FD_SECTBASEMASK
if (_floppy->stretch & FD_SECTBASEMASK) {
if (((_floppy->stretch & (FD_SWAPSIDES | FD_SECTBASEMASK)) ||
(g->stretch & ~(FD_STRETCH | FD_SWAPSIDES | FD_SECTBASEMASK)) != 0)
(FD_SWAPSIDES | FD_SECTBASEMASK)))
#define FD_SECTBASE(floppy) ((((floppy)->stretch & FD_SECTBASEMASK) >> 2) ^ 1)