struct header_t
{
    unsigned 8  big    magic_number[2];
    unsigned 32 little file_size;
    unsigned 16 little creator1;
    unsigned 16 little creator2;
    unsigned 32 little bmp_offset;

    invariant ok_magic_number = str(@magic_number) == 'BM';
}

struct dib_t
{
    unsigned 32 little header_size;

    enumerate (header_size)
    {
        12 :
        {
            unsigned 16 little width;
            unsigned 16 little height;
        }
        40 :
        {
            unsigned 32 little width;
            unsigned 32 little height;
        }
    }

    unsigned 16 little color_plane_count;
    unsigned 16 little bpp;

    if (header_size == 40)
    {
        unsigned 32 little compression_method;
        unsigned 32 little image_size;
        unsigned 32 little h_res;
        unsigned 32 little v_res;
        unsigned 32 little color_palette_count;
        unsigned 32 little important_color_count; // generally ignored
    }
}

struct pixel_row_t
{
    const pixel_size   = dib_header.width * (dib_header.bpp / 8);
    const padding_size = dib_header.width % 4;

    unsigned 8 big pixels[pixel_size];

    if (padding_size != 0)
        skip padding[padding_size];
}

struct main
{
    header_t    header;
    dib_t       dib_header;
    pixel_row_t pixel_row_set[dib_header.height] @ header.bmp_offset;
}