subsys/net/ip/utils.c - third_party/github/zephyrproject-rtos/zephyr - Git at Google

 /** @file
  * @brief Misc network utility functions
  *
  */

 /*
  * Copyright (c) 2016 Intel Corporation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #if defined(CONFIG_NET_DEBUG_UTILS)
 #define SYS_LOG_DOMAIN "net/utils"
 #define NET_DEBUG 1
 #endif

 #include <stdlib.h>
 #include <stdint.h>
 #include <stdbool.h>
 #include <string.h>
 #include <errno.h>

 #include <net/net_ip.h>
 #include <net/nbuf.h>
 #include <net/net_core.h>

 char *net_byte_to_hex(uint8_t *ptr, uint8_t byte, char base, bool pad)
 {
 	int i, val;

 	for (i = 0, val = (byte & 0xf0) >> 4; i < 2; i++, val = byte & 0x0f) {
 		if (i == 0 && !pad && !val) {
 			continue;
 		}
 		if (val < 10) {
 			*ptr++ = (char) (val + '0');
 		} else {
 			*ptr++ = (char) (val - 10 + base);
 		}
 	}

 	*ptr = '\0';

 	return ptr;
 }

 char *net_sprint_ll_addr_buf(const uint8_t *ll, uint8_t ll_len,
 			     char *buf, int buflen)
 {
 	uint8_t i, len, blen;
 	char *ptr = buf;

 	switch (ll_len) {
 	case 8:
 		len = 8;
 		break;
 	case 6:
 		len = 6;
 		break;
 	default:
 		len = 6;
 		break;
 	}

 	for (i = 0, blen = buflen; i < len && blen > 0; i++) {
 		ptr = net_byte_to_hex(ptr, ll[i], 'A', true);
 		*ptr++ = ':';
 		blen -= 3;
 	}

 	if (!(ptr - buf)) {
 		return NULL;
 	}

 	*(ptr - 1) = '\0';
 	return buf;
 }

 static int net_value_to_udec(char *buf, uint32_t value, int precision)
 {
 	uint32_t divisor;
 	int i;
 	int temp;
 	char *start = buf;

 	divisor = 1000000000;
 	if (precision < 0)
 		precision = 1;
 	for (i = 9; i >= 0; i--, divisor /= 10) {
 		temp = value / divisor;
 		value = value % divisor;
 		if ((precision > i) || (temp != 0)) {
 			precision = i;
 			*buf++ = (char) (temp + '0');
 		}
 	}
 	*buf = 0;

 	return buf - start;
 }

 char *net_sprint_ip_addr_buf(const uint8_t *ip, int ip_len,
 			     char *buf, int buflen)
 {
 	uint16_t *w = (uint16_t *)ip;
 	uint8_t i, bl, bh, longest = 1;
 	int8_t pos = -1;
 	char delim = ':';
 	unsigned char zeros[8] = { 0 };
 	char *ptr = buf;
 	int len = -1;
 	uint16_t value;
 	bool needcolon = false;

 	switch (ip_len) {
 	case 16:
 		len = 8;

 		for (i = 0; i < 8; i++) {
 			uint8_t j;

 			for (j = i; j < 8; j++) {
 				if (w[j] != 0) {
 					break;
 				}
 				zeros[i]++;
 			}
 		}

 		for (i = 0; i < 8; i++) {
 			if (zeros[i] > longest) {
 				longest = zeros[i];
 				pos = i;
 			}
 		}

 		if (longest == 1) {
 			pos = -1;
 		}
 		break;

 	case 4:
 		len = 4;
 		delim = '.';
 		break;
 	default:
 		break;
 	}

 	/* Invalid len, bail out */
 	if (len < 0) {
 		return NULL;
 	}

 	for (i = 0; i < len; i++) {

 		/* IPv4 address a.b.c.d */
 		if (len == 4) {
 			uint8_t l;

 			value = (uint32_t)ip[i];

