static int get_bits(Jpeg2000DecoderContext *s, int n)

{

    int res = 0;

    if (s->buf_end - s->buf < ((n - s->bit_index) >> 8))

        return AVERROR(EINVAL);

    while (--n >= 0) {

        res <<= 1;

        if (s->bit_index == 0) {

            s->bit_index = 7 + (*s->buf != 0xff);

            s->buf++;

        }

        s->bit_index--;

        res |= (*s->buf >> s->bit_index) & 1;

    }

    return res;

}
