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@csgroup.eu>
---
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

Hello:

This patch was applied to netdev/net-next.git (master)
by David S. Miller <davem@davemloft.net>:

On Fri, 18 Feb 2022 09:03:48 +0100 you wrote:
> 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@csgroup.eu>
> ---
> v2: Dropped the change in nft_csum_replace() as it would
> require nasty casts.
> 
> [...]

Here is the summary with links:
  - [net-next,v2] net: core: Use csum_replace_by_diff() and csum_sub() instead of opencoding
    https://git.kernel.org/netdev/net-next/c/0f6938eb2ecc

You are awesome, thank you!
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