module ChunkyPNG::Canvas::Adam7Interlacing

def adam7_multiplier_offset(pass)
  {
    :x_shift      => 3 - (pass >> 1), 
    :x_offset     => (pass & 1 == 0) ? 0 : 8 >> ((pass + 1) >> 1),
    :y_shift      => pass == 0 ? 3 : 3 - ((pass - 1) >> 1),
    :y_offset     => (pass == 0 || pass & 1 == 1) ? 0 : 8 >> (pass >> 1)
  }
end