added convience function to calculate size of bitmap in bytes

completed test converage

roaring/roaring.go

@@ -232,6 +232,18 @@ func (b *Bitmap) Count() (n uint64) {
 	return b.Containers.Count()
 }
 
+// Size returns the number of bytes required for the bitmap.
+func (b *Bitmap) Size() (numbytes int) {
+
+	citer, _ := b.Containers.Iterator(0)
+	for citer.Next() {
+		_, c := citer.Value()
+		numbytes += c.size()
+
+	}
+	return
+}
+
 // CountRange returns the number of bits set between [start, end).
 func (b *Bitmap) CountRange(start, end uint64) (n uint64) {
 	if b.Containers.Size() == 0 {

roaring/roaring_test.go

@@ -37,6 +37,29 @@ func TestContainerCount(t *testing.T) {
 		t.Fatalf("Count != CountRange\n")
 	}
 }
+func TestSize(t *testing.T) {
+	//array
+	a := roaring.NewFileBitmap(0, 65535, 131072)
+	if a.Size() != 6 {
+		t.Fatalf("Size in bytes incorrect \n")
+	}
+
+	//bitmap
+	b := roaring.NewFileBitmap()
+	for i:=uint64(0);i<2048;i++{
+		b.DirectAdd(i)
+	}
+
+	if b.Size() != 4096 {
+		t.Fatalf("Size in bytes incorrect \n")
+	}
+    //convert to rle
+	b.Optimize()
+	//rle
+	if b.Size() != 6 {
+		t.Fatalf("Size in bytes incorrect \n")
+	}
+}
 
 func TestCountRange(t *testing.T) {
 	tests := []struct {