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author committer Gerrit Renker 2006-12-20 10:25:55 -0800 David S. Miller 2006-12-22 11:12:01 -0800 9a036b9c33f74c989c4c8ac0abe05e0ed88f1f25 (patch) 7eadf26579e996975e35a5f34298937f7bd114e8 /include/net/tcp.h 1f8a5fb80e63aab63de81169ab749d73e7509e3f (diff)
[TCP]: Fix ambiguity in the `before' relation.
While looking at DCCP sequence numbers, I stumbled over a problem with the following definition of before in tcp.h: static inline int before(__u32 seq1, __u32 seq2) { return (__s32)(seq1-seq2) < 0; } Problem: This definition suffers from an an ambiguity, i.e. always before(a, (a + 2^31) % 2^32)) = 1 before((a + 2^31) % 2^32), a) = 1 In text: when the difference between a and b amounts to 2^31, a is always considered `before' b, the function can not decide. The reason is that implicitly 0 is `before' 1 ... 2^31-1 ... 2^31 Solution: There is a simple fix, by defining before in such a way that 0 is no longer `before' 2^31, i.e. 0 `before' 1 ... 2^31-1 By not using the middle between 0 and 2^32, before can be made unambiguous. This is achieved by testing whether seq2-seq1 > 0 (using signed 32-bit arithmetic). I attach a patch to codify this. Also the `after' relation is basically a redefinition of `before', it is now defined as a macro after before. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/tcp.h')
-rw-r--r--include/net/tcp.h9
1 files changed, 2 insertions, 7 deletions
 diff --git a/include/net/tcp.h b/include/net/tcp.hindex c99774f15eba..b7d8317f22ac 100644--- a/include/net/tcp.h+++ b/include/net/tcp.h@@ -242,14 +242,9 @@ extern int tcp_memory_pressure; static inline int before(__u32 seq1, __u32 seq2) {- return (__s32)(seq1-seq2) < 0;+ return (__s32)(seq2-seq1) > 0; }--static inline int after(__u32 seq1, __u32 seq2)-{- return (__s32)(seq2-seq1) < 0;-}-+#define after(seq2, seq1) before(seq1, seq2) /* is s2<=s1<=s3 ? */ static inline int between(__u32 seq1, __u32 seq2, __u32 seq3)