 			/* net_byte_to_udec() eats 0 */
 			if (value == 0) {
 				*ptr++ = '0';
 				*ptr++ = delim;
 				continue;
 			}

 			l = net_value_to_udec(ptr, value, 0);

 			ptr += l;
 			*ptr++ = delim;
 			continue;
 		}

 		/* IPv6 address */
 		if (i == pos) {
 			if (needcolon || i == 0) {
 				*ptr++ = ':';
 			}
 			*ptr++ = ':';
 			needcolon = false;
 			i += longest - 1;
 			continue;
 		}

 		if (needcolon) {
 			*ptr++ = ':';
 			needcolon = false;
 		}

 		value = (uint32_t)sys_be16_to_cpu(w[i]);
 		bh = value >> 8;
 		bl = value & 0xff;

 		if (bh) {
 			if (bh > 0x0f) {
 				ptr = net_byte_to_hex(ptr, bh, 'a', false);
 			} else {
 				if (bh < 10) {
 					*ptr++ = (char)(bh + '0');
 				} else {
 					*ptr++ = (char) (bh - 10 + 'a');
 				}
 			}
 			ptr = net_byte_to_hex(ptr, bl, 'a', true);
 		} else if (bl > 0x0f) {
 			ptr = net_byte_to_hex(ptr, bl, 'a', false);
 		} else {
 			if (bl < 10) {
 				*ptr++ = (char)(bl + '0');
 			} else {
 				*ptr++ = (char) (bl - 10 + 'a');
 			}
 		}
 		needcolon = true;
 	}

 	if (!(ptr - buf)) {
 		return NULL;
 	}

 	if (ip_len == 4) {
 		*(ptr - 1) = '\0';
 	} else {
 		*ptr = '\0';
 	}

 	return buf;
 }

 int net_addr_pton(sa_family_t family, const char *src,
 		  struct sockaddr *dst)
 {
 	if (family == AF_INET) {
 		struct in_addr *addr = (struct in_addr *)dst;
 		int i, len;

 		len = strlen(src);
 		for (i = 0; i < len; i++) {
 			if (!(src[i] >= '0' && src[i] <= '9') &&
 			    src[i] != '.') {
 				return -EINVAL;
 			}
 		}

 		memset(addr, 0, sizeof(struct in_addr));

 		for (i = 0; i < sizeof(struct in_addr); i++) {
 			char *endptr;

 			addr->s4_addr[i] = strtol(src, &endptr, 10);

 			src = ++endptr;
 		}

 	} else if (family == AF_INET6) {
 		/* If the string contains a '.', it means it's of the form
 		 * X:X:X:X:X:X:x.x.x.x, and contains only 6 16-bit pieces
 		 */
 		int expected_groups = strchr(src, '.') ? 6 : 8;
 		struct in6_addr *addr = (struct in6_addr *)dst;
 		int i, len;

 		if (*src == ':') {
 			/* Ignore a leading colon, makes parsing neater */
 			src++;
 		}

 		len = strlen(src);
 		for (i = 0; i < len; i++) {
 			if (!(src[i] >= '0' && src[i] <= '9') &&
 			    !(src[i] >= 'A' && src[i] <= 'F') &&
 			    !(src[i] >= 'a' && src[i] <= 'f') &&
 			    src[i] != '.' && src[i] != ':')
 				return -EINVAL;
 		}

 		for (i = 0; i < expected_groups; i++) {
 			char *tmp;

 			if (!src || *src == '\0') {
 				return -EINVAL;
 			}

 			if (*src != ':') {
 				/* Normal IPv6 16-bit piece */
 				addr->s6_addr16[i] = htons(strtol(src, NULL,
 								  16));
 				src = strchr(src, ':');
 				if (!src && i < expected_groups - 1) {
 					return -EINVAL;
 				}

 				src++;
 				continue;
 			}

 			/* Two colons in a row */

 			for (; i < expected_groups; i++) {
 				addr->s6_addr16[i] = 0;
 			}

 			tmp = strrchr(src, ':');
 			if (src == tmp && (expected_groups == 6 || !src[1])) {
 				src++;
 				break;
 			}

 			if (expected_groups == 6) {
 				/* we need to drop the trailing
 				 * colon since it's between the
 				 * ipv6 and ipv4 addresses, rather than being
 				 * a part of the ipv6 address
 				 */
 				tmp--;
 			}

