02cdce53f3
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> |
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.. | ||
netfilter | ||
addrconf.c | ||
addrconf_core.c | ||
addrlabel.c | ||
af_inet6.c | ||
ah6.c | ||
anycast.c | ||
datagram.c | ||
esp6.c | ||
exthdrs.c | ||
exthdrs_core.c | ||
fib6_rules.c | ||
icmp.c | ||
inet6_connection_sock.c | ||
inet6_hashtables.c | ||
ip6_fib.c | ||
ip6_flowlabel.c | ||
ip6_input.c | ||
ip6_output.c | ||
ip6_tunnel.c | ||
ip6mr.c | ||
ipcomp6.c | ||
ipv6_sockglue.c | ||
Kconfig | ||
Makefile | ||
mcast.c | ||
mip6.c | ||
ndisc.c | ||
netfilter.c | ||
proc.c | ||
protocol.c | ||
raw.c | ||
reassembly.c | ||
route.c | ||
sit.c | ||
syncookies.c | ||
sysctl_net_ipv6.c | ||
tcp_ipv6.c | ||
tunnel6.c | ||
udp.c | ||
udp_impl.h | ||
udplite.c | ||
xfrm6_input.c | ||
xfrm6_mode_beet.c | ||
xfrm6_mode_ro.c | ||
xfrm6_mode_transport.c | ||
xfrm6_mode_tunnel.c | ||
xfrm6_output.c | ||
xfrm6_policy.c | ||
xfrm6_state.c | ||
xfrm6_tunnel.c |