proc unpack(s: RStream, buf: var seq[byte], width: uint32, height: uint32)
{.raises: [IOError, UnpackError].} =
  ##  Unpack PaintShop bitmap.
  let start_offset = s.getpos
  let pitch: uint32 = (width + 7) div 8
  var eoi_found = false

  var o: uint32 = 0
  var y: uint32 = 0

  while not s.atend and y < height:
    let ctrl = s.read_byte

    case ctrl
    of CtrlLineWhite:
      when RUseCopyMem:
        zeroMem buf[o].addr, pitch
        o += pitch
      else:
        for _ in 0 ..< pitch:
          buf[o] = 0x00
          inc o
      inc y
  # […]