 			/* Calculate the amount of skipped zeros */
 			i = expected_groups - 1;
 			do {
 				if (*tmp == ':') {
 					i--;
 				}
 			} while (tmp-- != src);

 			src++;
 		}

 		if (expected_groups == 6) {
 			/* Parse the IPv4 part */
 			for (i = 0; i < 4; i++) {
 				if (!src || !*src) {
 					return -EINVAL;
 				}

 				addr->s6_addr[12 + i] = strtol(src, NULL, 10);

 				src = strchr(src, '.');
 				if (!src && i < 3) {
 					return -EINVAL;
 				}

 				src++;
 			}
 		}
 	} else {
 		return -EINVAL;
 	}

 	return 0;
 }

 static uint16_t calc_chksum(uint16_t sum, const uint8_t *ptr, uint16_t len)
 {
 	uint16_t tmp;
 	const uint8_t *end;

 	end = ptr + len - 1;

 	while (ptr < end) {
 		tmp = (ptr[0] << 8) + ptr[1];
 		sum += tmp;
 		if (sum < tmp) {
 			sum++;
 		}
 		ptr += 2;
 	}

 	if (ptr == end) {
 		tmp = ptr[0] << 8;
 		sum += tmp;
 		if (sum < tmp) {
 			sum++;
 		}
 	}

 	return sum;
 }

 static inline uint16_t calc_chksum_buf(uint16_t sum, struct net_buf *buf,
 				       uint16_t upper_layer_len)
 {
 	struct net_buf *frag = buf->frags;
 	uint16_t proto_len = net_nbuf_ip_hdr_len(buf) + net_nbuf_ext_len(buf);
 	int16_t len = frag->len - proto_len;
 	uint8_t *ptr = frag->data + proto_len;

 	if (len < 0) {
 		NET_DBG("1st fragment len %u < IP header len %u",
 			frag->len, proto_len);
 		return 0;
 	}

 	while (frag) {
 		sum = calc_chksum(sum, ptr, len);
 		frag = frag->frags;
 		if (!frag) {
 			break;
 		}

 		ptr = frag->data;

 		/* Do we need to take first byte from next fragment */
 		if (len % 2) {
 			uint16_t tmp = *ptr;
 			sum += tmp;
 			if (sum < tmp) {
 				sum++;
 			}
 			len = frag->len - 1;
 			ptr++;
 		} else {
 			len = frag->len;
 		}
 	}

 	return sum;
 }

 uint16_t net_calc_chksum(struct net_buf *buf, uint8_t proto)
 {
 	uint16_t upper_layer_len;
 	uint16_t sum;

 	switch (net_nbuf_family(buf)) {
 #if defined(CONFIG_NET_IPV4)
 	case AF_INET:
 		upper_layer_len = (NET_IPV4_BUF(buf)->len[0] << 8) +
 			NET_IPV4_BUF(buf)->len[1] -
 			net_nbuf_ext_len(buf) -
 			net_nbuf_ip_hdr_len(buf);

 		if (proto == IPPROTO_ICMP) {
 			return htons(calc_chksum(0, net_nbuf_ip_data(buf) +
 						 net_nbuf_ip_hdr_len(buf),
 						 upper_layer_len));
 		} else {
 			sum = calc_chksum(upper_layer_len + proto,
 					  (uint8_t *)&NET_IPV4_BUF(buf)->src,
 					  2 * sizeof(struct in_addr));
 		}
 		break;
 #endif
 #if defined(CONFIG_NET_IPV6)
 	case AF_INET6:
 		upper_layer_len = (NET_IPV6_BUF(buf)->len[0] << 8) +
 			NET_IPV6_BUF(buf)->len[1] - net_nbuf_ext_len(buf);
 		sum = calc_chksum(upper_layer_len + proto,
 				  (uint8_t *)&NET_IPV6_BUF(buf)->src,
 				  2 * sizeof(struct in6_addr));
 		break;
 #endif
 	default:
 		NET_DBG("Unknown protocol family %d", net_nbuf_family(buf));
 		return 0;
 	}

 	sum = calc_chksum_buf(sum, buf, upper_layer_len);

 	sum = (sum == 0) ? 0xffff : htons(sum);

 	return sum;
 }

 #if defined(CONFIG_NET_IPV4)
 uint16_t net_calc_chksum_ipv4(struct net_buf *buf)
 {
 	uint16_t sum;

 	sum = calc_chksum(0, (uint8_t *)NET_IPV4_BUF(buf), NET_IPV4H_LEN);

 	sum = (sum == 0) ? 0xffff : htons(sum);

 	return sum;
 }
 #endif /* CONFIG_NET_IPV4 */
	/** @file
	* @brief Misc network utility functions
	*
	*/

