code: func NewContainerBitmap(n int32, bitmap []uint64) *Container {
  	if bitmap == nil {
  		bitmap = make([]uint64, bitmapN)
  	}
  	// pad to required length
  	if len(bitmap) < bitmapN {
  		bm2 := make([]uint64, bitmapN)
  		copy(bm2, bitmap)
  		bitmap = bm2
  	}
  	c := &Container{typ: containerBitmap, n: n}
  	c.setBitmap(bitmap)
  	return c
  }
docs: // NewContainerBitmap makes a bitmap container using the provided bitmap, or
  // an empty one if provided bitmap is nil. If the provided bitmap is too short,
  // it will be padded.