#include <u.h>#include <libc.h> uchar classmask[4][4] = {	0xff, 0x00, 0x00, 0x00,	0xff, 0x00, 0x00, 0x00,	0xff, 0xff, 0x00, 0x00,	0xff, 0xff, 0xff, 0x00,}; voidmaskip(uchar *a, uchar *m, uchar *n){	int i; 	for(i = 0; i < 4; i++)		n[i] = a[i] & m[i];}