/*
 * NATv6: IPv6-to-IPv6 Network Prefix Translation as
 * proposed in RFC 6296.
 * Based on MAP66 (c) 2010 sven-ola()gmx.de
 * (c) 2011 mschiffer()universe-factory.net "I'm the one to blame for any problems with this version ;P"
 */

#ifndef _IP6T_NPTV6_COMMON_H
#define _IP6T_NPTV6_COMMON_H

#include "ip6t_NPTV6.h"
#include <net/ipv6.h>


#ifndef pr_devel
#  ifdef DEBUG
#    define pr_devel(fmt, ...) printk(fmt, ##__VA_ARGS__)
#  else
#    define pr_devel(fmt, ...) ({ if (0); })
#  endif
#endif

#ifndef NIP6_FMT
#  define NIP6_FMT "%04x:%04x:%04x:%04x:%04x:%04x:%04x:%04x"
#  define NIP6(addr) \
	ntohs((addr).s6_addr16[0]), \
	ntohs((addr).s6_addr16[1]), \
	ntohs((addr).s6_addr16[2]), \
	ntohs((addr).s6_addr16[3]), \
	ntohs((addr).s6_addr16[4]), \
	ntohs((addr).s6_addr16[5]), \
	ntohs((addr).s6_addr16[6]), \
	ntohs((addr).s6_addr16[7])
#endif


/* Ones' complement add */
static inline u_int16_t add16(u_int16_t a, u_int16_t b)
{
	a += b;
	return a + (a < b);
}

static bool translate_address(struct in6_addr *addr, const struct in6_addr *prefix, u_int16_t plen) {
	u_int16_t csum = 0;
	int o = plen / 16, b = plen % 16;
	int fix_word;
	int i;

	/* Fix checksum like specified in RFC 6296 */
	if (plen <= 48) {
		fix_word = 3;
	}
	else {
		for (fix_word = 4; fix_word < 7; fix_word++) {
			if (addr->s6_addr16[fix_word] != 0xffff)
				break;
		}
	}

	if (addr->s6_addr16[fix_word] == 0xffff) {
		/* Fail before the address is translated so the ICMP error can be sent */
		return false;
	}


	for (i = 0; i < o; i++) {
		csum = add16(csum, addr->s6_addr16[i]);
		csum = add16(csum, ~prefix->s6_addr16[i]);

		addr->s6_addr16[i] = prefix->s6_addr16[i];
	}

	if (b != 0) {
		u_int16_t bmask = 0xffff << (16-b);
		csum = add16(csum, addr->s6_addr16[o] & bmask);
		csum = add16(csum, ~(prefix->s6_addr16[o] & bmask));

		addr->s6_addr16[o] &= bmask;
		addr->s6_addr16[o] |= (prefix->s6_addr16[o] & bmask);
	}


	addr->s6_addr16[fix_word] = add16(addr->s6_addr16[fix_word], csum);
	if (addr->s6_addr16[fix_word] == 0xffff) {
		addr->s6_addr16[fix_word] = 0;
	}

	return true;
}

#endif /*_IP6T_NPTV6_COMMON_H*/