// least n. For best performance (avoiding function calls inside hot loops),
// the caller is the one responsible for first checking that d.bits.n < n.
func (d *decoder) ensureNBits(n int32) error {
	for {
		c, err := d.readByteStuffedByte()
		if err != nil {
			if err == io.ErrUnexpectedEOF {
				return errShortHuffmanData
			}
			return err
		}
		d.bits.a = d.bits.a<<8 | uint32(c)
		d.bits.n += 8
		if d.bits.m == 0 {