ipv6 fib: Use "Sweezle" to optimize addr_bit_test().
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 <948b80da4254122ea1e8973dd9930d46b7654cf3@linux-ipv6.org>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas