rem: v |= bit; ioctl(fd, set, &v);  v &= ~bit;
add: v ^= bit;
context: int ppi_toggle ( int fd, int reg, int bit ){  unsigned char v;  unsigned long get, set;  int rc;  rc = ppi_getops ( reg, &get, &set );  if (rc)    return -1;  ioctl(fd, get, &v);  v |= bit;  ioctl(fd, set, &v);  v &= ~bit;  ioctl(fd, set, &v);  return 0;}