	/*
	* Copyright (c) 2016 Intel Corporation
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#if defined(CONFIG_NET_DEBUG_UTILS)
	#define SYS_LOG_DOMAIN "net/utils"
	#define NET_DEBUG 1
	#endif

	#include <stdlib.h>
	#include <stdint.h>
	#include <stdbool.h>
	#include <string.h>
	#include <errno.h>

	#include <net/net_ip.h>
	#include <net/nbuf.h>
	#include <net/net_core.h>

	char net_byte_to_hex(uint8_t ptr, uint8_t byte, char base, bool pad)
	{
	int i, val;

	for (i = 0, val = (byte & 0xf0) >> 4; i < 2; i++, val = byte & 0x0f) {
	if (i == 0 && !pad && !val) {
	continue;
	}
	if (val < 10) {
	*ptr++ = (char) (val + '0');
	} else {
	*ptr++ = (char) (val - 10 + base);
	}
	}

	*ptr = '\0';

	return ptr;
	}

	char net_sprint_ll_addr_buf(const uint8_t ll, uint8_t ll_len,
	char *buf, int buflen)
	{
	uint8_t i, len, blen;
	char *ptr = buf;

	switch (ll_len) {
	case 8:
	len = 8;
	break;
	case 6:
	len = 6;
	break;
	default:
	len = 6;
	break;
	}

	for (i = 0, blen = buflen; i < len && blen > 0; i++) {
	ptr = net_byte_to_hex(ptr, ll[i], 'A', true);
	*ptr++ = ':';
	blen -= 3;
	}

	if (!(ptr - buf)) {
	return NULL;
	}

	*(ptr - 1) = '\0';
	return buf;
	}

	static int net_value_to_udec(char *buf, uint32_t value, int precision)
	{
	uint32_t divisor;
	int i;
	int temp;
	char *start = buf;

	divisor = 1000000000;
	if (precision < 0)
	precision = 1;
	for (i = 9; i >= 0; i--, divisor /= 10) {
	temp = value / divisor;
	value = value % divisor;
	if ((precision > i) \|\| (temp != 0)) {
	precision = i;
	*buf++ = (char) (temp + '0');
	}
	}
	*buf = 0;

	return buf - start;
	}

	char net_sprint_ip_addr_buf(const uint8_t ip, int ip_len,
	char *buf, int buflen)
	{
	uint16_t w = (uint16_t )ip;
	uint8_t i, bl, bh, longest = 1;
	int8_t pos = -1;
	char delim = ':';
	unsigned char zeros[8] = { 0 };
	char *ptr = buf;
	int len = -1;
	uint16_t value;
	bool needcolon = false;

	switch (ip_len) {
	case 16:
	len = 8;

	for (i = 0; i < 8; i++) {
	uint8_t j;

	for (j = i; j < 8; j++) {
	if (w[j] != 0) {
	break;
	}
	zeros[i]++;
	}
	}

	for (i = 0; i < 8; i++) {
	if (zeros[i] > longest) {
	longest = zeros[i];
	pos = i;
	}
	}

	if (longest == 1) {
	pos = -1;
	}
	break;

	case 4:
	len = 4;
	delim = '.';
	break;
	default:
	break;
	}

	/* Invalid len, bail out */
	if (len < 0) {
	return NULL;
	}

	for (i = 0; i < len; i++) {

	/* IPv4 address a.b.c.d */
	if (len == 4) {
	uint8_t l;

	value = (uint32_t)ip[i];

