blob: 48f93d4699322184302032e9374da471f2803c20 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
|
#include <stdint.h>
#include <ip_checksum.h>
unsigned long compute_ip_checksum(void *addr, unsigned long length)
{
uint8_t *ptr;
volatile union {
uint8_t byte[2];
uint16_t word;
} value;
unsigned long sum;
unsigned long i;
/* In the most straight forward way possible,
* compute an ip style checksum.
*/
sum = 0;
ptr = addr;
for(i = 0; i < length; i++) {
unsigned long v;
v = ptr[i];
if (i & 1) {
v <<= 8;
}
/* Add the new value */
sum += v;
/* Wrap around the carry */
if (sum > 0xFFFF) {
sum = (sum + (sum >> 16)) & 0xFFFF;
}
}
value.byte[0] = sum & 0xff;
value.byte[1] = (sum >> 8) & 0xff;
return (~value.word) & 0xFFFF;
}
unsigned long add_ip_checksums(unsigned long offset, unsigned long sum, unsigned long new)
{
unsigned long checksum;
sum = ~sum & 0xFFFF;
new = ~new & 0xFFFF;
if (offset & 1) {
/* byte swap the sum if it came from an odd offset
* since the computation is endian independant this
* works.
*/
new = ((new >> 8) & 0xff) | ((new << 8) & 0xff00);
}
checksum = sum + new;
if (checksum > 0xFFFF) {
checksum -= 0xFFFF;
}
return (~checksum) & 0xFFFF;
}
|
