func: static int get_bits(Jpeg2000DecoderContext *s, int n)
  
  {
  
      int res = 0;
  
      if (s->buf_end - s->buf < ((n - s->bit_index) >> 8))
  
          return AVERROR_INVALIDDATA;
  
      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;
  
  }
  