	/* net_byte_to_udec() eats 0 */
	if (value == 0) {
	*ptr++ = '0';
	*ptr++ = delim;
	continue;
	}

	l = net_value_to_udec(ptr, value, 0);

	ptr += l;
	*ptr++ = delim;
	continue;
	}

	/* IPv6 address */
	if (i == pos) {
	if (needcolon \|\| i == 0) {
	*ptr++ = ':';
	}
	*ptr++ = ':';
	needcolon = false;
	i += longest - 1;
	continue;
	}

	if (needcolon) {
	*ptr++ = ':';
	needcolon = false;
	}

	value = (uint32_t)sys_be16_to_cpu(w[i]);
	bh = value >> 8;
	bl = value & 0xff;

	if (bh) {
	if (bh > 0x0f) {
	ptr = net_byte_to_hex(ptr, bh, 'a', false);
	} else {
	if (bh < 10) {
	*ptr++ = (char)(bh + '0');
	} else {
	*ptr++ = (char) (bh - 10 + 'a');
	}
	}
	ptr = net_byte_to_hex(ptr, bl, 'a', true);
	} else if (bl > 0x0f) {
	ptr = net_byte_to_hex(ptr, bl, 'a', false);
	} else {
	if (bl < 10) {
	*ptr++ = (char)(bl + '0');
	} else {
	*ptr++ = (char) (bl - 10 + 'a');
	}
	}
	needcolon = true;
	}

	if (!(ptr - buf)) {
	return NULL;
	}

	if (ip_len == 4) {
	*(ptr - 1) = '\0';
	} else {
	*ptr = '\0';
	}

	return buf;
	}

	int net_addr_pton(sa_family_t family, const char *src,
	struct sockaddr *dst)
	{
	if (family == AF_INET) {
	struct in_addr addr = (struct in_addr )dst;
	int i, len;

	len = strlen(src);
	for (i = 0; i < len; i++) {
	if (!(src[i] >= '0' && src[i] <= '9') &&
	src[i] != '.') {
	return -EINVAL;
	}
	}

	memset(addr, 0, sizeof(struct in_addr));

	for (i = 0; i < sizeof(struct in_addr); i++) {
	char *endptr;

	addr->s4_addr[i] = strtol(src, &endptr, 10);

	src = ++endptr;
	}

	} else if (family == AF_INET6) {
	/* If the string contains a '.', it means it's of the form
	* X:X:X:X:X:X:x.x.x.x, and contains only 6 16-bit pieces
	*/
	int expected_groups = strchr(src, '.') ? 6 : 8;
	struct in6_addr addr = (struct in6_addr )dst;
	int i, len;

	if (*src == ':') {
	/* Ignore a leading colon, makes parsing neater */
	src++;
	}

	len = strlen(src);
	for (i = 0; i < len; i++) {
	if (!(src[i] >= '0' && src[i] <= '9') &&
	!(src[i] >= 'A' && src[i] <= 'F') &&
	!(src[i] >= 'a' && src[i] <= 'f') &&
	src[i] != '.' && src[i] != ':')
	return -EINVAL;
	}

	for (i = 0; i < expected_groups; i++) {
	char *tmp;

	if (!src \|\| *src == '\0') {
	return -EINVAL;
	}

	if (*src != ':') {
	/* Normal IPv6 16-bit piece */
	addr->s6_addr16[i] = htons(strtol(src, NULL,
	16));
	src = strchr(src, ':');
	if (!src && i < expected_groups - 1) {
	return -EINVAL;
	}

	src++;
	continue;
	}

	/* Two colons in a row */

	for (; i < expected_groups; i++) {
	addr->s6_addr16[i] = 0;
	}

	tmp = strrchr(src, ':');
	if (src == tmp && (expected_groups == 6 \|\| !src[1])) {
	src++;
	break;
	}

	if (expected_groups == 6) {
	/* we need to drop the trailing
	* colon since it's between the
	* ipv6 and ipv4 addresses, rather than being
	* a part of the ipv6 address
	*/
	tmp--;
	}

