batman-adv: move smallest_signed_int(), seq_before() and seq_after() into main.h

smallest_signed_int(), seq_before() and seq_after() are very useful
functions that help to handle comparisons between sequence numbers.
However they were only defined in vis.c. With this patch every
batman-adv function will be able to use them.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Sven Eckelmann <sven@narfation.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/net/batman-adv/main.h b/net/batman-adv/main.h
index 0150897acf63..80be5ad4fc9c 100644
--- a/net/batman-adv/main.h
+++ b/net/batman-adv/main.h
@@ -182,4 +182,20 @@ static inline int compare_eth(const void *data1, const void *data2)
 
 #define atomic_dec_not_zero(v)	atomic_add_unless((v), -1, 0)
 
+/* Returns the smallest signed integer in two's complement with the sizeof x */
+#define smallest_signed_int(x) (1u << (7u + 8u * (sizeof(x) - 1u)))
+
+/* Checks if a sequence number x is a predecessor/successor of y.
+ * they handle overflows/underflows and can correctly check for a
+ * predecessor/successor unless the variable sequence number has grown by
+ * more then 2**(bitwidth(x)-1)-1.
+ * This means that for a uint8_t with the maximum value 255, it would think:
+ *  - when adding nothing - it is neither a predecessor nor a successor
+ *  - before adding more than 127 to the starting value - it is a predecessor,
+ *  - when adding 128 - it is neither a predecessor nor a successor,
+ *  - after adding more than 127 to the starting value - it is a successor */
+#define seq_before(x, y) ({typeof(x) _dummy = (x - y); \
+			_dummy > smallest_signed_int(_dummy); })
+#define seq_after(x, y) seq_before(y, x)
+
 #endif /* _NET_BATMAN_ADV_MAIN_H_ */