From: Steffen Klassert <steffen.klassert@secunet.com>
To: David Miller <davem@davemloft.net>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
Steffen Klassert <steffen.klassert@secunet.com>,
<netdev@vger.kernel.org>
Subject: [PATCH 4/4] xfrm: branchless addr4_match() on 64-bit
Date: Tue, 11 Apr 2017 07:53:52 +0200 [thread overview]
Message-ID: <1491890032-28655-5-git-send-email-steffen.klassert@secunet.com> (raw)
In-Reply-To: <1491890032-28655-1-git-send-email-steffen.klassert@secunet.com>
From: Alexey Dobriyan <adobriyan@gmail.com>
Current addr4_match() code has special test for /0 prefixes because of
standard required undefined behaviour. However, it is possible to omit
it on 64-bit because shifting can be done within a 64-bit register and
then truncated to the expected value (which is 0 mask).
Implicit truncation by htonl() fits nicely into R32-within-R64 model
on x86-64.
Space savings: none (coincidence)
Branch savings: 1
Before:
movzx eax,BYTE PTR [rdi+0x2a] # ->prefixlen_d
test al,al
jne xfrm_selector_match + 0x23f
...
movzx eax,BYTE PTR [rbx+0x2b] # ->prefixlen_s
test al,al
je xfrm_selector_match + 0x1c7
After (no branches):
mov r8d,0x20
mov rdx,0xffffffffffffffff
mov esi,DWORD PTR [rsi+0x2c]
mov ecx,r8d
sub cl,BYTE PTR [rdi+0x2a]
xor esi,DWORD PTR [rbx]
mov rdi,rdx
xor eax,eax
shl rdi,cl
bswap edi
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
include/net/xfrm.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 43b93d1..9e3dc7b 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -845,9 +845,9 @@ static inline bool addr_match(const void *token1, const void *token2,
static inline bool addr4_match(__be32 a1, __be32 a2, u8 prefixlen)
{
/* C99 6.5.7 (3): u32 << 32 is undefined behaviour */
- if (prefixlen == 0)
+ if (sizeof(long) == 4 && prefixlen == 0)
return true;
- return !((a1 ^ a2) & htonl(0xFFFFFFFFu << (32 - prefixlen)));
+ return !((a1 ^ a2) & htonl(~0UL << (32 - prefixlen)));
}
static __inline__
--
2.7.4
next prev parent reply other threads:[~2017-04-11 6:00 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-11 5:53 pull request (net-next): ipsec-next 2017-04-11 Steffen Klassert
2017-04-11 5:53 ` [PATCH 1/4] xfrm: remove unused struct xfrm_mgr::id Steffen Klassert
2017-04-11 5:53 ` [PATCH 2/4] xfrm: use "unsigned int" in __xfrm6_pref_hash() Steffen Klassert
2017-04-11 5:53 ` [PATCH 3/4] xfrm: use "unsigned int" in addr_match() Steffen Klassert
2017-04-11 5:53 ` Steffen Klassert [this message]
2017-04-11 14:32 ` pull request (net-next): ipsec-next 2017-04-11 David Miller
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