if (i_width_aligned > UINT64_MAX/i_height_aligned)
    error();

uint64_t i_pixels_divided = ((uint64_t)i_width_aligned * i_height_aligned) / 8;

size_t bpp = p_pic->format.i_bits_per_pixel;

if (i_pixels_divided > SIZE_MAX/bpp)
    error();

uint64_t i_bytes = i_pixels_divided * bpp;

// use i_bytes to allocate space; no need for any more checks.