static int read_extra_header(FFV1Context *f)
{
    RangeCoder *const c = &f->c;
    uint8_t state[CONTEXT_SIZE];
    int i, j, k, ret;
    uint8_t state2[32][CONTEXT_SIZE];

    memset(state2, 128, sizeof(state2));
    memset(state, 128, sizeof(state));

    ff_init_range_decoder(c, f->avctx->extradata, f->avctx->extradata_size);
    ff_build_rac_states(c, 0.05 * (1LL << 32), 256 - 8);

    f->version = get_symbol(c, state, 0);
    if (f->version < 2) {
        av_log(f->avctx, AV_LOG_ERROR, "Invalid version in global header\n");
        return AVERROR_INVALIDDATA;
    }
    if (f->version > 2) {
        c->bytestream_end -= 4;
        f->micro_version = get_symbol(c, state, 0);
    }
    f->ac = f->avctx->coder_type = get_symbol(c, state, 0);
    if (f->ac > 1) {
        for (i = 1; i < 256; i++)
            f->state_transition[i] = get_symbol(c, state, 1) + c->one_state[i];
    }

    f->colorspace                 = get_symbol(c, state, 0); //YUV cs type
    f->avctx->bits_per_raw_sample = get_symbol(c, state, 0);
    f->chroma_planes              = get_rac(c, state);
    f->chroma_h_shift             = get_symbol(c, state, 0);
    f->chroma_v_shift             = get_symbol(c, state, 0);
    f->transparency               = get_rac(c, state);
    f->plane_count                = 1 + (f->chroma_planes || f->version<4) + f->transparency;
    f->num_h_slices               = 1 + get_symbol(c, state, 0);
    f->num_v_slices               = 1 + get_symbol(c, state, 0);

    if (f->chroma_h_shift > 4U || f->chroma_v_shift > 4U) {
        av_log(f->avctx, AV_LOG_ERROR, "chroma shift parameters %d %d are invalid\n",
               f->chroma_h_shift, f->chroma_v_shift);
        return AVERROR_INVALIDDATA;
    }

    if (f->num_h_slices > (unsigned)f->width  || !f->num_h_slices ||
        f->num_v_slices > (unsigned)f->height || !f->num_v_slices
       ) {
        av_log(f->avctx, AV_LOG_ERROR, "slice count invalid\n");
        return AVERROR_INVALIDDATA;
    }

    f->quant_table_count = get_symbol(c, state, 0);
    if (f->quant_table_count > (unsigned)MAX_QUANT_TABLES || !f->quant_table_count) {
        av_log(f->avctx, AV_LOG_ERROR, "quant table count %d is invalid\n", f->quant_table_count);
        f->quant_table_count = 0;
        return AVERROR_INVALIDDATA;
    }

    for (i = 0; i < f->quant_table_count; i++) {
        f->context_count[i] = read_quant_tables(c, f->quant_tables[i]);
        if (f->context_count[i] < 0) {
            av_log(f->avctx, AV_LOG_ERROR, "read_quant_table error\n");
            return AVERROR_INVALIDDATA;
        }
    }
    if ((ret = ffv1_allocate_initial_states(f)) < 0)
        return ret;

    for (i = 0; i < f->quant_table_count; i++)
        if (get_rac(c, state)) {
            for (j = 0; j < f->context_count[i]; j++)
                for (k = 0; k < CONTEXT_SIZE; k++) {
                    int pred = j ? f->initial_states[i][j - 1][k] : 128;
                    f->initial_states[i][j][k] =
                        (pred + get_symbol(c, state2[k], 1)) & 0xFF;
                }
        }

    if (f->version > 2) {
        f->ec = get_symbol(c, state, 0);
        if (f->micro_version > 2)
            f->intra = get_symbol(c, state, 0);
    }

    if (f->version > 2) {
        unsigned v;
        v = av_crc(av_crc_get_table(AV_CRC_32_IEEE), 0,
                   f->avctx->extradata, f->avctx->extradata_size);
        if (v) {
            av_log(f->avctx, AV_LOG_ERROR, "CRC mismatch %X!\n", v);
            return AVERROR_INVALIDDATA;
        }
    }

    if (f->avctx->debug & FF_DEBUG_PICT_INFO)
        av_log(f->avctx, AV_LOG_DEBUG,
               "global: ver:%d.%d, coder:%d, colorspace: %d bpr:%d chroma:%d(%d:%d), alpha:%d slices:%dx%d qtabs:%d ec:%d intra:%d\n",
               f->version, f->micro_version,
               f->ac,
               f->colorspace,
               f->avctx->bits_per_raw_sample,
               f->chroma_planes, f->chroma_h_shift, f->chroma_v_shift,
               f->transparency,
               f->num_h_slices, f->num_v_slices,
               f->quant_table_count,
               f->ec,
               f->intra
              );
    return 0;
}
Unknown