[PATCH net-next v2] net: core: Use csum_replace_by_diff() and csum_sub() instead of opencoding

[Christophe Leroy]

Open coded calculation can be avoided and replaced by the
equivalent csum_replace_by_diff() and csum_sub().

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
v2: Dropped the change in nft_csum_replace() as it would
require nasty casts.
---
 net/core/utils.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/utils.c b/net/core/utils.c
index 1f31a39236d5..938495bc1d34 100644
--- a/net/core/utils.c
+++ b/net/core/utils.c
@@ -476,9 +476,9 @@ void inet_proto_csum_replace_by_diff(__sum16 *sum, struct sk_buff *skb,
 				     __wsum diff, bool pseudohdr)
 {
 	if (skb->ip_summed != CHECKSUM_PARTIAL) {
-		*sum = csum_fold(csum_add(diff, ~csum_unfold(*sum)));
+		csum_replace_by_diff(sum, diff);
 		if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr)
-			skb->csum = ~csum_add(diff, ~skb->csum);
+			skb->csum = ~csum_sub(diff, skb->csum);
 	} else if (pseudohdr) {
 		*sum = ~csum_fold(csum_add(diff, csum_unfold(*sum)));
 	}
-- 
2.34.1