base.Div(y, x)
 			}
 
+			ensure256(base)
+
 			self.Printf(" = %v", base)
 			// Pop result back on the stack
 			stack.Push(base)
@@ -300,6 +310,8 @@ func (self *Vm) RunClosure(closure *Closure) (ret []byte, err error) {
 
 			base.Mod(y, x)
 
+			ensure256(base)
+
 			self.Printf(" = %v", base)
 			stack.Push(base)
 		case SMOD:
@@ -310,6 +322,8 @@ func (self *Vm) RunClosure(closure *Closure) (ret []byte, err error) {
 
 			base.Mod(y, x)
 
+			ensure256(base)
+
 			self.Printf(" = %v", base)
 			stack.Push(base)
 
@@ -321,6 +335,8 @@ func (self *Vm) RunClosure(closure *Closure) (ret []byte, err error) {
 
 			base.Exp(y, x, Pow256)
 
+			ensure256(base)
+
 			self.Printf(" = %v", base)
 
 			stack.Push(base)
@@ -838,3 +854,18 @@ func (self *Vm) Endl() *Vm {
 
 	return self
 }
+
+func ensure256(x *big.Int) {
+	maxInt, _ := new(big.Int).SetString("115792089237316195423570985008687907853269984665640564039457584007913129639935", 0)
+	if x.Cmp(maxInt) >= 0 {
+		x.SetInt64(0)
+
+		return
+	}
+
+	// Could have done this with an OR, but big ints are costly.
+
+	if x.Cmp(new(big.Int)) < 0 {
+		x.SetInt64(0)
+	}
+}