diff options
| -rw-r--r-- | include/net/checksum.h | 23 |
1 files changed, 21 insertions, 2 deletions
diff --git a/include/net/checksum.h b/include/net/checksum.h index 37a0e24adbe..a28f4e0f625 100644 --- a/include/net/checksum.h +++ b/include/net/checksum.h @@ -69,6 +69,19 @@ static inline __wsum csum_sub(__wsum csum, __wsum addend) return csum_add(csum, ~addend); } +static inline __sum16 csum16_add(__sum16 csum, __be16 addend) +{ + u16 res = (__force u16)csum; + + res += (__force u16)addend; + return (__force __sum16)(res + (res < (__force u16)addend)); +} + +static inline __sum16 csum16_sub(__sum16 csum, __be16 addend) +{ + return csum16_add(csum, ~addend); +} + static inline __wsum csum_block_add(__wsum csum, __wsum csum2, int offset) { @@ -112,9 +125,15 @@ static inline void csum_replace4(__sum16 *sum, __be32 from, __be32 to) *sum = csum_fold(csum_partial(diff, sizeof(diff), ~csum_unfold(*sum))); } -static inline void csum_replace2(__sum16 *sum, __be16 from, __be16 to) +/* Implements RFC 1624 (Incremental Internet Checksum) + * 3. Discussion states : + * HC' = ~(~HC + ~m + m') + * m : old value of a 16bit field + * m' : new value of a 16bit field + */ +static inline void csum_replace2(__sum16 *sum, __be16 old, __be16 new) { - csum_replace4(sum, (__force __be32)from, (__force __be32)to); + *sum = ~csum16_add(csum16_sub(~(*sum), old), new); } struct sk_buff; |