ENSURE(0 <= pos && pos < 0xff);
ENSURE(0 <= pos && pos < 255);
aspath_extract(void *seg, int pos){	u_char		*ptr = seg;	u_int16_t	 as = 0;	ENSURE(0 <= pos && pos < 0xff);	ptr += 2 + 2 * pos;	as = *ptr++;	as <<= 8;	as |= *ptr;	return as;}