add support for bit flip (negate) in roaring

roaring/roaring.go

@@ -673,6 +673,27 @@ func (b *Bitmap) Check() error {
 	return a
 }
 
+func (b *Bitmap) Flip(start, end uint64) *Bitmap {
+	result := NewBitmap()
+	itr := b.Iterator()
+	itr.Seek(start)
+	v, eof := itr.Next()
+	for i := start; i < end; i++ {
+		if eof {
+			result.add(i)
+		} else if v == i {
+			v, eof = itr.Next()
+		} else {
+			result.add(i)
+		}
+	}
+	for !eof {
+		result.add(v)
+		v, eof = itr.Next()
+	}
+	return result
+}
+
 // BitmapInfo represents a point-in-time snapshot of bitmap stats.
 type BitmapInfo struct {
 	OpN        int

roaring/roaring_test.go

@@ -168,7 +168,48 @@ func TestBitmap_Xor_BitmapBitmap(t *testing.T) {
 	}
 }
 
+// Ensure bitmap turn on and turn off
+func TestBitmap_Fipp_Empty(t *testing.T) {
+	bm := roaring.NewBitmap()
+	results := bm.Flip(0, 10)
+	if n := results.Count(); n != 10 {
+		t.Fatalf("unexpected n: %d", n)
+	}
+	results = results.Flip(0, 10)
+	if n := results.Count(); n != 0 {
+		t.Fatalf("unexpected n: %d", n)
+	}
+}
 
+// Test Subrange Flip should not affect bits outside of Range
+func TestBitmap_Fipp_Array(t *testing.T) {
+	bm := roaring.NewBitmap(0, 1, 2, 3, 4, 8, 16, 32, 64, 128, 256, 512, 1024)
+	results := bm.Flip(0, 5)
+	if n := results.Count(); n != 8 {
+		t.Fatalf("unexpected n: %d", n)
+	}
+	results = results.Flip(0, 5)
+	if n := results.Count(); n != 13 {
+		t.Fatalf("unexpected n: %d", n)
+	}
+
+}
+
+func TestBitmap_Fipp_Bitmap(t *testing.T) {
+	bm := roaring.NewBitmap()
+	size := uint64(10000)
+	for i := uint64(0); i < size; i += 2 {
+		bm.Add(i)
+	}
+	results := bm.Flip(0, size)
+	if n := results.Count(); n != size/2 {
+		t.Fatalf("unexpected n: %d", n)
+	}
+	results = results.Flip(0, size) //flipping back should be the same
+	if n := results.Count(); n != size/2 {
+		t.Fatalf("unexpected n: %d", n)
+	}
+}
 
 // Ensure bitmap can return the number of intersecting bits in two bitmaps.
 func TestBitmap_IntersectionCount_ArrayArray(t *testing.T) {