Fix a bug in bit_array's sub function (#2506)

libs/common/bit_array.go

@@ -189,7 +189,7 @@ func (bA *BitArray) Sub(o *BitArray) *BitArray {
 	if bA.Bits > o.Bits {
 		c := bA.copy()
 		for i := 0; i < len(o.Elems)-1; i++ {
-			c.Elems[i] &= ^c.Elems[i]
+			c.Elems[i] &= ^o.Elems[i]
 		}
 		i := len(o.Elems) - 1
 		if i >= 0 {

libs/common/bit_array_test.go

@@ -131,6 +131,34 @@ func TestSub2(t *testing.T) {
 	}
 }
 
+func TestSub3(t *testing.T) {
+
+	bA1, _ := randBitArray(231)
+	bA2, _ := randBitArray(81)
+	bA3 := bA1.Sub(bA2)
+
+	bNil := (*BitArray)(nil)
+	require.Equal(t, bNil.Sub(bA1), (*BitArray)(nil))
+	require.Equal(t, bA1.Sub(nil), (*BitArray)(nil))
+	require.Equal(t, bNil.Sub(nil), (*BitArray)(nil))
+
+	if bA3.Bits != bA1.Bits {
+		t.Error("Expected bA1 bits")
+	}
+	if len(bA3.Elems) != len(bA1.Elems) {
+		t.Error("Expected bA1 elems length")
+	}
+	for i := 0; i < bA3.Bits; i++ {
+		expected := bA1.GetIndex(i)
+		if i < bA2.Bits && bA2.GetIndex(i){
+			expected = false
+		}
+		if bA3.GetIndex(i) != expected {
+			t.Error("Wrong bit from bA3")
+		}
+	}
+}
+
 func TestPickRandom(t *testing.T) {
 	for idx := 0; idx < 123; idx++ {
 		bA1 := NewBitArray(123)