[IPV6]: Put addr_diff() into common header for future use.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 48 insertions, 0 deletions

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 65ec86678a08..98661fa4fc78 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -341,6 +341,54 @@ static inline int ipv6_addr_any(const struct in6_addr *a)
 }
 
 /*
+ * find the first different bit between two addresses
+ * length of address must be a multiple of 32bits
+ */
+static inline int __ipv6_addr_diff(const void *token1, const void *token2, int addrlen)
+{
+        const __u32 *a1 = token1, *a2 = token2;
+        int i;
+
+        addrlen >>= 2;
+
+        for (i = 0; i < addrlen; i++) {
+                __u32 xb = a1[i] ^ a2[i];
+                if (xb) {
+                        int j = 31;
+
+                        xb = ntohl(xb);
+                        while ((xb & (1 << j)) == 0)
+                                j--;
+
+                        return (i * 32 + 31 - j);
+                }
+        }
+
+        /*
+         *      we should *never* get to this point since that 
+         *      would mean the addrs are equal
+         *
+         *      However, we do get to it 8) And exacly, when
+         *      addresses are equal 8)
+         *
+         *      ip route add 1111::/128 via ...
+         *      ip route add 1111::/64 via ...
+         *      and we are here.
+         *
+         *      Ideally, this function should stop comparison
+         *      at prefix length. It does not, but it is still OK,
+         *      if returned value is greater than prefix length.
+         *                                      --ANK (980803)
+         */
+        return (addrlen << 5);
+}
+
+static inline int ipv6_addr_diff(const struct in6_addr *a1, const struct in6_addr *a2)
+{
+        return __ipv6_addr_diff(a1, a2, sizeof(struct in6_addr));
+}
+
+/*
  *      Prototypes exported by ipv6
  */