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authorAlexey Dobriyan <adobriyan@gmail.com>2017-03-25 19:41:17 +0300
committerSteffen Klassert <steffen.klassert@secunet.com>2017-03-27 07:04:14 +0200
commit6c786bcb29dd684533ec165057f437d5bb34a4b2 (patch)
treef185635c44186df8b31a7991ac26366a9fbd0481 /include/net/xfrm.h
parente1b0048e18d4637603cf6f43b9b24345abdeec5c (diff)
downloadlinux-6c786bcb29dd684533ec165057f437d5bb34a4b2.tar.bz2
xfrm: branchless addr4_match() on 64-bit
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>
Diffstat (limited to 'include/net/xfrm.h')
-rw-r--r--include/net/xfrm.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 43b93d1134ed..9e3dc7b81a4d 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__