screenpos
u16 w = scr_readw(screenpos(vc, offset, true));
return screenpos(vc, 2 * w_offset, viewed);
pos = (unsigned long)screenpos(vc, offset, viewed);
p = screenpos(vc, offset, viewed);
scr_writew(old, screenpos(vc, old_offset, true));
u16 *p = screenpos(vc, offset, true);