// least-significant places and masks off anything above.
	n = (br.n >> (br.bits - bits)) & ((1 << bits) - 1)
	br.bits -= bits
	return
}

func (br *bitReader) ReadBits(bits uint) (n int) {
	n64 := br.ReadBits64(bits)
	return int(n64)
}

func (br *bitReader) ReadBit() bool {
	n := br.ReadBits(1)
	return n != 0
}

func (br *bitReader) Err() error {
	return br.err

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 {