func (x *Index) Read(r io.Reader) error {
	// buffer for all reads
	buf := make([]byte, bufSize)

	// read length
	n64, err := readInt(r, buf)
	if err != nil {
		return err
	}
	if int64(int(n64)) != n64 || int(n64) < 0 {
		return errTooBig
	}
	n := int(n64)

	// allocate space
	if 2*n < cap(x.data) || cap(x.data) < n || x.sa.int32 != nil && n > maxData32 || x.sa.int64 != nil && n <= maxData32 {