if (code < 0)
if (code < 0){ fprintf(stderr, "invalid dc code at %d %d\n", s->mb_x, s->mb_y);
static inline int decode_dc(MpegEncContext *s, int component){    int code, diff;    if (component == 0) {        code = get_vlc2(&s->gb, dc_lum_vlc.table, DC_VLC_BITS, 1);    } else {        code = get_vlc2(&s->gb, dc_chroma_vlc.table, DC_VLC_BITS, 1);    }    if (code < 0)        return 0xffff;    if (code == 0) {        diff = 0;    } else {        diff = get_bits(&s->gb, code);        if ((diff & (1 << (code - 1))) == 0)             diff = (-1 << code) | (diff + 1);    }    return diff;}