From 02cdce53f3d0d3eee8188944c96150ee8c97100d Mon Sep 17 00:00:00 2001 From: =?utf8?q?YOSHIFUJI=20Hideaki=20/=20=E5=90=89=E8=97=A4=E8=8B=B1?= =?utf8?q?=E6=98=8E?= Date: Sat, 27 Mar 2010 01:24:16 +0000 Subject: [PATCH] ipv6 fib: Use "Sweezle" to optimize addr_bit_test(). addr_bit_test() is used in various places in IPv6 routing table subsystem. It checks if the given fn_bit is set, where fn_bit counts bits from MSB in words in network-order. fn_bit : 0 .... 31 32 .... 64 65 .... 95 96 ....127 fn_bit >> 5 gives offset of word, and (~fn_bit & 0x1f) gives count from LSB in the network-endian word in question. fn_bit >> 5 : 0 1 2 3 ~fn_bit & 0x1f: 31 .... 0 31 .... 0 31 .... 0 31 .... 0 Thus, the mask was generated as htonl(1 << (~fn_bit & 0x1f)). This can be optimized by "sweezle" (See include/asm-generic/bitops/le.h). In little-endian, htonl(1 << bit) = 1 << (bit ^ BITOP_BE32_SWIZZLE) where BITOP_BE32_SWIZZLE is (0x1f & ~7) So, htonl(1 << (~fn_bit & 0x1f)) = 1 << ((~fn_bit & 0x1f) ^ (0x1f & ~7)) = 1 << ((~fn_bit ^ ~7) & 0x1f) = 1 << ((~fn_bit ^ BITOP_BE32_SWIZZLE) & 0x1f) In big-endian, BITOP_BE32_SWIZZLE is equal to 0. 1 << ((~fn_bit ^ BITOP_BE32_SWIZZLE) & 0x1f) = 1 << ((~fn_bit) & 0x1f) = htonl(1 << (~fn_bit & 0x1f)) Signed-off-by: YOSHIFUJI Hideaki Signed-off-by: David S. Miller --- net/ipv6/ip6_fib.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index 2f9847924fa5..68119ef62869 100644 --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -127,12 +127,23 @@ static __inline__ u32 fib6_new_sernum(void) /* * test bit */ +#if defined(__LITTLE_ENDIAN) +# define BITOP_BE32_SWIZZLE (0x1F & ~7) +#else +# define BITOP_BE32_SWIZZLE 0 +#endif static __inline__ __be32 addr_bit_set(void *token, int fn_bit) { __be32 *addr = token; - - return htonl(1 << ((~fn_bit)&0x1F)) & addr[fn_bit>>5]; + /* + * Here, + * 1 << ((~fn_bit ^ BITOP_BE32_SWIZZLE) & 0x1f) + * is optimized version of + * htonl(1 << ((~fn_bit)&0x1F)) + * See include/asm-generic/bitops/le.h. + */ + return (1 << ((~fn_bit ^ BITOP_BE32_SWIZZLE) & 0x1f)) & addr[fn_bit >> 5]; } static __inline__ struct fib6_node * node_alloc(void) -- 2.20.1