Eric Biederman | 8ca8d76 | 2003-04-22 19:02:15 +0000 | [diff] [blame] | 1 | #include <stdint.h> |
| 2 | #include <ip_checksum.h> |
| 3 | |
| 4 | unsigned long compute_ip_checksum(void *addr, unsigned long length) |
| 5 | { |
| 6 | uint8_t *ptr; |
| 7 | volatile union { |
| 8 | uint8_t byte[2]; |
| 9 | uint16_t word; |
| 10 | } value; |
| 11 | unsigned long sum; |
| 12 | unsigned long i; |
| 13 | /* In the most straight forward way possible, |
| 14 | * compute an ip style checksum. |
| 15 | */ |
| 16 | sum = 0; |
| 17 | ptr = addr; |
| 18 | for(i = 0; i < length; i++) { |
| 19 | unsigned long value; |
| 20 | value = ptr[i]; |
| 21 | if (i & 1) { |
| 22 | value <<= 8; |
| 23 | } |
| 24 | /* Add the new value */ |
| 25 | sum += value; |
| 26 | /* Wrap around the carry */ |
| 27 | if (sum > 0xFFFF) { |
| 28 | sum = (sum + (sum >> 16)) & 0xFFFF; |
| 29 | } |
| 30 | } |
| 31 | value.byte[0] = sum & 0xff; |
| 32 | value.byte[1] = (sum >> 8) & 0xff; |
| 33 | return (~value.word) & 0xFFFF; |
| 34 | } |
| 35 | |
| 36 | unsigned long add_ip_checksums(unsigned long offset, unsigned long sum, unsigned long new) |
| 37 | { |
| 38 | unsigned long checksum; |
| 39 | sum = ~sum & 0xFFFF; |
| 40 | new = ~new & 0xFFFF; |
| 41 | if (offset & 1) { |
| 42 | /* byte swap the sum if it came from an odd offset |
| 43 | * since the computation is endian independant this |
| 44 | * works. |
| 45 | */ |
| 46 | new = ((new >> 8) & 0xff) | ((new << 8) & 0xff00); |
| 47 | } |
| 48 | checksum = sum + new; |
| 49 | if (checksum > 0xFFFF) { |
| 50 | checksum -= 0xFFFF; |
| 51 | } |
| 52 | return (~checksum) & 0xFFFF; |
| 53 | } |