{
    int cols_dim = mat->dims - 1;
    size_t cols = mat->size[cols_dim];
    CV_CheckLE(cols, (size_t)INT_MAX, "");  // 'int' only, size_t type is not supported for indexes
    size_t new_cols_idx = (size_t)indices[cols_dim] + inc;
    // only "cols" idx is allowed to be increased till the end
    // do not allow to jump forward because we should support non-contiguous layouts too (submats)
    CV_CheckLE(new_cols_idx, cols, "");
    if (new_cols_idx == cols)
    {
        indices[cols_dim] = 0;
        for (int dim = cols_dim - 1; dim >= 0; --dim)
        {
            int new_idx = indices[dim] + 1;
            if (new_idx != mat->size[dim])
            {
                indices[dim] = new_idx;
                return false;
            }
            else
            {
                indices[dim] = 0;
                continue;
            }
        }
        return true;
    }
    else
    {
        indices[cols_dim] = (int)new_cols_idx;
        return false;
    }
}

5, 6, 8