new-feature: array: add ExtendIndex to allocate additional 0-bits aft…

…er Bitmaps and Offsets

array/base.go

@@ -75,6 +75,28 @@ func (a *Base) InitIndex(index []int32) error {
 	return nil
 }
 
+// ExtendIndex allocaed additional 0-bits after Bitmap and Offset.
+//
+// Since 0.5.8
+func (a *Base) ExtendIndex(n int32) {
+	nword := (n + 63) >> 6
+
+	if nword <= int32(len(a.Bitmaps)) {
+		return
+	}
+
+	bitmaps := make([]uint64, nword)
+	copy(bitmaps, a.Bitmaps)
+
+	a.Bitmaps = bitmaps
+	a.Offsets = newRankIndex1(a.Bitmaps)
+	for i, word := range a.Bitmaps {
+		if word == 0 {
+			a.Offsets[i] = 0
+		}
+	}
+}
+
 // GetEltIndex returns the position in a.Elts of element[idx] and a bool
 // indicating if found or not.
 // If "idx" absents it returns "0, false".

array/base_test.go

@@ -113,6 +113,30 @@ func TestBaseInitIndex(t *testing.T) {
 	}
 }
 
+func TestBase_ExtendIndex(t *testing.T) {
+
+	ta := require.New(t)
+
+	a := &array.Base{}
+	err := a.InitIndex([]int32{0, 1, 64, 66})
+	ta.Nil(err)
+
+	a.ExtendIndex(-1)
+	ta.Equal([]uint64{3, 5}, a.Bitmaps)
+	ta.Equal([]int32{0, 2}, a.Offsets)
+
+	a.ExtendIndex(128)
+	ta.Equal([]uint64{3, 5}, a.Bitmaps)
+	ta.Equal([]int32{0, 2}, a.Offsets)
+
+	a.ExtendIndex(256)
+	fmt.Println(a)
+
+	ta.Equal([]uint64{3, 5, 0, 0}, a.Bitmaps)
+	ta.Equal([]int32{0, 2, 0, 0}, a.Offsets)
+
+}
+
 func TestBaseInit(t *testing.T) {
 
 	ta := require.New(t)