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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, write to the Free Software
16  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA  02110-1301 USA
17  */
18 
19 #include "hw/hw.h"
20 #include "net.h"
21 
22 #define PROTO_TCP  6
23 #define PROTO_UDP 17
24 
net_checksum_add(int len,uint8_t * buf)25 uint32_t net_checksum_add(int len, uint8_t *buf)
26 {
27     uint32_t sum = 0;
28     int i;
29 
30     for (i = 0; i < len; i++) {
31 	if (i & 1)
32 	    sum += (uint32_t)buf[i];
33 	else
34 	    sum += (uint32_t)buf[i] << 8;
35     }
36     return sum;
37 }
38 
net_checksum_finish(uint32_t sum)39 uint16_t net_checksum_finish(uint32_t sum)
40 {
41     while (sum>>16)
42 	sum = (sum & 0xFFFF)+(sum >> 16);
43     return ~sum;
44 }
45 
net_checksum_tcpudp(uint16_t length,uint16_t proto,uint8_t * addrs,uint8_t * buf)46 uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto,
47                              uint8_t *addrs, uint8_t *buf)
48 {
49     uint32_t sum = 0;
50 
51     sum += net_checksum_add(length, buf);         // payload
52     sum += net_checksum_add(8, addrs);            // src + dst address
53     sum += proto + length;                        // protocol & length
54     return net_checksum_finish(sum);
55 }
56 
net_checksum_calculate(uint8_t * data,int length)57 void net_checksum_calculate(uint8_t *data, int length)
58 {
59     int hlen, plen, proto, csum_offset;
60     uint16_t csum;
61 
62     if ((data[14] & 0xf0) != 0x40)
63 	return; /* not IPv4 */
64     hlen  = (data[14] & 0x0f) * 4;
65     plen  = (data[16] << 8 | data[17]) - hlen;
66     proto = data[23];
67 
68     switch (proto) {
69     case PROTO_TCP:
70 	csum_offset = 16;
71 	break;
72     case PROTO_UDP:
73 	csum_offset = 6;
74 	break;
75     default:
76 	return;
77     }
78 
79     if (plen < csum_offset+2)
80 	return;
81 
82     data[14+hlen+csum_offset]   = 0;
83     data[14+hlen+csum_offset+1] = 0;
84     csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);
85     data[14+hlen+csum_offset]   = csum >> 8;
86     data[14+hlen+csum_offset+1] = csum & 0xff;
87 }
88