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authorYOSHIFUJI Hideaki / 吉藤英明 <yoshfuji@linux-ipv6.org>2010-03-27 02:24:16 +0100
committerDavid S. Miller <davem@davemloft.net>2010-03-31 08:28:47 +0200
commit02cdce53f3d0d3eee8188944c96150ee8c97100d (patch)
tree38ac636007de481c46f60e3848e80883e1235080
parentsctp: Use ipv6_addr_diff() in sctp_v6_addr_match_len(). (diff)
downloadlinux-02cdce53f3d0d3eee8188944c96150ee8c97100d.tar.xz
linux-02cdce53f3d0d3eee8188944c96150ee8c97100d.zip
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 <yoshfuji@linux-ipv6.org> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/ipv6/ip6_fib.c15
1 files 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)