	/* Calculate the amount of skipped zeros */
	i = expected_groups - 1;
	do {
	if (*tmp == ':') {
	i--;
	}
	} while (tmp-- != src);

	src++;
	}

	if (expected_groups == 6) {
	/* Parse the IPv4 part */
	for (i = 0; i < 4; i++) {
	if (!src \|\| !*src) {
	return -EINVAL;
	}

	addr->s6_addr[12 + i] = strtol(src, NULL, 10);

	src = strchr(src, '.');
	if (!src && i < 3) {
	return -EINVAL;
	}

	src++;
	}
	}
	} else {
	return -EINVAL;
	}

	return 0;
	}

	static uint16_t calc_chksum(uint16_t sum, const uint8_t *ptr, uint16_t len)
	{
	uint16_t tmp;
	const uint8_t *end;

	end = ptr + len - 1;

	while (ptr < end) {
	tmp = (ptr[0] << 8) + ptr[1];
	sum += tmp;
	if (sum < tmp) {
	sum++;
	}
	ptr += 2;
	}

	if (ptr == end) {
	tmp = ptr[0] << 8;
	sum += tmp;
	if (sum < tmp) {
	sum++;
	}
	}

	return sum;
	}

	static inline uint16_t calc_chksum_buf(uint16_t sum, struct net_buf *buf,
	uint16_t upper_layer_len)
	{
	struct net_buf *frag = buf->frags;
	uint16_t proto_len = net_nbuf_ip_hdr_len(buf) + net_nbuf_ext_len(buf);
	int16_t len = frag->len - proto_len;
	uint8_t *ptr = frag->data + proto_len;

	if (len < 0) {
	NET_DBG("1st fragment len %u < IP header len %u",
	frag->len, proto_len);
	return 0;
	}

	while (frag) {
	sum = calc_chksum(sum, ptr, len);
	frag = frag->frags;
	if (!frag) {
	break;
	}

	ptr = frag->data;

	/* Do we need to take first byte from next fragment */
	if (len % 2) {
	uint16_t tmp = *ptr;
	sum += tmp;
	if (sum < tmp) {
	sum++;
	}
	len = frag->len - 1;
	ptr++;
	} else {
	len = frag->len;
	}
	}

	return sum;
	}

	uint16_t net_calc_chksum(struct net_buf *buf, uint8_t proto)
	{
	uint16_t upper_layer_len;
	uint16_t sum;

	switch (net_nbuf_family(buf)) {
	#if defined(CONFIG_NET_IPV4)
	case AF_INET:
	upper_layer_len = (NET_IPV4_BUF(buf)->len[0] << 8) +
	NET_IPV4_BUF(buf)->len[1] -
	net_nbuf_ext_len(buf) -
	net_nbuf_ip_hdr_len(buf);

	if (proto == IPPROTO_ICMP) {
	return htons(calc_chksum(0, net_nbuf_ip_data(buf) +
	net_nbuf_ip_hdr_len(buf),
	upper_layer_len));
	} else {
	sum = calc_chksum(upper_layer_len + proto,
	(uint8_t *)&NET_IPV4_BUF(buf)->src,
	2 * sizeof(struct in_addr));
	}
	break;
	#endif
	#if defined(CONFIG_NET_IPV6)
	case AF_INET6:
	upper_layer_len = (NET_IPV6_BUF(buf)->len[0] << 8) +
	NET_IPV6_BUF(buf)->len[1] - net_nbuf_ext_len(buf);
	sum = calc_chksum(upper_layer_len + proto,
	(uint8_t *)&NET_IPV6_BUF(buf)->src,
	2 * sizeof(struct in6_addr));
	break;
	#endif
	default:
	NET_DBG("Unknown protocol family %d", net_nbuf_family(buf));
	return 0;
	}

	sum = calc_chksum_buf(sum, buf, upper_layer_len);

	sum = (sum == 0) ? 0xffff : htons(sum);

	return sum;
	}

	#if defined(CONFIG_NET_IPV4)
	uint16_t net_calc_chksum_ipv4(struct net_buf *buf)
	{
	uint16_t sum;

	sum = calc_chksum(0, (uint8_t *)NET_IPV4_BUF(buf), NET_IPV4H_LEN);

	sum = (sum == 0) ? 0xffff : htons(sum);

	return sum;
	}
	#endif /* CONFIG_NET_IPV4 */