return the result in AddOverflow/SubUnderflow method

uint256.go

@@ -182,22 +182,22 @@ func (z *Int) Add(x, y *Int) *Int {
 	return z
 }
 
-// AddOverflow sets z to the sum x+y, and returns whether overflow occurred
-func (z *Int) AddOverflow(x, y *Int) bool {
+// AddOverflow sets z to the sum x+y, and returns z and whether overflow occurred
+func (z *Int) AddOverflow(x, y *Int) (*Int, bool) {
 	var carry uint64
 	z[0], carry = bits.Add64(x[0], y[0], 0)
 	z[1], carry = bits.Add64(x[1], y[1], carry)
 	z[2], carry = bits.Add64(x[2], y[2], carry)
 	z[3], carry = bits.Add64(x[3], y[3], carry)
-	return carry != 0
+	return z, carry != 0
 }
 
 // AddMod sets z to the sum ( x+y ) mod m, and returns z
 func (z *Int) AddMod(x, y, m *Int) *Int {
 	if z == m { // z is an alias for m  // TODO: Understand why needed and add tests for all "division" methods.
 		m = m.Clone()
 	}
-	if overflow := z.AddOverflow(x, y); overflow {
+	if _, overflow := z.AddOverflow(x, y); overflow {
 		sum := [5]uint64{z[0], z[1], z[2], z[3], 1}
 		var quot [5]uint64
 		rem := udivrem(quot[:], sum[:], m)
@@ -239,14 +239,14 @@ func (z *Int) SubUint64(x *Int, y uint64) *Int {
 	return z
 }
 
-// SubOverflow sets z to the difference x-y and returns true if the operation underflowed
-func (z *Int) SubOverflow(x, y *Int) bool {
+// SubOverflow sets z to the difference x-y and returns z and true if the operation underflowed
+func (z *Int) SubOverflow(x, y *Int) (*Int, bool) {
 	var carry uint64
 	z[0], carry = bits.Sub64(x[0], y[0], 0)
 	z[1], carry = bits.Sub64(x[1], y[1], carry)
 	z[2], carry = bits.Sub64(x[2], y[2], carry)
 	z[3], carry = bits.Sub64(x[3], y[3], carry)
-	return carry != 0
+	return z, carry != 0
 }
 
 // Sub sets z to the difference x-y
@@ -333,11 +333,11 @@ func (z *Int) Mul(x, y *Int) *Int {
 	return z.Set(&res)
 }
 
-// MulOverflow sets z to the product x*y, and returns whether overflow occurred
-func (z *Int) MulOverflow(x, y *Int) bool {
+// MulOverflow sets z to the product x*y, and returns z and  whether overflow occurred
+func (z *Int) MulOverflow(x, y *Int) (*Int, bool) {
 	p := umul(x, y)
 	copy(z[:], p[:4])
-	return (p[4] | p[5] | p[6] | p[7]) != 0
+	return z, (p[4] | p[5] | p[6] | p[7]) != 0
 }
 
 func (z *Int) squared() {

uint256_test.go

@@ -137,6 +137,7 @@ func randNums() (*big.Int, *Int, error) {
 	err := checkOverflow(b, f, overflow)
 	return b, f, err
 }
+
 func randHighNums() (*big.Int, *Int, error) {
 	//How many bits? 0-256
 	nbits := int64(256)
@@ -184,6 +185,7 @@ func testRandomOp(t *testing.T, nativeFunc func(a, b, c *Int), bigintFunc func(a
 		}
 	}
 }
+
 func TestRandomSubOverflow(t *testing.T) {
 	for i := 0; i < 10000; i++ {
 		b, f1, err := randNums()
@@ -195,7 +197,7 @@ func TestRandomSubOverflow(t *testing.T) {
 			t.Fatal(err)
 		}
 		f1a, f2a := f1.Clone(), f2.Clone()
-		overflow := f1.SubOverflow(f1, f2)
+		_, overflow := f1.SubOverflow(f1, f2)
 		b.Sub(b, b2)
 		if err := checkUnderflow(b, f1, overflow); err != nil {
 			t.Fatal(err)
@@ -205,6 +207,7 @@ func TestRandomSubOverflow(t *testing.T) {
 		}
 	}
 }
+
 func TestRandomSub(t *testing.T) {
 	testRandomOp(t,
 		func(f1, f2, f3 *Int) {
@@ -226,6 +229,7 @@ func TestRandomAdd(t *testing.T) {
 		},
 	)
 }
+
 func TestRandomMul(t *testing.T) {
 
 	testRandomOp(t,
@@ -237,6 +241,7 @@ func TestRandomMul(t *testing.T) {
 		},
 	)
 }
+
 func TestRandomMulOverflow(t *testing.T) {
 	for i := 0; i < 10000; i++ {
 		b, f1, err := randNums()
@@ -248,7 +253,7 @@ func TestRandomMulOverflow(t *testing.T) {
 			t.Fatal(err)
 		}
 		f1a, f2a := f1.Clone(), f2.Clone()
-		overflow := f1.MulOverflow(f1, f2)
+		_, overflow := f1.MulOverflow(f1, f2)
 		b.Mul(b, b2)
 		if err := checkOverflow(b, f1, overflow); err != nil {
 			t.Fatal(err)
@@ -258,6 +263,7 @@ func TestRandomMulOverflow(t *testing.T) {
 		}
 	}
 }
+
 func TestRandomSquare(t *testing.T) {
 	testRandomOp(t,
 		func(f1, f2, f3 *Int) {
@@ -268,6 +274,7 @@ func TestRandomSquare(t *testing.T) {
 		},
 	)
 }
+
 func TestRandomDiv(t *testing.T) {
 	testRandomOp(t,
 		func(f1, f2, f3 *Int) {
@@ -297,6 +304,7 @@ func TestRandomMod(t *testing.T) {
 		},
 	)
 }
+
 func TestRandomSMod(t *testing.T) {
 	testRandomOp(t,
 		func(f1, f2, f3 *Int) {