1/*
2 *  IP checksumming functions.
3 *  (c) 2008 Gerd Hoffmann <kraxel@redhat.com>
4 *
5 *  This program is free software; you can redistribute it and/or modify
6 *  it under the terms of the GNU General Public License as published by
7 *  the Free Software Foundation; under version 2 of the License.
8 *
9 *  This program is distributed in the hope that it will be useful,
10 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
11 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12 *  GNU General Public License for more details.
13 *
14 *  You should have received a copy of the GNU General Public License
15 *  along with this program; if not, see <http://www.gnu.org/licenses/>.
16 */
17
18#include "hw/hw.h"
19#include "net/net.h"
20
21#define PROTO_TCP  6
22#define PROTO_UDP 17
23
24uint32_t net_checksum_add(int len, uint8_t *buf)
25{
26    uint32_t sum = 0;
27    int i;
28
29    for (i = 0; i < len; i++) {
30	if (i & 1)
31	    sum += (uint32_t)buf[i];
32	else
33	    sum += (uint32_t)buf[i] << 8;
34    }
35    return sum;
36}
37
38uint16_t net_checksum_finish(uint32_t sum)
39{
40    while (sum>>16)
41	sum = (sum & 0xFFFF)+(sum >> 16);
42    return ~sum;
43}
44
45uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto,
46                             uint8_t *addrs, uint8_t *buf)
47{
48    uint32_t sum = 0;
49
50    sum += net_checksum_add(length, buf);         // payload
51    sum += net_checksum_add(8, addrs);            // src + dst address
52    sum += proto + length;                        // protocol & length
53    return net_checksum_finish(sum);
54}
55
56void net_checksum_calculate(uint8_t *data, int length)
57{
58    int hlen, plen, proto, csum_offset;
59    uint16_t csum;
60
61    if ((data[14] & 0xf0) != 0x40)
62	return; /* not IPv4 */
63    hlen  = (data[14] & 0x0f) * 4;
64    plen  = (data[16] << 8 | data[17]) - hlen;
65    proto = data[23];
66
67    switch (proto) {
68    case PROTO_TCP:
69	csum_offset = 16;
70	break;
71    case PROTO_UDP:
72	csum_offset = 6;
73	break;
74    default:
75	return;
76    }
77
78    if (plen < csum_offset+2)
79	return;
80
81    data[14+hlen+csum_offset]   = 0;
82    data[14+hlen+csum_offset+1] = 0;
83    csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);
84    data[14+hlen+csum_offset]   = csum >> 8;
85    data[14+hlen+csum_offset+1] = csum & 0xff;
86}
87